201. Anatomy of Pelvis/Perineum I

Question 1

Bony Pelvis

• components
• greater false vs. lesser true pelvis
• where is the sacral promontory
• what are the names of the 2 ligaments and their attachments and their fx
• what are components of pelvic brim
• what are sex differences in pelvis shape

Answer 1

Pelvis: L + R innominate bone + sacrum
Innominate bone: ischium + ilium + pubis
Greater (false) pelvis: ilium + iliac blades (support abd muscle, viscera, trunk)
Lesser (true) pelvis: form birth canal, obstetric fx
Sacral Promontory: landmark midline at top of S1
Ligaments: Sacrotuberous ligament (sacral spine to ischial tuberosity - OVER), sacrospinous ligament (sacral spine to ischial spine - UNDER) - fx to resist ant rotation of sacrum from body weight

Brim: Pubic tubercles + crests, pecten pubis, arcuate line of ilium (arched), ala “wing” of sacrum, sacral promontory

Females: longer pubis, wider subpubic angle, longer sacral alae, wider greater sciatic notch

Widest dimention: b/w arcuate lines of ilia
Narrowest: b/w ischial spines

Question 2

What are the muscles of the pelvic diaphragm?

Answer 2

Levator ani (puborectis - medial includes puborectal sling; pubococcygeus, iliococcygeus - lateral) - from middle pubis (below pelvic brim) to central tendon of perineum (perineal body)
Ischiococcygeus: from ischial spine to coccyx (bone to bone - tension but no elevation)

Question 3

Which organs are peritonealized in female?
What are the two folds in the female peritoneum?

What are 3 common kidney stone lodging sites?

Answer 3

Retroperitoneal: bladder, vagina, cervix, rectum
Peritonealized: uterus, sigmoid colon

Folds: vesico-uterine pouch, recto-uterine pouch

Stone: 1. Renal pelvis, 2. Over common iliac veins (crosses under these), 3. Entrance to bladder

Question 4

Rectum and Anal Canal

• what embryonic tissues meet here?
• what is the difference between true anal canal and surgical anal canal
• what muscles make up the rectum? External anal sphincter?
• what is the difference between structures above and below the pectinate line (2)?
• difference b/w int and ext hemorrhoids?

Answer 4

Splanchnopleure (hindgut) joins somatopleure (body wall)

True anal canal: below vertical anal valves/crypts (below pectinate line: site of cloacal membrane)

Surgical anal canal: top of anal ring (include crypts): felt on physical exam

Muscles

• Above pectinate line (rectum): smooth muscle (Outer longitudinal, inner circular - thickens to int anal sphincter)
• Below pectinate line (external anal sphincter): striated m. (always toned, continuous with levator ani)

Above Pectinate line:

• smooth muscle
• visceral sensory and parasymp fibers from S2-S4 plexus
• veins drain portal system: superior rectal vein = IMA = PV
• Lymph flows to para-rectal LNs - with internal iliac vessels - with Inf mesenteric vessels

Below Pectinate line

• striated muscle
• somatomotor nerves (pudendal nerve from S2-S4 plexus)
• veins drain systemic: middle/inf rectal veins = branches of internal iliac veins = IVC
• lymph to superficial inguinal LNs

Hemorrhoids:
Int: no pain, enlargement of mass of anastomotic veins
Ext: pain, itching

Question 5

Pelvic Plexus

• what is it?
• what does it include

Answer 5

AKA Inferior hypogastric plexus
- continuation of superior hypogastric plexus (on Abd aorta) via L/R hypogastric n. (how symps get to pelvis
Includes:
- symps (lumbar splanchnics)
- parasymps (pelvic splanchnics)
- visc sensory (both lumbar and pelvic)