7. Rectum And Anal Canal Anatomy

Question 1

How long is the rectum?

Answer 1

12-15cm

Question 2

What is the blood supply to the rectum?

Answer 2

Superior rectal artery - continuation of inferior mesenteric artery
Middle rectal artery - branch of internal iliac
Inferior rectal - branch of pudendal artery

Question 3

What is the venous drainage of the rectum?

Answer 3

Portal drainage through superior rectal vein

Systemic drainage through internal iliac vein - potential for Porto-systemic anastomoses

Question 4

Where does the anal canal start?

Answer 4

Proximal border of anal sphincter complex

Question 5

What are the factors required in anal canal continence?

Answer 5

Distensible rectum
Firm bulky faeces
Normal anorectal angle
Anal cushions - network of venous vessels 
Normal anal sphincters

Question 6

What are the 2 parts of the anal sphincter complex?

Answer 6

Internal involuntary sphincter

External anal sphincter

Question 7

What is the internal involuntary sphincter?

Answer 7

Thickening of circular smooth muscle

Under autonomic control

Question 8

What is the external anal sphincter?

Answer 8

Striated muscle
Deep section - upper anal canal, mixes with fibres from levator ani, joins with pubs-rectalis to form sling
Superficial and subcutaneous sections

Question 9

What is the nerve supply of the external anal sphincter?

Answer 9

Pudendal nerve

Question 10

Describe the process of defaecation?

Answer 10

1. Mass movement
2. Defaecation reflex - stimulus (distension in rectum), responses (contraction in rectum, sigmoid colon, relaxation of internal anal sphincter, contraction of external anal sphincter)
3. Increased pressure in rectum
4. Delay or defaecation

Question 11

What is the dentate line?

Answer 11

Junction of hindgut and proctodaeum (ectoderm) in anal canal

Question 12

What is above the dentate line?

Answer 12

Visceral pain receptors

Columnar epithelium

Question 13

What is below the dentate line?

Answer 13

Somatic pain receptors

Stratified squamous epithelia

Question 14

What are anal cushions?

Answer 14

Anus contains complex venous plexus
Divided into 3+ areas of tissues called anal cushions
Play a role in anal continence
There are connections between the vein and some arteries
Present from birth and a normal finding

Question 15

What’s are haemorrhoids generally?

Answer 15

Symptomatic anal cushions

Question 16

What are internal haemorrhoids?

Answer 16

Caused by loss of connective tissue support
Above dentate line
Relatively painless
Enlarge and prolapse through anal canal
Bleed bright red blood/pruritus

Question 17

What is the treatment for internal haemorrhoids?

Answer 17

Increased hydration/high fibres diet
Avoid straining
Rubber band ligation
Surgery

Question 18

What are external haemorrhoids?

Answer 18

Below dentate line
Swelling of the anal cushions which may then thrombosis
Very painful
Surgery has good outcomes

Question 19

What are anal fissures?

Answer 19

Linear tear in anoderm

Question 20

What causes anal fissures?

Answer 20

Passing of hard stool
Pain on defaecation
Haematochezia

Question 21

What is the underlying causation of anal fissures?

Answer 21

High internal anal sphincter tone

Reduced blood flow to anal mucosa

Question 22

What is the treatment for anal fissures?

Answer 22

Hydration, dietary fibre, analgesia
Warm baths
Medication trying to relax internal anal sphincter

Question 23

What are the causes of haematochezia?

Answer 23

Diverticulitis
Angiodysplasia
Colitis
Colorectal cancer
Anorectal disease
Upper GI bleeding

Question 24

What is malaena?

Answer 24

Black tarry stools
Offensive smelling
Due to haemoglobin being altered by digestive enzymes and gut bacteria

Question 25

What are the common causes of malaena?

Answer 25

Upper GI bleeding - peptic ulcer disease, variceal bleeds, upper GI malignancy, oesophageal/gastric cancer

Question 26

What are the uncommon causes of malaena?

Answer 26

Gastritis
Meckel’s diverticulum
Iron supplements