Archive | December, 2008

29. The anatomy, histology and development of the kidney.

29 Dec

29. The anatomy, histology and development of the kidney.

* Kidney is one of the 2 primary retroperitoneal organs, and is not part of the primary gut.

Anatomy of Kidney

Location: In middle compartment of retroperitoneal space, within the renal fascia, along with suprarenal gland. Located in paravertebral gutter against psoas major m.

SP – B/w T123 – L3/4, beside IVC/ab aorta B/c R lobe of liver is larger than the left, the R kidney is situated slightly lower than the left. The left kidney projects at the 11-12rib, and R is the 12th rib only.


  • R Kidney – (ant) – Liver, gallbladder, duodenum, R suprarenal gland, R colic flexure, asc colon, loops of SI

  • L Kidney – (ant) suprarenal gland, stomach, spleen, pancreas, L colic flexure, SI, desc colon

  • Both Kidneys – (post) – (sup) diaphragm, (inf, from lat to med) transverse m aponeurosis, quadratus lumborum m, and psoas major m.

Fxn – prod and excrete urine, filter waste from blood, and maintain electrolyte balance, and regulate BP by producing vasoactive substances.


External structures:

Kidney has 3 coverings:

Renal fascia – that covers both kidneys like a huge tent like structures, separates the retroperitoneal cavity into 3 compartments.

This renal fascia also divides the fat that surrounds the kidney into two layers =

  • inside the renal fascia, is perirenal fat, between the capsule of the kidney fascia.

  • Outside the renal fascia is the pararenal fat. (Peri means around it , like perimeter, and Para means next to, or almost in but not quite, like paranormal, or paraplegic)

Each kidney then as a separate adipose layer, within the fascia is perirenal fat.

Lastly, each kidney has a fibrous capsule, called renal capsule. This capsule, unlike in other organs, does not send CT septa into the kidney and is therefore removable easily.

Renal sinus – is the inner cavity of the kidney (not part of parenchyme, the tissue stuff, just an empty space), which leads the hilum of the kidney. Structures that enter/ leave here = renal a/v, minor calices, major calices, renal pelvis, lymph vessels, renal fat, ANS fibers

Renal hilum – entrance into the renal sinus. Ant–> post is located the renal v, a, then the ureter = VAU

Internal Structure:

Within each kidney, there is a an outer cortex, and inner medulla. Structures within the cortex and medulla will be discussed in further detail in the histology section.

Cortex: The cortex is the outer part of the kidney and projects into the inner medulla region, between the renal pyramids, as renal columns.

Medulla: The medulla is arranged into triangle shaped renal pyramids, that end in a renal papilla, which then lead into the minor calyx (each minor calyx drains one lobe of the kidney)

  • 3-4 minor calices join to form the major calices.

  • The major calices all join to form the renal pelvis –> that becomes the ureter.

  • The function unit of the Kidney is called the nephron. It is made up of a renal corpuscle ( made up of capillaries surrounded by the Bowman’s capsule, which has visceral and parietal layers. The renal corpuscle leads into a series of tubules surrounded by a arterial network, that aids in filtering urine.

Urine flow: From the urinary pole of the renal corpuscle –> prox convoluted tubule –> prox straight tubule –> desc limb, or desc part of thin segment–> Loop of Henle –> asc limb, or asc part of thin segment –> distal straight tubule –> distal convoluted tubule –> collecting duct –> papillary duct (at base of renal papilla) –> minor calyx –> major calyx –> renal pelvis –> ureter –> urinary bladder –> urethra

A longitudinal section, B nephron and adjacent blood vessels; 1 renal papilla, 2 renal column, 3 capsule, 4 renal pyramid, 5 calyx, 6 ureter, 7 renal pelvis, 8 renal vein, 9 renal artery, 10 interlobar artery, 11 arcuate artery, 12 interlobular artery, 13 interlobar vein, 14 cortex, 15 interlobular vein, 16 renal sinus, 17 arcuate vein, 18 medulla, 19 vasa recta, 20 loop of Henle, 21 collecting duct, 22 arcuate vein, 23 arcuate artery, 24 proximal convoluted tubule, 25 glomerulus, 26 Bowmans capsule, 27 distal convoluted tubule
kidney 1: A longitudinal section, B nephron and adjacent blood vessels; 1 renal papilla, 2 renal column, 3 capsule, 4 renal pyramid, 5 calyx, 6 ureter, 7 renal pelvis, 8 renal vein, 9 renal artery, 10 interlobar artery, 11 arcuate artery, 12 interlobular artery, 13 interlobar vein, 14 cortex, 15 interlobular vein, 16 renal sinus, 17 arcuate vein, 18 medulla, 19 vasa recta, 20 loop of Henle, 21 collecting duct, 22 arcuate vein, 23 arcuate artery, 24 proximal convoluted tubule, 25 glomerulus, 26 Bowman’s capsule, 27 distal convoluted tubule

Blood Supply

  • Arteries: Renal a supplies the kidney, located @ L1 of ab aorta, the 2nd paired visceral branch from the aorta

    • Renal a splits into 5 segmental branches –> each segmental br has ant/post br –> interlobar arteries, running within the renal columns –> splits into 2 arcuate arteries, which arch over the base of the renal pyramids –> interlobular a, within the cortical labyrinth between the medullary rays (will talk about these structures in histo, dont worry about them now) –> have arteriolar system that goes to the renal corpuscle and tubular system –> interlobular v –> rest of the v follow the arteries mentioned prev.

    • Renal a also gives inf supra renal a, and possibly branches to ureter.

  • Veins: Veins within kidney, follow arteries, until getting to renal v –> IVC R renal v is a little lower, and much shorter than L renal v, b/ c IVC is located on the right side of vert. column.

Lymph Drainage : Lymph vessels in the kidneys follow the arteries –> renal sinus –> hilum –> para-aortic and common iliac l.n. –> lumbar trunks –> cisterna chyli

Renal innervation: N. of kidney from the renal n plexus = PNS/SNS fibers, from ab/pelvic splanchnic n.

  • PNS = @ origin of renal a, is the location of the aortico-renal plexus, with pre-ggl fibers from all 3 splanchnic n (Greater, Lesser, Least) –> post ggl fibers –> organ

  • SNS = From T12 – L2 run through sympathetic trunk to least splanchnic n and lumbar splanchnic n, comes the pre ggl fibers –> renal ggl (not the same as aortico renal plexus) –> post ggl fibers –> kidney/ ureters

  • Most supply renal a/v and branches, to decrease urine production

  • PARS – PNS = Aortico-renal, Renal = SNS


  • Pathway of Ureters = from renal hilum (lies most post. ) –> runs in retro peritoneal space, ant to psoas m, and crosses the bifurcation of the common iliac a, and rec. blood from those arteries.

  • Topography of ureter

    • R ureter – behind desc part of duod, post to root of mesentery, post to gonadal a/v

    • L ureter – post to left colic a/v, next to gonadal vessels, post to sigmoid a and sup rectal a (in sigmoid mesocolon)

    • Both = pass behind Ductus deferens (or cardinal ligaments/ uterine a/v in females), and enter bladder on the lower/post side.

  • Blood supply = branches from various a it passes

  • Innervation = W/in renal pelvis = least splanchnic n from T 12 Abdomen/pelvis = lumbar splanchnic n (SNS), Pelvic splanchnic n give PNS innervation along the entire ureter.

Suprarenal glands:

  • Location: on top of each kidney, medially, below diaphragm, is pyramid shaped on R side, and semilunar shaped on L side, also covered by renal fascia, and has a fibrous capsule.

  • Topography:

    • R = r lobe of liver (bare area), R kidney

    • L = Lesser sac, pancreas, L kidney

  • Parts:
    • Cortex –> prod steroid hormones, including mineralocorticoids (aldosterone), glucocorticoids (cortisone), and sex hormones

    • Medulla –> derived from embryonic neural crest cells, rec pre-ggl SNS fibers directly and secrets epinephrine and norepinephrine.

  • Blood Supply:

    • Arteries:

      • a) Sup suprarenal a – from inf phrenic a (ab aorta)

      • b) Mid suprarenal a – from aorta directly

      • c) Inf suprarenal a – from renal a

    • Veins

      • R suprarenal v –> IVC

      • L suprarenal v –> L renal v –> IVC

Histology = Kidney Slide # 60 * H&E

Structures to Identify:

  • renal corpuscles

  • renal column

  • renal pyramids

  • cortical labyrinth

  • medullary rays

  • Cortex

  • Medulla

  • Cortex corticis

  • a/v

  • renal corpuscles

  • tubular system

  • urinary pole

  • vascular pole

  • Juxta glomerular apparatus = macula densa, JG cells, (dont have to identify mesengial cells)

General Info:

  • Main organ of urinary system

  • conserve body fluids and electrolytes

  • remove metabolic wastes like urea, uric acid, and other debris

  • produce urine as ultrafiltrate of blodd that is modified by selective resorption /secretion by kidney tubule cells

  • 10cm long, bean shaped, between T12-L3

  • about 20-30 renal pyramids

Nephron is fxn’l unit of the kidney . There are two types of nephron, classified depending on their location within the kidney.
1. Cortical nephron – located anywhere in the cortex, long thick segments, short thin segments
2. Justamedullary nephron – located at the cortio-medullary border, near base of pyramid, where arcuate arteries are.  have short thick segments and long thin segments that go almost to the bottom of the renal pyramid. have more hypotonic enviroment, to produce a concentrated urine.

* Look the same with in slide.

Parts of nephron, in order of flow :
Renal corpuscles –> proximal convoluted tubule, proximal straight tubule, descending limb, loop of Henle, ascending limb, distal straight tubule, distal convoluted tubule.


Cortex characterized by renal corpuscles and their tubules including convoluted and straight parts of nephron, the collecting tubules and extensive vascular network.

Renal corpuscle

  • Renal corpuscle consists of glomerular capillary bed surrounded by double layer of epith cap (Bowman’s capsule),

  • space between glomerulus and capsule is called capsular or urinary space.
  • Each capsule has afferent arteriole and efferent arteriole, and has two layers: a inner visceral layer, and outer parietal layer.

  • The visceral layer of the capsule surrounds the capillaries of the glomerulus with modified epithelial cells called podocytes.

  • There are two poles to the corpuscles = urinary pole, where there tubular system starts from, and the vascular pole, where the arterioles enter/exit

Blood enters corpuscles through specialize mechanism of corpuscle:  Filtration Apparatus, which is located in the area between the podocyte fingers and the endothelium of the capillaries.

Layers in barrier b/w capillaries and epith lining of Bowman’s capsule:

1. Glomerular Basement membrane

2. Podocytes lining capillaries assist GBM in further filtration via unique structures containing finger like structures called pedicles that interweave between each other.

3. The Slit Membrane

  • The basement membrane of the endothelium of capillaries and the basement membrane of the podocytes fuse,

  • each basement membrane has two layers: an outer fibrous membrane and an inner basal lamina.

  • the two fibrous membranes touch each other and fuse, forming one single layer.

  • Therefore, the filtration barrier between the capillaries and the podocytes is made up of the following layers:

    • 1. The endothelium of the a/v

    • 2. the glomerular basement membrane = made of three layers (GBM)

      • a) Lamina rara interna = the basal lamina of endothelium

      • b) Lamina densa = the fused 2 fibrous layers of the basement membranes of both endothelium of capillaries and podocytes

      • c) Lamina rara externa = the basal lamina of the podocyte

    • 3. The Slit membrane = CT covering the spaces between podocytes.

  • So picture it like this: Put your hands up together, and put your fingers between each other, but without clasping them together or weaving your fingers together. Picture your hands holding a giant messed up ball of yarn and then imagine cling film over your hands, covering the spaces between your fingers. The yarn is the glomerular capillary bed, your hands is the Bowman’s capsule (the palm being the visceral layer and outside skin being the parietal layer), and your fingers are the podocytes interdigitating, with the cling film between your “podocytes” is the slip membrane, covering the spaces between the podocytes.

  • Filtration happens in the cling film area, that is to say, that it only occurs between the podocytes, where the slit membrane is located

With in the cortex, one can also the see the next part of the nephron, the proximal convoluted tubule, and its counterpart on the way back from the loop of Henle, the distal convoluted tubule.

You have to be able to show both of them

Prox  convoluted tubule

  • simple cuboidal epith

  • v. visible BM

  • irregular lumen

  • border between cells indistinct

  • acidophillic cytoplasm = lots of mitochondria

  • brush border present

  • basal striations

Distal convoluted tubule

  • less in # than proximal in cortex

  • cytoplasm lighter

  • cell boundaries seen

  • very smooth wide lumen

  • cuboidal cells still

  • brush border cannot be seen (doesn’t mean it’s not there)

  • striations present, but not seen well

Juxtaglomerular apparatus

Between the renal corpuscle’s vascular pole and the distal convoluted tuble is a structure called the Juxta-Golmerular Apparatus, with 3 parts:.
1. Juxtaglomerular cells.

