Session 7: Distal GI Tract Pathology Flashcards
Definition of diarrhoea.
Loose or watery stools. More than 3 times a day
General pathophysiology of diarrhoea.
Unwanted substance in the gut are present and the body wants to get rid of it. Usually comes down secretions of ions to let water follow, instead of increased gut motility. The colon becomes overwhelmed due to the increased water content in the colon and diarrhoea occurs.
What are the two broad categories of diarrhoea?
Osmotic diarrhoea and secretory diarrhoea
Give broad causes of secretory diarrhoea. (General)
Either too much ion secretion into the bowel or not enough absorption of sodium.
Explain secretory diarrhoea due to too much ion secretion and common causes.
A net secretion of Cl- and HCO3- due to toxins, virus, medication or e.g. serotonin acting on CFTR to make it hyperactive. This leads to a colon lumen with too much Cl- and water will follow.
Causes secretory diarrhoea due to not enough sodium absorption.
Too little absorption of sodium due to e.g. reduced surface area of the intestines for absorption, damage to mucosa and intestinal wall like in Crohn’s. Intestinal rush leading to reduced time for absorption of sodium.
Explain osmotic diarrhoea
Due to malabsorption of nutrients in the small intestines leading to a build up of the osmotic gradient in the intestines.
Give causes of osmotic diarrhoea.
Celiac disease, lactose intolerance, antacids like magnesium sulphate. E.g. lactose intolerance leads to lactose in the large intestines. This leads to osmotic force keeping water from being absorbed.
Stool volume of osmotic diarrhoea vs secretory diarrhoea
In osmotic there is only a moderate increase whereas in secretory diarrhoea there is a very large volume excreted.
Response to fasting in osmotic diarrhoea vs secretory diarrhoea.
Osmotic diarrhoea ceases on fasting where as secretory diarrhoea does not.
Osmolality of stool in osmotic diarrhoea vs secretory diarrhoea.
Normal or increased in osmotic. Normal in secretory
Definition of constipation
Straining during defecations, Lumpy or hard stools, Feeling of incomplete evacuation, feeling of obstruction or blocking. Having fewer than 3 unassisted bowel movements in a week
Risk factors of constipation.
3:1 female:male, medication, low level of physical activity, age (very young <4 and old)
Give causes of slow colonic transport.
Large colon, fewer peristaltic movements and shorter ones, fewer intestinal pacemaker cells present, hypothyroidism, diabetes, parkinson’s, MS
Treatment of constipation
Psychological support, increased fluid intake, increased physical activity, laxatives, increased dietary fibres, fibre medication.
Give examples of laxatives.
Osmotic, stimulatory, stool softeners.
What is the appendix?
A diverticulum off the caecum with a complete longitudinal muscle layer.
Give examples of locations of the appendix.
Retro-caecal, pelvic, sub-caecal, Para-ileal
Why is the position of the appendix important?
Because it will change the clinical presentation of appendicitis.
Give the broad categories of appendicitis.
Acute with mucosal oedema. Gangrenous with transmural inflammation and necrosis. Perforation.
Explain the ‘classic’ cause of appendicitis.
A blockage of the appendiceal lumen leading to increased pressure in the appendix. This can be due to lymphoid hyperplasia following a viral infection, faecolith or a foreign body. This leads venous pressure to rise and oedema in the appendix. Ischaemia in the wall of the appendix follows and can cause bacteria to follow.
Classic presentation of appendicitis.
Poorly localised peri-umbilical pain, anorexia, nausea and vomiting, a low grade fever and as the appendicitis gets worse following 12-24 hours right iliac fossa pain
How is it possible to have appendicitis but no pain in right iliac fossa?
If the appendix is positioned retro-caecal or pelvic then it will not reach the right iliac fossa and reach the parietal peritoneum.
Pain in retro-caecal or pelvic appendicitis.
Supra-pubic pain, right sided rectal pain or vaginal pain.
In which people might appendicitis be difficult to diagnose?
In children and pregnant women.
Explain why appendicitis might be hard to diagnose in children.
History is difficult and symptoms may be much more non-specific.
Explain why appendicitis might be hard to diagnose in pregnant women?
Their anatomy is altered.
