Physiology and pharmacology of the large intestine and water balance in the GI Tract Flashcards
what are the 4 parts of the colon?
- ascending
- transverse
- descending
- sigmoid
what makes up the large intestine?
- colon
- caecum
- appendix
- rectum
what does the large intestine receive?
approximately 1000 ml of ileocecal material (indigestible residues, unabsorbed biliary components, unabsorbed fluid) per day
what is entry into the large intestine permitted by?
gastroilial reflex through the ileocecal sphincter
how does the gastroilial reflex permit entry into the large intestine?
- maintains a positive resting pressure
- relaxes in response to distension of the small intestine
- contracts in response to distension of the ascending colon
- is under the control the vagus nerve, sympathetic nerves and enteric neurones
what are the primary functions of the large intestine?
- absoprtion of H20, Na+ and Cl- (secretion of k+,HCO3- and mucus)- converts liquid content of ileocecal material into solid
- absorption of short chain fatty acids (carbohydrate not absorbed by small intestine is fermented to short chain fatty acids)
- reservoir- storage of colonic contents
- periodic elimination of faeces -voluntary control
what are the patterns of motility in the large intestine?
- Haustration (non-propulsive segmentation)
- Peristaltic propulsive movements (mass movement)
- Defaecation
Describe haustration.
haustra are saccules caused by contraction of the circular muscle – similar to segmentation in function, but much lower frequency– contributes to long transit time (16 – 48 hours)
Describe mass movement.
simultaneous contraction of large sections (about 20 cm) of the circular muscle of the ascending and transverse colon (haustra disappear) - drives faeces into distal regions
when does mass movement occur and why?
-Occurs about one to three times daily
-Typically triggered by a meal (often breakfast) via the gastrocolic response involving gastrin and
extrinsic nerve plexuses
