Distal GI tract Pathology Flashcards
Define diarrhoea. What is the pathophysiology?
A symptom that occurs in many conditions where you have:
Loose or watery stools
>3 times a day
Acute (<2 weeks)
Unwanted substances in gut stimulate secretion and motility to remove them, primarily down to epithelial function of secretion, colon is overwhelmed and can’t absorb the quantity of water it receives from ileum (normally 99% absorption)
What are the two broad categories of diarrhoea? explain how each come about.
Osmotic - osmotically active, poorly absorbed solutes in bowel lumen draws water in e.g. some laxatives, lactose intolerance, antacids (MgSO4) ,(stops when person fasts)
Secretory - body secretes electrolytes into gut lumen and water follows e.g. salmonella, E.coli, laxatives. Net secretion of chloride or bicarbonate into lumen and too little absorption Na+ mucosal disease/ bowel resection SA reduced e.g. coeliac/ IBD and reduced contact time e.g. diabetes
Define constipation. Risk factors
Suggestive of hard stools, difficulty passing stools or inability to pass stools
- straining during _> 25% defections
- lumpy/ hard stools _>25%
- feeling incomplete evacuation _>25%
- feeling obstruction/ blockage _>25%
- having <3 unassisted bowel movements a week
Female (3:1)
Certain medications e.g. codeine
Low physical activity level
Older or <4yrs
Pathophysiology of constipation
Normal transit constipation (often related psychological stressors e.g. IBS, anxiety)
Slow colonic transport e.g. megacolon, fewer peristaltic movements and shorter ones, fewer intestinal pacemaker cells (intestinal cells of cajal), systemic disorder (hypothyroidism, diabetes), Ns disease (Parkinson’s, Ms)
Defaecation problems (can’t coordinate muscles/ disorders pelvic floor or anorectum)
Describe the 3 movements of the colon
- Peristalsis (contraction behind and dilation in front, during digestion)
- Mass movement - food stored in TC/ AC -> gastrocolic reflux -> rectum distends (intense prolonged peristalsis, strips area clear of contents)
- Segmentation - shuttle contractions, during fasting, moves material forwards and back facilitating absorptive processes
Treatments of constipation
✅psychological support
Increased fluid intake
Increased activity
Increased dietary fibre
Fibre medication
Laxatives (osmotic MgSO4, disaccharides) (stimulatory, Chloride channel activators) (stool softeners)
Appendix blood supply, and location. How does this impact where you feel pain with appendicitis, when might this change?
The appendix is a diverticulum of the caecum . Complete longitudinal layer of muscle
Separate blood supply to caecum through a Mesentery (mesoappendix) from ileocolic branch of SMA
Retro-caecal, pelvic, sub-caecal, para-ileal
If long appendix, rectal/ pelvic pain.
Foregut so peri-umbilical pain -> touches parietal peritoneum so localised right-iliac fossa (midgut) - mcburney’s point (1/3 way from ASIS to umbilicus)
Categories of appendicitis
Acute (mucosal oedema), gangrenous (transmural inflammation and necrosis), perforated
Causes of appendicitis
Classic explanation: blockage of appendiceal lumen creates a higher pressure in the appendix (faecolith, lymphoid hyperplasia (few weeks after viral infection, lymphoid ring), foreign body) -> venous pressure rises (oedema appendix walls) -> harder arterial blood supply -> ischaemia walls -> bacterial invasion
Alternative explanation: viral/ bacterial infection -> mucosal changes that allow bacterial invasion of appendiceal walls
Symptoms of appendicitis
Classic presentation (<60%): Poorly localised peri-umbilical pain, anorexia, nausea/ vomiting (stretch receptors gut), low grade fever, after 12-24hrs pain more intense right iliac fossa
If appendix retro- caecal or pelvic may not get pain right iliac fossa - parietal peritoneum doesn’t come in contact then Amy get supra-pubic pain, right sided rectal/ vaginal
Children more non-specific
Pregnancy- pushes anatomy up
Signs of appendicitis
Appear slightly ill
Slight fever/ tachycardia
Generally lie quite still as peritoneum is inflamed
Localised right quadrant tenderness
Rebound tenderness in right iliac fossa appears relatively specific (McBurney’s point 2/3 of way from umbilicus to ASIS)
Diagnosis and treatment appendicitis
Blood test - raised WBC
History/ physical examination especially if rebound tenderness RIF
Pregnancy test/ urine dipstick rule out UTI
If non-classical presentation Ct scan distended doesn’t fill contrast
✅open appendicectomy, laparoscopic appendicectomy
What is diverticulosis?
Asymptomatic, occurs in colon (85% sigmoid c), outpouchings of mucosa and submucosa herniate through the muscularis layers along where nutrient vessels (vasa recta) penetrate the bowel wall. Thought to be caused by increased intra-luminal pressure (low fibre diet/ constipation)
What is diverticula disease?
Patient experiences pain but there is no inflammation/ infection
What is acute diverticulitis? What is the pathophysiology? What’s the inference between uncomplicated and complicated?