Signs of appendicitis.
Patients appear slightly ill. There is a slight fever as well as tachycardia. Localised right quadrant tenderness once the appendix has started to push on the parietal peritoneum. Rebound tenderness
Explain rebound tenderness.
In right iliac fossa. Upon pushing by the right iliac fossa there is generally no increased pain on the pressure but on release instead.
Where do you test for rebound tenderness?
McBurney’s point
What is McBurney’s point?
A point 2/3 of the way from umbilicus to ASIS.
Investigations of appendicitis.
Blood tests with raised WBC which may be very non-specific. History and physical examination. Rebound tenderness. ALWAYS tests for pregnancy and urine dip to rule out ectopic or UTI. CT scan (not common)
Treatment for appendicitis.
Open appendicectomy or laparoscopic appendicectomy (increasingly common)
What is diverticulosis?
An asymptomatic condition where outpourings are found in the mucosa and submucosa which herniate through the muscular layers.
Where does diverticulosis most commonly occur?
In the sigmoid colon along where nutrient vessels known as vasa recta penetrate the bowel wall.
Causes of diverticulosis.
Thought to be caused by increased intra-luminal pressure.
Why does diverticulosis most commonly occur in the sigmoid colon?
Due to higher pressure in the sigmoid colon due to storage of faeces.
What is symptomatic diverticulosis called?
Diverticular disease.
What is acute diverticulitis?
When the diverticula become inflamed and/or perforate with bleeding and abscess formation.
What is the difference between diverticular disease and acute diverticulitis?
Diverticular disease is diverticula with accompanying pain but no inflammation. In acute diverticulitis there is inflammation and/or perforation.
Rough percentage of people with diverticulosis which develop acute diverticulitis.
25%
Pathophysiology of acute diverticulitis.
Similar to appendicitis. The entrance of the diverticula is blocked by faeces or faecolith. This leads to inflammation and allows bacterial invasion of the wall of the diverticula. This can then lead to perforation.
Two types of diverticulitis.
Uncomplicated and complicated.
What is uncomplicated diverticulitis?
When the inflammation and/or small abscess are confined to the colonic wall.
What is complicated diverticulitis?
When there are larger abscesses, fistula or perforation.
Stage classification of diverticulitis.
Stage 1-4. Hinchey classification.
Outline stage 1-4 in diverticulitis.
1 - Pericolonic abscess, 2 - Pelvic abscess 3 - Purulent peritonitis Stage 4 - Faecal peritonitis
Symptoms of diverticulitis.
Abdo pain usually in left lower quadrant. Fever. Bloating. Constipation. Haematochezia.
Signs of diverticulitis.
Localised abdominal tenderness. Distension. Reduced bowel sounds. Signs of peritonitis following perforation.
Investigations of diverticulitis.
Blood tests like raised WBC, pregnancy test. Ultrasound CT Colonoscopy Elective colonoscopy (more favourable)
Why might colonoscopy be complicated in diverticulitis?
Risk of causing iatrogenic perforation.
Treatment of diverticulitis.
Antibiotics, fluid resuscitation, analgesia. (Generally enough to treat uncomplicated diverticulitis) Surgery in case of complicated.
Anatomy of the rectum.
12-15 cm through the pelvic floor. Continuous band of out longitudinal muscles unlike the taeniae coli of the rest of the colon. Curved shape anterior the sacrum. 1/3 upper is extraperitoneal, 1/3 middle is retroperitoneal and 1/3 lower has no peritoneum.
Function of the rectum.
Temporary storage of faeces prior to defaecation.
What stimulates the urge to defaecate?
Stretching of the rectum.
Arterial supply of the rectum.
1/3 upper - Superior rectal artery 1/3 middle - middle rectal artery 1/3 inferior - inferior rectal artery
What does the SRA arise from?
IMA
What does the MRA arise from?
Internal iliac artery
What does the IRA arise from?
Pudendal artery
Venous drainage of the rectum.
Portal drainage via superior rectal vein. Systemic drainage through the internal iliac vein (middle and inferior rectal veins)
Where is the start of the anal canal?
The proximal border of the anal sphincter complex.
How does the rectum point?
Anteriorly
How does the anal canal point?
