35. The anatomy, histology and development of the seminal vesicle and prostate gland.

35. The anatomy, histology and development of the seminal vesicle and prostate gland.

Anatomy of Seminal Vesicle & Prostate Gland

Seminal Vesicle:
*Retroperitoneal, except the tip, which is intraperitoneal

General Info:

• long tube (10-15cm), that coils down into 5cm
• produces seminal fluid – alkaline substance, w/ fructose, choline
• enclosed by dense endopelvic fascia
• are lobular glandulated structures that are actually pockets that formed off of the DD
• lower end becomes narrow & from ducts which join ampulla of DD –> make ejaculatory duct
• Does NOT store spermatozoa

Topography:

• @ post side of prostate
• located inf/lat to ampulla of DD, against the fundus of the bladder
• tip lie post to ureters, where peritoneum of rectovesical pouch separates it from rectum
• inf end separated from rectum via rectovesical septum

Blood Supply:

• inf vesicle a/v (int iliac a)
• middle rectal a/b (int iliac a)

Lymph Drainage: int iliac l.n.

Nerve Supply:
SNS – controls rapid contraction, during ejaculation – superior lumbar & hypogastric n
PNS – pelvic splanchnic n, inf hypogastric (pelvic) plexus

Ejaculatory Duct:

General Info:

• union of ductus deferens
• formed @ neck of bladder
• enters prostate @ post surface –> runs down, med, forward –> opens lateral to seminal collicus, on prostate urticle on post wall of prostatic urethra
• peristaltic contractions of musc layer of ductus deferens & ejaculatory ducts
• propel spermatozoa w/ seminal fluid into urethra

Blood Supply: deferential a (inf vesicle a)
veins –> prostatic and vesical venous plexus

Lymph drainage: ext iliac l.n.

Nerve supply: inf hypogastric plexus

Prostate
below the bladder, and is around prostatic urethra
prostatic capsule – has a dense CT fibrous capsule
prostatic sheath – has a soft CT capsule around fibrous one – derived from pelvic fascia
is continuous w/ paraproctium (the CT fibers around rectum), and paracysticum (CT fibers around bladder)

Two parts:
Glandular portion (2/3)
lat – make most of pass of prostate, lat to urethra
post – behind urethra, below ejaculatory duct CLINICAL NOTE – is palpable via rectal exam
med – around urethra, b/w it and ejaculatory duct

• Prostatic glands – produces seminal fluid that causes odor of semen
  • contains Prostatic specific antigen (PSA), prostaglandins, citric acid, acid phosphatase, proteolytic enzymes
  • make about 20% of seminal fluid
  • this fluid + secretions of seminal vesicles + secretions of bulbourethral glands + sperm = semen
• Urethral crest:
  • on post wall of prostatic urethra, and has # of openings for prostatic ducts on either side
  • has ovoid shaped enlargement called seminal collicus – where 2 ejaculatory ducts, prostatic utricle open
  • @ top of colliclus = prostatic utricle, small impression (analogous to female vagina)
• Prostatic sinus:
  • groove b/w urethral crest & wall of prostatic urethra
  • rec duct of prostate glands

Fibromuscular portion (1/3)
ant – ant to urethra, no glandular substance

Topography:

• ant = pelvic wall, musc fibers, has retroperitoneal fat in front of it, b/w it and pubic symphysis
• post = seminal vesicle, ductus deferens, ampulla of rectum
• sup = bladder
• inf = urethral sphincter, deep perineal m, UG diaphragm, levator ani

Blood supply: inf vesicle a, middle rectal a
drained by prostatic venous plexus (b/w  fibrous capsule & prostatic sheath) –> int iliac v

Nerve supply:
Both PNS/SNS to contract smooth m
PNS – pelvic splanchnic n (S2-S4)
SNS – inf hypogastric plexus

Histology of Seminal Vesicle & Prostate Gland

Slide # 69 Prostate *H&E

Structures to Identify:

• prostatic glands
• capsule
• glandular epithelium
• smooth m
• excretory ducts
• prostatic stones
• CT stroma

General Info:

• located inferior to neck of bladder
• seminal vesicle combine with the ductus deferens and open as ejaculatory duct here
• surrounded by dense CT capusle
• urethra leaves bladder and passes through bladder, and is called prostatic urethra.
• largest  accessory sex gland, several functional zones
• 30-50 glands arranged in concentric layers = mucosal, submucosal, and peripheral
  • Mucosal –> secrete directly into urethra
  • Submucosal/Peripheral –> secrete into urethra via ducts
• Secretions
  • Citric acid
  • Fibronalysin
  • Serine Protease (PSA) –> Clinical NOTE: if increased, can be early sign of prostatic cancer

Epith: transitional (urothelium) epithelium

Prostatic Glands

• look like popcorn
• have glandular epith = simple columar epith –> cuboidal
• are small, branched tubulo acinar glands
• may have circular very pink prostatic stones
  • calcifications of cellular debris in the gland
  • # increases with age
  • Very characteristic of prostate. — LOOK FOR THESE, if u think it is the prostate.
• between glands = fibromuscular stroma, with loads of smooth m bundles, and collagen and elastic fibers

Prostatic stones

The stroma encircles an area called the seminal collicus, that has no glands

At top of seminal collicus, is located the C shaped urethra, with the utricle underneath. Ejaculatory ducts open on either side of utricle

*cant see uticle and ejaculatory ducts in slide, but need to know them theoretically

on the lateral sides of the collicus are the prostatic sinuses (the end of the C), where the ducts of the glands open into.

