S8.2 Pathology Of The Distal GI Tract

Question 1

Outline the pathophysiology of diarrhoea?

Answer 1

Unwanted substance in gut stimulates secretion to remove it, colon unable to absorb the increasing amount of water

Question 2

What is osmotic diarrhoea and what causes it?

Answer 2

Gut lumen contains too much osmotic material
Can be from ingesting poorly absorbed materials or from the inability to absorb nutrients
Can stop with fasting

Question 3

What is secretory diarrhoea and what causes it?

Answer 3

Too much ion secretion due to toxins affecting ion transport messengers
Also too little Na absorption
Therefore net effect is water movement into lumen
Cannot stop with fasting

Question 4

What is the pathophysiology of constipation?

Answer 4

Caused by slow colonic transport (e.g megacolon, Parkinson’s) or defecation problems (e.g cannot coordinate muscles of defecation).

Question 5

What are the risk factors and treatment of constipation?

Answer 5

Risk factors: female, old age, low exercise

Treatment: increased fluid/activity/fibre, laxatives

Question 6

Describe where appendicitis pain originally presents, and then where this pain moves to and why?

Answer 6

Initially has periumbilical pain as visceral (non-specific) peritoneum affected
Then later touches parietal peritoneum which has somatic origin and produces specific RIF pain

Question 7

What are the two causes of appendicitis?

Answer 7

Blockage of appendices lumen

Infection

Question 8

How does blockage cause appendicitis?

Answer 8

Blockage of appendiceal lumen (e.g foreign body/faecolith) causes venous pressure to rise.
This prevents arterial blood supply from ileocolic artery leading to ischaemia of appendix walls and bacterial invasion

Question 9

How does infection cause appendicitis?

Answer 9

An infection can cause mucosal changes that allow bacterial invasion of appendiceal walls

Question 10

What are the symptoms of appendicitis?

Answer 10

Periumbilical pain, anorexia, vomiting, RIF pain 12h later (unless appendix is in retro-caecal or pelvic position)

Question 11

What signs will you find on a patient with appendicitis?

Answer 11

Rebound tenderness

Fever

Question 12

How do you diagnose and treat appendicitis?

Answer 12

Diagnosis: bloods, examination, pregnancy test to rule out
Treatment: appendicectomy

Question 13

What is diverticulosis?

Answer 13

Outpouchings of mucosa and submucosa in the colon which herniate through muscularis layers
Caused by raised intra-luminal pressure.

Question 14

What is acute diverticulitis?

Answer 14

When the diverticula become inflamed or perforate.

Occurs in diverticulosis

Question 15

Outline the pathophysiology of acute diverticulitis

Answer 15

Faeces block entrance to diverticula, inflammation allows bacterial invasion of diverticula walls

Question 16

What is the difference between uncomplicated and complicated diverticulitis?

Answer 16

Uncomplicated diverticulitis – small abscess confined to colon wall
Complicated diverticulitis – large abscess that perforates

Question 17

What are the symptoms of acute diverticulitis?

Answer 17

LIF pain
Haematochezia (anal blood loss)
Constipation

Question 18

What is the diagnosis and treatment of acute diverticulitis?

Answer 18

Diagnosis: blood tests (raised WBC), pregnancy test to rule out ectopic, USS, CT
Treatment: antibiotics, analgesia, surgery for large abscess in complicated

Question 19

What is the functions of the rectum?

Answer 19

Rectum allows temporary storage of faeces prior to defecation.

Question 20

Describe the arteries of the rectum

Answer 20

Superior rectal artery; continuation of IMA
Middle RA from internal iliac
Inferior RA from pudendal artery

Question 21

Describe the veins of the rectum

Answer 21

Portal drainage through superior rectal vein

Systemic drainage through internal iliac vein

Question 22

Describe the the effect of the pubo-rectalis sling on the anal canal

Answer 22

Pubo-rectalis sling makes rectum point anteriorly and anal canal posteriorly

Question 23

Describe the features of the anal canal above and below the dentate line

Answer 23

Above: IMA, pelvic nerve, columnar epithelia
Below: pudendal artery, pudendal nerve, stratified squamous epithelia

Question 24

What features does the anal canal need for defecation to occur?

Answer 24

A distensible rectum
Anal cushions
Normal anorectal angle

Question 25

Outline the 4 stages of defecation

Answer 25

Mass movement
Defecation reflex
Increased pressure in rectum
Defecation - relaxed anal sphincter

Question 26

What are haemorrhoids?

Answer 26

These are anal cushions which tell us the composition of faecal matter and aid continence.

Question 27

Describe the pathology of internal haemorrhoids

Answer 27

Can enlarge and prolapse through anal canal.
Occur above dentate line so are painless.
Treatment: increased hydration and avoid straining

Question 28

Describe the pathology of external haemorrhoids

Answer 28

Swelling of anal cushions which can then thrombose. Occur below pectinate line so feel pain.
Treatment: surgery

Question 29

What is an anal fissure?

Answer 29

Linear tear in anoderm.

Results in pain on defecation and haematochezia.

Question 30

What are some causes of anal fissures?

Answer 30

High internal anal sphincter tone

Reduced blood flow to anal mucosa

Question 31

What is the treatment for anal fissures?

Answer 31

Hydration
Warm bath
Medication to relax anal sphincter

Question 32

Name some conditions which result in haematochezia (blood through rectum)

Answer 32

Diverticulitis, angiodysplasia, colitis, colorectal cancer, haemorrhoids, anal fissure, upper GI bleed.

Question 33

What is melaena?

Answer 33

Black tarry stools, due to Hb being altered by digestive enzymes and gut bacteria.

Question 34

Name some conditions which result in melaena

Answer 34

Peptic ulcer disease, variceal bleeds, gastric cancer.