Posteriorly
Explain the cause of the rectum pointing anteriorly and then the anal canal posteriorly.
The pubo-rectalis muscle changes the direction of the anatomy leading to a anorectal angle.
Give the factors required for the anal canal to retain its continence.
Distensible rectum Firm and bulky faeces Normal anorectal angle Anal cushions Normal and healthy anal sphincter.
What are the two parts of the anal sphincter complex?
The internal involuntary sphincter. The external voluntary sphincter.
What is the internal involuntary sphincter?
A thickening of circular smooth muscle.
Control of the internal involuntary sphincter.
Autonomic control and accounts for 80% of resting anal pressure.
What is the external voluntary anal sphincter?
It has a deep section within the upper anal canal that mixes with fibres from elevator ani. It joins with the pubo-rectalis to form sling. There are also superficial and subcutaneous sections.
Nerve supply of the external voluntary anal sphincter.
Pudendal nerve
How much of the resting anal pressure does the external voluntary anal sphincter account for?
20%
Explain steps leading up to defaecation.
Mass movement leads to the defaecation reflex. The stimulus is stretch and the response is contraction of the rectum and sigmoid colon. There is a relaxation of the IAS and contraction of EAS. This leads to an increase in pressure of the rectum. There is then either delay or defaecation.
Explain what happens in delay of defaecation.
Contraction of EAS and contraction of puborectalis. This can also lead to reverse peristalsis in the rectum to relieve pressure.
Explain what happens if defaecation occurs.
Relaxation of EAS. There is also relaxation of pubo-rectalis and forward peristalsis in rectum and sigmoid colon. The vasalva manoeuvre also occur to increase abdo pressure.
What is the dentate line?
A junction of handgun and proctodaeum.
Pain receptors above the dentate line.
Visceral pain receptors that usually only respond to stretch and not a lot to pain. Pathology above the dentate line is therefore generally painless.
Epithelium above the dentate line.
Columnar epithelium.
Pain receptors below the dentate line.
Somatic pain receptors. Leading to more pain if pathology is below the dentate line.
Epithelium below the dentate line.
Stratified squamous epithelium
What are anal cushions?
The anus contains a complex venous plexus. This is divided into three areas of tissues which is called anal cushions. There are connections between the veins and some arteries.
Function of the anal cushions.
Involved in the continence of the anal canal.
What are haemorrhoids?
Symptomatic anal cushions.
Classifications of haemorrhoids.
Internal haemorrhoids External haemorrhoids
Which classification is more common?
Internal haemorrhoids
Cause of IH.
Loss of connective tissue support
Where can IH be found?
Above the dentate line making them relatively painless.
Complications of IH.
Enlargement and prolapse through the anal canal leading to bleeding by bright red blood and pruritus.
Treatment of IH.
Increased hydration and fibre diet Avoid straining Rubber band ligation to strip off the blood supply and cause ischaemia. Surgery
Where can external haemorrhoids be found?
Below the dentate line.
Explain EH.
Swelling of the anal cushions below the dentate line. These are painful. Can cause thromboses external haemorrhoids.
Treatment of EH.
Surgery
What is an anal fissure?
Linear tear in the anoderm usually found in the posterior midline.
Signs and symptoms of anal fissure.
Passing of hard stools (can also follow diarrhoea) A lot of pain on defaecation usually described as passing razorblades. Haematochezia.
Cause of anal fissures.
High internal anal sphincter tone. Reduced blood flow to the anal mucosa
Treatment of anal fissures.
Hydration Dietary fibres Analgesia Warm baths Medication Anything that allows relaxation of the internal anal sphincter and reduce its tone.
Common causes of haematochezia. (In rough order of frequency)
Diverticulitis Angiodysplasia Colitis Colorectal cancer Anorectal disease like haemorrhoids, anal fissures. Upper GI bleeding
What is melaena?
Black tarry stools which are offensive smelling.
What is melaena due to?
Haemoglobin being altered by digestive enzymes and gut bacteria.
Common causes of melaena.
Upper GI bleed like in peptic ulcer disease. Variceal bleeds. Upper GI malignancy. Oesophageal/gastric cancer.
Uncommon causes.
Gastritis Meckel’s diverticulum Iron supplements
