Distal Gi Tract Pathology Flashcards
What is diarrhoea
Definition- diarrhoea is a symptom and occurs in many conditions
• Loose or watery stools
•More than 3 times a day
•Acute diarrhoea (less than 2 weeks)
Describe the pathophysiology of diarrhoea
Pathophysiology •Unwanted substance in gut stimulates secretion and motility to get rid of it- diarrhoea •Primarily down to epithelial function (secretion) rather than increased gut motility (although this does occur) (Problem with absorptionn or secretion primarily. Sped up motility = less contact time for stuff to be absorbed)`
• The end product is too much water in stool
•Colon is overwhelmed and cannot absorb the quantity of water it receives from ileum
•There is normally 99% absorption of water from gut
• Leaving only 100 mls in stool/day
How is fluid normally move down the GI tract
Fluid movement down GI tract- normal conditions
• Remember that water is not actively moved across gut
•Follows osmotic forces generated by the movement of electrolytes/nutrients
• Paracellular/transcellular
In diarrhoea Two broad categories- Osmotic & secretory
What is secretory diarrhoea
Secretory- Electrolyte transport is messed up Too much secretion of ions (net secretion of chloride or bicarbonate)
• Cause of diarrhoea will affect the messenger systems that control ion transport
• Infectious toxins (we will look at examples in infection lecture)
Too little absorption of sodium • Reduced surface area for absorption • Mucosal disease/ bowel resection - Coeliac or inflammatory bowel disease (Crohn’s) • Reduced contact time (intestinal rush) • Diabetes/?IBS
What is osmotic diarrhoea
Osmotic- the gut lumen contains too much osmotic material (malabsorption)
• Ingesting material that is poorly absorbed (antacids- magnesium sulphate)
• Inability to absorb nutrients (eg lactose in lactase deficiency)
• Will settle if you stop consuming offending substance
Define constipation
Definition- suggestive if hard stools, difficulty passing stools or inability to pass stools
• Straining during ≥25% of defecations
• Lumpy or hard stools in ≥25% of defecations
• Feeling of incomplete evacuation in ≥25% of defecations
• Feeling of obstruction or blockage to defecation in ≥25% of defecations
• Having fewer than three unassisted bowel movements a week
What are teh risk actors for constipation
Risk factors
• Female vs male (3:1)
• Certain medications
• Low level of physical activity (Eg if you’ve had a stroke and have problems with mobility)
• Increasing age (but also common in children under 4 years old)
Describe teh apthophysiology of constipation
• Normal transit constipation (often related to other psychological stressors)
• Slow colonic transport
- Large colon (megacolon)
- Fewer peristaltic movements and shorter ones
- Fewer intestinal pacemaker cells present (interstitial cells of Cajal)
- Systemic disorders (hypothyroidism, diabetes)
• Nervous system disease (Parkinson’s, MS)
- Defaecation problems
- Cannot coordinate the muscles of defaecation/disorders of the pelvic floor or anorectum
What are the treatments for constipation
Treatments
• Psychological support
•Increased fluid intake
•Increased activity
•Increased dietary fibre (only useful for mild constipation)
•Fibre medication (may not 100% help)
•Laxatives- (Please note similarity with causes of diarrhoea)
- Osmotic (magnesium sulphate, disaccharides
- Stimulatory (chloride channel activators)
- Stool softeners
Give a brief overview of the appendix
- The appendix is a diverticulum off the caecum
- Has a complete longitudinal layer of muscle (colon has incomplete bands called teniae coli)
- Separate blood supply to caecum coming up through a mesentery (mesoappendix) from the ileocolic branch of SMA
- Location of the appendix is important because it changes the presentation of acute appendicitis
- Retro-caecal
- Pelvic
- Sub-caecal
- Para-ileal (pre or post)
What is the classic presentation of apendiciti
Classic appendicitis: Slight dilation - visceral afferent s - t10 dermatome - vague periumbilical pain. As it grows it can touch the parietal peritoneum, so get pain in right iliac fossa
But appendix can be in a different position and may not touch the parietal peritoneum
What are the broad categories of appendicitis