Excretory ducts: columnar epith, stains darker than glands

Slide # 68 Seminal Vescicle *H&E

Structures to Identify:

• epithelium
• LP
• 2 muscular layers = circular, longitudinal
• irregular large lumen, with mucosal folds
  
• ductus deferens, if seen

General Info:

• an outgrowth of the ductus deferens
• produce yellowish, viscous fluid,  that contains high amt of fructose,which is energy for sperm
• produce most of the fluid found in semen
• are elongated glands on the posterior side of the bladder
• duct of seminal vesicle combines with ductus deferens to make ejaculatory duct
• vesicles are single tubes whcih are coiled and folded on themselves
• in cross section, look like separate lumens, but it is all one

Secretions contain:

• fructose
• other simple sugars
• amino acids
• ascorbic acids
• prostaglandins (originally discovered in prostate, IMP in inflammatory processes)

Cross section through region of ampulla of DD, so can see both DD and seminal vesicle

Ampulla muscular coat, tinner than rest of DD, and has secretory epithelium

Mucosa

• Epith = columnar or pseudostratified columnar, very invaginated (kinda looks like lumen of gallbladder)
• has mucosal crypts, made by infoldings of the mucosa
• LP
  • smooth m
  • rich in elastic fibers
  • very cell rich
  • goes into the primary mucosal folds
• secondary mucosal folds are the ones that u cant see open up into epithelium (look like closed sacs)

Muscular Layer

• rest on thick layer of smooth m cont w. DD
• smooth musch has inner circular and outer longitudinal layer
• contractions of smooth m. wall during ejaculation pushes substances through ejaculatory duct

Adventia – no peritoneal covering

Embryology  of Seminal Vesicle & Prostate Gland

Genital Duct formation:
Paramesonephric duct starts to develop, but later regresses, due to MIF

Mesonephric duct forms = epididymis, ductus deferens, seminal vesicle, ejaculatory duct, efferent ducts of testis

33. The anatomy and development of the female external genital organs. The histology of the vagina.

Anatomy:The anatomy of  the female external genital organs.

Vulva (female external genital organs)

Similar to male genital organs except:

• vagina pierces UG diaphragm
• urethra associates w/ ant wall of vagina
• genital folds do not unite @ midline –> instead forms vestibule
• bulbus does not unite @ midline

Vulva is made up of:

1. mons pubis
2. labia majora
3. labia minor
4. clitoris
5. vestibule
6. bulbus vestibuli
7. greater vestibular glands
8. vaginal orifice
9. ext. urethral orifice

Mons Pubis:

• rounded elevation of pubic area above symphysis
• subcutaenous CT – inc @ puberty, dec w/ menopause
• covered w/ pubic hair = secondary sexual sign (maturity)

Labia Majora:

• external covering of the vestibule
• contain fat as well, and smooth m bundles
  
• also covered w/ hair
• L & R join @ ant/post commissure – post usually disappears after having a child
  
• bulb of vestibule and glands below them
• round ligament inserts here after emerging from inguinal canal
• outer surface is covered w/ pigmented skin w/ many sebaceous glands
  

Labia Minora:

• small hairless folds w/in labia minora
• enclose the vestibule directly
• united posteriorly via frenulum of labia minora, clitoris
  
• unites ant to form prepuce of clitoris
• contain bulbospongiosus m
• high # of nerve endings = primary erogenic organ

Clitoris (homologus to male penis)
a) Root

• crura of clitoris originate from inf ramus of pubis
• ischiocavernosus m covers the crura
• L & R crus join @ midline and angle down to form body

b) Body

• suspended from pubis symphysis via suspensory ligament
• made from union of corpora cavernosa

c) Glans

• made from corpora cavernosum
• under cover of prepuce when flaccid
• protrudes when erected
• rich in n endings –> stimulate for orgasm

Vestibule

• space enclosed by labia minora
• has ext urethral orifice
• openings of paraurethral glands
  
• contains openings of vagina, urethra, and greater vestibular glands

Bulbus vestibuli (analogous to bulb of penis, corpus spongiosum)

• don’t unite @ midline
• separated by vagina
• become erect during sexual excitement = erectile tissue
  
• open labia minora
• bulbospongiosus m. covers bulb

Vaginal orifice

• located @ post part of vestibule
• behind ext opening of urethra
• Hymen closes off vaginal opening, leaves an opening, breaks during 1st sexual intercourse

Ext urethral orifice

• small opening @ ant part of vestibule
• just in front of ant wall of vagina
• 2-3 cm post to clitoris
• contains ducts of paraurethral glands (analogous to prostate) – will secrete the female ejaculate
  

Greater vestibular glands

• @ post end of bulb of vestibule
• behind vaginal orifice
• open @ side of labia minora
• secrete lubricant (mucus) during sexual excitement
• also surrounded by bulbospongiosus m
  
• lubricate vaginal orifice for penetration

Blood supply:

• ext pudendal a (femoral a) – supplies skin
• int pudendal a (int iliac a) – skin , sexual organs, perineal muscle
  
  • labial a
  • deep dorsal a of  clitoris
    
• drained by int pudendal v

Lymph Drainaga: superficial inguinal lymph nodes

Nerve supply:

• Ilioinguinal n (lumbar plexus)
• genital br of genitofemoral n (lumbar plexus)
• pudendal n
• cut br of femoral n

PNS = inc vaginal secretion, excitation of clitoris, erection for tissue in bulbs of vestibule

Vagina:

Function = organ of copulation & birth

• excretory duct for menstrual blood
• inf part of birth canal
• participates in sexual intercourse

General Info:

• runs  from cervix of uterus –> vestibule
• 7-9 cm, usually flat
• has transverse folds, which flatten during sex to accomadate penis = rugae
• 30-40 degrees back from vertical plane
• opens into vestibule of vulva
• opening partially closed off by hymen

• upper end divided into 4 fornices = 1 ant, 1 post, 2 lat that surround vaginal portion of cervix
  • ant fornix = shallowest, touches fundus of bladder
  • post fornix = deepest and touches rectouterine pouch, covered w/ peritoneum of rectum post
  • lat fornix = uterus, uterine a/v – w/in broad lig of uterus

Various Views of Vagina - Topography, internal structure, etc

Topography:

• ant = urethra in urethrovaginal septum, space b/w vagina and septum = urethrovaginal space
• post = loops of SI (sup), rectum via rectovaginal septum
• lat = contact cervix of uterus (sup)
• inf = levator ani m, UG diaphragm, perineal body

supported by:

• upper part = levator ani m, transverse cervical lig, pubocervical lig, sacrocervical lig
  
  • (ligaments together = paracolpium of vagina)
  • fibers merge w/ fibers of paraproctium(post) and paracysticum (ant)
• middle part = UG diaphragm
• lower part = perineal body

Blood supply:

• vaginal a (uterine a)
• vaginal br of int pudendal a (inf part of vagina), middle rectal a (middle part of vaginal), int iliac a

Venous drainage = vaginal venous plexus –> pelvic venous plexus –> int iliac v

Lymph Drainage:

• Sup part = int/ext  iliac l.n.
• Mid part = int iliac l.n
• Inf part = sacra and common iliacn l.n., superficial inguinal l.n.
  

