Lecture 20 - Physiology of the Large Intestine Flashcards
What are Hastra?
saccules/ lumps that give LI its segmented appearance
Mechanical digestion in the large intestine
Chyme enters through ileocecal valve, haustral churning, low peristalsis
Chemical digestion in large intestine
Very limited, bacterial enzymes ferment remaining carbohydrates to produce flatus, amino acids broken down
What is flatus?
gas in or from the stomach or intestines
Are segmental contractions more or less predominant in LI than propulsive movements?
more, propulsive movements only happen 3-4 times a day
What are mass movements in LI?
giant migrating contraction, intense and prolonged peristalsis which can clear sections of colon of all contents
Where do mass movements occur in GI Tract?
only LI
What triggers motility of colon?
morning wakening, in response to stretch in stomach and digestion by products in SI
What increases colon transit time?
eating fibres (increase faecal weight, reducing Transit time)
stress (may increase motility)
What decreases colon transit time?
bad diet, immobility, old age, being a female (statistically have slower transit time compared to men)
How much water is absorbed by LI everyday?
500-100ml (only 100ml reabsorbed)
What is faeces made of?
undigested food, inorganic salts, sloughed off epithelial cells (cells moved of interior of mucosa), bacterial products and bacteria
Where in LI is there a greater risk of faecal impaction?
descending colon
Process of defaecation
- chyme moves down descending part of colon
- reflex initiated by distension of rectum
- parasympathetic input relaxes internal anal sphincter and contraction of external sphincter (involuntary)
- increased pressure in rectum, longitudinal muscle shortens
- voluntary contractions of diaphragm and abdomen
- external anal sphincter opens
Causes of constipation
idiopathic (bad diet - low fibre, low fluid intake), gender (women more susceptible, psychiatric, disease, latrogenic (morphine, laxative abuse)
Causes of Diarrhoea that don’t normally require treatment
dietary indiscretion, mild food poisoning
Causes of diarrhoea usually requiring treatment
disease, drug-induced (cholinergic drugs), travel
Causes of IBS
abnormal GI motility, psychological factors (anxiety), food allergens, bile acids, processed foods, luminal compounds, altered serotonin levels
Cause of Haemorrhoids
excessive straining due to constipation
What are haemorrhoids?
overdistended veins in submucosa of lower rectum
Complications caused by haemorrhoids
thrombosis of local blood vessels
What medications can be given to help with haemorrhoids?
bulk/lubricant laxatives to ease defaecation, topical preparations (anusoyl), local anaesthetics, anti-inflams such as hydrocortisone to relieve symptoms
2 regions of the colon
proximal and distal
What part of colon can be reached rectally?
distal
What part of colon can only be reached via oral route?
proximal
Where in LI is fluid enough for drug absorption?
only ascending colon (think descending is where impaction etc. can occur as fluid is drawn out from chyme)
Some functions of gut microbacteria
metabolism of indigestible material, vitamin synthesis, neurochemical synthesis, anti-inflam affects, promote bone growth
Factors affecting microbiome
diet, age, host genetics, exercise, antibiotics, smoking, geographical impacts
Interventions to regulate microbiome in gut
probiotics, faecal microbiota transplant, phage (virus) therapy to selectively target bacteria
