Pelvis Flashcards
What is the pelvic girdle and the pelvic cavity?
Pelvic Girdle: the hip bones and sacrum, the attachment site for the lower limbs to the body
Pelvic Cavity (true pelvis): the inferior-most body cavity. The space between the pelvic brim and pelvic outlet
The pelvic cavity has an inlet and an outlet. The outlet is closed in life by ligaments and muscles (pelvic diaphragm)
The upper part of the pelvis forms part of the abdominal wall (false pelvis). The lower part (true pelvis) contains the pelvic viscera.
What is the pelvic girdle?
Hip bones (right & left): Fusion at puberty of ilium, ischium & pubis
Sacrum:
Fusion of 5 sacral vertebrae
Joints – link axial & appendicular skeleton:
Anteriorly at the pubic symphysis
Posteriorly at sacroiliac joint
What is the pelvic diaphragm?
Pelvic diaphragm (pelvic floor muscles) Functions:
- Close the pelvic outlet
- Forms a ‘hammock’ to support the pelvic viscera.
- Like the thoracic diaphragm, this is striated skeletal muscle
What are the pelvic floor muscles called?
Pelvic floor consists of 2 muscles:
1) Levator ani (made up of puborectalis, pubococcygeus, iliococcygeus)
2) Coccygeus
Pelvic diaphragm is innervated by the pudendal nerve and branches of S4/S5
What is the pelvic gut?
The distal part of the GI tract is retroperitoneal/subperitoneal
Rectum: the distal part of the large intestine, continues from the sigmoid colon and stores faeces. Begins near S3 level
Anal Canal: the most distal part of the GI tract, controls defecation
What are the 2 curves of the rectum?
Sacral flexure: concave anteriorly
Anorectal flexure: convex anteriorly
What are the peritoneal relations of the rectum?
Upper third: covered by peritoneum on 3 sides
Middle third: covered by peritoneum on anterior side only
Bottom third: outside (below) peritoneal cavity- sub peritoneal
What is the blood supply of the Rectum and Anal Canal?
Superior Rectal Artery: from inferior mesenteric artery
Middle Rectal Artery: from internal iliac artery
Interior Rectal Artery: from internal pudendal artery
What is the innervation of the rectum?
Sympathetic: lumbar splanchnic nerves and superior and inferior hypogastric plexuses
Parasympathetic: pelvic splanchnic nerves (S2-4)
Sensory: follow the parasympathetic supply.
What is the structure of the anal canal?
Upper anal canal – Gut:
- Autonomic nerves
- Superior rectal vein -> portal vein
- Superior and middle rectal art. (From inf. mesenteric art.)
- Internal iliac lymph nodes
- Gut (columnar) epithelium
Lower anal canal – skin:
- Pudendal nerve (somatic)
- Inferior rectal vein -> pudendal vein -> internal iliac vein
- Inferior rectal art. (from Inferior pudendal art.)
- Superficial inguinal lymph nodes
- Stratified squamous epithelium
The border between upper and lower = pectinate line
What is the anal sphincter?
Internal anal sphincter (part of upper system):
- Smooth muscle
- Involuntary control
- Sympathetic contracts
- Parasympathetic relaxes
- A continuation of the gut wall
External anal sphincter:
- Striated muscle
- Voluntary control
- Inferior rectal nerve (a branch of pudendal)
- Merges with pelvic diaphragm
The action of defecation is under reflex control – contraction of internal and external sphincters is inhibited and the rectum/anal canal empties.
Children learn to override the reflex (up to a point).
The internal sphincter is too weak to work alone – it requires at least some of the external sphincter for continence.
What are anal folds and valves?
Anal valves: grooves between the folds
Anal columns: folds of epithelium
What does the puborectalis muscle do?
- Part of the pelvic floor
- Muscular “sling”
- Straightens anorectal junction for defecation
Puts kink in anal canal to keep faeces in
What are hemorrhoids?
AKA “piles,” these are venous tissue protruding through the mucosa of the anal canal.
Can be external or internal
What are the lymphatics of the rectum and anus?
- Anal canal drains to superficial inguinal lymph nodes and internal iliac lymph nodes
- Rectum drains to into internal iliac nodes and superior and middle rectal lymph nodes
What is the internal anatomy of the bladder?
Trigone: smooth region of the inside of the bladder connecting the left and right ureteral orifices with the urethral orifice
Note that the smooth trigone is mesodermal in origin while the rest of the bladder is endodermal.
Detrusor muscle: smooth muscle in walls of the bladder. Contracts for urination.
Sympathetic - hypogastric nerve. (T10-L2) Parasympathetic - pelvic splanchnic nerves (S2-4)
Sensory: travels via parasympathetic path
What is the blood supply of the bladder?
Superior vesical arteries: supply anterosuperior parts of the bladder.
Males: inferior vesical arteries supply the fundus and neck of the bladder.
Females: the vaginal arteries replace the inferior vesical arteries and send small branches to posteroinferior parts of the bladder
Venous drainage of bladder is via numerous small veins that form the vesicle venous plexus, which eventually drains to the internal iliac vein
Note that the pathway is different in males and females: Females: vesicle venous plexus communicates with vaginal venous plexus
Males: vesicle venous plexus communicates with prostatic venous plexus
What is the peritoneal relationships of the bladder?
While empty, the bladder is subperitoneal
While full, the bladder presses the peritoneum up and the bladder is preperitoneal and rises above the superior border of the pubic bone
What is the prostate gland?
-Male only
-Sits below the bladder and wraps around the urethra
Contributes secretions to seminal fluid
In older men, the prostate enlarges (benign prostatic hyperplasia), obstructing the urethra