  • @ vascular pole,

  • smooth m. cells of tunica media of afferent arteriole is replace by epith-like cells with granules in cytoplasm =  Juxtaglomerular cells.

  • secrete renin as part of Renin-angiotensin system

2. Mesengial cells

  • Also in apparatus are mesengial cells (no need to locate)

  • chemoreceptor cells @ vascular pole

  • activated by sensing the ion concentration in blood in macula densa,

  • in other regions, help clean glomerular basement membrane

  • secrete erythropoeitin.

  • found with in and out of glomerulus, so named that  way = Extra glomerular, Intra glomerular mesengial cells

3.Macula Densa

  • Lastly, the distal convoluted tuble right next to the vascular pole will have cells next to the JG cells that are a bit different.

  • They are a darker row of cells on the side of the distal convoluted tube

  • just next to the vascular pole = Macula Densa.

Within the cortex, is also the medullary rays. Contain = proximal straight tubules, distal straight tubules and the collecting ducts.

NOTE – area of cortex above the level of medullary rays is called the cortex corticis.

The characteristics of the straight part of tubules pretty much same as convoluted, Just look for thin eosinophillic tube structures with fuzzy lumen = prox, and very thin tubules with almost no staining in wall = distal.

Collecting ducts
, not part of nephron, lumen is wide and the cells making up the wall is much bigger. usually widest lumens in this area. lightly stained cuboidal epithelium

location of renal pyramids – remember that the base of the pyramid faces the cortex, and the apex of the pyramid (renal papilla) faces the hilum.

The cortex projects into medulla between renal pyramids as renal columns. (don’t have to show that)

Area between the medullary rays = cortical labyrinth

located where renal corpsucles end *NONE in medulla
contains only straight tubules, and asc and desc limbs of loop of Henle , as well as collecting tubules.

  • @ apex of pyramid, (bbttom of slide) on one side of slide, can see the edge of the renal papilla – where it enters the minor calyx. You will see a slit in the slide, with one side’s epith v. thick and pink related to the other side of the slide. This is where the transistion urothelium of the minor calyx turns into the columnar epithelium covering the papilla. The one more lateral (and thicker) is the minor calyx.
  • Also the location to find the papillary ducts. – large lumen, lined by tall columnar pale staining cells.
  • base of papilla has a stratified columnar epith
  • to identify the Loops of Henle

    • look for v. thin  tube like structures.

    • They look like thin capillaries

    • only with a thicker epithelium

    • simple squamous epithelium
    • no RBCs within their lumen.

    • To find them , you have to go alll the way down to the lower edge of the slide.

Blood Supply:

Blood flow in kidney v. different from other organs due its filtration function.

  • From renal a –> interlobular a (renal columns) –> arcuate a (at base of pyramid) –> interlobular arteries ( cortical labyrinth) –> give multiple afferent arterioles to renal corpuscle.

  • Here’s where it is different. Normally from capillaries you get venules leaving. In the kidney, instead, another arteriole leaves the glomerular capillary bed, the efferent arteriole

  • from renal corpuscle –> efferent arteriole –> this then forms a second capillary bed around the tubular system we’ve discussed. –> then venules come from this capillary bed, and the veins follow the arteries.

There are three types of arterial branch of the efferent arterioles:
1. Cortical nephrons – aff a –> glomerulus –> eff a –> 2nd capillary bed local to the first one –> venules

2. Juxta medullary nephrons – aff a –> glomerulus –> eff a –> doesnt break into 2nd capillary bed right away, instead follow tubules all the way down to medulla (long thin segment, remember?) into the pyramid  –> uturn  –> come back up –> venules These long arterioles following the long segments of tubules staight down into medulla are called the vasa recta.

3. Capsular nephron (minor) – located in cortex corticis, the eff. a can form a star shaped capillary bed just under the capsule of the kidney = stellate capillary bed.  Cannot be seen in slide.

Slide # 61 Kidney Tangential section

  • Same structures cut the opposite way. can see the cross section of straight tubules.

  • characteristics the same.

  • the bubble like, more clear area = medullary ray

  • Eosinophillic area = cortical labyrinth

  • find interlobular a here, about 6 around each column.

  • Identify same parts as first slide

Slide #62 Kidney * H&E + Indian Ink

  • Ink injected while animal is still alive, and H&E added posthumously

  • a/v stained black, so can see all parts of vascular system: glomeruli, arcuate a, vasa recta, stellate capillary bed seen at top, under capsule.

  • Star shape not visible due way of cutting.

Embryology of Kidney:

  • Intermediate mesoderm from long ridge on post (dorsal) body wall = urogenital ridge.

  • Part of this ridge = nephrogenic cord –> becomes urinary system

  • Nephrogenic cord  –> splits into pronephros, mesonephros, metanephros

  • Pronephros = most cranial, forms pronephric tubules, and pronephric duct, regresses in wk 5, not fxn’l in humans

  • Mesonephros = middle structures, from mesonephric tubules and ducts (Wolffian duct), fxn’l for only a short period of time. The duct will still exite, and opens into urogenital sinus.

  • Metanephros = most caudal, forms from outgrowth of mesonephric duct = ureteric bud, and from mesoderm grouping within nephrogenic cord called metanephric mesoderm. , forms @ wk 5, and fxn’l @ wk 10

  • The ureteric bud penetrates the metanephric mesoderm, and then divides to form: ureters, renal pelvis, major and minor calyces, and collecting ducts.

  • Collecting ducts push the metanepheric mesoderm to form vesicles (pouches), that become all the parts of the nephron.

Ascent of Kidneys:

  • metanephros located w/in sacral region, but ends up at level of T12-L3.

  • B/c of increase amt of growth caudal to metanephros.

  • While ascending, kidneys rotate 90 degrees, so hilum faces medially.

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28. The retroperitoneum. Development of body cavities. The histology of the parathyroid gland.

28 Dec

28. The retroperitoneum. Development of body cavities. The histology of the parathyroid gland.

Retroperitoneal Space

The retro peritoneal space is seperated into the 3 compartments by the renal fasica. This fascial covering is like a tent that is closed susuperiorly and open inferiorly.

Ant Chamber = b/w peritoneum and renal fascia, has all secondary retroperitoneal organs

  • asc colon
  • desc colon
  • duodenum (except sup hor part)
  • pancreas (except tail, sometimes)
  • Br. of sup mesenteric a, celiac trunk, sup/inf mesenteric v, portal v, common bile duct

Middle Chamber = w/in renal fasica, has primary retroperitoneal organs.

  • kidneys
  • suprarenal glands
  • ureters
  • Ab aorta + branches
  • IVC + branches
  • Thoracic duct
  • Cisterna Chyli

Post Chamber = b/w renal fascia and transverse fascia(post ab wall)

  • asc lumbar v (becomes azygos v, once crosses diaphragm into thoracic cavity)
  • Greater/Lesser splanchnic n
  • SNS trunk
  • Subcostal n.
  • Lumbar plexus + branches
  • Ilioinguinal n.
  • Inohypogastric n
  • Obturator n
  • Genitofemoral n
  • Gonadal a/v

The histology of the parathyroid gland.
Slide 35: Parathyroid glands * H&E
General Info:
generally have 4 parathyroid glands
2 sup/2 inf
sit on posterior surface of thyroid gland

With naked eye: small, pale, round specimen

  • connect to thyroid via CT capsule
  • CT trabeculae extend from capsule –> substance of the gland
  • CT trabeculae w/ a/v  that make capillaries
  • cells of parathyroid gland arranged into clumps, surrounded by capillaries
  • Structure of gland: islands of adipose tissue in stroma & rich in a/v
    cells form zigzag cells cords

2 main cells types:
Chief Cells

  • most numerous
  • differentiate during embryonic development
  • pale stained nucleus
  • round and pale, slightly acidophilic cytoplasm
  • cytoplasm contains:
    • lipofuchsin vesicles
    • lipid droplets
    • large accumulation of glycogen
    • membrane limited vescicle = store PTH

produce Parathryoid hormone

  • maintain proper calcium levels in EC body fluid
  • raises calcium level on blood
  • opposite action as calcitonin (prod by parafollicular cells in thyroid glands)
  • NOTE – release of PTH depends primarily on Ca levels in blood, not on PTH

PTH stimulates:

  1. Bone resorption
    1. -stimulates activity & increases the proliferation of osteoclasts in bones
    2. increases osteolytic activities, release of more calcium into blood stream
  2. Kidney tubule re-absorption of Ca2+ -distal convoluted tubules inc both resorption of Ca from glomerular filtrate,
  3. Urinary PO4 excretion –  and elimates of PO4, Na, K+ ions into urine, dec Po4 conc in blood, CSF
  4. Kidney activation of Vit D3 – causes kidneys to form calcitrol, active form of Vit D
  5. Intestinal action – increases Ca absorption from GI tract/bloodstream

Oxyphil Cells

  • larger than chief cells w/ smaller nucleus
  • less numerous than chief cells
  • more scattered than chief cells
  • acidophilic cytoplasm, smaller dark stained nuclei
  • function unclear, inc in # w/ age
  • differentiate @ puberty
  • found singly or clusters

develop from endodermal cells derived from 3rd & 4th pharyngeal arches
inf – 3rd
sup – 4th
Cheif cells are active in regulating fetal Ca2+ metabolism
Oxyphil cells differentiate @ puberty

Embryology: Development of body cavities.

From intraembryonic mesoderm –> 3 portions:
paraaxial mesoderm
intermediate mesoderm
lat plate mesoderm

lat plate mesoderm splits into somatic/ splanchnic mesoderm
splanchnic mesoderm is continuous w/ wall of yolk sac

somatic and splanchnic mesoderm border the intraembryonic cavity
@ 1st intra/extra embryonic cavity are connected, after embryo folds (cephalo-caudally, laterally)
this splits intraembryonic region into thoracic & ab region

Serous membranes:
splanchnic mesoderm
– forms visceral layer of mesothelium (pleura, pericardium, peritoneum)
somatic mesoderm – forms parietal layer
Both layers become continous @ ventral and dorsal mesentery

  • ventral = is all along gut tube, mesoderm band from caudal end of foregut –> end of hindgut
  • dorsal = from caudal end of foregut –> upper duodenum (from thinning of mesoderm of septum transversum)

Seperation of cavities:

Separation of cavities – done  by the formation of lungs/diaphragm

1. Development of Lungs:

  • Septum transversum – mesoderm plate b/w thoracic cavity & yolk sac
    • makes 2 pericardioperitoneal canals on either side of foregut
    • Lungs grow & expand to form
    • pleuropericardial folds –> from small ridges on primitive thoracic cavity
    • mesoderm of body wall divides into
      • 1. definitive wall of thorax
      • 2. pleuropericardial membranes – contain  common cardinal v & phrenic n
        • After sinus venosus & heart  change position, they move to midline & fuse w/ each other and root of lung —>
        • this divides the thoracic cavity into the definitive pleural/pericardial cavities

2. Diaphragm of Lungs:

Made from 4 structures:

  1. Septum transversum
  2. 2 pleuroperitoneal membranes –> expand med/ant to fuse w/ mesentery of esophagus, & septum transversum
  3. Musc of lat/dorsal body wall
  4. Mesentery of esophagus (makes the crura of diaphragm)

27. The portal vein. The portal-systemic anastomoses. The lymphatic dranaige of the abdominal and pelvic organs. The histology of the suprarenal gland. Development of the 2 external features of the fetus. External features of a matured newborn. Twin pregnancy. Fetal membranes in twins.

27 Dec

27. The portal vein. The portal-systemic anastomoses. The lymphatic dranaige of the abdominal and pelvic organs. The histology of the suprarenal gland. Development of the 2 external features of the fetus. External features of a matured newborn. Twin pregnancy. Fetal membranes in twins.

Anatomy: The portal vein. The portal-systemic anastomoses. The lymphatic dranaige of the abdominal and pelvic organs.