Nerve supply: for autonomic innervation see topic # 40

• Inf hypogastric plexus
• pelvic splanchnic n

Minimals for this topic:

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208. Define the visceral relations of the vagina?

• The vagina is related anteriorly to the uterus and bladder and is fused with the urethra. Posteriorly, the vagina is related to the recto-uterine pouch, the rectum and the perineal body. The lateral fornix of the vagina is related to the ureter and uterine artery. At its upper aspect the vagina fuses with the uterus, so that it encloses the vaginal part of the cervix.

Slide #75 Vagina *H&E

Stuctures to Identify:

• str squamous non keratinized epithelium
• LP
• 2 muscular layers
• adventia, with n/possible ganglia and sk. musc

* So if you see a thick epithelium that fades from pink to white as u move up = VAGINA

General Info:

• no glands here – all lubrication done by cervical glands and Bartholin’s glands at entrance
• epithelium thickens and secretes glycogen under influence of estrogen
• Vaginal bacteria changes the glycogen into lactic acid — acidity protects the vaginal canal from pathogens

Epith

• is very characteristic of vagina
  
• THICK,  str squamous epithelium  with mucosal folds
• has Langerhan’s cells @ base
  
• CT papilla coming up from under lying LP
• very faint because very rich in glycogen, which can be washed away in slide prep.
  

Vaginal pale epithelium, notice the lymphocytes and Langerhan's cells at base of epith, as well as CT papilla

LP

• aka semi cavernous tissue = b/c a/v similar to cavernous tissue of penis
• dense reg CT filled with elastic tissue for stretching of vaginal wall
• MALT, lymph nodules, a/v
• underlying submucosa interweaves with it
• no definitve border between LP and submucosa = NO muscularis mucosae

Muscular Layer

• Inner longitudinal layer, outer oblique layer

Adventia

• lots of a/v and n bundles
• may have PNS ggl
• May have skeletal m fibers from perineal m – not part of vagina, just attached to wall of it

32. The anatomy, histology and development of the uterine tube and uterus.

Anatomy of Uterus/Uterine Tube

Uterus:

Location: b/w bladder (ant) and rectum (post), above and leads to vagina

Function: Major organ of gestation

General Info:
7-8 cm long, 5-7 cm wide, 2-3 cm wide
2 main parts = corpus (upper 2/3) and cervix (lower 1/3) , connected via isthmus

• Cervix protrudes into vagina @ angle of 60-70 degress = anteversion ( angle b/w vagina and cervical canal)
• Body inclines forward and bends over fundus of bladder, attached to cervix w/ angle of another 60 degrees = anteflexion ( angle b/w jxn of cervix and body)

Topography:

• ant = fundus of bladder
• post = coils of SI, and via pouch of Douglas, the rectum
• lat = cardinal ligament @ level of cervix (part of parametrium), that carries the uterine a/v
• sup = fundus of uterus touches SI coils
• inf = supported by pelvic diaphragm, UG diaphragm, round, broad, lateral cervical ligaments, pubovesical, sacrocervical, retro-uterine ligaments

Parts:

Cervical portion:
has 2 areas:
Vaginal portion – protrudes into vagina,surrounded by vaginal fornices

• has rounded end and ext os of uterine canal w/in it
• @ ext os, simple columnar epith –> str squamous
  
• If no kids (nulliparous) – opening is round, and small
• If kids (multiparous) – opening is slit like

Supravaginal portion – embedded into CT of visceral pelvic fascia (via parametrium), in direct contact w/ broad ligament (myometrium)

Cervical Canal:

• terminal portion of uterine cavity
• has impermeable plug of mucus,
  • helps prevent entrance of pathogens
    
  • that becomes permeable during ovulation –
  • does allow sperm to penetrate
• b/w cervix and isthmus of uterus = int histological os – where wall of cervix changes to uterus histologically

Epith of cervix isn’t shed in menstruation like the epith of rest of uterus = simple columnar, # of glands inc in this area – they secret the mucus to make mucus plug
keeps closed until few hours before birth – then begins to dilate to allow head thru – this is due to high amt of collagen and smooth M in cervix

Cervix doesn’t have real myometrium, called it, but really has less smooth m and more elastic fibers compared to rest of uterus

NOTE: (Please do not be confused by the 50 names out there for the same thing)

• Int opening of isthmic canal = anatomical int os (does not exist in pregnancy)
• Int opening of uterus = int os = histological int os = external opening of isthmus (isthmic canal)
• Ext opening of uterus = external os

Corpus

Biggest part of uterus
covered by broad ligament = called the mesometrium of uterus, attaches it to lateral body wall
bends over the bladder (ant)

Has two special parts : fundus & isthmus
Fundus

• area above the level of uterine tubes
• laterally, ends in uterine horns –> lead to uterine tube

Isthmus

• narrow part locared b/w cervix & corpus of uterus
• same histological structures as corpus of uterus
• incorporated into cavity of uterus during pregnancy – @ 2nd 1/2 of pregnancy, isthmus opens up, so anat int os ceases to exist, only histo os and ext os still there
  
• isthmic canal – canal w/in the isthmus
• Int anatomical os – b/w isthmic canal and uterine cavity

Wall of Uterus
Perimetrium = outer layer, peritoneum & underlying subserosa
Myometrium = middle musc layer, has sublayers
Endometrium = innermost layer, layer removed during menstruation

Ligaments of Female Pelvis

1. Broad ligament of uterus – 2 layers of peritoneal covering, from lat margin of uterus –> lat pelvic wall
   • holds uterus in position
   • contains: uterine tube, a/v, round ligament, ovarian ligament proper, urete, uterovaginal n. plexus, lymph vessels
2. Mesovarium – fold of peritoneum that connects ant surface of ovary w/ post layer of broad ligament
3. Mesosalpinx – fold of broad ligament that suspends the uterine tube
4. Mesometrium–  fold of broad lig below mesosalpinx, and meso-ovarium, lat wall of uterus –> pelvic wall
   
