Distal GI tract pathology Flashcards
What is Diarrhoea?
Loose or watery stools more than 3 times a day
(Acute Diarrhoea = less than 2 weeks)
What are the 2 main classes of diarrhoea? Briefly explain each
Osmotic and Secretory
Osmotic: osmotic chyme increases osmotic pressure drawing water into lumen. Diarrhea stops when fasting
Secretory : no chyme needed, ion movement causes large amounts of water to enter lumen. Diarrhoea does not stop when fasting
Explain the underlying problem in secretory diarrhoea
- Too much secretion of ions (Cl- or HCO3-) into the GI lumen
- Commonly caused by infectious toxins
- Too little reabsorption of Na+ due to:
- reduced surface area for reabsorption
- Mucosal disease/ bowl resection
- Reduced contact time → reduced contact time
Explain the underlying cause of osmotic diarrhoea
- Gut lumen contains too much osmotic material due to malabsorption
- Ingested material poorly absorbed e.g. antacids are not absorbed
- Inability to absorb nutrients e.g. lactose intolerance
- Will settle if you stop consuming the offending substance
What is constipation?
Hard stools, difficult to pass
- straining during >25% defecations
- Lumpy or hard stools >25% defecations
- Feeling incomplete evacuation >25% defecations
- Fewer than three unassisted bowel movements a week
What are some risk factors for constipation?
- Female vs male (3:1)
- Certain medication e.g. codeine
- Low level of physical activity
- Increases with age
- Common in children under 4
What things can cause constipation?
- Normal transit constipation → related to psychological stressors
- Slow colonic transport → greater transport time = more water rabsorbed
- megacolon
- fewer perilstaltic moveement
- fewer intestinal pacemaker cells
- systemic disorders; hypothyroid &diabetes
- nervous system disorders; Parkinson’s, MS
- Defecation problems → cannot coordinate muscles for defecation
How does faeces movement change during fasting and digestion?
In fasting: material moves back and forth (shuttle contractions) in colon to faciliation absorption
In digestion: mass movement progressive waves force material to the rectum
What treatment can you give for constipation?
- Psychological support
- Increased fluid intake
- Increased activity
- Increased dietary fibre
- Fibre medication
- Laxatives
Describe the anatomy of the appendix
- A diverticulum off the caecum
- Complete longitudinal layer of muscle
- Has a separate blood suppl to the caecum from a branch of the ileocolic branch of SMA
- Location can be retrocaecal, pelvic, subcaecal, paraileal which will change the presentation of appendicitis
What are the 3 broad categories of appenticitis?
- Acute (mucosal oedema)
- Gangrenous (transmural inflammation and necrosis)
- Perforated
Explain the classic explanation of appendicitis
-
Blockage of the appendix lumen creates higher pressure in the appendix
- can be blocked by faecolith, lymphoid hyperplasia, foreign body
- Causes venous pressure to rise → oedema in walls of appendix → can reduce blood supply
- Ischemia in walls of appendix
- Bacterial invasion follows
Explain the alternative explanation for appendicitis
Viral or bacterial infection causing mucosal changes allowing bacterial invasion of appendiceal walls
What is the classic presentation of appendicitis?
- poorly localised peri-umbilical pain
- anorexia
- nausea/ vomiting
- pain localises to right iliac fossa after 12-24 hrs
In what circumstances would you not see the classical presentation of appendicitis?
- If appendix is retro-caecal you might not get right, iliac fossa pain → pain may be elsewhere
- Children give non specific symptoms
- Pregnancy alters anatomy → pain higher up
What signs do you see in appendicitis?
- Patients appear slightly ill
- Slight fever/ tachycardia
- Lie quite still as peritoneum is inflammed
- Localised right quadrant tenderness
- Rebound tenderness in right iliac fossa
- Push in and let go → pain on letting go
How do you diagnose appendicitis?
- Blood test- looking for raised WBC (non- specific)
- History/ examination
- Do pregnancy test in women
How do you treat apendicitis?
Surgery: either open or laproscopic appendicectomy
Describe the blood flow to the rectum
Several arteries join to form a plexus
- superior rectal artery (continuation of IMA)
- middle rectal artery - from internal iliac
- inferior rectal - from pudendal artery
Describe the venous drainage of the rectum
Dual drainage
- Portal drainage through superior rectal vein
- Systemic drainage through internal iliac vein
Describe the anatomy of the anal canal
A narrowed portion of GI tract that continues on from the rectum
- starts at the proximal border of the anal sphincter complex
- Rectum points anteriorally
- Pubo-rectalis sling then changes the direction of anatomy
- Anal canal points posteriorally
Describe the anal sphincter complex
Internal involuntary sphincter
- Thickening of smooth muscle
- under autonomic control
- 80% of resting pressure
External anal sphincter
- striated muscle
- mixes with fibres from levator ani
- superficial and subcutaneous sections
- 20% of resting pressure
What are internal haemorrhoids, how are the caused and what are the symptoms?
Internal haemorrhoids are caused by a loss of connective tissue support
They are above the dendate line so relatively painless
Can enlarge and prolapse through anal canal
May see bright red blood / pruritis (itching)
What are external haemorrhoids?
Swelling of anal cushions that may thrombose
Below the dendate line so very painful