Portal Venous System


system of vessels in which blood collected from structures of the primitive gut – all unpaired visceral organs.
Stomach, Spleen, Liver, Intestines, Pancreas, GB

From those organs –> portal v –> liver sinusoids –> IVC (after filtration)

Portal v – formed by union of splenic v & sup mesenteric v, just post to border b/w head and neck of pancreas
Inf mesenteric v joins either one or jxn b/ w the two
located in Porta Hepatis b/w hepatic a proper, common bile duct
w/in hepatoduodenal ligament

Carries into Liver:

  • hormones – Insulin, Glucagon, Somatostatin from pancreas
  • RBC degradation products (ex/ bilirubin)
  • Absorbed food + other materials (not lipids) – amino acids, H20, salts, sugars etc
  • antibodies secreted by spleen products

Veins that drain into portal v

  1. Sup mesenteric v
    • w/ a @ R side of mesenteric root,
    • rec veins that correspond to art of sup mesenteric a
    • Inf pancreaticoduodenal v, L colic v, middle colic v
  2. Splenic v – union of branches from around spleen
    • Short gastric v, splenic br, pancreatic br, L gastroepiploic v
  3. Inf mesenteric v – union of sup rectal v, sigmoid v, L colic v
  4. L gastric v
  5. Paraumbilical v – in falciform lig, usually closed
    • but dilate in portal hypertension
    • connect  L branches of portal v w/ sub cutaneous v in umbilical region
    • (br of sup/inf epigastric, thoracoepigatric + sup epigastric v)

Portal Systemic Anastomosis
B/w portal system & either SVC/IVC
very important, since need to fxn during liver insufficiency,
to transport blood from portal –> systemic circulation directly
CLINICAL NOTE:   Portal Hypertension – Inc BP in portal v system, caused by pregnancy, cirrhosis of liver –> blood will flow to lower pressure areas –> veins that are anastomosed w/ veins that will flow into vena cava instead

1. Esophageal Anastomosis

  • formed b/w L gastric (to portal v) of stomach + esophageal v (azygos system)
  • In case of portal hypertension, these veins can enlarge or erupt –> bleeding
  • esophageal v located w/in walls of esophagus,
  • if they enlarge – will protrude more into lumen of esophagus
  • if erupt can cause bleeding into lumen of esophagus = verices

2. Rectal Anastomosis

  • b/w sup rectal v (inf mesenteric v) + mid rectal v (int iliac v) = hemorroidal v
  • In case of portal hypertension,  veins of int hemorrhoidal plexus enlarge & cause  internal hemorrhoids

3. Paraumbilical Anastomosis

  • located around umbilicus
  • b/w sup/inf epigastric & paraumbilical v
    • Inflow limb is recanalized umbilical v (in round lig of liver)
    • Outflow limb is towards the superficial + deep abdominal anastomosis systems
    • Special v located around umbilicus
    • running radial towards it, establish the connection b/w inflow – outflow part = paraumbilical v
  • In portal hypertension, paraumbilical v. enlarges, elevate from ant ab wall, causing classical symptom = Caput medusae

4. Retroperitoneal anastomosis

  • loc @ retropertineum, least important connection
  • formed b/w v of abdominal v & v of duod/colon = veins of Retzius
  • these veins could be cut if enlarges – bleeding in retroperitoneal space

The lymphatic drainage of the abdominal and pelvic organs.



Histology:The histology of the suprarenal gland.

Embryology: Development of the 2 external features of the fetus. External features of a matured newborn. Twin pregnancy. Fetal membranes in twins.

9th week –> birth = fetal period
growth in length = 3/4/5th months –>
CRL = crown-rump length
CHL = crown-heel length

Month 4 (see figure)

External Features: At four months fetal skin is transparent enough for underlying blood vessels to be seen clearly. Fingernails are well established and toenails begin to form. Nostrils by this time are almost formed and eyes move from the lateral sides of the head to the ventral side. Soft and thin hairs, called lunugo hairs, begin to grow on the scalp

Month 5

External Features: At five months, sebaceous glands accumulated at the surface of the skin begin to deposit verniz caseosa, which serves as a protective coating for the epidermis. The lanugo hairs that began formation during the fourth month now cover most of the entire body. Eyelids and eyebrows develop and abdomen begins to fill out.

Month 6

External Features: By the sixth month and the end of the second trimester, fetal skin is now red and wrinkled and lanugo hairs have darkened.

Month 7

External Features: At seven months, the fetus continues the development of hair and the scalp hairs grow beyond the length of the thin lanugo hairs that developed during the second trimester. Eyelashes are well developed and eyelids begin to open.

Month 8

External Features: By the eighth month, the skin is pink and smooth, the eyes are capable of reacting to light and the fingernails have grown long enough to reach the tip of the fingers.

Month 9

External Features: Toenails grow up to the tip of the toes and fingernails grow beyond the fingertips. The skin is fully covered in vernix caseosa (which serves to protect the epidermis) and most of the lanugo hairs are shed. By this time, the placenta weighs about 500grams and the umbilical cord becomes central in the abdomen.


26. The anatomy and development of the vertebral column. The histology of the thymus.

26 Dec

26. The anatomy and development of the vertebral column. The histology of the thymus.

Anatomy: vertebral column.

Vertebral Column

33 vert
= 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral vert, 4 fused coccyx vert

Parts of Vertebral Column

Parts of Vertebral Column


  • bifid spinous process (short)
  • foramina w/in transverse process = transverse foramina for vert a/v/n
  • smaller body w/ sup surface concave, inf surface convex
  • neural arch for med primarily by laminae
  • very short pedicles
  • transverse processes have ant/post tubercle for scalene m


most mobile of all vert
b/c curved bodies = flex/extention
shallow slope/ant process = lat flexion
atlas/axis = rotation

Special cervical vertebrae:
C1 atlas

  • no body, supports skill
  • widest of Cervical vertebrae
  • ant/post arches + paired trans processes
  • w/ occ condyles sup = atlanto-occipital joints
  • w/ axis inf = atlanto-axial joints

C2 atlas

  • smallest transverse process
  • characterized by dens = odontoid process
  • projects sup into ant arch of atlas
  • making pivot point around atlas = rotation


  • makes the vertebral prominence
  • long horizontal, one head spinous processes
  • covered w/ nuchal lig, supraspinous lig, back m

Thoracic vert

  • get bigger T1 –> T12 (bodies)
  • costal facet to articulate w/ ribs
    • @ where pedicle med body (sup)
    • @ end of trans process of ribs (inf)
  • spinous process = point downward, overlapping below
  • Movement = min flexion, lat flexion, rotation

Lumbar vert

  • Massive body
  • small & strong transv process, point back
  • almost NO Rotation:
    • -Upper face in (art facets)
    • -Lower are in & face out
  • Movement: flex, ext, lat flexion
  • L5 = largest, have mammillary and accessory processes


  • large wedge shaped bone
  • 4 pairs of foramina ->
    • ant = pelvic sacral foramina = ant rami of S1-S5
    • post = dorsal sacral foramina = post rami of S1-S5
  • makes post part of pelvic brim
  • provides stability for pelvis

Bony Markings:
sacral promontory = ant edge of S1
Ala = massa lata w/ hip bones = sacro-iliac joint
Med sacral crest
Sacral hiatus = lamina of S5 not fused, locks like upside down “V”

Curvatures of Spine:

  • 4 curvatures: cervical, thoracic, lumbar, sacral
  • provide flexible support
  • thoracic & sacral curve post – are the primary curves = develop from embryonic life
  • cervical & lumbar curve ant – are the secondary curves = develop in life

    • cervical = happens when infant holds his head up
    • lumbar = happens when infant begins to walk and is upright
    • caused by diff thicknesses of ant/post parts of IV disks

IV Joints:
1/4 of total spinal cord length
holds weight of spine
flexable enough to allow movement

Disk –> none b/w atlas & axis
1. Anulus fibrosis
concentric layer of fibrous cartilage & tissue
bind vert column together
absorbs SHOCK

2. Nucleus pulposis

remnant of embryonic notochord
reticular/ collagen fiber w/in mucus
equalize pressure, absorb shock

Vert Column Ligs
Intraspinous lig –> b/w lower edge of 1 to upper edge of next
Supraspinous lig –> across spinous pr, merge w/ intraspinous lig

Nuchal lig
is thickened supraspinous lig from C7 –> ext occ protuberance
makes triangular fibrous septum med b/w musc on post side of neck

Ligamentum Flavum

holds laminae together, maintain upright posture
pierced during Lumbar puncture to get CSF
yellow fibroelastic tissue

* all 3 above limit flexion of vertabrae column

Ant longitudinal lig – front and side of vert bodies
stronger than post, skull –> sacrum
widens as goes down, inc stability as weight increase
supports anulus fibrosus ant

Post longitudinal lig
– on vert canal on backs of bodies
narrow @ the body of vert, wider @ disks
narrows as desc,
support post bodies & anulus fibrosus post

Muscles of Vertebral Column
Paravertebral m – covered by fascia, ext, rot of Head & Neck, Trunk
1.Short rotator m – transv process of 1 –> spinous pr. base of vert above
2.Long rotator m – transv process of 2 –> base of sp pr of 2 vert above
3. Multifundous m – transv process of 1 –> side of sp pr of 3-5 vert above
*all 3 =  rotation of upper spine to opp side

Erector spinae m
– sacrum –> upper thorax
Joined @ origin, arise from a tendon that originate from spines of L1-5, iliac crest, post sacrum

  1. Spinalis – inserts of sp pr of upper Thoracic vert
  2. Longissimus – lower 9 ribs, transv pr. of vert next to them & mastoid process
  3. Iliocostalis lumborum – lower 6 ribs
  • *Ext, rotate, lat flex of vert column & head
  • One side only = lat flexion
  • Both sides = ext of Lumbar/thoracic spine

NOTE – Splenius, Longissimus cervicis, semispinalis are also vert m, but in neck mostly, so covered in that topic


Spinal Cord

  • upper 2/3 of vert canal
  • covered by 3 meningeal layers:
    • Pia, Arachnoid, Dura
    • b/w pia & arachnoid = subarachnoid space = CSF
    • b/w dura & vert canal wall = epidural space = fat, CT, a/v
      • CLINICAL NOTE =  epidural anasthetic
    • Dural sac (open sup, tapers as desc to S2) – cont w/ dura of brain
  • spinal cord connects to dura layer = denticulate lig

Cervical & Lumbar parts larger to make Brachial & Lumbar & Sacral plexus

In Embryonic life, cord runs whole length of vert column
but after birth, spinal column grows faster than cord
so cord end @ L1-2, spliting into branches
= Cauda Equina



Histology: The histology of the thymus.

Embryology: development of the vertebral column.


25. The abdominal aorta and inferior vena cava. The histology of the pineal body. Differentiation of the entoderm, folding of the embryo.

25 Dec

25. The abdominal aorta and inferior vena cava. The histology of the pineal body. Differentiation of the entoderm, folding of the embryo.

The abdominal aorta and inferior vena cava.

Abdominal Aorta

General Info:

  • Arteries that supply the visceral organs and posterior abdominal wall arise from the abdominal aorta.
  • goes from aortic hiatus of diaphragm –> L4, where it splits into L & R common iliac a


  • Ant *sup –> inf* = celiac plexus, celiac ggl, body of pancreas, splenic & L renal v, horizontal part of duodenum, coils of SI
  • Post = bodies of T12-L4, branches of L lumbar v –> IVC
  • Right = azygos v, cisterna chyli, thoracic duct, L crus of diaphragm, R celiac ggl
  • Left = L crus of diaphragm, L celiac ggl


4 main groups:
1. Paired parietal br

  1. Inf phrenic a – 1st br of ab aorta, originates below aortic hiatus => inf surface of diaphragm
  2. sup suprarenal a => suprarenal gland
  3. Lumbar a – 4 pairs of them => musc, structures of post ab wall

2. Unpaired parietal br

  • Med sacral a – originally paired, but L & R side join, org@ bifurcation of aorta , desc down sacrum @ midline

3. Paired visceral branches

  1. Middle Suprarenal – originates just below inf phrenic a => suprarenal gland
  2. Renal => kidney, R renal a is longer than L, and runs deep to IVC
    • inf suprarenal => suprarenal gland
  3. Gonadal a => testis, ovaries,

4. Unpaired visceral branches

Celiac Trunk => supplies FOREGUT

Left Gastric a (smallest br) => abdominal esophagus, lesser curve of stomach

  • runs in phrenico gastric lig,
  • runs up and L to cardia of stomach
  • gives rise to esophageal and hepatic br,
  • turns R and runs along lesser curve to supply it

Splenic a

  • long turtous a, runs deep to stomach along sup border of pancreas, and enters the lienorenal lig
  • gives 10 pancreatic br, main ones are inf dorsal, caudal pancreatic
  • short gastric br => fundus, reach stomach via gastro splenic lig
  • L gastro-epiploic (gastro-omental) => gr. curve of stomach, anastomose w/  R gastro epiploic
    • located w/in gastro colic lig