5. Proper Ovarian ligament – fibromusc cord from uterine end of ovary –> side of uterus below uterine tube w/in broad lig
6. Suspensory ligament of ovary – band of peritoneum that runs sup/lat from end of ovary –> pelvic wall, has ovarian a/v, lymph vessels
7. Lat/Transverse Cervical (Cardinal) Lig of Uterus (aka ligament of Mackenrodt’s) – fibromuscular condensations of pelvic fascia from cervix (hence, cervical) & lat fornix of vagina –> pelvic wall, run w/in parametrium of uterus
8. Parametrium – fibrous CT that runs w/in mesometrium, connects uterus to lat pelvic wall
9. Paracolpium – fibrous CT that connects the lat wall of vagina –> lat pelvic wall, fibers merge w/ those of para cysticum (for bladder)
10. Pubocervical ligament – firm bands of CT from post surface of pubis –> cervix of uterus
11. Sacrocervical(uterine) ligament – firm fibromuscular bands of pelvic fascia from lower end of sacrum –> to cervix, upper end of vagina *palpable in rectal exam
12. Pubovesical ligament – pelvic fascia bands from neck of bladder (or prostate in male) –> pelvic bone
13. Rectouterine ligament – holds cervis back and up and sometimes elevate a shelf-like fold of pertioneum (recto-uterine folds – called sacro-genital folds in male)
    • isthmus of uterus –> post wall of pelvis, lat to rectum

Ligament relations of Uterus & Uterine tube

Connective tissue ligaments of female pelvis

Also, peritoneal covering over pelvic organs in female create 2 pouches:
1. Vesicouterine Pouch

• ant = bladder
• post = uterus
• lat = vesicouterine folds

2. Rectouterine pouch – aka Douglas pouch

• ant = uterus
• post = rectum
• lat = rectouterine folds
• floor = post fornix of vagina, in direct contact w/ ampulla of rectum *can be felt there via rectal exam

CLINICAL NOTE: This is deepest point of peritoneal cavity in female, any excess peritoneal fluid will collect there
blood in pouch can indicate the presence of ectopic pregnancy

Pouces and ligaments/Topography of Female Pelvis

Blood Supply: primarily uterine a, secondarily ovarian a

• Uterine a enters parametrium via cardinal ligament of ovary
  • when it reaches isthmus, divides into large asc uterine br
  • small desc uterine br
  • also has ovarian and tubal br
  • @ cardinal lig  – uterine a/v crosses ureter and have vessels in fromt
• Ovarian a
  • has ovarian and tubal br that anastomose w/ same br of uterine a
• Veins = uterovaginal plexus of veins –> int/ext iliac v

Blood Supply of Uterus, Uterine tube

Lymph Drainage:
1. Fundic region = aortic nodes via ovarian lymph vessels
2. Corpus = ext iliac and sup inguinal nodes
3. Cervix = int iliac and sacral nodes

Nerve Supply = branches of hypogastric n plexus,

Uterine Tube:
non united part of Mullerian duct (embryo)
Location: from horn of uterus –> ends in ampulla @ uterine end of ovaries

Function:

• carries fertilized or unfertilized ovum from ovary to uterus, for Implantation
• via action of the cilia on its epithelium, and contraction of musc wall, also carries sperm towards the ovary
• Connects uterine cavity w/ peritoneal cavity
• Fertilization occurs in ampulla or infundibulum of uterine tube

Parts:
1. Infundibulum – funnel-shaped distal portion over end of ovary

• has 20-30 fimbriae, which attach to ovary
• move to guide oocyte in after ovulation
• communicates w/ peritoneal cavity via abdominal ostium

2. Ambulla – FERTILIZATION

• widest and longest part of uterine tube
• INTRAPERITONEAL
• attached w/in broad ligament via mesosalpinx

3. Isthmus – short 2.5 cm long area that leads to horn of uterus

4. Uterine part

• part that attaches to uterine wall
• opens into uterine cavity via  uterine ostium

Blood supply = tubal br of ovarian and uterine a, veins run w/ a

Lymph drainage = run to aortic/lumbar nodes

Nerve supply = pelvic/ovarian n. plexus, that run in mesosalpinx

Minimals related to this topic:

196.    Describe the relation of the ovary to the uterine tube!
The upper or tubal end of the ovary is closely related to the uterine tube. The infundibulum has irregular fringes called fimbriae that project from the margin of the infundibulum to the ovary.
197.    Define the term “broad ligament of the uterus” and list those structures that are located within its substance!
A double layered peritoneal ligament extending from the sides of the uterus to the lateral walls and the floor of the pelvis.
Structures: uterine tube, round lig. of uterus, ovarian lig., epoophoron, paroophoron, uterine vessels, uterovaginal venous plexus, nerves.

198.    Define the term “parametrium”!
The loose connective tissue found between the two diverging layers of the broad ligament of uterus, which connects the lateral part of the cervix with the pelvic wall.
199.    Define the position of the uterus under normal conditions?
In the axis of the true pelvic, in anteflexion (bends forward) and anterversion (inclines forward)

200.    Define the term anteflexion and anteversion of the uterus!
Anteversion: the cervix is inclined anteriorly at an acute angle (appr. 60°-70°) to the vagina.
Anteflexion: the body of the uterus is bent anteriorly at an acute angle (appr. 60’-70’) to the cervix.

201.    Describe visceral relations of the uterus!
anterior    : posterior wall of bladder,
posterior    : anterior surface of rectum, small intestines,
above    : small intestines,
lateral    : ureter, before its opening into the urinary bladder.

202.    What is the epithelium of the a.) cervical canal and b.) vaginal portion of the uterus?
simple columnar mucous producing epithelium, with scatterd ciliated cells,
stratified squamous non keratinizing epithelium.

203.    Describe the peritoneal relations of the uterus!
The body and the posterior aspect of the supravaginal portion of the cervix is enclosed between the two layers of the broad ligament. The peritoneum reflects from the uterus posteriorly to the rectum and anteriorly to the urinary bladder forming the rectouterine and vesicouterine pouches, respectively.

204.    Define the term “Douglas pouch”?
Rectouterine pouch. Reflection of the peritoneum from the rectum to the uterus. The deepest point of the peritoneal cavity.

205.    List those structures that help to fix the uterus in its original position!
Vagina, pelvic and urogenital diaphragms, round lig., ovarian lig., vesicouterine fold, rectouterine fold, thickenings of the visceral pelvic fascia, broad lig., parametrium.

206.    Which lymph nodes receive lymph from the a.) fundus, b.) body and c.) cervix of the uterus?
aortc, external iliac, superficial inguinal lymph nodes,
external iliac lymph nodes,
internal iliac and sacral lymph nodes.

