Distal GI Tract Pathology

Question 1

What is the definition of diarrhoea?

Answer 1

A symptom that occurs in many conditions

Loose watery stools
More than 3 times a day

Acute diarrhoea -less than 2 weeks

Question 2

What is the pathophysiology of diarrhoea?

Answer 2

Unwanted substance in gut stimulates secretion and motility to get rid of it.

Primarily down to epithelia function (secretion) rather than increased gut motility (although this does occur)

Colon is overwhelmed and cannot absorb the quantity of water it receives from the ileum.

There is normally 99% absorption of water from the gut, leaving only 100mls in stools / day

Question 3

How dos fluid normally move down GI tract?

Answer 3

Water is not actively moved across the gut but follows osmotic forces generated by the movement of electrolytes / nutrients

Normally 10/12L out of stomach and only poo out 100ml - lots of absorption

Question 4

What are the broad causes of diarrhoea?

Answer 4

Secretory - electrolyte transport is messed up
-Too much secretion of ions (net secretion of chloride or bicarbonate)
-This will mess up the messenger systems that control ion transport. e.g. caused my infectious toxins.
Too little absorption of Na - reduce SA for absorption,
-Mucosal disease / bowel resection (Coeliac or IBD)
-Reduced contact time (diabetes / IBS)

Osmotic - the gut lumen contains too much osmotic material (malabsorption)

• Ingesting material that is poorly absorbed
• Inability to absorb nutrients (lactase deficiency)

-Osmotic diarrhoea will stop if you stop ingesting the substance; in secretory, diarrhoea will carry on until underlying pathology has settled down.

Question 5

What is constipation?

Answer 5

Hard stools, difficulty passing stools or inability to pass stools.

In over 25% of bowel movements:

• Straining
• Feeling of incomplete evacuation
• Obstruction or blockage to defecation

Also fewer than 3 unassisted bowel movements in a week.

Question 6

What are the risk factors for constipation?

Answer 6

Females:Males
Certain medications
Low levels of physical activity (immobile)
Increasing age
Children under 4

Question 7

What is the pathophysiology of constipation?

Answer 7

3 different ways:

Normal transit constipation
-Psychological stressors

Slow colonic transport

• Large colon (megacolon)
• Fewer peristaltic movements and shorter ones
• Fewer intestinal pacemaker cells present
• Systemic disorders (hypothyroidism, diabetes)
• Nervous system disease (Parkinson’s, MS)

Defaecation problems

• Cannot coordinate muscles of defaecation
• Disorders of the pelvic floor or anorectum

Question 8

What are the treatments for constipation?

Answer 8

Psychological support
Increased fluid intake 
Increased activity
Increased dietary fibres
Fibres medication 
Laxatives -Osmotic/Stimulatory/Stool softeners

Question 9

What is appendicitis?

Answer 9

Swelling of appendix

Periumbilical pain their right iliac fossa.
BUT, this pattern of pain depends on where the appendix it.

Question 10

What are the broad categories of appendicitis?

Answer 10

Acute (mucosal oedema)

Gangrenous (transmural inflammation and necrosis)

Perforated

Question 11

What are the causes of appendicitis?

Answer 11

Classical- blockage (faecolith, lymphoid hyperplasia, foreign body) of appendiceacal lumen created higher pressure in the appendix
This causes venous pressure to rise, causing oedema in the walls of the appendix.
This makes it harder for arterial blood to supply the appendix resulting in ischaemia in the walls. A bacterial infection will then follow.

Alternatively:
A viral bacterial infection causes mucosal changes that allow bacterial invasion of appendiceal walls.

Question 12

What are the symptoms of appendicitis?

Answer 12

Classical presentation (<60% of cases)

• Poorly localised peri-umbilical pain
• Nausea / vomiting
• Low grade fever
• After 12-14 hours, intense pain in RIF

Question 13

What are the signs of appendicitis?

Answer 13

ill
Lie still 
Slight fever / tachycardia 
Localised right quadrant tenderness 
Rebound tenderness in RIF appears relatively specific.

Question 14

How do you diagnose appendicitis?

Answer 14

Blood test - raised WBC but non-specific

History / physical exam - if classical, could be enough, especially if rebound tenderness in RIF

Pregnancy test / urine dip to rule out UTI (no ectopics as can be similar pain)

CT - distended appendix that doesn’t fill with contract.

Question 15

How do you treat appendicitis?

Answer 15

Open appendectomy

Lacroscopic appendicectomy

Question 16

What is diverticulosis?

Answer 16

Multiple pouches (diverticula) in the colon (85% in sigmoid) that are not inflamed.

These are outpockets of the colonic mucosa and submucosa through weaknesses of muscularis layers in the colon wall.

They typically cause no symptoms and occur where nutrient vessels (vasa recta) penetrate the bowel wall.

The are thought to be caused by increased intra-luminal pressure (low fibres diet)

Question 17

What is acute diverticulitis?

Answer 17

This is when the diverticula becomes inflamed or perforate (+/- bleeding and abscess formation)

Occurs in up to 25% of people with diverticulosis

Question 18

What are the symptoms of acute diverticulitis?

Answer 18

Abdominal pain at the site of the inflammation - usually left lower quadrant (most in sigmoid colon)

Fever

Bloating

Constipation (inflammation can block colonic lumen)

Haematochezia (fresh red blood in stools)

Question 19

What are the signs of diverticulitis?