Common Hepatic a
=> Liver, GB, foregut part of duod, pancreas

  • Proper hepatic a (runs in hepatoduodenal lig), reach liver thru it
    • R hepatic a => R lobe liver, porta hepatis
      • Cystic a => GB
    • L hepatic a => L lobe, cuadate, quadrate lobe of liver
    • R Gastric a => lesser curve, runs thru hepatoduodenal lig, anatomose w/ L gastric a
  • Gastroduodenal a
    • sup pancreaticoduodenal a => prox duodenum, head of pancreas
      • sup ant/post br
    • R gastroepipolic a => Gr curve of stomach, in gastro colic lig, anastomose w/ L gastroepiploic a

Branches of Celiac Trunk

Branches of Celiac Trunk

Sup Mesenteric a  = MIDGUT
emerges right below celiac trunk, behind neck of pancreas
w/ sup mesenteric ggl
uncinate process of pancreas wraps around it
crosses in front of inf horizontal part of duodenum = pars tecta
then branches run w/in mesentery of SI

Inf pancreaticoduodenal a (retroperitoneal br)=> distal duodenum, part of head of pancreas
cross transv colon –> splits into ant/post br, which anatomose w/ ant/post br of sup pancreaticoduodenal a
Intestinal branches => Jejunum & Ileum
12-15 br that make the arterial arcades that run in mesentery of SI
Iliocolic a (aka Ilio cecal)  => cecum (runs in mesocecum), appendix, terminal part of ileum

  • (starts retroperitoneal –> intraperitoneal, before entering organs)
  • Asc colic a
  • ant/post cecal a
  • appendicular a

R colic a => colon
has asc/desc br, that can arise from sup mesenteric  a or iliocolic a as well
Middle colic a => prox 2/3 of transverse colon (runs in transverse mesocolon)

Inf mesenteric a = HINDGUT
originates from aorta @ L3, crosses psoas major m
emerges under root of mesentery
passes L. behind peritoneum
goes to desc/sigmoid colon, and upper rectum

L colic a => desc colon, distal 1/3 transv colon

  • asc/desc br
  • terminal part enters transv mesocolon
  • forms Arcus Riolani, by anastomosing w/ middle colic a (sup mesenteric a) = Cavo-Caval anastomosis

Sigmoid a
=> sigmoid colon

  • is first retroperitoneal –> runs in mesosigmoid
  • forms anastomosis w/ L colic a, sup rectal a
  • this can be cut in rectal surgery to extend a => Sudeck pt – site on the large intestine where the lowest sigmoid artery anastomoses with the superior rectal artery.

Sup rectal a
=> upper 1/3 rectum

  • desc in pelvis and dives into 2 br that follow sides of rectum
  • anatomose w/ middle & inf rectal a = Porto-caval anatomosis
    • Portal v blockage can cause hemorroids in this area
Relations of Ab aorta & IVC

Relations of Ab aorta & IVC

NOTE – Notice there are 2 crossing points when it comes to the aorta and IVC

– @ the beginning, the IVC is actually in front and to R of aorta, therefore L renal v is much longer than R one, having to cross the aorta

@ end, aorta bifurcates above the IVC, so common iliac veins are deep to arteries

Inferior Vena Cava

  • begins ant to L5, made by union of common iliac v
  • ant to bifurcation of aorta
  • on R side of L5—>L3, on R psoas major m
  • passes thru Caval opening in central part of diaphragm
  • enters R atrium of heart

Receives all veins that correspond to a of abdominal aorta (celiac trunk, sup/inf mesenteric a):

  • Common Iliac v
  • 3rd/4th Lumbar v
  • R testicular / ovarian v (L –> renal v)
  • Renal v
  • Asc lumbar v
  • R suprarenal v (L –> renal v)
  • Inf phrenic v
  • Hepatic v

The histology of the pineal body.

Differentiation of the entoderm, folding of the embryo.

In general, endoderm germ layer –> makes GI tract

2 kinds of folding:

1. Craniocaudal folding –

  • embryonic disk starts to bulge into amniotic cavity
  • to fold cephalocaudally
  • most pronounced in head and tail region – forms head and tails folds formed
  • ant part of endoderm = foregut – covered by buccopharyngeal membrane, later opens to make oral opening
  • midgut = midsection w/ connection to yolk sac = vitelline duct
  • hindgut = tail region, covered by cloacal membrane, opens to form anus

2. Lat folding –

  • due to growth of somites
  • embryo folds laterally = rounded appearence
  • ventral body wall formed, except where yolk sac connected

Both foldings = makes allantois –> into body of embryo = later becomes cloaca
distal portion of it is still connected to yolk sac
remnant of it= urachus

Derivatives of endoderm:
epith lining of respiratory tract
parenchyme of thryroid, parathyroid gland, liver, pancreas
reticular stroma = tonsils, thymus
epith = bladder + urethra, tympanic cavity, auditory tube

24. The anatomy and histology of the spleen. Differentiation of the ectoderm.

24 Dec

24. The anatomy+ histology of the spleen. Differentiation of the ectoderm.

* Completely Intraperitoneal, except at the hilum, where splenic vessels enter/ exit, part of FOREGUT

Anatomy of Spleen:

General Info:

  • Ovoid, usually purplish, pulpy mass about the size+ shape of one’s fist.
  • Largest of the lymphatic organs
  • Spleen varies in size, weight+ shape, it is usually app. 12 cm long+ 7 cm wide
  • It participate in the body defense system as a site of lymphocyte(white blood cell) proliferation+ of immune surveillance+ response.
  • PRENATALLY= a hematopoietic organ
  • After birth = is involved in identifying, removing + destroying expanded red blood cells+ broken- down platelets, in recycling iron+ globin. S
  • serves as a blood reservoir
  • storing RBC+ platelets+ to a limited degree
  • can provide a sort of”self transfusion” as a response to the stress imposed by hemorrhage.

Location: Located in the left upper abdominal quadrant or hypochondrium, where it receives the protection of the lower thoracsic cage

Surface Projection:

  • b/w 8th & lower border of 11th rib,
  • Ant = tip of 11th L rib,
  • Post = 2 finger medial to L inguinal line,
  • Long axis runs along the post part of 10th rib

Topography: 2 main surfaces – Costal & Visceral

  • Costal – contact w/ rib cage & diaphragm
    • In the costal region, it rests on the colic flexure
    • associated post w/ 9-11 th ribs+ separated from them by the diaphragm+ the costodiaphragmatic recess
  • Visceral – contact w/ abdominal organs = impressions made by them
    • Gastric – ant/med, fundus of stomach
    • Renal – behind, L kidney
    • Colic – below, L Colic flexure of LI
    • Hilum – splenic branches of the splenic artery+ vein enter+ leave, SPLENIC HILUM often in contact with the tail of the PANCREAS, L boundary of the omental bursa.

Function: Hemopoetic function or Immune System function

  • Primary Functions:
    • produces lymphocytes & antibodies
    • phagocytosis of damaged blood cells
    • storage of blood cells
    • proliferation of lymphocytes
    • formation of blood cells in fetal life
    • removal of macromolecular antigens from blood
    • retrieval of Fe from RBC Hemoglobin
  • Secondary Functions:
    • Antigen presentation by APCs = immune response
    • Activation and proliferation of B & T cells
    • differentiation of B cells and plasma cells
    • secretion of antibodies on white pulp
    • blood storage

Blood Supply:

  • The SPLENIC Artery is the largest branch of the celiac trunk+ follows a tortuous course
    • post to the omental bursa
    • ant to the left kidney+ along the sup. border of the pancreas.
  • SPLENIC VEIN: is formed by several tributaries that emerge from the hilum.
    • It is joined by the Inf Mesenteric v & runs post. to the body+ tail of the pancreas throughout most of its course.
    • The splenic vein unites with the Sup mesenteric v post. to the neck of the pancreas, to form the PORTAL VEIN.

Lymph Drainage: The splenic lymphatic vessels leave the lymph nodes in the splenic hilum+ pass along the splenic vessels to the pancreaticosplenic lymph nodes.

Innervation: The nerves of the spleen, derived from the celiac nerve plexus, are distributed mainly along branches of the splenic artery+ are vasomotor in function.

Peritoneal relations: Spleen is a soft, vascular(sinusoidal) mass with a FIBROELASTIC CAPSULE, entirely surrounded by peritoneum except at the SPLENIC HILUM. These ligaments, containing splenic vessels, are attached to the hilum of the spleen, on its medial aspect

  • Gastrosplenic lig (ant) – connects spleen to greater curve of stomach, spleen contacts the post. wall of the stomach+ is connected to its greater curvature by the GASTROSPLENIC lig
  • Phrenicolieanal lig (post)
  • Lienorenal lig – * If tail of pancreas is retroperitoneal, then inf gastrophrenic lig forms pancreaticolienal ligament & carries splenic a/v –> spleen, Inf border of phrenico lienal extends –> L colic flxure = phrenicocolic lig, and supports spleen inferiorly = nest of spleen

CLINICAL NOTE – frequently ruptured by fractured ribs & repair difficult, may be removed surgically w/ minimal  effect on body function –> function assumed by other reticuloendthelial organs, like Liver.

Histology of Spleen:

Slide #24 Spleen * H&E

Structures to Identify:

  • red pulp
  • white pulp
  • lymphatic follicles
  • germinal center
  • central a
  • trabecular v
  • venous sinuses

General Info:

  • largest lymph organ, on L side of Ab cavity
  • The spleen contains a large quantity of blood, that is expelled periodically into the circulation by the action of the smooth muscle in its capsule+ trabeculae.
  • thin fibrous capsule of the spleen
    • is composed of dense, irregular, fibroelastic CT.
    • fibrous capsule is thickened at the splenic hilum
    • divides spleen into compartments called splenic pulp
    • made of collagen w/ myofibroblasts
  • CT trabeculae, arising from the deep aspect of the capsule,
    • carry blood vessels to+ from parenchyma or splenic pulp, the substance of the spleen.
    • round or nodular and may contain a/v = trabecular a/v
  • White Pulp – site of lymphatic nodules
  • Red Pulp – site of sinues and cords

NOTE: PALS = T lymphocytes, Nodules = B lymphocytes

White Pulp – lymphatic nodules with germinal center around a central artery

The spleen is characterized by numerous aggregation of lymphatic nodules. These nodules constitute the white pulp of the organ.The lymphatic nodules also contain, GERMINAL CENTERS, that decrease in no. with age. NO distict cortex+ a medulla, as seen in lymph nodes. NO subcapsular or trabecular sinuses. The capsule+ trabeculae in the spleen are thicker than those around the lymph nodes+ contain some smooth muscle cells. The large lymphatic nodules =  white pulp of the spleen. Each nodule normally exhibits a peripheral zone with densely packed small lymphocytes = the peri-arterial lymphatic sheeth = PALS, aka Thymus dependent zone,

The central artery, in the lymphatic nodule, has a peripheral or an eccenteric position. Because the artery occupies the center of the periarterial lymphatic sheath, it is called the central artery. The cells found in the periarterial lymphatic sheath are mainly T cells. A germinal center may not always be present. In the more lightly stained germinal center are found B cells, many medium- sized lymphocytes, some small lymphocytes+ lymphoblasts.

  • White pulp is the side of immune response to bloodborne antigens
  • T cells surround the central arteries,
  • Whereas B cells are mainly in the lymphatic nodules
  • Antigen- presenting cells + macrophages are found in the white pulp.
  • Passing through each lymphatic nodule is a blood vessel called a CENTRAL ARTERY, that is located in the periphery of the lymphatic nodules.
    • Central arteries are branches of trabecular arteries,
    • become ensheathed with lymphatic tissue
    • between the venous sinuses+ form a spongy meshwork of reticular CT
    • usually obscured by the density of other tissue.

Red Pulp – consists of splenic cords+ splenic(blood) sinusoids

The red pulp contains the SPLENIC CORDS+ VENOUS SINUSES that course between the cords. These represent the branches of the central artery after it leaves the lymphatic nodule. Capillaries+ pulp veins are also present.

  • Splenic cords of Billtoth
    • Splenic cords are thin aggregation of lymphatic tissue containing small lymphocytes, associated cells+ various blood vessels.
    • loose meshwork of reticular cells & fibers w/ high # of RBCs
    • contain macrophages, lymphocytes, plasma cells, granulocytes, & enterocytes
  • Splenic sinuses
    • are dilated vessels lined with modified endothelium of rod shaped cells that appear cuboidal in transverse sections.
    • Endothelium has longitudinal axis parallel to direction of vessels
    • prominent IC spaces
    • no continuous basal lamina & wraps loops around sinuses (perpendicular to long axis)
    • mostly washed out due to increased # of RBCs
  • Also present in the red pulp are the pulp arteries.
    • surrounded by PAMS –  Peri-Arteriolar Macrophage sheath – macrophages w/ hemosiderin pigment granules
  • CT trabeculae with trabecular artery+ trabecular vein are evident
    • These vessels have endothelial tunica intima+ muscular tunica media
    • tunica adventitia is not apparent because the CT of the trabeculae surrounds the tunica media.

