10 Rectum and Anal Canal

Question 1

What vertebral level marks the beginning of the rectum?

Answer 1

S3, at the rectosigmoid junction.

Question 2

With which structure is the rectum continuous proximally?

Answer 2

The sigmoid colon.

Question 3

With which structure is the rectum continuous distally?

Answer 3

The anal canal (at the anorectal junction).

Question 4

What flexure does the rectum form as it follows the sacrum and coccyx?

Answer 4

The sacral flexure.

Question 5

What structure maintains the angle of the anorectal flexure?

Answer 5

The puborectalis muscle.

Question 6

What is the function of the puborectalis muscle?

Answer 6

It maintains the anorectal angle, aiding continence.

Question 7

name the labels

Answer 7

the dotted line is roughly where the pelvic floor is so based on that you could say that the anal canal is part of the perineum based on that definition

Question 8

Can you describe what features you could see here

Answer 8

• anal canals
• at the bottom of the anal canals there are anal valves
• anocutaneous line that divides the anal canal to the skin that divides the anal canal to the cutaneous skin

Question 9

what is the start and end of the anal canal?

Answer 9

starting from that anal rectal junction and then ends at the anal cutaneous line, anything underneath is perianal skin

Question 10

How many transverse folds does the rectum contain internally?

Answer 10

Three.

Question 11

What is the name of the dilated portion of the rectum that holds faeces?

Answer 11

The rectal ampulla.

Question 12

Where is the rectal ampulla located?

Answer 12

Between the middle transverse rectal fold and the anorectal line.

Question 13

What are anal columns and how are they formed?

Answer 13

Mucosal folds formed by underlying arterial plexuses protruding into the anal canal.

Question 14

What connects the distal ends of the anal columns?

Answer 14

Anal valves.

Question 15

label the diagram and list the changed in epithelium in A, B, C, D

Answer 15

A- simple columnar like the rest of the GI tract
B- stratified squamous
C- stratified non keratinized squamous
D- skin= keratinized stratified squamous epithelium

Question 16

what sort of epithelium is the entire gi tract basically?

Answer 16

simple columnar epithelium

Question 17

What structure is formed by the collective anal valves?

Answer 17

The dentate (pectinate) line.

Question 18

What does the dentate (pectinate) line represent anatomically?

Answer 18

The junction between the endoderm-derived superior part and ectoderm-derived inferior part of the anal canal.

Question 19

What epithelium lines the colorectal zone of the anal canal?

Answer 19

Simple columnar epithelium.

Question 20

What characterises the transitional zone of the anal canal?

Answer 20

A transition from simple columnar to stratified squamous epithelium.

Question 21

What epithelium lines the squamous zone?

Answer 21

Stratified non-keratinised squamous epithelium.

Question 22

What lies below the anocutaneous line?

Answer 22

Perianal skin lined with stratified keratinised squamous epithelium.

Question 23

Why is knowledge of anal canal epithelial zones clinically important?

Answer 23

For differentiating rectal vs. anal carcinoma.

Question 24

label the diagram

Answer 24

Question 25

What artery supplies the superior rectum?

Answer 25

Superior rectal artery (branch of inferior mesenteric artery).

Question 26

What artery supplies the middle rectum?

Answer 26

Middle rectal artery (branch of internal iliac artery).

Question 27

What artery supplies the inferior rectum and anal canal?

Answer 27

Inferior rectal artery (branch of internal pudendal artery).

Question 28

What forms the anastomotic network in the rectum?

Answer 28

The superior, middle, and inferior rectal arteries.

Question 29

describe venous drainage above the pectinate line

Answer 29

🔵 Above the Pectinate Line (Visceral drainage — part of the portal system): Vein: Superior rectal vein Drains into: Inferior mesenteric vein Then into: Splenic vein → Portal vein 🧠 Clinical relevance: Part of the portal venous system → can be involved in internal haemorrhoids and portal hypertension.

Question 30

describe venous drainage below the pectinate line

Answer 30

🔴 Below the Pectinate Line (Somatic drainage — part of the systemic circulation): 1. Middle rectal vein Drains into: Internal iliac vein 🧠 Clinical relevance: Links both with above and below drainage; contributes to portocaval anastomosis. 2. Inferior rectal vein Drains into: Internal pudendal vein Then into: Internal iliac vein → Common iliac vein → Inferior vena cava 🧠 Clinical relevance: Part of the systemic venous system → involved in external haemorrhoids (painful due to somatic innervation).

Question 31

label the diagram

Question 32

Into which vein does the superior rectal vein drain?

Answer 32

Inferior mesenteric vein (portal system).

Question 33

Into which vein does the middle rectal vein drain?

Answer 33

Internal iliac vein (systemic circulation).

Question 34

Into which vein does the inferior rectal vein drain?

Answer 34

Internal pudendal vein → internal iliac vein.

Question 35

What is a portocaval anastomosis?

Answer 35

A connection between portal (superior rectal) and systemic (middle/inferior rectal) venous systems.

Question 36

What is the embryological origin of the anal canal above the pectinate line?

Answer 36

Endoderm.

Question 37

What is the embryological origin of the anal canal below the pectinate line?

Answer 37

Ectoderm.

Question 38

What type of innervation exists above the pectinate line?

Answer 38

Visceral motor and sensory (autonomic).

Question 39

What type of innervation exists below the pectinate line?

Answer 39

Somatic sensory (from inferior rectal nerves).

Question 40

What lymph nodes drain the region above the pectinate line?

Answer 40

Internal iliac lymph nodes.

Question 41

What lymph nodes drain the region below the pectinate line?

