Anatomy 4 – Pelvic Fascia, Rectum, Anal Canal

anterior wall of pelvic cavity
pubic bone and pubic symphysis, anterior portions of levator ani muscles

lateral wall of pelvic cavity
ilium, ischium, obturator internus muscle and fascia, lateral portions of levator ani, medial to obturantor internus muscle are the obturator artery and nerve and other branches of the internal iliac artery

posterior wall of pelvic cavity
sacrum, coccyx, sacroiliac joint, sacrotuberous ligament, sacrospinous ligament, piriformis and coccygeus muscles, medial to the piriformis muscle are the sacral plexus, autonomic plexuses and branches of the internal iliac artery

branches of the posterior trunk of internal iliac artery
iliolumbar artery, lateral sacral artery, superior gluteal artery

iliolumbar artery
branch of posterior trunk of internal iliac artery

supplies posterior abdominal wall and iliac fossa

lateral sacral artery
branch of posterior trunk of internal iliac artery

passes through anterior sacral foramina to supply sacral canal

superior gluteal artery
branch of posterior trunk of internal iliac artery

usually passes out of pelvis between lumbosacral trunk and anterior ramus of S1 above piriformis to supply gluteal muscles and skin

branches of anterior trunk of internal iliac artery
umbilical artery, superior vesical artery, inferior vesical artery (M), middle rectal artery, obturator artery, internal pudendal artery, inferior gluteal artery, uterine artery (F), vaginal artery (F)

umbilical artery
branch of anterior trunk of internal iliac artery

vestigial remnant which carried blood from fetus to placenta, contained within median umbilical fold

superior vesical artery
branch of anterior trunk of internal iliac artery

usually arises from umbilical artery to supply superior bladder and distal ureter

inferior vesical artery
branch of anterior trunk of internal iliac artery

male structure only

supplies inferior bladder, seminal vesical, prostate, ureter

middle rectal artery
branch of anterior trunk of internal iliac artery

courses medially to rectum, anastomoses with the superior rectal artery (from IMA) and inferior rectal artery (from internal pudendal artery)

obturator artery
branch of anterior trunk of internal iliac artery

accompanies obturator n. to supply medial thigh

often originates from external iliac a. or inferior epigastric a.

internal pudendal artery
branch of anterior trunk of internal iliac artery

exits the pelvis through the greater sciatic foramen inferior to the piriformis muscle

passes through lesser sciatic foramen with the pudendal nerve to enter and supply the perineum

inferior gluteal artery
branch of anterior trunk of internal iliac artery

exits the pelvis through the greater sciatic foramen inferior to the piriformis

passes between S1 and S2, or S2 and S3 anterior rami

external iliac artery
often the source of the origin of the obturator artery as it passes superior to the pelvic brim

gonadal artery
testicular or ovarian arteries arose from abdominal aorta

ovarian artery travels in the suspensory ligament of the ovary

testicular artery enters inguinal canal

median sacral artery
from near the bifurcation of the aorta

anastomoses with the lateral sacral artery and iliolumbar artery

superior rectal artery
last branch of inferior mesenteric artery

supplies rectum and upper anal canal

anastomoses with the middle and inferior rectal arteries

uterine artery
branch of anterior trunk of internal iliac artery

courses in the broad ligament to reach the cervix

ascends lateral to the uterus to reach the uterine tube where it anastomoses with the ovarian artery

passes superior to the ureter

vaginal artery
usually a branch of the uterine artery, but may be a separate branch of the anterior trunk of the internal iliac artery

supplies vagina, bladder, rectum

takes the place of an inferior vesical artery seen in males

plexuses of pelvic organs drain into
internal iliac vein, and then into the inferior vena cava

portal system bypass in pelvic region
anastomoses between middle + inferior rectal veins with the superior rectal vein (superior rectal v. drains into portal system)

valveless veins in pelvic region are important clinically because
they connect to vertebral venous plexuses and lumbar veins and provide a route for spread of infection

lymphatic drainage of pelvis and perineum
ultimately drains into aortic nodes

inferior structures close to external surface (lower vagina, lower anal canal, scrotum) drain into inguinal nodes first

sacral plexus
formed from the lumbosacral trunk (L4, L5) and the anterior rami of S1-S4

located on the medial surface of the piriformis muscle

motor and sensory to pelvis and lower limb

coccygeal plexus
small plexus derived from S4, S5, Co

forms the sensory anococcygeal n. to the skin of the anal triangle, perianal skin, sacrococcygeal joint

