Anal Canal

Question 1

What is the anal canal?

Answer 1

• the portion of the large intestine between the pelvic diaphragm and the anus
• lower portion of the GI tract

Question 2

What are the anal columns?

Answer 2

• 5 to 10 longitudinal folds of mucosa which lie in the upper half of the anal canal
• each column contains a small branch of the superior rectal artery and small tributary of the superior rectal vein

Question 3

What are the anal valves?

Answer 3

crescent-shaped folds which connect the lower ends of the anal columns

Question 4

What are the anal sinuses?

Answer 4

recesses located between the anal valves and the wall of the anal canal

Question 5

What is the pectinate line?

Answer 5

marks the lower limit of the anal valves around the circumference of the anal canal

Question 6

What is the anal pecten?

Answer 6

a bluish white zone inferior to the pectinate line

Question 7

What is the anocutaneous line?

Answer 7

distal termination of the anal canal, where it meets the skin

Question 8

What is the internal anal sphincter?

Answer 8

• a continuation of the smooth muscle layer of the rectum below the pelvic diaphragm
• it is under involuntary control

Question 9

What is the external anal sphincter?

Answer 9

• surrounds the anal canal
• skeletal muscle
• three parts:
  1. subcutaneous
  2. superficial
  3. deep

Question 10

What is the nerve supply to the external anal sphincter?

Answer 10

nerve to external anal sphincter from S4

Question 11

What is the function of the external anal sphincter?

Answer 11

• closes anal orifice

- its contraction can be increased voluntarily

Question 12

What is the blood supply of the rectum and anal canal?

Answer 12

• superior rectal artery (from inferior mesenteric a.)
• middle rectal artery (from internal iliac a.)
• inferior rectal artery (from pudendal a.)
• median sacral artery (from abdominal aorta)

Question 13

What are internal hemorrhoids?

Answer 13

• varicosities of the superior rectal vein
• cause bulging of the anal columns
• occur above the pectinate line and are generally painless

Question 14

What are external hemorrhoids?

Answer 14

• varicosities of the inferior rectal vein
• occur below the pectinate line and may be very painful
• high risk group: long distance truck drivers

Question 15

What are causes for both internal and external hemorrhoids?

Answer 15

• pregnancy
• heavy lifting
• sitting
• straining - chronic constipation
• portal hypertension - morbid underlying cause

Question 16

What is important about the pectinate line?

Answer 16

• it marks an important division within the anal canal

- it divides the anal canal into an upper (visceral) two thirds and a lower (somatic) one third

Question 17

What does the epithelium look like above and below the pectinate line?

Answer 17

• Above: columnar or cuboidal

- Below: stratified squamous

Question 18

What is the nerve supply above and below the pectinate line?

Answer 18

• Above: autonomic fibers

- Below: pudendal nerve

Question 19

What is the venous drainage above and below the pectinate line?

Answer 19

• Above: superior rectal vein

- Below: middle and inferior rectal veins

Question 20

What type of hemorrhoids develop above and below the pectinate line?

Answer 20

• Above: internal

- Below: external

Question 21

What is the lymph drainage above and below the pectinate line?

Answer 21

• Above: internal iliac

- Below: superficial inguinal

Question 22

Where does fecal material accumulate?

Answer 22

• sigmoid colon

- rectum is normally empty

Question 23

Describe the mechanism of defecation.

Answer 23

1. The sigmoid colon empties its contents into the rectum through mass peristaltic movement.
2. The longitudinal muscle layer of the rectum and the anterior abdominal wall muscles contract, increasing pressure within the rectum.
3. The puborectalis relaxes, decreasing the angle of the perineal flexure.
4. The internal anal sphincter is opened by the increase in pressure (as well as autonomic parasympathetic influence).
5. The external anal sphincter is relaxed under voluntary control.