Answer 19

Localised abdominal tenderness

Distention

Reduced bowel sounds

Signs of peritonitis (following perforation)

Question 20

How do you diagnose diverticulitis?

Answer 20

Blood test - raised WBC

Pregnancy test - rule out ectopic

USS

CT

Colonoscopy - if large haematochezia

Elective colonoscopy (after symptoms have settled) to determine causes of symptoms if unclear.

Question 21

How do you treat acute diverticulitis?

Answer 21

Antibiotics, fluid resuscitation, analgesia.

Surgery if perforation or large abscess need to be drained..

Question 22

Describe the rectum

Answer 22

12-15cm long passes through the pelvic floor.

Has a continuous band of outer longitudinal muscles

Curved shape anterior to sacrum

Parts of it are covered in peritoneum and parts are extra-peritoneal.

Temporary storage of fecaes prior to defaecation - stretching of rectum stimulates urge to deficaete.

Question 23

Describe the blood supply to rectum and anal canal

Answer 23

Superior rectal artery - continuation of inferior mesenteric.

Middle rectal artery - continuation of internal iliac.

Inferior rectal artery - continuation of prudential artery

Question 24

Describe the venous drainage of the rectum and anal canal

Answer 24

Portal drainage through the superior rectal vein

Systemic drainage through the internal iliac vein -there is potential for porto-systemic anastomosis here.

Question 25

Describe the anatomy of the anal canal

Answer 25

The anal canal is a narrowed portion of the GI tract that continues on from the rectum.

Question 26

What is the start of the anal canal?

Answer 26

It starts from the proximal border of the anal sphincter complex. The rectum points anteriorly whereas the anal canal points posteriorly. This change in direction occur because of the pubo-rectalis sling.

Question 27

What factors are required for continence

Answer 27

``` Dstensible rectum Firm, bulky faeces Normal anorectal angle Anal cushions Normal anal sphincters ```

Question 28

What is the anal sphincter complex?

Answer 28

Made from both the internal and external sphincter. Internal, involuntary sphincter: - Thickening of circular smooth muscle - Under autonomic control (80% of resting anal pressure. External anal sphincter: - Striated muscle - Deep section is in the upper anal canal. It mixes with fibres from levator ani and joins with pubo-rectalis to form a sling. - Superficial and subcutaneous sections - Nerve supply from pudendal nerve - 20% of resting pressure.

Question 29

Describe the process of defecation

Answer 29

Mass movements lead to defecation reflex This then leads to increased pressure in rectum and you can either delay or defecate

Question 30

What is the dentate line and what does this separate?

Answer 30

The dentate line is the junction between the hindgut and the proctodaeum (ectoderm) Above: Visceral pain receptors, columnar epithelium Below: somatic pain receptors, stratified squamous epithelia

Question 31

What are anal cushions?

Answer 31

They are a complex venous plexus that is divided into three areas called anal cushions. These play a role in anal continence -inflate and deflate There are connections between the veins and some arteries They are present from birth and a normal finding

Question 32

What are internal haemorrhoids?

Answer 32

Symptomatic anal cushions (haemorrhoids) - Loss of connective tissue support - Above dentate line - Relatively painless - Enlarge and prolapse through anal canal - Bleed bright red / pruritus Treatment: - Increased hydration / high fibre diet - Avoid straining - Rubber band ligation - Surgery

Question 33

What are external haemorrhoids?

Answer 33

Below dentate line so painful. Swelling of anal cushions which may then thrombus Surgery

Question 34

What are anal fissures?

Answer 34

Linear tear in the anoderm (usually posterior midline) - Passing of hard stools (Diarrhoea?) - Haematochezia

Question 35

What are the causes of anal fissures?

Answer 35

High anal sphincter tone Reduced blood flow to anal mucosa

Question 36

What are the treatments for anal fissures?

Answer 36

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

Question 37

What are some common causes of haematochezia?

Answer 37

Diverticulitis Angiodysplasia (small vascular malformation in the bowel) Colitis (IBD, infective) Colorectal cancer Anorectal disease (haemorrhoids, anal fissure) Upper GI bleeding - large bleed with fast transit

Question 38

What is melaena?

Answer 38

Black tarry stools that are often foul smelling. It occurs due to Hb being altered by digestive enzymes and gut bacteria.

Question 39

What are some common causes of melaena?

Answer 39

Upper GI bleeding: - Peptic ulcer disease - Variceal bleeds - Upper GI malignancy - Oesophageal/ gastric cancers Uncommon causes: - Gastritis - Meckel's diverticulum - Iron supplements.

Question 40

In appendicitis, when would you not get paining the right iliac fossa?

Answer 40

If the appendix is retro-caecal or pelvic as the parietal peritoneum does not come into contact with the inflamed appendix. Instead, suprapubic or right sided rectal or vaginal pain. Also possible in children as symptoms are much more non-specific or in pregnancy as the anatomy is altered.

Question 41

Describe the pathophysiology of diverticulitis

Answer 41

Similar to appendicitis. - Entrance to diverticula is blocked by faeces - Inflammation eventually allows bacterial invasion of the wall of the diverticula - Can lead to perforation. It is uncomplicated if the inflammation and small abscess is confined to the colonic wall and complicated if the abscess is larger, there are fistulas or it has perforated.