Broad categories
• Acute (mucosal oedema)
• Gangrenous (transmural inflammation and necrosis)
• Perforated
What are the causes of appendicitis
Causes •Classic explanation
• blockage of appendiceal lumen creates a higher pressure in the appendix (faecolith, lymphoid hyperplasia, foreign body)
• This causes venous pressure to rise (causing oedema in walls of appendix)
• This makes it harder for arterial blood to supply appendix
• Ischaemia in walls of appendix
• Bacterial invasion follows
Lymphoid nodules for eh in virus - lymphoid hyperplasia - can obstruct the lumen of the appendix. A fecalith can also block the appendix. Blocks can set off a chain reaction - bacterial proliferation. - infection - perforation
- Alternative explanation
- A Viral or bacterial infection causes mucosal changes that allow bacterial invasion of appendiceal walls
What are the symptom TOMS of appendicitis
Classic presentation (<60% of cases) • Poorly localised peri-umbilical pain • Anorexia • Nausea/vomiting • Low grade fever • After 12-24 hours pain is felt more intensely in right iliac fossa
- If appendix is retro-caecal or pelvic in its position you may not get right iliac fossa pain
- Parietal peritoneum in right iliac fossa does not come in contact with inflamed appendix • Supra-pubic pain, right sided rectal or vaginal pain
- Children make it difficult to diagnose
- History is difficult • Symptoms are much more non-specific
- Pregnancy
- Anatomy is altered
What are teh signs of appendicitis
• Patients 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 to be relatively specific
Push in, then rebound is painful
Describe the diagnosis and treatment of appendicitis
- Blood tests- Raised WBC- very non specific
- History/physical examination- if classic then this might be enough
- Especially if rebound tenderness in RIF
- Pregnancy test/urine dip to rule out pregnancy or UTI
- In non-classical presentations (in the US)
- CT scan will show distended appendix that doesn’t fill with contrast Treatment
- Open appendicectomy
- Laparoscopic appendicectomy
What is diverticulosis
• Diverticulosis is asymptomatic
•Occurs in the colon (85% in sigmoid colon)
•Outpouchings of mucosa and submucosa herniate through the muscularis layers
•Occurs along where nutrient vessels (vasa recta) penetrate the bowel wall
•Thought to be causes by increased intra-luminal pressure (low fibre diet)
Higher pressure in gut lumen.. left side of colo, esp sigmoid coon, . Further along the gut, need higher luminal pressure to move stuff along bc its less watery. Where nutrient arteries come in - weak point - thighs is where the diverticula go out
What is diverticula disease
Please note that Diverticular disease is when the patient experiences pain but there is no inflammation/infection
What is diverticulitis
- Acute diverticulitis is when the diverticula become inflamed or perforate (+/-bleeding and abscess formation)
- Occurs in up to 25% of people with diverticulosis
Pathophysiology is similar to that involved in appendicitis
• Entrance to diverticula is blocked by faeces
• Inflammation eventually allows bacterial invasion of the wall of the diverticula
• Can lead to perforation
Uncomplicated diverticulitis
• Inflammation and small abscesses confined to colonic wall
Complicated diverticulitis
• Larger abscesses, fistula, perforation
What are the signs and symptoms of acute diverticulitis
Symptoms • Abdominal pain at the site of the inflammation
• Usually the left lower quadrant (most in sigmoid colon) •Fever (there is inflammation & infection) •Bloating •Constipation (the inflammation can block the colonic lumen) •Haematochezia (occasionally large amounts of blood loss)
Signs •Localised abdominal tenderness •Distension •Reduced bowel sounds •Signs of peritonitis (following perforation)
Desvreubt the diagnosis and treatment of acute diverticulitis
Blood tests
• Raised WBC, pregnancy test (to exclude ectopic), •Ultra sound scan (USS) •CT scan •Colonoscopy if large haematochezia •Elective colonoscopy (after symptoms have settled) to determine causes of symptoms if unclear
Treatment •Antibiotics, fluid resuscitation, analgesia
• In uncomplicated diverticulitis, analgesia and oral antibiotics (and follow up) may be all that is required.
