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

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

Topography:

• 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

Branches:

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

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

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