Histology of Uterus/Uterine Tube

Slide #76 Uterus, Proliferative phase

Structures to Identify:

• all layers of wall
• simple columnar lining epithelium
• simple tubular glands
• a/v – arteries have a fused tunica mucosa
• LP w/ spinocellular CT

General Info:

• Endometrium (same as mucosa) changes with menstrual cycle
• Menstrual cycle
  • Day 1-5 = Menstruation
  • Day 5-6 Regeneration
  • Day 6-14 Proliferative/Estrogen phase
  • Day 14-28 Secretory/Progesterone/Luteal phase
• Uterus provides the site of implantation of fertilized embryo and formation for placenta
• Note that the embryo grows within the wall of the uterus, causing the lumen to narrow, and forms a separate amniotic sac – the embryo does not grow in uterus lumen per se.

Endometrium

• innermost layer, is equivalent to mucosa in other slides
• changes made in endometrium based on hormones produced by ovaries
• To tell that it is Uterus look for: v THICK mucosa, with loads of glands, and is very basophillic

Epith

• simple columnar epith (ciliated and non ciliated cells)
• epith is lower because this is the start of the cycle
• non-ciliated cells will secret hormones in second part of cycle

LP

• cell rich CT highly vascularized
• simple tubular glands – inactive in this  stage
• b/w glands, spinocellular CT & a/v
  • the endometrial stroma, which resembles mesenchyme
    
  • is highly cellular+ contains abundant intercellular ground substance.
  • cells  = stromal cells like in ovary
• thickness depends on stage in cycle
• Has two layers = Statum Functionalis superiorly, and Stratum Basalis inferiorly
• Blood Supply:
  • RADIAL ARTERIES, (branches from the arcuate arteries in myometrium), enter the basal layer of the endometrium, where it give off small straight arteries that supply this region of the endometrium.
  • The main branches of the radial artery continous upward, become highly coiled SPIRAL ARTERY
  • Spiral arteries give off numerous arterioles, that often anastomoses, as they supply a rich capillary bed.
  • Lacuna= dilated segmants, may also occur in the venous system, that drains the endometrium.
  • The straight arteries+ the proximal part of the spiral arteries do not change during the menstrual circle.
  • The distal portion of the spiral ateries undergoes degeneration+ regeneration, with each menstrual cycle, under the influence of estrogen+ progesteron.

Note the smooth and oval glands in the endothelium = def proliferative phase uterus

Stratum Functionalis

• the one that proliferate+ degenerate during menstrual cycle
• during this phase of the menstrual cycle, the endometrium varies from 1 to 6 mm in thickness.
• UTERINE GLANDS(simple tubular): surface epithelium invaginate into the underlying lamina propria, the endometrial stroma.
• containing fewer ciliated cells
• If the glands are oval and smooth in the section, then you know it is proliferative stage.
  
• Separated into upper Compact Layer, and inner Spongy layer
  

Stratum Basalis

• minimal changes in the is layer between stages in the uterus
• regeneration of epithelium starts from the stromal cells and glands in this layer
• large amount of cells int his layer – even more so than in basal layer

NO MUSC MUCOSA/ SUBMUCOSA separate the endometrium from the myometrium.

Myometrium

• is the thickest layer of the uterine wall

• composed of 3 undefined layers of smooth muscle bundles: you see cross, oblique, longitudinal sections.

• the smooth muscle bundles in the inner+ outer layers are predominantly oriented parallel to the long axis of the uterus.

• muscle separated by interstitial CT
• lots of a/v. —> tunica media of arteries merges with smooth m of the myometrium
• arcuate a in myometrium =  vascular zone
  • separates the uteine wall into three zones – Supra vascular, vascular, and perivascular below.

  • 6- 10 arcuate arteries coming from the uterine artery that anastomose in the myometrium

Perimetrium

• adventia/serosa
• on sup surface of uterus, covered with peritoneum –> serosa
• In other surfaces of uterus, is infraperitoneal –> covered with  adventia
• If adventia, can possibly see ggl cells and nerve cells
  

PROLIEFERATING PHASE REGULATED BY  ESTROGEN:

• at the end of the menstrual phase, the endometrium consits of a thin band of CT(about 1 mm) thick, containing the basal portion of the uterine gland+lower portion of the spiral arteries. = stratum basale the layer, that was sloughed off was the stratum functionale.
• Stromal, endothelial+ epithelial cells in the stratum basale proliferate rapidly, following changes can be seen:
• Epithelial cells in the basal portion of the glands reconstitute the glands &  migrate to cover the denuded endometrial surface.
• Stromal cells:  proliferate, secrete collagen, & ground substance
• Spiral arteries lenghten, as the endometrium is reestablished, these arteries are only slightly coiled+ do not extend into the upper third of the endometrium.
• Continous until 1 day after ovulation, which occurs at about day 14, of a 28- day cycle.
• At the end of this phase, the endometrium has reached a thickness of about 3 mm.
• The glands have narrow lumina+ relatively straight, but have a slightly wavy appearance.
• Accumulation of glycogen are present in the basal portion of the epithelial cells.

Slide #77 Uterus, Secretory phase

See the white space between the cells of stroma? And the twisted glands? = Secretory Phase Uterus

Structures are the same as listed above, with some key differences

Endometrium

• Stratum functionalis –
  
  • MUCH thicker,
    
  • uterine glands are now larger and wavy, not oval shaped –> increase size due to secretion within
    
    • inside of glands are pale because secretions are mostly carbs
      
  • arteries are also more coiled , and become more prominent in this layer
    • increase in volume, to prepare for menstruation, the next phase
      
• Stratum basalis –
  
  • less cells in interstitial tissue, more white space between cell
  • the increased interstitial fluid between the cells is called Interstitial EDEMA
  • more WBC, monocytes, neutrophils, granulocytes
  • straight a in this layer —> coiled arteries in fuctional layer
• Stromal cells become decidual cells –> preperation for formation of placenta
  

Myometrium

• more smooth m fibers

SECRETORY PHASE IS REGULATED BY PROGESTERON

• The stimulation for transformation is the implantation of the blastocyst.
• Large, pale cells rich in glygogen result from this transformation,
• they create a specialized layer that facilitates the seperation of the placenta from the uterine wall at the termination of pregnancy.

