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38. The perineum. The formation of the placenta. The structure of the matured placenta.

8 Jan

38. The perineum. The formation of the placenta. The structure of the matured placenta.

Flash cards:

Perineum  - Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger

Perineum - Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger


Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger

Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger

Perineum 2  - Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger

Perineum 2 - Anatomy Topic Notecard - Right Click and select "View this Image" to see it larger

Anatomy of  the perineum.

diamond shaped space w/ same boundaries as pelvic outlet
inf to pelvic diaphragm (& UG diaphragm)



  • ant = pubic symphysis
  • post = tip of coccyx
  • ant/lat = ischiopubic ramus
  • lat = ischial tuberosity
  • post/lat = sacrotuberous lig

Layers of Perineum: (outside –> in)

  1. Skin
  2. subcutaneous adipose tissue
  3. Superficial perineal fascia
  4. Superficial perineal space
    • bulb/crura of penis/clitoris
    • sup transverse perineal  m
    • ischiocavernosus m
    • bulbospongiosusm
    • a/v/n
  5. UG diaphagm
    • Inferior fascia of UG diaphragm = deep perineal fascia = perineal membrane
    • deep transverse perineal m (post) + sphincter urethra (ant)
    • superior fascia of UG diaphragm
  6. Deep perineal space – ant continuation of ischio-anal fossa, has pudendal canal
  7. Pelvic diaphragm
    • inferior fascia of levator ani m
    • levator ani m
    • superior fascia of levator ani m
  8. Lesser pelvis

NOTE = Inf fascia of UG diaphragm is the SAME AS  deep perineal fascia is SAME AS = perineal membrane

Layers of Perineal Area Female

Layers of Perineal Area Female

Perineal Layers Male

Perineal Layers Male

A line b/w the 2 ischial tuberosities, divides the perineum into 2 triangles
ant = Urogenital triangle
post = anal triangle

Urogenital Triangle
A. Superficial perineal space

b/w inf fascia of UG diaphragm & membranous layer of sup perineal fascia (Colles’)

Superficial Perineal Space

Superficial Perineal Space

1. Colles fascia

  • deep membranous layer of sup perineal fascia
  • inf boundary of sup perineal fascia
  • cont w. tunic dartos of scrotum, w/ sup fascia of pelvis & w/ Scarpa’s fascia of ant ab wall

2. Perineal Membrane

  • inf fascia of UG diaphram & lies b/w it and ext genitalia
  • perforated by urethra & attached  to post margin of UG diaphragm & ischiopubic rami
  • thickened ant to form transverse lig of perineum, covers the inf pubic rami
  • lies post to deep dorsal v of penis/clitoris

3. M of sup  perineal space

a) Ischiocavernosus m – ischial tuberosity –> ischiopubic rami –> corpus cavernosum

contains perineal br of pudendal n
helps maintain erection of penis, by compressing the crus of penis, & deep dorsal v of penis
this stops venous return of blood from area
b) Bulbospongiosus m
(M) = perineal body, fibrous raphe of bulb of penis
(F) = perineal body
(M) = corpus spongiosum & perineal membrane
(F) = pubic arch, dorsum of clitoris

Action of musc:
(M) = compress bulb of penis, stop venous return –> keep erection,
contraction of corpus spongiosum –> expel urine or semen

(F) = compress eretile tissue of bulb of vestibule –> constrict vaginal orifice

c) Superficial transverse perineal m
ischial rami of tuberosities –> perineal body (tendon)
stabilizes central tendon (perineal body)

d) Perineal body (central tendon)
fibromuscular mass @ center
site of attachment for UG diaphragm m.

e)Bartholin’s gland (bulbourethral glands)
compressed in sex & secrete mucus to lubricate vagina
ducts open in vestibule b/w labia minora below hyme

B. Deep perineal space

b/w sup/inf fascia of UG diaphragm

UG diaphragm
deep transverse perineal m, sphincter urethrae m
b/w 2 pubic rami & ischial rami
inf fascia provide attachment to bulb of penis
pierced by membranous urethrae (M) or urethra & vagina (F)
does not reach pubic symphysis ant

Bulbourethral Glands
lie b/w fibers of sphincter urethrae in deep perineal space
on post/lat side of membranous urethra
ducts pass thru inf fascia of UG diaphragm to open into bulbous part of penile urethra

M of deep perineal space
a)Deep transverse perineal m
inf surface of ischial rami –> med tendionous raphe and perineal body (in Female = vaginal wall)
stabilizes perineal body and supports the prostate and vagina

b) Sphincter Urethrae m
Inf pubic ramus –> median raphe and perineal body
surrounds the body of membranous urethra in male
inf part = attached to ant/lat wall of vagina (F) = urethrovaginal sphincter that compresses urethra and vagina

Anal Triangle
the Post triangle – everything posterior to the line b/w 2 ischial tuberosities

Ischioanal fossa
space lateral to rectum-anal canal, & medial to by levator ani & its fascia that lines the pelvis


  • ant = post border of sup/deep transverse perineal m
  • post = glut max m, sacrotuberous lig
  • sup/med = sphincter ani ext + levator ani m
  • lat = obturator fascia over obturator ani m
  • floor = skin over anal triangle


