- The transverse midplane diameter, measured between the ischial
spines, is the smallest dimension of the pelvic outlet.
- The levator ani muscleforms most of the pelvic floor and its puborec-
talis portion (rectal sling) is the principal mechanism for maintenance of
fecal continence when the rectum is full.
- The rectumis usually empty because feces are stored in the sigmoid colon.
Movement of feces into the rectal ampulla generates the urge to defecate.
- Metastatic carcinoma of the rectummay be widely disseminated within
the abdomen, pelvis, and inguinal region. The upper rectum drains along
the superior rectal lymphatics. The mid-rectum drains along middle rec-
tal lymphatics. The lower rectum drains along the inferior rectal lym-
phatics and then along both internal and external pudendal lymphatic
channels. The lower part of the anus drains to superficial inguinal nodes.
High-Yield Facts 59
Afferent limb of the detrusor Pelvic plexus and pelvic splanchnic nerves
(bladder-emptying) reflex (parasympathetic pathways) to spinal segments S2–S4
Efferent limb of the detrusor Pelvic splanchnic nerves (parasympathetic pathways)
reflex from S2–S4
URINARY BLADDER INNERVATION IS BY BOTH SYMPATHETIC
AND PARASYMPATHETIC ROUTES
Function Pathway
- Urinary continenceof the partially full to full urinary bladder is a func-
tion of the external urethral sphincter.
•A patent urachus(rare) allows reflux of urine through the umbilicus.
- The testesdevelop as retroperitoneal structures and remain so in the
scrotum. Testicular torsion has high potential for testicular ischemia and
necrosis.
- The testicular pampiniform plexusfunctions as a countercurrent heat
exchanger that maintains testicular temperature a few degrees below
core body temperature.
- The superior mesenteric artery may compress the left renal vein, which
receives the left testicular vein. The result may be varices of the
pampiniform plexuson the left side with reduced fertility.