Menstrual phase *Dont need to know for test, just theory to understand *

• results from a decline in the ovariation secretion of progesterone+ estrogen

• CORPUS LUTEUM produces hormones for about 10 days if fertilization does not occur.
• As hormone levels rapidly decline, changes occur in the blood supply to the stratum functionale.
• Periodic contractions of the walls of the spiral arteries, lasting for several hours, cause the stratum functionale.

Periodic conctraction of the walls of the spiral arteries, lasting for several hours stratum functionale to become ischemic.

• Glands stop secreting+ the endometrium shrinks in heigh as the stroma becomes less edematous.
• After about 2 days, extended periods of arterial contraction, with only brief periods of blood flow, cause disruption of the surface epithelium+ rupture of the blood vessels.
• When spiral arteries close off, blood flows into the stratum basale, but not in the stratum functionale.
• Blood, uterine fluid+ sloughing stromal+ epithelial cells from the stratum functionale constitute the vaginal discharge.
• As patches of tissue separate from the endometrium, the torn ends of veins, arteries+ glands are exposed.
• In the absence of fertilization, cessation of bleeding would accompany the growth+ maturation of new ovarian follicels.
• The epithelial cells would rapidly proliferate+ migrate to restore the surface epithelium as the proliferative phase of the next cycle begins.
• In the absence of ovulation( a cycle refered to as an anovulatory cycle), a corpus luteum does not form, and progesterone is not produced.
• In the absence of progesterone, the endometrium does not enter the secretory phase until menstruation.

Slide #76 Uterus, Pregnant * H&E

Structures to Identify

• endometrium with glands = decidua basalis
• myometrium
• chroion frondosum (primary villi)
• embryonic cavity
• primary, secondary, tertiary villi
• chorion leave
• decidua capsularis, marginalis, parietalis
• a/v

General Info:

This slide is not as difficult as it may seem.  Look at the picture to the right to first familairize yourself with the layers listed.

First look for a long white tube with a thick wavy over covering –> this is the embryonic (amniotic) cavity.

• On one side of it is chorion frondosum, with all the villi inside
• Villi contain fetal blood
  • between the villi is the intervillus space that houses maternal blood
• lateral to the chorion frondosum, is decidua basalis
• on the other side of the amniotic cavity, is the chorion laeve, with the decidua capsularis lateral to that.

Villi

• Villi are projections from the decidua that house branches of the uterine a/v, and contain fetal blood
• they project into the space between the decidual layers.
• maternal blood surrounds them in intervillous space
• Free gas exchange occurs between the villi and intervillous space
• 2 types of villi: anchoring villi (attached to chorion), floating villi (free floating)
• made from trophoblast cells – which makes two layers of cells – syncytiotrophoblast (outer) & cytotrophoblast (inner)
  
• Primary villus
  • 2 layers of trophoblast cells only
• Secondary villus
  • 2 layers with extra embryonic mesoderm in w/in
  • light center – look for white space in center
  • may have small a/b near the center
• Tertiary villus
  • the largest ones
  • only syncytiotrophoblast layer, much bigger, with a/v near periphery

Slide #74 Uterine Tube * H&E

Labyrinth like lumen of Uterine tube

Structures to Identify:

• simple columnar epithelium
• peg cells (right ovulation, might not be there)
• LP
• muscular layer
• a/v
• mesothelium (cells of perimetrium)
• adipocytes

Lumen: very labyrinth like – looks like a fern

• protrusion into lumens from mucosa
• amt of labyrinth depends  on location where section was taken –> less in infudibulum, more closer to uterus
• Do NOT confuse with Prostate. The folds look similar, but there are no prostatic calcifications, and there is only one lumen here, not a bunch of small fuzzy tubules
• 
• Epith and LP of Uterine Tube, with ciliated and peg cells shown

Epith

• simple columnar epithelium – do NOT say psuedo stratified
• some cells ciliated
  • these are shorter and have less cilia at times,
  • After ovulation , are taller with more cilia,
  • depending on hormones released in ovarian cycle (estrogen)
• thickness changes w/ menstrual cycle
• the non ciliated cells = peg cells
  • secrete mucin = carbs for sperm
    
  • expelled from epith when dead (die after excreting their mucin)
  • project into lumen
  • look like nails
  • look for long cells in a bump on top of epith
• During proliferative phase of uterus, with increase amount of estrogen, the cilated cells become larger and have more ciliae – peg cells secret more mucin

L.P.

• loose CT, with a/v
• numerous fibroblasts with collagen and reticular fiber
• supports the CT papilla projections into the mucosa

No Musc. mucosae or Submucosa

Muscular coat (Musc ext)

• inner ciruclar, outer longitudinal layers
• more developed closer to uterus
• has PNS ggl/nfibers – may be able to find them

Outer coat = serosa

• made of double layer of broad ligament with a/v inside
• made of mesothelial cells
• has a/v + adipocytes
  

Embrology of Uterus/Uterine Tube

• PARAMESONEPHRIC DUCTS  develop into the MAIN GENITAL DUCTS OF THE FEMALE.

• 3 parts can be recognized in each duct:

  • a cranial vertical portion that opens into the abdominal cavity

  • a horizontal part that crosses the mesonephric duct

  • a caudal vertical part that fuses with its partner from the opposite side.

• With descent of the ovary, the first 2 parts develop into the uterine tube+ the caudal parts fuse, to form the uterine canal.

• When the second part of the paramesonephric ducts moves mediocaudally, the urogenital ridges gradually come to lie in a transverse plane.

• DUCTS fuse in the midline, a broad transverse pelvic fold is established.

• BROAD LIGAMENT OF THE UTERUS: fold, which extends from the lateral sides of the fused paramesonephric ducts toward the wall of the pelvis.

• The uterine tube lies in its upper border, and the ovary lies on its post. Surface.

• UTERORECTAL POUCH+ UTEROVESICAL POUCH are devided by the uterus+ broad ligaments

• CORPUS+ CERVIX of the uterus coming from the fused paramesonephric ducts.

• MYOMETRIUM(= muscular coat of the uterus)+ Peritoneal covering(perimetrium) = layer of mesenchyme

18. The peritoneum. The peritoneal cavity. The development of the peritoneum.. The histology of tonsils.

Anatomy of the peritoneum & the peritoneal cavity.