When the diverticula (outpouchings of mucosa and submucosa) become inflamed or perforate (+/- bleeding and abscess formation)
Occurs up to 25% of ppl with diverticulosis
Pathophysiology: entrance to diverticula is blocked by faeces, inflammation eventually allows bacterial invasion of the wall of the diverticula, can lead to perforation (similar to appendicitis)
Uncomplicated diverticulitis -inflammation and small abscesses confined to colonic wall
Complicated- larger abscesses, fistula, perforation (-> peritonitis)
Symptoms and signs of acute diverticulitis
Symptoms: abdo pain at site of inflammation (usually left lower quadrant- most in sigmoid colon), fever, bloating, constipation, haematochezia (large amounts blood loss in stool)
Signs: localised abdo tenderness, distension, reduced bowel sounds, signs of peritonitis (following perforation)
Diagnosis and treatment of acute diverticulitis
Diagnosis:
- blood tests (raised WBC, pregnancy exclude ectopic)
- USS
- CT scan
- colonoscopy if large haematochezia
- elective colonoscopy (after symptoms settled, determine cause if unclear)
Treatment:
-antibiotics
-fluid restriction
-analgesia
If complicated may also need: - surgery if perforation or large abscesses need to be drained
- occasionally partial colectomy if other treatments failed
Describe the structure of the rectum
12-15 cm long, passes through pelvic floor, continuous band outer longitudinal muscles, curved shape anterior to sacrum, parts covered in peritoneum, distal parts extra-peritoneal
Temporary storage of faeces prior to defaecation
Describe the blood supply to the rectum
Several arteries that form a plexus
Superior rectal A - continuation of IMA
Middle rectal A - internal iliac A
Inferior R A - pudendal A
Venous drainage: dual drainage
Portal through superior rectal vein and systemic through internal iliac vein (potential for Porto-systemic anastomosis -> rectal varices)
Describe the structure of the anal canal including the dentate line
Anal canal is narrowed portion of GI tract that continues from rectum
Starts at proximal border of anal sphincter complex, points anteriorly, pubo-rectalis sling changes direction of anatomy so anal canal points posteriorly (this kink helps keep continence)
Contains the dentate/ pectinate line (junction of hindgut and proctodaeum = ectoderm)
- above dentate line (visceral pain receptors only stretch sensation and columnar epithelium)
- below the dentate line (somatic lain receptors and SS epithelium)
What factors are required for the anal canal to aid in continence?
Distensibke rectum, firm bulky faeces, normal anorectal angle (pubo-rectalis sling), anal cushions, normal anal sphincter
Describe the anal sphincter complex
Internal involuntary sphincter - thickening of circular smooth muscle, under autonomic control (80% resting anal pressure)
External anal sphincter - striated muscle, deep section, mixes with fibres from levator ani, joins with pubs-recital is to form sling, superficial and subcutaneous sections, VoLUNTARY control from pudendal nerve (20% of resting pressure)
Describe the steps that lead to defecation
Mass movement ->
defection reflex (stimulus of distension in rectum causes contraction rectum/ sigmoid colon/ external anal sphincter and relaxation of internal anal sphincter)->
increased pressure in rectum ->
Either:
-delay (contraction of EAS/ puborectalis-> reverse peristalsis in rectum)
OR
- defection (relaxation EAS/ puborectalis, forwards peristalsis rectum/ sigmoid colon, valsalva maneuver increased abdo pressure)
What are anal cushions and when are they a problem?
Anus contains complex venous plexus divided into 3+ areas tissues called anal cushions, play role in anal continence.connections between veins and some arteries (right anterio, left, right posterior)
When these become symptomatic = haemorrhoids
What are the two classifications of haemorrhoids? Include symptoms and treatment
Symptomatic anal cushion
- Internal haemorrhoids (most common) - loss of Ct support above dentate line, relatively painless, enlarge and prolapse through anal canal, bleed bright red blood/ pruritis
✅increased hydration, high fibre diet, avoid straining, rubber band ligation cut off blood supply, surgery if extreme
- External haemorrhoids - below dentate line, swelling of anal cushions which may then thrombose (clot within haemorrhoids -> skin tags), V painful, surgery has good outcomes
What is an anal fissure? Causes, symptoms, treatment
Linear tear in anoderm (SS epithelium in anal canal usually posterior midline) - passing of hard stools but can also follow diarrhoea, lots of pain on defaecation, haematochezia
Causes: high internal anal sphincter tone, reduced blood flow to anal mucosa
✅ hydration, dietary fibre, analgesia, warm baths, medication to relax IAS
Commonest causes haematochezia
Most common to least
- diverticulitis
- angiodysplasia (small vascular malformation in bowel wall spontaneously bleed)
- colitis (IBD, infective)
- colorectal cancer
- anorectal cancer (haemorrhoids, Amal fissure)
- upper GI bleeding (large bleed with fast transit)
What is melaena? causes?
Black tarry stools - offensive smelling, due to Hb being altered by digestive enzymes and gut bacteria
Commonest causes:
- upper GI bleeding
- peptic ulcer disease
- variceal bleeds
- upper gi malignancy
- oesophageal/ gastric cancer
Uncommon causes:
Gastritis
Meckel’s diverticulum
Iron supplements
