rectum and anal canal

Question 1

What is the rectum?

Answer 1

The terminal part of the large intestine, continuous with the sigmoid colon at the level of S3 vertebra (rectosigmoid junction).

Question 2

What is the meaning of ‘rectum’ in Latin, and is it accurate?

Answer 2

‘Rectum’ means straight, but the rectum has several flexures

Question 3

What are the two major flexures of the rectum?

Answer 3

Sacral flexure – follows the curve of the sacrum and coccyx

Anorectal (perineal) flexure – occurs where the rectum perforates the pelvic floor

Question 4

What maintains the angle of the anorectal flexure?

Answer 4

The puborectalis muscle.

Question 5

What are the three transverse rectal folds?

Answer 5

Internal rectal folds that help support fecal matter before defecation.

Question 6

What is the rectal ampulla?

Answer 6

The dilated part of the rectum between the middle transverse rectal fold and the anorectal line, where fecal matter is temporarily stored.

Question 7

What are anal columns, and what forms them?

Answer 7

Mucosal folds in the anal canal, produced by the underlying arterial plexus.

Question 8

What connects the distal ends of the anal columns?

Answer 8

Anal valves, which together form the pectinate (dentate) line.

Question 9

What is the clinical significance of the pectinate (dentate) line?

Answer 9

It is an important landmark, marking the division between visceral (autonomic) and somatic innervation, affecting pain sensation and blood supply.

Question 10

How is the anal canal epithelium divided?

Answer 10

It is divided into four zones based on epithelial characteristics

Question 11

what are the different zones in anal canal epithelium

Answer 11

Zone A: Colorectal zone
Zone B: Transitional zone
Zone C: Squamous zone
Zone D: Perianal skin (keratinized squamous)

Question 12

Which zone in the anal canal is lined with simple columnar epithelium?

Answer 12

Zone A (Colorectal zone) – It has the same epithelium as the rest of the GI tract.

Question 13

What is the function of the transitional zone (Zone B) in the anal canal?

Answer 13

It serves as a transition between simple columnar and stratified squamous epithelium.

Question 14

What type of epithelium lines the squamous zone (Zone C) of the anal canal?

Answer 14

Stratified non-keratinized squamous epithelium.

Question 15

What is Zone D, and how is it different from the other zones?

Answer 15

Zone D is below the anocutaneous line, forming the perianal skin, lined with keratinized squamous epithelium.

Question 16

Why is the knowledge of anal canal epithelial zones clinically significant?

Answer 16

It helps in differentiating rectal from anal carcinomas, as tumors may arise from different epithelial types.

Question 17

What are the three major arteries supplying the rectum?

Answer 17

Superior rectal artery – Continuation of the inferior mesenteric artery

Middle rectal artery – Branch of the internal iliac artery

Inferior rectal artery – Branch of the internal pudendal artery

Question 18

What is a portocaval anastomosis in the rectum?

Answer 18

A venous connection between the portal system (superior rectal vein) and the systemic circulation (middle & inferior rectal veins).

Question 19

What is the pectinate line?

Answer 19

The pectinate line indicates the junction of the superior (visceral, endoderm-derived) and inferior (somatic, ectoderm-derived) parts of the anal canal.

Question 20

What does the pectinate line reflect embryologically?

Answer 20

It reflects the transition between two different embryological origins: the endoderm (visceral) and ectoderm (somatic).

Question 21

What are the main differences reflected by the pectinate line?

Answer 21

Differences in histology, arterial supply, innervation, venous drainage, and lymphatic drainage.

Question 22

What is the arterial supply above the pectinate line?

Answer 22

Superior rectal artery.

Question 23

What is the arterial supply below the pectinate line?

Answer 23

Inferior rectal artery.

Question 24

What is the venous drainage above the pectinate line?

Answer 24

Superior rectal vein, which drains into the portal venous system.

Question 25

What is the venous drainage below the pectinate line?

Answer 25

Inferior rectal vein, which drains into the caval venous system.

Question 26

What is the nerve supply above the pectinate line?

Answer 26

Autonomic nerve fibers from the inferior hypogastric plexus, sensitive to stretch.

Question 27

What is the nerve supply below the pectinate line?

Answer 27

Somatic nerve fibers from the inferior rectal nerves, sensitive to pain, temperature, touch, and pressure.

Question 28

What is the lymphatic drainage above the pectinate line?

Answer 28

To internal iliac lymph nodes.

Question 29

What is the lymphatic drainage below the pectinate line?

Answer 29

To superficial inguinal lymph nodes

Question 30

What causes haemorrhoids?

Answer 30

Dilation of the internal rectal venous plexus causes protrusion into the anal canal, leading to internal haemorrhoids.

Question 31

What condition can contribute to the development of haemorrhoids?

Answer 31

Portal hypertension can contribute, though it is not necessarily required for haemorrhoid formation.

Question 32

What are external haemorrhoids?

Answer 32

External haemorrhoids are thromboses in the veins of the external rectal venous plexus.

Question 33

Why are internal haemorrhoids usually not painful?

Answer 33

They arise above the pectinate line, where the innervation is autonomic and sensitive to stretch, not pain.

Question 34

Why can external haemorrhoids be painful?

Answer 34

They are supplied by somatic sensory fibers, which are sensitive to pain, temperature, touch, and pressure.

Question 35

What structures are required for fecal continence and defecation?

Answer 35

The lower rectum, external anal sphincter, and internal anal sphincter work together to maintain continence and facilitate defecation.

Question 36

What triggers relaxation of the internal anal sphincter?

Answer 36

Distention and stretching of the rectum (due to accumulating fecal material) trigger a reflexive action, relaxing the internal anal sphincter via parasympathetic innervation.

Question 37

How can defecation be voluntarily deferred?

Answer 37

By conscious contraction of the external anal sphincter.

Question 38

What is the role of the puborectalis muscle in fecal continence?

Answer 38

It maintains fecal continence by forming a sling around the rectum, helping to maintain the anorectal angle.

Question 39

What can cause fecal incontinence?

Answer 39

Damage to the pelvic floor muscles, the anal sphincters, or the pudendal nerve.

Question 40

What nerve supplies the external anal sphincter

Answer 40

The pudendal nerve.

Question 41

How can damage to the pudendal nerve occur?

Answer 41

can be damaged during childbirth, leading to sphincter atrophy and incontinence.

Question 42

How does the pectinate line affect anorectal carcinoma?

Answer 42

Differences in histology and lymphatic drainage above and below the pectinate line influence the types of tumors that occur and the direction of metastasis.

Question 43

Where do lymphatic vessels drain above the pectinate line?

Answer 43

Into the internal iliac lymph nodes.

Question 44

Where do lymphatic vessels drain below the pectinate line?

Answer 44

Into the superficial inguinal lymph nodes.