• Definition of Peritoneum = is  a continuous, glistening+ slippery transparent serous membrane,  lines the andominopelvic cavity+ invests the viscera.

• The peritoneum consists of two continuous layers, both layers of peritoneum consists of mesothelium, a layer of simple squamous epithelial cells:
  • Parietal peritoneum, which lines the internal surface of the abdomino-pelvic wall
    • has same a/v/n/lymphatics, as the region of wall that it covers
    • is sensitive to pressure, pain, heat+ cold+ laceration.
    • Remember = Parietal = Pain* same goes for parietal pleura in thoracic cavity
    • Pain from FOREGUT = expressed in EPIGASTRIC region, MIDGUT = UMBILICAL region, HINDGUT = PUBIC region.
    • nerve supply = phrenic n, lower IC n, subcostal n, Iliohypogastric n, Ilioinguinal n
  • Visceral peritoneum, which covers visceral organs like the stomach+ intestines.
    • has same a/v/n/lymphatics, as the organ it covers
    • Stimulated primarily by stretching + chemical irritation
    • nerve supply = visceral n, ANS pathways

RELATIONSHIP of the VISCERA TO THE PERITONEUM:

• Intraperitoneal organs:  are almost covered with visceral peritoneum (e.g. the stomach+ spleen)
• Extraperitoneal – only organ that is extra– peritoneal is the ovary
• Retroperitoneal – 2 types – more on this later
  • Primary  – always has been located behind the peritoneum
  • Secondary – was originally intraperitoneal, but now is located behind the peritoneal cavity
• Infraperitoneal – located below the peritoneal cavity, usually covered superiorly with peritoneum

PERITONEAL REFLECTIONS – support viscera and contain a/v/n

1 Sup point of peritoneum, 2 inner aspect of the abdominal wall , 3 superior surface of the urinary bladder, 4 over the uterus in the female, 5 into the pouch of Douglas, 6 anterior surface of the rectum onto the posterior abdominal wall, 7 root of the mesentery of the small intestine. 8 horizontal part of the duodenum, 9 gastrocolic ligament, GO= greater omentum (11), 12 anterior surface of the stomach, 13 lesser omentum, EF = epiploic foramen, LPC = lesser peritoneal cavity (lesser sac)

Omentum

• Lesser Omentum – double layer peritoneum, from porta hepatis –> lesser curve + sup hor part of duodenum
  • hepatogastric & hepatoduodenal ligaments
  • form ant wall of lesser sac
  • carry L & R gastric a/v b/w 2 layers of peritoneum
  • free lower margin for = proper hepatic a, bile duct, and portal v
• Greater Omentum – hangs down like apron from gr. curve of stomach –> covering transverse colon & other ab viscera
  • carry R & L gastroepiploic a/v along greater curve
  • adheres to areas of inflammation and wraps around inflammed areas
  • prevents serous diffuse peritonitis = accumulating peritoneal fluid w/ fibrin & leukocytes

Mesentaries

• Mesentary Proper – fan shaped double fold of peritoneum, suspends jejunum & ileum from post ab wall
  • forms a root (duod-jej flexure –> R iliac fossa)
  • free border encloses SI
  • contains sup mesenteric & SI a/v/n/lymph vessels
• Transverse Mesocolon – connect post surfac of transv. colon –> post ab wall
  • fuses w/ gr. omentum to form gastrocolic lig
  • contains middle colic a/v/n/lymphatics
• Sigmoid Mesocolon – inverted V shaped peritoneal fold
  • connects sigmoid colong to pelvic wall
  • contains sigmoid a/v
• Mesoappendix – connects appendix to mesentery of ileum
  • contains  appendicular a/v

Peritoneal Folds –  reflections w/ free edges

• Umbilical folds – 5 folds of peritoneum below umbilicus
  • Lat umbilical folds = contain inf epigastric a/v
  • Medial umbilical folds = contain umbilical a
  • Median umbilical folds = contain remnant of urachus = connects urinary bladder of the fetus with the allantois, a structure that contributes to the formation of the umbilical cord
• Retrouterine folds – extension from cervix of uterus, along side of rectum to pelvic wall (post) and form Rectouterine pouch of Douglas
• Ileocecal fold – terminal ileum –> cecum

Peritoneal Ligaments

• Gastrosplenic lig – from L greater curve –> hilus of spleen, has short gastric a/v, L gastroepiploic a/v
• Splenorenal lig – Hilus of spleen –> L Kidney, has splenic a/v, has tail of pancreas
• Gastrophrenic lig – Upper greater curve –> diaphragm
• Gastrocolic lig – Greater curve –> transverse colon, absorbed into greater omentum, usually
• Phrenicocolic lig – Colic flexure –> diaphragm
• Falciform lig – sickle shaped peritoneal fold, connects liver –> diaphragm & ant ab wall
  • border b/w R & L Lobe (ant)
  • contains ligamentum teres hepatis, and paraumbilical v, which cxts L portal v w/ subcut v in umbilical regions
• Ligamentum Teres Hepatis – aka round ligament of liver, lies in lower free marginof falciform ligament, is L border of quadrate lobe on visceral surface of liver, remnant of umbilical v
• Coronary Lig – peritoneal reflection from diaphragmatic surface of liver  onto diaphragm, encloses bare area of liver
  • has R & L extensions that form R & L triangular ligaments
• Ligamentum Venosum – fibrous remnant of ductus venosus, lies in fissure  on inf surface of liver, forms L border of caudate lobon visceral surface of liver 

 

Start @ 1 and follow around the peritoneal cavity. 2. Back of the abdomen, anterior surface of the right kidney, pass through the epiploic foramen, along the posterior wall of the lesser peritoneal cavity, 3 then up along the renal lienal ligament 4 onto the posterior surface of the stomach 5. Your finger will continue through the epiploic foramen again to turn around the free margin of the lesser omentum 6, then over the anterior surface of the stomach again 7. Continue to follow around the greater curvature of the stomach 8 until you reflect again along the gastrolienal ligament 9. Your finger will now pass around the spleen, onto the left kidney to the parietal peritoneum and back to the falciform ligament fl.