Arterial Flow:

Central a  (white pulp) –> branches –> marginal sinus –> red pulp –> straight arterioles –> pericellular arterioles –> arterial capillaries –> empty directly into the reticular meshwork of spleen –> splenic sinuses & cords of red pulp –> blodd exposed to macrophages (in sheathed arterioles, arterile capilaries) –> squeeze through walls of splenic sinus = Open circulation

Venous Flow:

Blood collected in sinuses –> tributaries of trabecular v –> larger v –> splenic v –> joins sup/inf mesenteric v –> hepatic portal v.

Embryology of Spleen:

  • Develops from mesoderm, w/in dorsal mesogastrium
  • development starts w/in the 5th week
  • spleen appears as proliferation of mesoderm
  • with the rotation of mesogastrium, goes into the post side of the abdomen
  • remains intraperitoneal
  • supported by lienogastric (to greater curve of stomach) and lienorenal lig (to L kidney)
  • Mesenchymal cells in the developing spleen differentiate to form the capsule, trabeculae, and reticular framework.
  • Development involves establishment of mesenchymal trabeculae within a blood vascular network consisting of a large number of endothelial sinuses.

Embryology- Differentiation of Ectoderm:

  • Ectoderm is one of the three layers of the trilaminar germ disk
  • Cells remaining in the epiblast after endoderm and mesoderm are produced = ectoderm
  • @ beg of 3rd week, the ectoderm layer has shape of disk that is broader towards the head (cranial portion), than the tail end(caudal).
  • After notochord and prechordal mesoderm form, these cause ectoderm on top of them to thicken and form neural plate
  • Cells of neural plate = neuroectoderm — process = neuralation
  • From Wikipedia:
    Generally speaking, the ectoderm differentiates to form the nervous system, epidermis, and the outer part of integument.

    In vertebrates, the ectoderm has three parts: external ectoderm (also known as surface ectoderm), the neural crest, and neural tube. The latter two are known as neuroectoderm.

23. Anatomy, Histology, & Embryology of the Pancreas

23 Dec

23. Anatomy, Histology, & Embryology of the Pancreas

*Pancreas is secondary retroperitoneal, with the exception of the tail, the foregut.

Anatomy of Pancreas

  • Location: Within the curve of the duodenum, located in the epigastric and left hypochondriac regions

  • Surface Projection: Surface projection of is different depending on the part of it, and will be entailed later.

  • Topography: touches the doudenum, the spleen, the left kidney, the lower border of the stomach.

  • Function: releases secretions in an exocrine fashion, namely pancreatic juice, which it then secretes into the duodenum through the major duodenal papilla, or papilla of Vater. This major pancreatic duct is also called the duct of Wirsung. Endocrine secretions include glucagon and insulin into the blood.

  • Parts:

    • Head – located between L1-2 in curve of the duodenum, to the descending and horizontal parts of it. develops mainly from the ventral pancreatic bud, except the upper part, which is from the dorsal pancreatic bud. Is located right to the sup mesenteric a/v.SP = head of pancreas is anterior loc to IVC, right renal a/v, left renal v Uncinate process– at lower head behind sup mesenteric a/v
    • Neck – short, 1-2cm, sup mesenteric a/v go behind the neck, @ notch below neck, called pancreatic notch. Ant surface of neck covered with peritoneum, and moves along with movements of pylorus of stomach. Sup mesenteric v and splenic v combine behind the neck of pancreas, to form portal v.
    • Body – loc @ L1-2, in front of vert column, posterior to lesser sac Has 3 surfaces:
      • Ant – covered by peritoneum, and indirectly contacts post stomach, lies in floor of lesser sac, helps form gastric bed >
      • Post – contact with aorta, sup mesenteric a/v, L kidney & renal vessels, and L suprarenal gland, Splenic a runs in tortous path superior to it, and has groove for splenic v.
      • Inf – touches 3rd and 4th part of duod Omental tuberosity – in sup surface of body below celiac trunk, contact with visceral surface of liver. (T12-L1 midline)
    • Tail – loc. at left costal arch, 2-3 fingers lat to T12, runs to hilum of spleen.
      • Can be retroperitoneal or intraperitoneal.
      • If shorter, than usually retroperitoneal, like the rest of pancreas. Then a small peritoneal ligament = pancreaticolineal lig extends from tip of tail –> hilum of spleem. Splenic a/v enter spleen through this ligament.
      • If longer, intraperitoneal, and splenic a/v can go directly to spleen.
    • Ducts:
      • Main pancreatic duct = Duct of Wirsung, duct of ventral pancreatic bud, begins in tail and runs along entire pancreas, till head, where it turns inf and runs with common bile duct. Opens at major duodenal duct – Ampulla of Vater, which is gaurded by sphincter of Oddi, after joining bile duct.
      • Accessory pancreatic duct = Santorini’s duct can open into main or minor duodenal papilla, sometimes both. minor duodenal papilla located 2cm above major one, Begins in lower portion of the head, and drains small portion of head and body.
      • Clinical NOTE – Bile ducts is embedded into a groove on the post/sup side of the head. If tumors are located within the head, this can block bile flow into the duodenum, resulting in jaundice.
  • Blood Supply: B/c develops from FOREGUT – supplied by branches of celiac trunk.
    • Splenic a – supplies derivatives of dorsal pancreatic bud –> neck, body, tail of pancreas located on shallow groove on sup/post side of pancreas. 10 branches, that can form arterial arcades (networks) with branches from gastroduodenal a and sup mesenteric a
    • Sup pancreaticoduodenal a (gastroduodenal a) & Inf pancreaticoduodenal a (sup mesenteric a ) splits into ant/post branches to supply the head of the pancreas
    • Most veins empty into splenic v, which is embedded into the back of the pancreas itself
  • Lymph Drainage
    • lymph vessels follow the arteries and drain into pancreatiosplenic nodes that lie along splenic arteries. The ones by the head go to pyloric lymph nodes, as well.
    • These two sets of nodes drain into celiac, hepatic, and sup mesenteric lymph nodes
  • Innervation
    • PNS – (+) digestion, secretion, vasodilation.
      • From CN X, carries pre ggl fibers to submucosal and myenteric plexus within walls of organs, with short post ggl PNS fibers.
      • Go to parenchyme (acinar cells and islets of Langerhans)
      • Inc Insulin secretion, Inc glucagon secretion
    • SNS – (-) digestion, secretion, vasoconstriction
      • SNS –> (T5-T9) from thoracic splanchnic n –> aortic hiatus –> celiac ggl plexus around the celiac trunk –> post ggl fibers run with branches of celiac trunk.
      • Go to pancreatic glands and parenchyme (pancreatic acinar cells and islets of Langerhans)
      • dec insulin secretion, inc glucagon secretion

Peritoneal ligaments:Peritoneal ligaments: none ,except for the tail sometimes, which can be located with in the pancreaticolienal ligament.

Histology Pancreas slide # 59 *H&E

Structures to Identify:

  • intercalated duct
  • intralobular duct

  • a/v/capillaries

  • Islets of Langerhans

  • Secretory acinus

  • A,B,D, cells

  • CT septa lobules

General Information

  • Digestive gland with head, neck, body , tail regions

  • Mixed gland with endocrine and exocrine functions


  • Tubuloacinar glands manily composed of serous secretory units

  • Secretions proteolytic enzymes

  • Proteolytic Endo-peptidases: trypsinogen, chemotrypsinogen

  • Exopeptidases: procarboxypeptidases, proaminopeptidases, alpha amylases, lipases nucleolytic enzymes

  • Has hormonal/ neural control regulation: Secretin – inc. fluid secretion, CCK – pro enzyme secretion Chyme of stomach and duodenum stimulate enteroendocrine cells to secrete CCk and Secretin → causes pancreas to secrete

  • Forms most of pancreas, has tightly packed serous acini – circular gland, small circular lumen, darkly stained. zymogen cells arranged in lobule fashion

  • Lobules seperated by thin intralobular, and interlobular CT septa – have blood vessels, interlobular ducts, pacinian corpsucles

  • Pacinian corpsucle – concentric circles, lighter than surrounding acini, is a sensory receptor


  • Islets of Langerhans (Pancreatic Islets) – highly vascularized epitheloid tissue

  • alpha, beta, delta, cells in periphery, beta cells also in center.

  • light staining, globular, with thin CT capsule surrounding it.

  • Pyramid shaped cells facing central lumen,

  • Secretions go to large vacular network of capillaries just outside the islets,

  • Excretes into intercalated duct, lined by low cuboidal epithelium

Alpha cells – glucagon – inc amount of glucose in blood

Beta cells – insulin – dec amount of glucose in blood

Delta cells -Somatostatin – inhibits the other two

Duct flow:

Within the islets, flow into pale staining centro acinar cells within lumen → intercalated (same as intralobular) ducts → interlobular ducts (simple cuboidal epith) in interlobular CT septa → larger ducts ( also interlobular, but with stratified columnar epith)

Embryology – Development of Pancreas

  • Endodermal lining of forgut forms two outgrowths, ventral pancreatic bud and dorsal pancreatic bud

  • Within both buds, endodermal tubules surr. by mesoderm –> branch to from acinar cells and ducts (exocrine part).

  • Clumps of cells within exocrine part form, and become the future islets (endocrine part)

  • Remember how the duodenum rotates 90 degrees clockwise? Because of this, the ventral bud (ant) rotates also – dorsally (post) and fuses with the dorsal bud already there to form adult pancreas

  • Ventral bud = uncinate process and lower part of head of pancreas

  • Dorsal bud = rest of pancreas

  • Main pancreatic duct (of Wirsung) = formed by distal dorsal bud and all of ventral bud

  • Acc pancreatic duct (of Santorini) = prox part of dorsal bud

  • Endoderm origin = acinar cells, islet cells, simple columnar and cuboidal lined parts of duct system

  • Visceral mesoderm = CT surrounding them, and a/v/capillaries

Anim :

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22. The anatomy, histology and development of the liver and biliary ducts and gallbladder.

22 Dec

22. The anatomy, histology and development of the liver and biliary ducts and gallbladder.

*Liver is intraperitoneal, except for bare area, and has FOREGUT origin

Anatomy of Liver

  • General Info
    • largest gland in the body and largest organ(after skin)
    • weighs app. 1500 g; 2.5 % of adult body weight
    • in late fetus: twice as large( 5% of body weight)
  • Location
    • lies mainly in the right upper quadrant of the abdomen
    • hidden and protected by the thoracic cage and diaphragm
    • normal liver lies deep to ribs 7-11 on the right side and crosses the midline towards the left nipple.
    • L. occupies most of the right hypochondrium, the upper epigastrium and extends into the left hypochondrium
    • inf to the diaphragm, which separate it from the pleura, lungs, pericardium and heart
  • Function
    • all nutrition absorbed from the gastrointestinal tract are initially conveyed first to the liver by the portal venous system(except for fat)
    • metabolic activities, glycogen storage and secretion of bile,
    • degrade or conjugate toxic substances to render them harmless
    • Protein synthesis
    • Heparin production
    • Breakdown of Hemoglobin
    • Hematopoiesis = RBC production
    • Storage of vitamins, Fe, and Cu
    • Bile function:
      • bile passes from the liver via the biliary ducts
      • R & L Hepatic ducts, join to form the common bile duct, which unite to form the cystic duct to form the bile duct
      • the liver produces bile continuously,
      • between meals it accumulates and is stored in the gallbladder, which also concentrates the bile by absorbing water and salts.
      • when food arrives in the duodenum, the gallbladder sends concentrated bile through the bile ducts to the duodenum
  • Surface Projection
    • Upper border = 5th rib @ mid inguinal line
    • Lower border = @ ant axillary line –> midinguinal line, follows the R costal arch, then @ end of 10th, asc obliquely into epigastrium, crosses midline @ transpyloric line, @ 8th L rib, enters hypochondrium
    • Lower and upper border meet jsut medial to L midinguinal line
  • Topography
    • 2 surfaces = diaphragmatic, and visceral.
    • the diaphragmatic surface of the liver is smooth and dome shaped, where it is related to the concavity of the inf surface of the diaphragm
    • Impressions on the visceral surface:

      1) gastric + pyloric areas: right side of the ant. aspect of the stomach

      2) duodenal area: sup. part of the duodenum

      3) lesser omentum: extends into the fissure for the ligamentum venosum

      4) fossa for gallbladder

      5) colic area: right colic flexure + right transverse colon

      6) renal+ suprarenal areas: right kidney + suprarenal gland

  • Parts
    • separated into R & L lobe ant by falciform ligament (a fold of peritoneum that attaches the liver to ant ab wall)
    • (post) – split into 4 lobes by a number of structures that make a “H” pattern on the visceral surface
      • 4 lobes are : R, L, caudate, and quadrate. (quadrate functionally part of L lobe, and caudate functionally part of both)
      • H made up of R and L sagittal fissures & transverse limb:
        • R-ant = fossa of gallbladder (sits on quadrate)
        • R-post = IVC fossa
        • L ant = falciform and round ligament
        • L post = ligamentum venosum, and hepatogastric lig.
        • Transverse limb = Porta Hepatis = ( portal vein, hapatic artery + lymphatic vessels+ hepatic nerve plexus+ hepatic ducts that supply + drain the liver enter and leave it.
      • Round ligament = remnant of umbilical v., @ inf free edge of falciform ligament
      • Ligamentum venosum = remnant of Ductus venosus, which shunts a significant majority (80%) of the blood flow of the umbilical vein directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver.
  • Peritoneal Relations of Liver
    • subphrenic recesses: sup. extensions of the peritoneal cavity(greater sac) exists between diaphragm + ant. + sup. aspects of the diaphragmatic surface of the liver
      • seperated into right and left recesses by the falciform ligament
    • suphepatic space= portion of the supracolic compartment of the peritoneal cavity immediately inf. to the liver
    • hepatorenal recess= posterosuperior extension of the suphepatis space, lying between the right part of the visceral surface of the liver and kidney/ suprarenal gland
      • cavity- deepest part(deepest next to rectovesical pouch) in supine position, fluid draining from the omental bursa flows into this recess.
      • communicates ant. with the right subphrenic recess
      Recesses of Liver

      Recesses of Liver

      Ligaments of Liver

      Ligaments of Liver

    • bare area of liver: diaphragmatic surface is covered with visceral peritoneum, except there.
      • It lies in direct contact with the diaphragm.
      • is demarcated by the reflection of peritoneum from the diaphragm to it as the ant(upper) + post(lower) layers of the coronary ligament.
    • Right triangular ligament: end  of coronary lig on R side
    • Left triangular ligament: end of coronary lig of L side
    • Hepatogastric ligament
    • Hepatorenal ligament
    • Hepatoduodenal ligament = remnant of ventral mesoduodenum, connect portal v. and duodenal cap
    • Hepatogastric and hepatoduodenal ligament together make up the borders of epilploic (omental) foramen, that leads from greater sac to lesser sac (behind the stomach), some say it also makes up the lesser omentum
    • ventral mesogastrium – liver develops in this, and the liver divides it into two ligaments: the lesser omentum & falciform ligament.
    • Bare area – no peritoneal coverage. Borders on both sides is falciform ligament, anterior and posterior leaf of coronary ligament, triangular ligament where ant/post leaves of coronary ligament unite. *Location of where hepatic v enter IVC
  • Blood Supply
    • receives O2  blood from hepatic a
    • have many many many variations
    • de-O2, nutrient rich, poss toxic blood –> portal v (portal v discussion another topic, please look at that one)
    • Hepatic a proper –>ascends in hepatoduodenal lig (R edge of lesser omentum) splits into R and L Hepatic a, R hepatic gives cystic a, Hepatic a immediately split into segmental branches
      • R Hepatic = R lobe, R 1/2 of caudate lobe
      • L Hepatic = L lobe, quadrate lobe, L 1/2 of caudate lobe
    • Hepatic v – drains blood of liver, usually 3 of them, Sinusoids of liver –> bigger br –> hepatic v –> IVC (@ bare area)
  • Lymph supply
    • Liver is major lymph producing organ
    • Superficial lymph nodes
      • in fibrous capsule of liver, just below the peritoneum
    • Deep lymph nodes
      • in CT with portal triads and hepatic v.
    • Superficial  l.n.  from ant diaphragmatic and visceral surface, and deep lymph vessels from around portal triads –> hepatic nodes, along hepatic vessels and ducts in lesser omentum–> celiac nodes –> cisterna chili
    • Superficial l.n. from post diaphragmatic and visceral surface –> bare area of liver –> phrenic nodes, a or to lymph nodes with hepatic v to IVC, thru diaphragm –>  post mediastinal nodes –> R lymph/thoracic duct
    • lymph can also go –>  L gastric, parasternal, and from round ligament area, umbilical nodes.
  • Innervation
    • hepatic n plexus @ porta hepatis, these branches come from the celiac plexus which sits around the celiac trunk
    • SNS = from celiac plexus
    • PNS = ant/post vagal trunks
    • N fibers run with arteries

Biliary Ducts & Gall Bladder

*Intraperitoneal, part of foregut


  • Location
    • Jxn of R 9th CC and lat border of rectus abdominus  where midinguinal line crosses 10th rib (fundus of it)
  • General Info/Topography
    • Pear shaped sac on inf surface of liver in fossa b/wR lobe and quadrate lobe.
    • lies right next to the 1st/2nd part of  diaphragm
    • touches transverse part of colon
  • SP = above, can only be palpated if gallstone present * made of calcifications of cholesterol and/or bilirubin. Gallstones more common in women than men, especially those with multiple pregnancies and/or overweight, and older.
  • Function
    • receives and stores bile and concentrated by absorbing H20 and salts and stores it
    • contracts to expel bile via (+) by CCK, which is produced by duodenal mucosa when food arrives there
    • Bile used to breakdown fat and fat soluble vitamins
  • Parts
    • Fundus – wide end, projects from the inf border of liver, located at tip of right 9th CC
    • Body – on visceral surface of liver, in GB fossa
    • Neck – narrow, tapered and runs towards porta hepatic, location of cystic duct
  • Blood Supply
    • primarily cystic a, from R Hepatic a
    • cystic v

      • from the biliary ducts and neck of gallbladder –> portal v, joins v from hepatic ducts and upper bile duct
      • from fundus and body –> visceral surface of liver –> hepatic sinusoids
  • Lymph Drainage
    • cystic lymph nodes –> hepatic lymph nodes –> celiac lymph nodes
  • Innervation
    • SS = R phrenic n
    • SNS = celiac plexus
    • PNS = CN X
    • fibers run with cystic a.

Biliary System:

  • Bile is made in Liver and stored in gallbladder. Bile is released into the duodenum when food arrives, and therefore fat needs to be broken down. Hepatocytes  secrete bile into bile canaliculi in b/w them.
  • Bile canaliculi unite to from intrahepatic bile ducts, that lie in portal triads with the hepatic portal v and hepatic arteries.
  • Bile ductules combine to form R and L Hepatic ducts
  • R & L Hepat ducts combine to form  Common Hepatic Duct
  • Cystic duct to gall bladder is from common hepatic duct
    • have spiral valves (Heister’s valves) which keep duct open si if common bile duct closed, bile –> cystic duct –> GB
  • Common Hepatic + Cystic duct = Common bile duct
    • 10 cm long and 1 cm in diameter
    • lies in b.w hepatic a and portal v
    • ususally embedded into post. surface of the head of the pancreas.
    • Left side of the desending part of the duodenum, the bile duct comes into contact with the main pancreatic duct.
    • These ducts run oblique through the wall of this part of the duodenum, where they unite to form the hepatopancreatic ampulla, the dilation within the major duodenal papilla.
    • distal end of ampulla opens into great duodenal papilla (about 1/3 way down descending part of duodenum, also called papilla of Vater, or Greater Duodenal papilla)
  • Sphincter of Oddi holds the opening of the papilla closed  – there are three parts to it, forming a sphincter for the bile duct, pancreatic duct, and for the papilla itself. PNS activity opens it.

Histology of Liver and Gallbladder

#57 Pig Liver * H&E

Structures to Identify:

  • Fxn’l lobule
  • central v
  • Bile duct
  • hepatic a
  • portal v
  • CT septa
  • lymph nodule
  • sinusoids
  • bile canaliculi
  • Kupffer cells
  • Glisson’s capsule
  • Hepatocytes (parenchyme)

Low power magnification: you see the lobular patternof the human liver, but less CT than for pic liver. Pig liver shows hepatic lobules the best b/c of prominent CT septa invaginating from surrounding Glisson’s capsule.

Medium power magnification:  hepatic lobules containing the central vein are dermacated by narrow stripes of interlobular CT made of reticular fibers.

Organization of Hepatic Lobules:

  • Functional units of the liver, described as lobules or acini, are made up of irregular interconnecting sheets of hepatocytes seperated from one another by the blood sinusoids.
  • parenchyme of liver is hepatocyte – normally 2 layers with sinusoids in b/w
  • Sinusoids convery mixed blood of Liver –> drain into central v.
  • radiating from central v –> periphery of lobule = plates of hepatic cells, with hepatic sinusoids in b/w, where venous and arterial blood mix
  • Space of Disse = b/w hepatocytes basal surface (sinusoids),

    • Perisinisoidal space b/w endoth of sinusoids and parenchyme
    • have microville that go into space and absorb protein from sinusoids
    • contain Ito cells and hepatocytes


3 ways of describing Hepatic lobules:

  • Classical lobule model – has at its center the v surrounded by  Space of Mall, (b/w CT stroma and outermost hepatocytes), sinusoids, and hepatic triad
  • Portal lobule model – emphasizes exocrine fxn of liver and has bile duct in center (part of portal triad)
  • Liver acinus model – best correlation among blood perfusion and metabolic activity and liver pathology
    • eliptical region between 2 central v and interlobular septum, divided into 3 zones
    • hepatic a, portal v, and bile duct from portal triad at periphery of lobules

Portal tracts contain the portal triad: with in the interlobular CT septa, each lobule has several portal triads surrounding it.

  1. interlobular vein: branch of portal vein

  2. interlobular artery: a branch of the proper hepatic artery, a thick- walled vessel with smaller diameter and the typical structure of arterioles or arteries

  3. interlobular bile duct: ducts of variable size, lined by simple cuboidal or columnar epithelium

Cells of Liver

  • Kupffer cells – belong to MPS, derived from monocytes, lie in sinusoid walls with endothelium, have pacytoic capabilites to help degrade RBCs and Fe/ferritin. In case of splenectomy, # inc to make up the difference in Hgb and RBC breakdown = see them best in RAT slide #57C, special staining required to see properly.
  • Ito cells – in space of Disse, stores vit A (precursor of retinol) that is needed for proper vision.
    • Note = In pathological cases, differentiate into myofibroblasts and secrete collagen, causing  fibrosis.
  • Hepatocytes – main parenchymal cells of liver, last 5 months, need lots of mitochondria for energy
    • polyhedral in shape
    • tight junction in b.w w/ bile canaliculi
    • peroxisomes (H2O2 –> H2O +O2)
    • Smooth ER to detox drugs
    • Endocrin fxn = secret apolipoproteins
    • lysosomes for degradation

More General Info

  • Liver cells are large, polygoneal cells with round, centrally located nucleus and prominent nucleus
  • Binucleate cells are seen in this section. The hepatocytes form flat, anastomosing cords;
  • Sinusoids are found between the hepatic cords, the sinusoids are lined by a discontinous layer of endothelium with flattend and condensed nuclei.
  • Kupffer cells are also present there, they are larger+ darker then the other cells of the sinusoids; sinusoids contain all the cellular elements of blood
  • The space as a fine slit between the sinusoid lining cells + the hepatocytes(the space of disse)is at the limit of the resulution of the LM.
  • Sometimes the hepatic capsule(Glisson’s capsule) is visible as a thin layer of CT, covered by simple squamous epithelium(visceral peritoneum) on the surface.
  • It also contains substances that bind to metabolites in the intestine to aid absorption.
  • A series of ducts of increasing diameter diameter + complexity, beginning with canaliculi between individual hepatocytes + ending with the common bile duct, deliver bile from the liver + gallbladder to the duodenum.