•Surgery if perforation or large abscesses need to be drained
• Occasionally partial colectomy is required if other treatments have failed
Describe rectum and anal canal anatomy
These are the last sections of the GI tract
• Involved in defaecation
•The location of the anorectal junction is a source of mild debate Rectum •12-15cm long passes through the pelvic floor
•Has a continuous band of outer longitudinal muscle
• unlike the taeniae coli of the rest of the colon
•Curved shape anterior to sacrum
•Parts of it are covered in peritoneum
- Parts are extra-peritoneal
•Temporary storage of faeces prior to defaecation (usually scored in distal transevrse or descending colon)
- Stretching of rectum stimulates urge to defaecate
Describe teh blood supply an venous drainage of the rectum and Anal canal
Blood supply to rectum is from several arteries that form a plexus
• Superior rectal artery -continuation of Inferior mesenteric artery
•Middle rectal artery- internal iliac •Inferior rectal- pudendal artery
Venous drainage
•Portal drainage through superior rectal vein -> inf mesenteric
•Systemic drainage through internal iliac vein
• Potential for porto-systemic anastomosis
Rise in portal reassure - rise in portal venous reassure - harder for blood to drain the ouch imv
Rectum drains through portal and systemic
Descrbe the anatomy of the anal canal
The anal canal is a narrowed portion of the GI tract that continues on from the rectum
• Where is the start of anal canal?
• The proximal border of the anal sphincter complex
• Rectum points anteriorly
• Pubo-rectalis sling changes the direction of the anatomy
• Anal canal points posteriorly
What are the factors involved in continence
Factors required • Distensible rectum • Firm bulky faeces • Normal anorectal angle • Anal cushions • Normal anal sphincters Dentate line is the end of the hindgut. - hindcgt has columnar btu afterward sratfied squamous
What is the anal sphincter complex
• Internal involuntary sphincter
◦ Thickening of circular smooth muscle
• This is under autonomic control (80% of resting anal pressure)
- External anal sphincter is striated muscle
- Deep section
- Upper anal canal
- Mixes with fibres from levator ani
- Joins with pubo-rectalis to form sling • Superficial and subcutaneous sections
- Nerve supply from pudendal nerve
- 20% of resting pressure
Descrbe the defecation reflex
Ss
What is the dentate line
Anal canal contains the Dentate line
◦ Junction of hindgut and proctodaeum (ectoderm)
Above the dentate line
• Visceral pain receptors
• Columnar epithelium
Below the dentate line
• Somatic pain receptors
• Stratified squamous epithelia
What are teh anal cushions
Anal cushions
• The anus contains a complex venous plexus
• Divided into 3+ areas of tissues called anal cushions
• Play a role in anal continence
• There are connections between the veins and some arteries
• Present from birth and a normal finding
What are haemorrhoids
• Symptomatic anal cushions (haemorrhoids)
•Two classifications
• Internal heamorrhoids (most common)
- Caused by loss of connective tissue support
- Above dentate line,
- Relatively painless
-Enlarge and prolapse through anal canal
-Bleed bright red blood/pruritis
Treatment • Increased hydration/ high fibre diet • Avoid straining • Rubber band ligation • Surgery
Wha are external haemorrhoids
Below dentate line
• Swelling of the anal cushions which may then thrombose
• Painful++
• Surgery has good outcomes (thrombosed external haemorrhoids)
What is an anal fissure
Linear tear in the anoderm (usually posterior midline)
• Passing of hard stool (but can also follow diarrhoea??)
• Pain on defaecation++ (passing razor blades)
• Haematochezia
Underlying causation
• High internal anal sphincter tone
• Reduced blood flow to anal mucosa
Treatment
• Hydration, dietary fibre, analgesia
• Warm baths
• Medication trying to relax the internal anal sphincter
What is haematochezia
Rough order of frequency • Diverticulitis •Angiodysplasia (small vascular malformation in bowel wall) •Colitis - IBD, infective •Colorectal cancer •Anorectal disease • Haemorrhoids, anal fissure •Upper GI bleeding • Large bleed with fast transit
What is Malaena
Black tarry stools
• Offensive smelling
•Due to the haemoglobin being altered by digestive enzymes and gut bacteria
Common causes •Upper GI bleeding
• Peptic ulcer disease • Variceal bleeds • Upper GI malignancy • Oesophageal/ gastric cancer
Uncommon causes
• Gastritis • Meckel’s diverticulum • Iron supplements