obturator nerve
not a part of the sacral plexus

L2 – L4

passes through the pelvis to eventually innervate the medial thigh

sciatic nerve
major branch of sacral plexus

L4-S3

motor to posterior thigh, all of leg, foot

posterior femoral cutaneous nerve
major branch of sacral plexus

superior gluteal nerve
major branch of sacral plexus

L4-S1

motor to gluteus medius + minimus, tensor fascia lata

inferior gluteal nerve
major branch of sacral plexus

L5-S2

motor to gluteus maximus

pudendal nerve
major branch of sacral plexus

S2-S4

motor to external urethra and anal sphincters, levator ani

sensory to skin of perineum, penis, clitoris

minor branches of sacral plexus
n. to obturator internus and superior gemellus, n. to quadratus femoris and inferior gemellus, n. to piriformis, nn. to levator ani, coccygeus,external anal sphincter, coccygeal plexus (via anococcygeal nerve)

sympathetics in pelvis
superior hypogastric plexus divides into right and left hypogastric nerves, which rejoin to form inferior hypogastric plexus which distributes to pelvic viscera and external genitalia

sympathetic splanchnic nerves depart from the sympathetic ganglia to enter the hypogastric nerves/inferior hypogastric plexus

parasympathetics in pelvis
arise from anterior rami of S2-S4 as pelvis splachnic nerves to enter inferior hypogastric plexus

distribute to pelvic viscera, external genitalia, lower digestive tract up to the splenic flexure of the large intestine

cavernous nerves
form from prostatic plexus in males and uterovaginal plexus in females

distribute to external genitalia for sexual arousal by piercing UGD to supply erectile tissue for erection and ejaculation

endopelvic fascia
a continuation of the extraperitoneal CT encountered in the abdomen

when it envelops the pelvic organs (false capsules) it is considered to be visceral fascia

when it lines the muscular walls of the pelvis it is considered to be parietal fascia

tendinous arch of levator ani
specialization of parietal fascia

attachment of pelvic diaphragm

pudendal canal
specialization of parietal fascia

derived from obturator fascia in ischioanal fossa

superior and inferior fascia of the pelvic diaphragm
specialization of parietal fascia

inferior fascia is continuous with the external anal sphincter and fuses with the fascia of the UG diaphragm

neurovascular sheath
specialization of visceral fascia

fascial ligaments
specialization of visceral fascia

help support pelvic organs

often contain a neurovascular bundle or structures entering/leaving viscera

rectum extends from
rectosigmoid junction (SV3) to anorectal junction (where the rectum passes through the pelvic diaphragm)

rectum is pulled anteriorly by
puborectalis muscle as it passes through the pelvic diaphragm

lateral flexures
rectum has 3 lateral flexures

2 to the right, 1 to the left

marked internally by transverse rectal folds

most distensible part of the rectum
ampulla

pararectal fossa
superior part of rectum is covered anteriorly and laterally by peritoneum

anal canal extends from
anorectal junction to anus

epithelial lining of anal canal changes at
distal to the pectinate line into stratified keratinized skin

anal aperture is controlled by
internal (parasympathetic innervation) and external (voluntary) anal sphincters

a portion of the external anal sphincter is derived from the puborectalis muscle

above the pectinate line the anal canal is supplied by
superior and middle rectal arteries

below the pectinate line the anal canal is supplied by the
inferior rectal artery

above the pectinate line the anal canal is drained by
superior rectal vein into inferior mesenteric vein, and middle rectal vein into internal iliac vein

below the pectinate line the anal canal is drained by
inferior rectal vein into internal iliac vein

veins freely anastomose to form 2 venous plexuses (internal and external rectal plexuses)

internal rectal plexus
located between internal sphincter and mucosal covering of anal canal

drains into superior rectal vein

external rectal plexus
surrounds the external sphincter and drains into middle and inferior rectal veins

important site for portal-caval anastomoses

lymphatics of upper rectum
inferior mesenteric nodes to aortic nodes

lymphatics of inferior rectum and anal canal above pectinate line
internal iliac nodes

lymphatics of anal canal below pectinate line
superficial inguinal noves

innervation above pectinate line
vasomotor to blood vessels = sympathetics

smooth muscle including internal anal sphincter = parasympathetics via pelvic splanchnics cause relaxation, while sympathetics cause contraction

sensory fibers for distention follow pelvic splanchnics (parasympathetics)

relatively insensitive to pain

innervation below the pectinate line
motor to external anal sphincter (voluntary) from pudendal nerve and branches from sacral plexus

sensation (pain, temperature, touch) from pudendal n.

internal hemorrhoids
dilations of the internal venous plexus above the pectinate line involving the superior rectal veins

covered with mucosa

not painful initially but they do bleed and may become strangulated

external hemorrhoids
dilations of the external venous plexus below the pectinate line involving the inferior rectal veins

covered with stratified squamous epithelium

highly innervated, painful and itchy, may contain blood clots

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