Endocrine v Exocrine Function

  • each liver has both exocrine + endocrine functions;
  • exocrine secretion of the liver:
    • secretes bilirubin (byproduct of  RBC breakdown produced by Kupffer cells)
    • Antibodies – produced in LP of SI/LI taken from blood by hepatocytes –> bile –> lumen of SI = control bacteria level there.
    • produce bile which contains conjugated+ degrated waste products that are delivered back to the intestine for disposal.
    • release up to 1L of bile to canaliculi daily
    • Bile flow:  Bile canaliculi –> bile duct –> hepatic duct –> cystic duct –> gallbladder –>cystic duct –> common bile duct –> duodenum
  • The endocrine secretion of the liver
    • are released directly into the blood that supplies the liver cells
    • these secretions include albumin, nonimmune alpha + beta globulins, prothrombin + glycoprotins including fibronectin
    • activation of vitamin D, thyroxin, and growth hormone
    • Glucose (released from stored glycogen) + T3  (the more active deiodination product of thyroxine), are also released directly into the blood.

Blood Supply/Lymph Drainage w/in liver

  • from portal v (spleen, stomach, pancreas, SL, LI) + hepatic a proper
  • portal blood contains:
    • absorbed degrade materials from GI tract
    • blood cells from spleen
    • pancreatic endocrine secretions
  • venous blood from portal v mixes with arterial blood from hepatic a proper in a 75%/25% ratio in portal capillaries
  • flows within perilobular a/v
  • as said perviously, blood drains into sinusoids, lined with discontinous endothelium– which allows the communication of hepatic blood with hepatocytes
  • remember that blood and bile never mix, they have seperate flow channels
  • Lymph –> Space of Mall, located in endothelial lining –>drain into v. –> thoracic duct

# 57A Pig Liver *AZAN

  • blue = collagen
  • stains CT capsule, loose CT (collagen type I and II)
  • stains reticular fibers in space of Disse
  • AZAN = azocarmine red, and aniline blue

#57C Rat Liver * Toluidin Blue & Nuclear fast red

  • Structures to Identify: sinusoids, Kupffer cells, Endothelium cells, Hepatocytes, Bile canaliculi
  • To demonstrate structures of parenchyme of liver
  • Kupffer cells are clearly visible, b/c they phagocytose the dye – present in sinusoids
  • Hepatocytes clearly defined
  • NFR stains nuclei red
  • Sometimes, bile canaliculi will be visible b/w hepatocytes

#58 Human Liver *H&E

  • Structures to Identify:  portal v, bile duct, hepatic a/v, central v, parenchyme, lymph nodules
  • same features as rat, but CT stroma not as prominent
  • if hepatic v, present, it will be alone and not in hepatic triad

Histology of Gallbladder #56 *H&E

Structures to Identify:

  • Mucosa – deep folds when GB empty
  • smooth m
  • glands ( only in neck region)
  • Rokitansky-Aschoff sinuses
  • a/v
  • adventia/serosa

General Info

  • concentrates and stores bile for delivery into duodenum – done by salt active transport from bile and passive movement of H2O in response to salt transport
  • Bile flow = R/L Hepatic ducts –> common hepatic duct –> cystic duct –> GB–> cystic duct –> common bile dcut –> duodenal papilla of Vater


  • characterized by tall columnar epithelium with so called  diverticuli or crypts, where the mucosa makes deep folds. LOOK FOR THESE – v. characteristic of GB = Rokitansky – Aschoff sinuses

    • advential invaginations of mucosal membrane
    • common site of bile stones inflammation, as these can close themselves off into closed sacs, where bacteria can collect
    • can extend into musc. layer
    • from as a result of inc pressure in GB and damage to wall of GB
  • has absorption function like in SI/LI
  • concentration of mitchondria found on basal/apical surfaces
  • Na/K ATPases on lat cell surfaces (not seen, theory only)
  • cells also have microvilli to increase surface area = absorption of H2O andminerals = concentrate bile
  • LP = rich in fenestrated capillaries for absorption and lymphocytes as usual

No Submucosa or Musc Mucosa!!

Musc ext

  • below LP, contains unordered smooth m layers
    • contract when activated by hormones from SI enteroendocrine cells
    • contract dec volume of GB –> bile expelled into cystic duct
  • lots of elastic fibers interwoven with it
  • have CT covering smooth m bundles with a/v/lymphatics/nevers

Outer Layers:

  • On Liver side = adventia – (CT layer rich in elastic fibers, n fibers, adipose tissue – no peritoneal coverage)
    • if is adventia, will have intercalated ducts to absorb bile and aberrant bile ducts = Ducts of Luschka
      • these ducts are non-functional
      • located on post wall of GB
      • may be present, are remnants of bile duct system
      • look like small lumen surrounded by cuboidal epithelium
      • none are connected to lumen of GB, some may be connected to liver
  • On unattached side = serosa – (visceral peritoneum, layer of mesothelium and loose CT
    • subserosa with it = thin squamous like layer

Embryology of Liver/Gallbladder

  • Liver primordium appears in the middle of 3. week, as outgrowth of the endodermal epithelium at the distal end of the foregut
  • This outgrowth, the hepatic diverticulum, or liver bud, consits of rapidly proliferating cells that penetrate the septum transversum= the mesodermal plate between the pericardial cavity and the stalk of the yolk sac.
  • While hepatic cells continue to penetrate the septum, the connection between the hepatic diverticulum+ the forgut (duodeneum) narrows, forming the bile duct.
  • A small  ventral outgrowth is formed by the bile duct, + and this outgrowth gives rise to the gallbladder+ the cystic duct.
  • During furhter development, epithelial liver cords intermingle with the vitelline + umbilical veins, which form hepatic sinusoids.
  • Liver cords differentiate into the parenchyme(liver cells) + form the lining of the biliary ducts.
  • Hematopoietic cells, Kupfer cells + CT cells are derived from mesoderm of the septum transversum
  • When liver cells have invaded the entire septum transversum, so that the organ bulges caudally into the abdominal cavity–> mesoderm of the septum transversum lying between the liver and the foregut+ the liver+ ventral abdominal wall become membranous –> forming the lesser omentum+ falciform ligament.
  • Together, having formed the peritoneal connection between the forgut+ the ventral abdominal wall, they are known as the ventral mesogarstrium.

The surface of the liver differentiate into visceral peritoneum, exept on its cranial surface.

  • In this region, the liver remains in contact with the rest of the original septum transversum.
  • this portion of the septum, which consits of densey packed mesoderm, will form the central tendon of the diaphragm
  • the surface of the liver that is in contact with the tendon of the diaphragm = bare area of the liver (never covered by peritoneum)

@ 10 th week: weight of liver app. 10 % of the total body weight

  • this may be attributed partly to the large numbers of sinusoids,also imp. Factor: is its hematopoietic function.
  • large nests of proliferating cells, which produce red + white blood cells, lie between hepatic cells+ and wall of the vessels.
  • this activity gradually subsides, during the last 2 month of intrauterine life + only small hematopoietic islands remain at birth.the weight of the liver is then only 5% of the total body weight.

@ 12th week: bile is formed by hepatic cells

  • since the gallbladder + cystic duct have developed + the cystic duct has joined the hepatic duct to form the bile duct, bile can enter the gastrointestinal tract, consequence= contents take on a dark green colour.
  • due to positional changes of the duodenum, the entrance of the bile ducts gradually shifts from the initial ant. position to a posterior one, and consequently the bile duct passes behind the duodenum.

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21. Anatomy, Histology, & Embryology of the Large Intestine

21 Dec

Anatomy, Histology, & Embryology of the Large Intestinecolon

*Considered partially intraperitoneal, and partially retroperitoneal, partially midgut & hindgut

Anatomy of the Large Intestine

  • Location: occupies a large area in the abdominal cavity, from ileocecal jxn to anus, approx 1. m long

  • Distinguishing Characteristics: Has the teniae coli, the three enlargements of outer longitudinal layer of musc externa, haustra – the bumps formed between each teniae (like little houses), and omental (epiploic) appendices – the peritoneum-covered sacs of fat attached all along the colon

    • 3 tenia are:
      • Omental – near attachment of greater omentum
      • Mesocolic – @ attachment of mesocolon
      • Tenia Libre (free)
  • Surface Projection: Don’t need to know all of it, just how to find cecum, and appendix

    • location of cecum = intersection between transtubercular and midinguinal line

    • appendix – clinically important to treat appendicitis. Can point in any direction. Located in two ways:

      • Make a line starting at umbilicus → ASIS, and point at jxn between 1st and 2nd third = McBurney’s point

      • Make a line between umbilicus and mid point of inguinal ligament, and find jxn b/w mid and lat third

  • Topography: will be discussed with each part of colon

  • Function: convert liquid contents of ileum into semisolid feces by absorbing water, salts, and electrolytes. Also secretes mucus onto the feces, to lubricate them for easier defecation/

  • Parts:

1.  Cecum – blind sac at proximal end of cecum, in right iliac fossa, covered by peritoneum, but has no mesentery attachment, can be palpated if filled with gas or feces about 2.5 cm about midpoint of inguinal ligament, location of ileocecal opening (leading from SI

2. Vermiform appendix – a narrow worm like sac that projects off the cecum (location listed above), possible lymphatic function b/c has lymph tissue in wall, suspended from ab wall via mesoappendix, normally 6-10 cm long, and 2-3 cm in diameter.

  • Clinical Note – If inflammed, will spasm, and cause PAIN. (NOTE that most pain felt in the abdominal organs is sensed by peritoneal coverage), but pain funnily enough, usually felt in epigastrium, not at location of appendix

3. Asc Colon – from cecum → hepatic (R colic) flexure, is secondary retroperitoneal. And is covered anteriorly by peritoneum, and not posteriorly. Histologically speaking, this means the anterior side has serosa and the posterior side has adventia. Passes over R kidney. SP = 3 fingers wide lat to R mid inguinal line

4. Transverse Colon – from R colic flexure → L colic flexure. SP of R flexure = Just below R lobe of liver @ transpyloric line. SP of L flexure = 3 fingers above transpyloric line, and 2 fingers lateral to L midinguinal line

  • NOTE – the prox 2/3 of transverse colon is MIDGUT, and distal 1/3 of transverse colon is HINDGUT.
  • Held in place by the transverse mesocolon, and sticks to posterior wall of lesser sac, lies along inferior border of pancreas, and continous posteriorly with parietal peritoneum, and is intraperitoneal
  • L colic flexure is attached to diaphragm via phrenicocolic ligament
  • Crosses Liver, Stomach, pancreas, and is imbedded into greater omentum

5. Descending Colon – is also secondary retroperitoneal, and runs from L colic flexure → sigmoid colon, Peritoneum covers it ant only, passes anterior to left kidney. SP = 2 fingers lat to L midinguinal line

6. Sigmoid Colon – S shaped, links desc colon to rectum @ S3, intraperitoneal, has a peritoneal attachment called sigmoid mesocolon, with left ureter and left common iliac bifurcation behind it

Note: Rectum and Anal Canal discussed below.

  • Blood Supply: Blood up until distal 1/3 of transverse colon is supplied by Sup. Mesenteric a, as it is MIDGUT, after it is HINDGUT, so blood supplied by Inf Mesenteric a. Veins follow the arteries

    • Sup mesenteric a:

      • cecum = iliocecal a (same as iliocolic a)

      • appendix = appendicular br off iliocecal a

      • asc colon and prox 2/3 transverse colon = iliocecal and right colic a.

    • Inf mesenteric a:

      • dist 1/3 transverse colon = middle colic a, left colic a

      • desc colon = left colic a, sigmoid a

      • sigmoid colon = sigmoid a

  • Lymph Drainage

    • Lymph vessels also tend to follow arteries. Lymph drains into paracolic nodes → then flow into lymph nodes named for the arteries that supply the area. Meaning, if area is supplied by middle colic a, lymph flows to middle colic lymph nodes.

  • Innervation

    • PNS – (+) digestion, secretion, vasodilation.