THE PERITONEAL CAVITY

• located within the abdominal cavity &  continous inf. to the pelvic cavity.
• =  a potenial space between the parietal+ visceral layers of peritoneum
• contain no organs
• contains a thin film of peritoneal fliud = which is composed of water, electrolytes+ other substances derived from interstitial fliud in adjacent tissues.
• peritoneal fluid lubricates the peritoneal surfaces, enabling the viscera to move over each other without friction and allowing the movements of digestion
• Contains leukocytes+ antibodies that resists infection.
• Lymphatic vessels, particularly on the inf.surface of the unceasingly active diaphragm, absorb the peritoneal fluid.

In  Males: the peritoneal cavity is completely closed

In Females: connected to extra-peritoneal cavity through the uterine tubes, uterine cavity, & vagina

• split into Lesser Sac & Greater Sac

Lesser Sac = Omental Bursa

• irregular space that lies behind liver, lesser omentum, stomach, upper ant part of greater omentum
• closed sac, except for cxn w/  greater sac via epiploic foramen
• 3 recesses:
  • Sup. recess – being liver, stomach, lesser omentum
  • Inf recess – behind stomach, extends into layers of greater omentum
  • Splenic recess – extends to the L to the hilus of spleen

Greater Sac

• extends across entire area of abdomen and from diaphragm –> pelvic floor
• 5 recesses:
  • Subphrenic recess – peritoneal pocket b/w diaphram & ant/sup part of liver
    • separates into R & L recesses by falciform lig
  • Subhepatic recess – peritoneal pocket b/w liver & transverse colon
  • Hepatorenal recess – deep peritoneal pocket b/w liver (ant) & kidney (post)
  • Morison’s pouch = formed by R subhepatic & hepatorenal recess
    • comminucates w/ subphrenic recess, lesser sac via epoploic foramen, and R paracolic gutter(to pelvic cavity)
  • Paracolic recess – (aka gutters) – lies lat to asc/desc colon

Epiploic foramen (of Winslow) – natural opening b/w lesser and greater sacs

• Sup = peritoneum of caudate lobe of liver
• Inf = peritoneum of 1st part of duodenum
• Ant = free edge of lesser omentum
• Post = peritoneum covering IVC

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

Histology – Tonsils

Slide #25 Palatine Tonsils *H&E

 Structures to Identify:

• tonsillar crypts
• str. sq. non keratinizing epith
• lymph nodules (primary and secondary)
• muscle bundles
• germinal centers
• CT capsule 

With naked eye: dark, blue, partially encapsulated specimen w/ deep crypts

General Info:

• The palatine tonsilles(faucial tonsils)are paired, ovoid structures that consits of dense accumulation of lymphatic tissue located in the mucous membrane of the fauces(the junction of the oropharynx + oral cavity).
• The epithelium that forms the surface of the tonsil dips into the underlying CT in numerous places, forming crypts known as tonsillar crypts.
• Numerous lymphatic nodules are evident in the walls of the crypts.
• Tonsils guard the opening of the pharynx, the common entry to the respiratory+ digestive tracts.
• CLINCAL NOTE: can become inflamed because of repeated infection in the oropharynx+ nasopharynx+ can even harbour,
  • bacteria can cause repeated infections if they are overwhelmed.
  • debris and abcteria that collects in tonsilar crypts are hard to clean, as not enough saliva to clean them
  • When this occurs, the inflamed palatine tonsils+ pharyngeal tonsils ( also called adenoids) are removed surgically.

Important Histological Features

• C.T. capsule on one side, oral mucosa on other side

• Stratified squamous nonkeratinizing epithelium, lymphocytes invade epithelium within the crypt

  • this epith is present in both palatine and lingual tonsils

• Mucous membrane, lamina propria enlarged contains lymphatic nodules

  • NOTE = W/in nodule s= B lymphocytes, b/w them = T lymphocytes 

• Stroma, each lobules has a cortex+ medulla, the cutting plane of the section determines whether you can see both or not

• surrounded by a  dense fibroelastic CT capsule (red)

• Extends trabeculae to the margin of the cortex and medulla, which can contain fat, a/v

• Below CT capsule = skeletal m fibers,  but not as much as in lingual tonsil

• CORTEX- darker stained(blue)

  • Blood vessels with epithelioreticular cell sheath, cytoreticulum

  • Different than CT has no reticular fibers

  • Contains epithelioreticular cells as the stroma. Ovoid nucleus, larger cell, lighter colour = lymphoreticular mesrk

• large # of High Endothelial Venules (HEVs)

Embryo

• Develops form endoderm instead of mesoderm, unlike regular ct, mostly small lymphocytes
• epithelial lining of 2nd pharyngeal pouch – forms buds that penetrate surrounding mesenchyme
• mesenchyme => becomes palatine tonsil primordium
• in 3rd – 5th, invaginated by lymph tissue, forming tonsil

Slide #26 Lingual Tonsils *H&E

Structures to Identify:

• tonsilar crypts
• CT
• salivary glands
• Str. Sq. non-keratinizing epith
• lymph nodules
• skeletal m

With Nake Eye: A solid specimen with a darker region on one side

General Info:

• aggregation of lymph tissue located at root of tongue, posterior to sulcus terminalis
• not usually inflammed, as very accessible to saliva, and tonsilar crypts are not that deep for debris to collec

Histological Characteristics:

• has a str. squamous non-keratinized epith – very characteristic of oral mucosa, lines surface, and dips down in very shallow tonsillar crypts
• tonsillar crypts form deep invaginations on surface of tongue, ext. deep into LP
• Many lymph nodules, some secondary.
  • nodules =  B lymphocytes, b/w nodules = T lymphocytes
• LP = adipose tissue,  mucus acini of lingual glands, ducts of glands, lymphoreticular tissue
• Below LP, is the skeletal musc. coming from the tongue – bright red color

To be sure it is lingual tonsil = look for the str sq non kerat epith, large amts of skeletal m, lingual mucus glands, NO CT capsule

Embryology – The development of the peritoneum

The peritoneum develops ultimately from the mesoderm of the trilaminar embryo. As the mesoderm differentiates, one region known as the lateral plate mesoderm splits to form two layers separated by an intraembryonic coelom. These two layers develop later into the visceral and parietal layers found in all serous cavities, including the peritoneum.

As an embryo develops, the various abdominal organs grow into the abdominal cavity from structures in the abdominal wall. In this process they become enveloped in a layer of peritoneum. The growing organs “take their blood vessels with them” from the abdominal wall, and these blood vessels become covered by peritoneum, forming a mesentery