TBL21 - Rectum

Question 1

Where are the rectum and anal canal derived from? What do they transform the posterior cloaca into?

Answer 1

1) The rectum and anal canal (to be studied later) are derived from the distal hindgut
2) They transform the posterior cloaca into the anorectal canal

Question 2

What does the rectal mucosa contain that is similar to what the mucosa of the colon contains? Where do the taeniae coli terminate? What does the rectal muscularis externa consist of?

Answer 2

1) Like the colon, the rectal mucosa contains intestinal crypts mainly lined by goblet cells
2) The taeniae coli terminate in the sigmoid colon
3) Thus, the rectal muscularis externa consists of an inner circular layer and an outer longitudinal layer of smooth muscle

Question 3

What does the rectum follow? What does the puborectal sling form in relation to the tip of the coccyx? What structure does the sling create and what is its function?

Answer 3

1) The rectum follows the curve of the sacrum and coccyx
2) The puborectal sling forms an 80⁰ angle anteroinferior to the tip of the coccyx
3) The sling creates the dilated ampulla of the rectum, which holds the accumulating fecal mass until defecation

Question 4

How does the puborectal sling contribute to fecal continence?

Answer 4

The roughly 80° anorectal flexure is an important mechanism for continence, being maintained during the resting state by the tonus of the puborectalis muscle, and by its active contraction during peristaltic contractions if defecation is not to occur

Question 5

Which viscera can be palpated during rectal exams in males and females?

Answer 5

1) The uterus, cervix, ovaries, prostate gland, & seminal glands
2) Enlarged internal iliac lymph nodes, pathological thickening of the ureters, swellings in the ischioanal fossae [e.g., ischio-anal abscesses and abnormal contents in the rectovesical pouch in the male or the rectouterine pouch in the female] may also be palpated

Question 6

What is the rectum mainly supplied by? Where does lymph from the rectum mainly drain into?

Answer 6

1) The rectum is mainly supplied by the superior rectal artery, the termination continuation of the IMA
2) Lymph from the rectum drains mainly into the inferior mesenteric lymph nodes

Question 7

What portion of the rectum is covered by the parietal peritoneum and where is it in relation to the pelvic pain line? Where is visceral pain from the proximal rectum referred to?

Answer 7

1) Only the proximal portion of the rectum is covered by parietal peritoneum; thus, it is superior to the pelvic pain line
2) Visceral pain from the proximal rectum is referred to the pubic (hypogastric) region

Question 8

Where is visceral pain from the distal rectum referred to?

Answer 8

Visceral pain from the distal rectum, which is below the pelvic pain line, is referred via DRG at S2-S4 to the posterior thighs and perineum