  • ischioanal fat
  • inf rectal a/v/n (from int pudendal a, pudendal n)
  • perineal br of post femoral cut n

On lateral wall, running through obturator fascia = Alcock’s canal aka pudendal canal

  • contains pudendal n
  • int pudendal a/v

Muscles of Anal Triangle
1. Obturator Internus – lat rotation of thigh
inner surface of obturator mem –> med side of greater trochanter of femur
has tendon that passes around lesser sciatic notch
(n to obturator)

2.Sphincter Ani Ext – closes the anus
Tip of coccyx & anococcygeal lig –> central tendon of perineum (perineal body)
(inf rectal n)

3. Levator Ani m – support and raise pelvic floor
body of pubis, arcus tendonous of levator ani (thickened part of obturator fascia, ishial spine) –> coccyx & anorectal raphe/lig
has 3 parts: puborectalis, pubococcygeus, iliococcygeus
has as ant fibers (most med) = levator prostatae, pubovaginalis
(br of ant rami of S3-4 + perineal br of pudendal n)

4.Coccygeus m – support and raise pelvic floor
ischial spine & sacrospinous lig –> coccyx + lowers sacrum
(br of S4-5)

Pelvic Diaphragm
= levator ani m + coccygeus m

divides pelvis into 2 compartments:
1. superior =  w/ viscera
2. inf = ischiorectal fossa

Pelvic Diaphragm

Pelvic Diaphragm

Inf to pelvic diaphragm = UG diaphragm
is on the ant portion of perineum, and ischioanal fossa posteriorly
made up of sup/inf fascia + deep/sup transverse perineal m
w. perineal body in center

Deep transverse m has urethra & vagina pierce it
m goes around urethra, forms sphincter urethra (M) & urethrovaginal sphincter(F)
does NOT attach to symphysis,
there is a space b/w it and symphysis = retropubic space, where deep/dorsal a of pelvis exit

Nerve Supply:

  • Pudendal n (S2-4)
    • passes thru gr. sciatic foramen, b/w piriformis & coccygeus m –> crosses ischial spine & enters perineum w/ int pudendal a
    • thru lesser sciatic foramen –> pudendal canal
    • Gives rise to:
      • inf rectal n – several br. in canal, crosses ischio-anal fossa => sphincter ani ext m, skin around anus
      • perineal n – arises in canal
        • deep br => all perineal m
        • sup br => br to scrotum, labia majora
  • Deep dorsal n – thru perineal mem b/w 2 layers => skin, foreskin, glans
    • lies on dorsum of clitoris or penis

Blood Supply::

  • Int pudendal a – leaves pelvis thru gr. sciatic foramen below piriformis & coccygeus m –> enters perineum via lesser sciatic foramen around ischial spine
    • Branches:
      • Inf rectal a – w/ in canal, thru wall of it, br => m and skin around anal canal
      • perineal a – => superficial perineal m, transv perineal br, post scrotal/labial br
      • a of bulb => bulb of penis, bulbourethral glands (M), vestibular bulbs & gr vestibular glands (F)
      • urethral a – corpus spongiosum, glans of penis
      • deep a – pierce perineal mem –> run thru center of corpus cavernosum => erectile tissue of penis & clitoris
      • dorsal a – pierce perineal mem & pass thru suspensory lig of penis/clitoris, runs along dorsum on each side of deep dorsal v and deep to Buck’s fascia & superficial to tunica albuginea => glans & foreskin
  • Ext pudendal a– from femoral a
    • runs thru saphenous ring & passes med over spermatic cord (or round ligament of uterus)
    • => skin above pubis, penis, scrotum or labia majora
  • Veins of pelvis
    • deep dorsal v
      • unpaired veins, that begins in sulcus behind glans & lies in dorsal midline ,
      • deep to Buck’s fascia & sup to tunica albuginea –> leaves perineum thru gap b/w arcuate pubic lig & transv. perineal lig –> suspensory lig, below arcuate pubic ligament and drains into –> prostatic and pelvic venous plexus
    • sup dorsal v – runs toward pubic symphysis b/w sup & deep fascia in dorsum of penis
      • divides into R & L br,
      • terminates in sup pudendal v –> drains into gr. saphenous v

Lymph Drainage:

  1. Lymph drainage of perineum – occurs via sup inguinal l.n
    • rec lymph from lower ab wall, buttocks, penis, scrotum, labia majora, lower vaginal/anal canal
    • nodes have efferent vessels that drain primarily into –> ext iliac nodes –> lumbar nodes
  2. Lymph drainage of Pelvis
      • –> common iliac l.n. –> lumbar nodes
    • follows int iliac v –> int iliac nodes –> lumbar nodes
    • Int iliac nodes -rec upper part of rectum, vagina and other pelvic organs
  3. upper rectum –> inf mesenteric nodes –> aortic nodes
  4. testis/ovaries drains along gonadal vessels –> aortic nodes

Histology : The structure of the matured placenta.

Embryology: The formation of the placenta.

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