Anal Canal

Question 1

What is the anal canal surrounded by to help faecal continence?

Answer 1

internal and external anal sphincters

Question 2

Where is the internal anal sphincter?

Answer 2

Surrounds upper 2/3 of anal canal

Question 3

What is internal anal sphincter formed from?

Answer 3

Thickening of the involuntary circular smooth muscle in the bowel wall

Question 4

Where is the external anal sphincter?

Answer 4

surrounds the lower 2/3 of the anal canal (and so overlaps with the internal sphincter)

Question 5

Which sphincter is voluntary?

Answer 5

External

Question 6

What does external anal sphincter blend with superiorly?

Answer 6

the puborectalis muscle of the pelvic floor

Question 7

What forms the anorectal junction / ring?

Answer 7

formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle (puborectalis forms sling which creates angle)

Question 8

What divides the anal canal?

Answer 8

The pectinate line

Question 9

What does the pectinate line mark?

Answer 9

Different embryological origins

Question 10

Where is above the pectinate line derived from?

Answer 10

Embyronic hindgut (endoderm)

Question 11

Where is below the pectinate line derived from?

Answer 11

Ectoderm of the proctodeum

Question 12

Describe the epithelial lining of the superior aspect of the anal canal?

Answer 12

Columnar epithelium (same as the rectum)

Mucosa is organised into longitudinal folds, known as anal columns.

These are joined together at their inferior ends by anal valves.

Above the anal valves are small pouches which are referred to as anal sinuses – these contain glands that secrete mucus.

Question 13

What are anal columns?

Answer 13

Mucosa in the superior aspect of the anal canal that has been organised into longitudinal folds

Question 14

What are the anal columns joined by?

Answer 14

Anal valves

Question 15

What are found above the anal valves?

Answer 15

Anal sinuses

Question 16

What do anal sinuses secrete?

Answer 16

Mucus

Question 17

What do the anal valves collectively form?

Answer 17

an irregular circle – known as the pectinate line

Question 18

Describe the epithelial lining of the inferior aspect of the anal canal

Answer 18

Lined by non-keratinised stratified squamous epithelium (known as the anal pecten). It is a pale and smooth surface, which transitions at the level of the inter-sphinteric groove to true skin (keratinised stratified squamous).

Question 19

What happens to the epithelial lining at the inter-sphinteric groove?

Answer 19

Transitions to true skin (keratinised stratified squamous)

Question 20

What is located laterally to the anal canal?

Answer 20

Ischioanal fossae

Question 21

Describe the artery supply of above the pectinate line

Answer 21

Superior rectal artery (branch of IMA)

Anastomosing branches from the middle rectal artery.

Question 22

Describe the artery supply of below the pectinate line

Answer 22

Inferior rectal artery (branch of the internal pudendal artery)

Anastomosing branches from the middle rectal artery.

Question 23

Describe the venous drainage of above the pectinate line

Answer 23

Superior rectal vein, which empties into the inferior mesenteric vein (portal venous system).

Question 24

What does the superior rectal vein empty into?

Answer 24

Inferior mesenteric vein

Question 25

Describe the venous drainage of below the pectinate line

Answer 25

Inferior rectal vein, which empties into the internal pudendal vein (systemic venous system).

Question 26

Describe the nerve supply of above the pectinate line

Answer 26

Visceral innervation via the inferior hypogastric plexus.

Sensitive to stretch.

Question 27

Describe the nerve supply of below the pectinate line

Answer 27

Somatic innervation via the inferior rectal nerves (branches of the pudendal nerve)

Sensitive to pain, temperature, touch and pressure.

Question 28

Describe the lymphatics of above the pectinate line

Answer 28

Internal iliac lymph nodes

Question 29

Describe the lymphatics of below the pectinate line

Answer 29

Superficial inguinal lymph nodes

Question 30

What are haemorrhoids?

Answer 30

Pathological haemorrhoids are observed in people who suffer from constipation, prolonged straining when defecating, or raised intra-abdominal pressure (e.g pregnancy, ascites).

They can cause bleeding and itchiness, and depending on the severity, can be managed conservatively or surgically.