Rectum

Question 1

Rectum function and origin:

Answer 1

• storage container for stool/fecal matter.
• distal continuation of sigmoid colon.

Question 2

Where does the transition between sigmoid colon and rectum occur?

Answer 2

• rectosigmoid junction. Around S3.

Question 3

Ampulla of the rectum:

Answer 3

• distal end of rectum.
• where most of the fecal material is stored prior to defecation.

Question 4

What occurs at the rectosigmoid junction (S3)?

Answer 4

• sigmoid colon to rectum.
• mucosa changes from ruffled inner layer to smooth inner layer.
• teniae coli, haustra, and epiploic appendages lost.

Question 5

Arterial blood supply to rectum:

Answer 5

1. superior rectal artery (branch of inferior mesenteric)
2. middle rectal artery (branch of internal iliac)
3. inferior rectal artery (branch of internal iliac)

Question 6

Venous blood supply to rectum:

Answer 6

PORTACAVAL ANASTOMOSES

1. superior rectal vein (inferior mesenteric; portal)
2. middle rectal vein (internal iliac; caval)
3. inferior rectal vein (internal iliac; caval)

Question 7

Rectal peristalsis is stimulated by:

Answer 7

parasympathetic innervation

Question 8

Route of parasympathetic innervation to the rectum:

Answer 8

• Pelvic splanchnics.
• Synapse in Rectal plexus (inferior hypogastric plexus).
• Stimulate postganglionics to cause peristalsis.

Question 9

Puborectalis muscle location and function:

Answer 9

• maintains fecal continence.
• forms puborectal sling.
• Stretches from pubic bone on one side, posterior around rectum, and then attaches to pubic bone on other side creating a sling-like muscle.

Question 10

Puborectalis contraction effect on rectum/anal canal:

Answer 10

• kink between rectum and anal canal.
• anal canal projects superiorly and anteriorly.
• rectum projects superiorly and posteriorly.

Question 11

How does defecation occur?

Answer 11

• puborectalis relaxes.
• rectum and anal canal straightens.