      • Midgut = from CN X, which carries pre ggl fibers to submucosal/myenteric plexus, which sends short post ggl fibers within the wall of the organ

      • Hindgut = from S2-4, via sacral splanchnic n

    • SNS – (-) digestion, secretion, vasoconstriction

      • Midgut = fibers from sup mesenteric ggl run with lesser splanchnic n, which run with arterial branches of sup mesenteric a

      • Hindgut = preggl fibers from L1-3 lumbar n → Inf mesenteric ggl → post ggl n fibers go to hindgut

  • Peritoneal ligament mentioned above

Histology Large Intestine #53 H&E

Structures to Identify:

  • All Layers
  • simple columnar epith
  • Crypts of Leiberkuhn
  • lymph tissue (GALT)
  • goblet cells
  • a/v
  • tenia (if present)
  • Myenteric plexus
  • Submucosal plexus

General information

  • Wall has same basic layers as SI, but NO kerkring folds or villi or paneth cells

  • Layers: Mucosa, Submucosa, Musc. Ext, and either serosa & adventia


  • simple columnar epith with brush border and goblet cells (loads of them)absorbative functio

  • Has intestinal glands = crypts of Leiberkuhn

  • LP = lymphoreticular connective tissue, location of Crypts of Leiberkuhn (intestinal glands), goblet cells, enteroendocrine cells (GEP cells), absorbative cells

  • has collagen table,layer of collagen which assists the resorbed water to enter capillaries via passive diffusion

  • well developed GALT (primary lymphatic nodules for production of Iga + secondary ones at times)

  • B lymphocytes formed in secondary follicles become APCs called follicular dendritic cells, found at border b/w mental zone and germinal center (larger eosinophillic nucleus)

  • pericryptal fibroblast sheath

  • NO lymph vessels (slow rate of metastasis in colon cancer)

  • stem cells located at bottom of crypt = zone of replication

  • Old goblet cells become tall and thin = tuft cells

  • Basement membrane very well defined

  • Musc. Mucosae present


  • lymph nodules might be seen, nothing else remarkable

  • fibroblasts, fibers, support cells, etc

  • Meissner’s nerve plexus

Muscularis Externa

  • very unusual, has same inner circular layer and outer longitudinal, but outer layer is primarily condensed into three muscular bulges called teniae coli, maybe some longit muscle in between them, but very thin, if at all.

  • 3 Teniae = Tenia mentali, mesocolica, & liber ( last one free, faces down, no attachment)

  • No tenia coli in appendix and in rectum, longit layer is continuous there

  • can find a/v here

  • location of Myenteric plexus

External Layer

  • may be either subserosa/serosa or adventia → if slice taken from anterior side of LI, then is serosa, but if from posterior side, then has adventia. Histologically mostly the same, adventia is thicker a bit.

  • If serosa, will have lots of adipose – indicating the epiploic appendices

Large Intestine #54 *AZAN

  • nucleus = red/purple

  • cytoplasm = pink

  • RBC = red

  • collagen = blue

  • musc = red

Vermiform Appendix # 52 * H&E

Structures to Identify

  • irregular lumen

  • lymph nodules w/ germinal centers

  • all 4 layers : mucosa, submucosa, musc externa, serosa

  • a/v

  • glands

General Information

  • described as worm like structure, arises from cecum and forms sac about 8cm long

  • b/c not open, can easily get inflammed and has to be surgically removed

  • may have role in B lymphocyte maturation, presence of mature lymphatic nodules, larger appearance in children

  • wall of appendix like SI, but no valves of Kerkring, or villi, so in that respect, ressembles colon


  • simple columnar epithelium with goblet cells and enterocytes

  • LP – sometimes invaginates into submucosa and musc. Mucosae (which is barely visible in some areas, and is discontinuous)

  • has MANY lymph nodules

  • goblet cells, enteroendocrine cells

  • lymphoreticular CT


  • normal structures, dense CT and extra a/v

  • eosinophillic, lots of collagen

  • Meissner’s plexus

Musc Ext

  • inner circular and outer longitudinal layer
  • NO tenia, layers are continuous the whole way around, they unite at origin of appendix
  • Myenteric plexus between 2 layers

NOTE – Appendix is intraperitoneal, so is totally covered with serosa

Comparison of Histology of SI v LI

Comparison of Histology of SI v LI

Embryology of Large Intestine

  • Epithelium (includes goblet cells, paneth cells in SI, and enteroendrocrine cells) is derived from endoderm

  • all other layers of LI are derived from visceral mesoderm (mean LP, musc mucosa, submucosa, musc ext, serosa or adventia)

  • MIDGUT = Cecum, Appendix, Asc colon, prox 2/3 transverse colon

  • Midgut forms U shaped loop (midgut loop) that herniates through the primitive umbilical ring into extraembryonic coelom @ wk 6
  • Midgut loop has cranial end, and caudal end – LI rotates 180 degrees → sup root goes below and behind inf root
  • Caudal end forms cecal diverticulum, (cecum and appendix), and the rest of the caudal limb forms lower ileum, and parts of colon mentioned
  • After rotation of 270 degrees counter clockwise around the superior mesenteric a, the cecum bud ascends to visceral surface of liver → R colic flexure
  • Cecum falls to R Iliac fossa → asc/transverse/desc colon formed
  • HINDGUT = distal 1/3 transverse colon, desc colon, sigmoid colon, rectum, anal canal
  • Cranial end of hindgut → becomes the parts of colon mentioned
  • terminal end of hindgut is endoderm lined pouch called cloaca, which touches surface ectoderm of proctodeum to form cloacal membrane
  • Cloaca split into ant and post areas by urogenital septum, which splits it into an anterior ugogenital area and posterior recto-anal area
  • Cloacal membrane becomes anal membrane posteriorly, and urogenital membrane anteriorly

Anim =

Anim2 =

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20. The anatomy, histology and development of the small intestine.

20 Dec

20. The anatomy, histology and development of the small intestine.

* Is made of foregut/midgut, and almost entirely intraperitoneal, except for part of duodenum

Anatomy of Small Intestine
General Info:
Consisting of 3 parts: duodenum, jejunum, + ileum
Function: Is the primary site for absorbtion of nutrients from ingested material,
Extends from the pylorus to the iliocecal junction, where the the ileum joins the cecum.
pyloric part of the stomach empties into the duodenum, regulated by the pyloric sphincter

Duodenum in Situ

Duodenum in Situ


  • First and shortest part of the small intestine, is also the widest+ most fixed part.
  • Duodenum makes a C- shaped around the head of the pancreas.
  • Duodenum begins at the pylorus on the right side+ ends at the duodenojejunal junction on the left side.
  • Junction: app. At the level of the L2 vertebra, 2-3 cm to the Lof the midline, the duodenojejunal flexure.
  • Most of the duodenum is fixed by peritoneum to structures on the posterior abdominal wall+ is considered partially retroperitoneal.

Topography of Duodenum:

Topography of Duodenum

Topography of Duodenum

Parts and Surface Projection of Duodenum

Parts and Surface Projection of Duodenum

Duodenum is divisible in 4 parts:
Sup(first) part: only part that is intraperitoneal

  • SP =  lies anterolat. to the body of the L1 vertebra (2cm R of it)
  • Topography = liver, GB, SVC, Aorta, portal v, right crus of diaphragm
  • connected to liver via hepatoduodenal lig
  • first 2 cm of the sup. part of the duodenum,
  • immediately distal to the pylorus
  • has a mesentery,  is mobile.& called ampulla

Descending(second) part: retroperitoneal

  • SP =  descends along the right sides of the L1- L3 vertebrae, 1 finger med to R mid inguinal line
  • Topography = R kidney, transverse mesocolon, common bile duct, SI loops
  • location of major duodenal papilla of Vater, entrance of bile duct and major pancreatic duct
    • papilla is closed off by Sphincter of Oddi
    • division between FOREGUT & MIDGUT
    • acc pancreatic duct can open online here, or in separate opening = minor duodenal papilla

Horizontal(Third) part: 6-8 cm long

  • SP = crosses the L3 vertebrae.
  • Topography = IVC, aorta, sup mesenteric a/v, SI loops, R crus of diaphragm
  • Sup. To it is the head of the pancreas and its uncinate process.
  • Sup mesenteric a/v cross in front, w/ aorta & IVC behind = area of crossing = pars tecta

Ascending(fourth) part: short(5 cm

  • SP = begins at the left of the L3 vertebrae+ rises sup. As far as the sup. Border of the L2 vertebrae.
  • Topography = Aorta, left crus diaphragm, loops of SI
  • terminates @ duodenal-jejunal jxn –> fixed by suspensory lig (of Trietz) to R crus of diaphragm
    • if the musc by the ligament contracts, this lifts the flexure and widens the angle of it, make it easier for contents to move thru it


Blood Supply:

  • B/c the duodenum arises from FOREGUT, & MIDGUT –> will be supplied by 1st, celiac trunk, then 2nd sup mesenteric a
  • FOREGUT PART ( b4 the major duod papilla): sup pancreaticoduodenal a (gastroduodenal a of celiac trunk)
  • MIDGUT PART (after papilla): inf pancreaticoduodenal a (sup mesenteric a)
  • both anastomose w/ each other
  • Venous drainage: duodenal v –> portal v
Blood Supply of duodenum

Blood Supply of duodenum

CLINICAL NOTE: Ileus – Ileus is a partial or complete non-mechanical blockage of the small and/or large intestine, caused by a manual obstruction, either by twisting or large strucutre stuck in bowel, or by dec blood flow to area

Lymph Drainage:

  • ant lymph vessels –> pancreaticoduodenal l.n. –> pyloric l.n –>cysterna chyli
  • post lymph vessels –> run behind head of pancreas –> sup mediastinal l.n.
  • can also go to celiac l.n

Nerve Supply:

  • from CN X (PNS), SNS nerves via celiac/sup mesenteric plexuses – around the arteries

Jejunum & Ileum

*Intrapertioneal – mesentarium proper connect them w/ dorsal body wall –> root of mesentery

Function: complete digestion and absorption of H2O, electrolytes, nutrients and minerals


  • prox 2/5 of SI
  • Emptier, larger in diameter, and thicker wall than ileum
  • has plicae circulares (circular folds), tall and closely packed
  • NO Payer’s patches
  • Translucent area = windows –> b/w blood vessels of mesentery
  • Less prominent arterial arcades (than ileum)
  • longer vasa recta  (straight a ) compared w/ ileum


  • distal 3/5 of SI
  • occupies false  pelvis in R lower quadrant of abdomen
  • has Peyer’s patches
  • shorter plicae circulares, more mesenteric fat, and arterial arcades than jejunum

Intestines are considered to have 2 edges:

  1. Mesenteric
    • line of attachment of mesenterium proper,
    • a/v, lymph and nerves sent and leave here
    • The mesentery is a fan- shaped fold of peritoneum that attaches the jejunum+ ileum to the posterior abdminal wall.
    • The root of the mesentery is directly oblique, inf.+ to the right.
      • It extends from the duodenojejunal junction, left of L2 –> to the ileocolic junction by  R sacroiliac joint.
        The avarage length of the mesentery from its root to the intestinal border is 20 cm.
      • Root of Mesentery crosses:
        • R crus of diaphragm
        • R psoas major m, R ureter
        • R genitofemoral n, R SNS trunk
        • R gonadal vessels
        • IVC, Aorta
        • 3rd part of duodenum

    W/in attachment line: sup mesenteric a/v, mesenteric plexus (ANS), Lymph network of SI

  2. AntiMesenteric
    • surgery is done on this side in order not to disrupt those structures

Blood Supply:

  • all MIDGUT = sup mesenteric a
    • make arterial arcades that run w/in the mesentery of Jejuno-Ileum
    • from the arcades come the vasa recta – straight arteries
  • drained by sup mesenteric v
    • joins splenic v, behind the jxn b/w pancreas head/neck, to form portal v
    • inf mesenteric v can drain into sup mesenteric v, splenic v, or jxn b.w the 2

Lymph Drainage:

  • lymph vessels run w/in mesentery
    • l.n located along arteries, close to the wall, and around the prox part of sup mesenteric a
    • –>  sup mesenteric l.n. (prox), ileocolic l.n. (dist)

Nerve Supply:

  • have a perivascular nerve plexus, run w/ arteries
  • SNS = from T5-9 –> celiac plexus via SNS trunk & splanchnic n
    • dec motility and secretion, VC
  • PNS = synpase on celiac/sup mesenteric ggl –> post ggl fibers run in myenteric/submucosal plexuses of SI wall
    • inc motility and secretion, VD

Histology of Small Intestine

Anim = structure of the small intestine.

Comparison of Histology of SI v LI

Comparison of Histology of SI v LI

Embryology: development of the small intestine.

Anim = Development of the Stomach, Omenta and Duodenum

Anim2 = Rotation of the Intestine

  • Primitive gut consists of foregut, midgut, hindgut
  • Foregut = Esophagus, Stomach, pancreas, liver, spleen, biliary tree, GB, and prox duodenum
  • Midgut = distal duodenum, SI, and LI until distal 1/3 of transverse colon = cranial limb of intestinal loop
  • For a while, due to rapid growth of abdominal organs, loops of SI herniate into umbilical region
  • @ abt wk 8, it rotates 270 degrees around the axis of sup mesenteric a — continues to grow
  • cranial limb, now on R side of body
  • as body grows and relative size of liver/kidney decrease, midgut returns into ab cavity fully @ wk 10
  • As it is coming out, it rotates another 180 degrees around sup mesenteric a
  • cranial limb will emerge 1st and settle on L side of body
  • mesentery will change in size as SI loops move