Answer 41

Superficial inguinal lymph nodes.

Question 42

Why are haemorrhoids above the pectinate line painless?

Answer 42

Due to visceral innervation.

Question 43

Why are haemorrhoids below the pectinate line painful?

Answer 43

Due to somatic innervation.

Question 44

What causes internal haemorrhoids?

Answer 44

Dilation of the internal rectal venous plexus.

Question 45

What can exacerbate internal haemorrhoids?

Answer 45

Portal hypertension.

Question 46

What causes external haemorrhoids?

Answer 46

Thrombosis in external rectal venous plexus.

Question 47

What makes internal haemorrhoids typically painless?

Answer 47

Their location above the pectinate line (visceral innervation).

Question 48

What makes external haemorrhoids painful?

Answer 48

Their location below the pectinate line (somatic innervation).

Question 49

Which sphincter is under involuntary control?

Answer 49

Internal anal sphincter.

Question 50

Which sphincter is under voluntary control?

Answer 50

External anal sphincter.

Question 51

What nerve supplies the external anal sphincter?

Answer 51

Pudendal nerve.

Question 52

What triggers reflexive relaxation of the internal sphincter?

Answer 52

Rectal distention from faeces.

Question 53

Which muscle supports the external anal sphincter in maintaining continence?

Answer 53

Puborectalis.

Question 54

What can damage the pudendal nerve during childbirth lead to?

Answer 54

Sphincter atrophy and faecal incontinence.

Question 55

What lymph nodes are involved in metastasis of rectal carcinoma (above pectinate line)?

Answer 55

Internal iliac lymph nodes.

Question 56

What lymph nodes are involved in metastasis of anal carcinoma (below pectinate line)?

Answer 56

Superficial inguinal lymph nodes.

Question 57

Why do tumours above and below the pectinate line behave differently?

Answer 57

Due to different embryological origins, drainage, and innervation.

Question 58

What passes through the pelvic floor at the anorectal junction?

Answer 58

The rectum transitions into the anal canal.

Question 59

What structure is responsible for forming the anorectal angle?

Answer 59

Puborectalis muscle.

Question 60

What articulates with the coccyx in the context of rectal curvature?

Answer 60

The sacral flexure of the rectum.

Question 61

What forms the visible landmark within the anal canal separating upper and lower parts?

Answer 61

Dentate (pectinate) line.

Question 62

What passes posterior to the internal anal sphincter?

Answer 62

External anal sphincter.

Question 63

What defines the histological boundary for different epithelial types in the anal canal?

Answer 63

The anocutaneous line.

Question 64

What forms the internal rectal venous plexus?

Answer 64

Tributaries of the superior rectal vein.

Question 65

What muscle, when damaged, may contribute to rectal prolapse?

Answer 65

Puborectalis.

Question 66

What is the main arterial supply below the dentate line?

Answer 66

Inferior rectal artery.

Question 67

What structure marks the end of the rectum and the beginning of the anal canal?

Answer 67

The anorectal line.

Question 68

What does the middle rectal artery supply?

Answer 68

The middle portion of the rectum.

Question 69

Which zone of the anal canal is continuous with the perianal skin?

Answer 69

Zone D (below the anocutaneous line).

Question 70

Which lymph nodes would rectal cancer spread to first?

Answer 70

Internal iliac lymph nodes.

Question 71

What allows defecation to be consciously delayed?

Answer 71

Voluntary contraction of the external anal sphincter.

Question 72

What forms the boundary between GI epithelium and perianal skin?

Answer 72

Anocutaneous line.

Question 73

What connects the superior rectal artery to systemic circulation?

Answer 73

Portocaval anastomoses.

Question 74

What is the function of the rectal ampulla?

Answer 74

Temporary storage of faeces before defecation.

Question 75

What differentiates the epithelial lining of Zones A and B in the anal canal?

Answer 75

Simple columnar vs stratified non-keratinised squamous epithelium.

Question 76

What part of the anal canal is derived from endoderm?

Answer 76

The part above the pectinate line.

Question 77

What contributes to internal haemorrhoid formation?

Answer 77

Internal venous plexus dilation.

Question 78

What type of epithelium lines the perianal skin?

Answer 78

Stratified keratinised squamous epithelium.

Question 79

What maintains faecal continence during increased intra-abdominal pressure?

Answer 79

Coordinated action of puborectalis, levator ani, and anal sphincters.

Question 80

What part of the anal canal is innervated by autonomic fibres?

Answer 80

The area above the pectinate line.

Question 81

What nerve is most at risk during childbirth contributing to incontinence?

Answer 81

Pudendal nerve.

Question 82

What is the embryological junction of the endoderm and ectoderm in the anorectum?

Answer 82

The pectinate line.

Question 83

What zone of the anal canal includes the anal columns and valves?

Answer 83

The colorectal and transitional zones.

Question 84

What contributes to pain perception in external haemorrhoids?

Answer 84

Somatic innervation via inferior rectal nerves.

Question 85

What anastomosis is significant in portal hypertension?

Answer 85

Portocaval anastomosis in the rectal venous system.

Question 86

What lymphatic drainage is relevant for anal carcinoma below the dentate line?

Answer 86

Superficial inguinal lymph nodes.

Question 87

What artery is a direct continuation of the inferior mesenteric artery?

Answer 87

Superior rectal artery.

Question 88

What vein is involved in systemic drainage of the anal canal?

Answer 88

Inferior rectal vein.

Question 89

What forms the transition point between involuntary and voluntary control in the anal canal?

Answer 89

The junction between the internal and external anal sphincters.