Lecture 20 Flashcards
Large intestine vs small intestine structure?
Large intestine has bulges (haustra)
Mechanical digestion in large intestine?
Chyme enters through ileocaecal valve from ileum to cecum, haustral churning (segmentation) -> peristalsis occurs slowly (want to compact/concentrate contents)
Chemical digestion in large intestine?
Is very limited. Only bacterial enzymes present - ferment remaining carbohydrate to produce flatus, remaining amino acids are broken down
Motility patterns in large intestine?
Segmental contraction, slow peristaltic contractions, mass movements
Mass movements?
Not seen elsewhere is digestive tract, where contraction clears sections of the colon of all its contents
What causes increase in colonic motility?
Morning wakening (sleeping = minimal pressure), stress,
What causes decrease in colonic motility?
Diet (fibre increases faecal weight), immobility leads to constipation, women have slower transit than men
Ascending colon (right colon)?
Is relatively fluid (consistency of muesli with large aggregates beginning to form)
Transverse colon?
Less water and some gas
Descending colon?
Risk of impaction in faeces (become too concentrated), drinking fluids is important
What does faeces consist of?
Undigested food, inorganic salts, sloughed off epithelial cells, bacterial products, bacteria
Defaecation process?
Reflex initiated by distension (swelling) of rectum (parasympathetic input to open internal anal sphincter – involuntary).
Increased pressure in rectum (longitudinal muscle pushes contents down), voluntary contractions of diaphragm/abdomen, external anal sphincter opens
Disorders of large intestine?
Diarrhoea, constipation, irritable bowel syndrome (IBS), haemorrhoids
Causes of IBS?
Abnormal GI motility, anxiety, altered serotonin levels (more in GI tract than in brain), bile acids (irritate the bowel)
Treatments for IBS?
Antidepressants , change diet (keep food diary to target common factors), antispasmodic (dicyclomine) - important to reassure patients (often fear of cancer)
