Ch.3 - Anal Physiology

Question 1

Where does the internal sphincter begin proximally?

Answer 1

At the anorectal ring. It’s a continuation of the innter circular smooth muscle

Question 2

When unstimulated, the internal sphincter is contracting or relaxing?

What % of the resting anal tone does the internal sphincter provide?

Answer 2

Contracting.

50-75% of the resting tone of anus

Question 3

What is Treitz’ muscle

Answer 3

Suspensory muscles that hold the hemorrhoid complex in place

Question 4

What is the baseline pressure of the rectum?

How often does it get the low amplitutde contractions?

How high can the rectal pressure get?

Answer 4

5mmHg

Every 6-12s

As high as 100mmHg

Question 5

How do ppl who had complete proctectomies and anal anastomoses have preserved sensation to defecate?

Answer 5

Receptors for proprioception live, not in the rectum, but in the anal canal and levators

Question 6

How do people with complete protecting + anal anastomoses still have an urge to defecate?

Answer 6

Intact levators

Question 7

What innervates the rectum?

Answer 7

Mixed sympathetic and parasympathetic from the hypogastric nerves and the sacral parasympathetic nerves through the pelvic plexi

Answer 8

false because there is significant crossover innervation around the anus

Question 9

How does SNS work?

Answer 9

Nobody knows exactly. But

1) peripheral motor stimulation of the anal sphincter complex
2) changes in theb motor/ sensory fx of the combined functional anorectal unit

Question 10

Spinal cord injury above what level interrupt control and sensation of the abdominal and pelvic floor musculature + colon and rectum?

Answer 10

Above T7

Question 11

What is RAIR?

Answer 11

Rectoanal inhibitory reflex.

Allows highly innervates sensitive epithelial lining of the upper anal canal to sample the contents of the distal rectum to determine its quality and consistency

Question 12

What is levator Ani syndrome?

Answer 12

Dull pain high in the rectum, made worse by sitting

Should last >20 min, other causes excluded

May be related to prolonged contraction -> compression of vasculature -> relative ischemia

Question 13

What is proctalgia fugax?

Answer 13

Sudden severe anal pain, lasting seconds to minutes then disappears completely.

May be related to thickened internal sohincter

Question 14

How do hormone changes during pregnancy affect pelvic floor?

Answer 14

Progesterone, released during pregnancy, acts by suppressing contraction of smooth muscle and prevents premature uterine contraction

This can lead to decreased gut motility, diminished tonic contraction of anal sphincters