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
What is Diverticulosis?
An outpouching of mucosa and submucosa, herniating through the muscularis layers of the bowel
Occurs where nutrient vessels penetrate bowel creating an area of weakness
Where do the majority of diverticulosis occur? Why here?
85% in the sigmoid colon
At this stage of the colon, stools have formed so needs higher pressure to move it along. This high pressure predisposes to diverticulosis
What is acute diverticulitis?
When diverticula become inflammed/ perforate
Occurs in 25% of people with diverticulosis
How does acute diverticulitis occur?
- Entrance to diverticula blocked by faeces
- Inflammation allows bacterial invasion of wall of diverticula
- Can lead to perforation
What is the difference between complicated and uncomplicated diverticulitis?
Uncomplicated: inflammation and small abscess confined to colonic wall
Complicated: Larger abscesses, fistula, perforation
What is divertocular disease?
Where patient experiences pain in diverticula but there is no inflammation/ infection
What are the symptoms of acute diverticulitis?
- Abdominal pain at site of inflammation
- Fever
- Bloating
- Constipation
- Haematochezia (blood in stool)
What are the signs of acute diverticulitis?
- Localised abdominal tenderness
- Distension
- Reduced bowel sounds
- Signs of peritonitis (if perforated)- won’t want to move at all due to pain
How do you diagnose acute diverticulitis?
- Ultrasound
- CT scan
- Colonoscopy if large haematochezia (but careful not to perforate)
- Elective colonoscopy after symptoms settle to determine cause
How do you treat acute diverticulitis?
- Antibiotics
- Fluid resusciation
- Analgesia
- Surgery if perforated
- Drained if its a large abscess
Describe the anatomy of the rectum
- 12-15 cm long
- Continuous band of outer longitudinal muscle
- Curved to the shape of the sacrum
- Some parts covered in peritoneum
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
What 5 factors are required for continence?
- distendible rectum
- firm, bulky faeces
- normal anorectal angle
- anal cushions
- normal anal sphincters
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
Describe the gastrocolic reflex of defecation
- Mass movement into the bowel
- Rectum distends triggering defecation reflex
- Rectum and sigmoid colon contract
- internal anal sphincter relaxes
- external anal sphincter contracts → pressure builds in the rectum
- Either delay → external sphincter contracts, reverse perilstalises into rectum
- Or defectation → relaxation of external sphincter, puborectalis relaxed straightening angle of rectum, forward perilstalsis
How does the rectum differ below and above the dendate line?
Above:
- Visceral pain receptors
- Columnar epithelium
Below:
- somatic pain receptors
- Stratified Squamous Epithelium
What are anal cushions?
A complex of 3 areas of tissue with venous plexus’
Play a role in anal continence
What are haemorrhoids?
Symptomatic Anal cushions
Either internal or external
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)
How would you treat internal haemorrhoids?
- Increase hydration and fibre in the diet
- Avoid straining
- Rubber band ligation
- Surgery
What are external haemorrhoids?
Swelling of anal cushions that may thrombose
Below the dendate line so very painful
What is an anal fissure and how does it present?
A linear tear in the anoderm below the dendate line
Presents with pain on defecation and haematochezia
What is the underlying cause of an anal fissure?
- High internal sphincter tone
- Reduced blood flow to the anal mucosa
- Passing of hard stools
How do you treat an anal fissure?
- Hydration, dietary fibre, analgesia
- Warm baths
- Medication to try and relax the internal anal sphincter
What are some common causes of haematochezia?
- Diverticulitis
- Angiodysplasia (vascular malformation in bowel wall)
- Colitis
- Colorectal cancer
- Anorectal disease - haemorrhoids, anal fissure
- Upper GI bleed
What is melaena and how is it formed? Give some common causes
Melaena is black, tarry, offensive smelling stools. Formed due to Hb being altered by digestive enzymes and gut bacteria
Common causes:
- Upper GI bleeding
- Pepic ulcer disease
- Variceal bleeds
- Upper GI Malignancy
- Oesophageal/ Gastric cancer
