Physiology and pharmacology of the large intestine and water balance in the GI Tract Flashcards Preview

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Flashcards in Physiology and pharmacology of the large intestine and water balance in the GI Tract Deck (10)
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1

what are the 4 parts of the colon?

-ascending
-transverse
-descending
-sigmoid

2

what makes up the large intestine?

-colon
-caecum
-appendix
-rectum

3

what does the large intestine receive?

approximately 1000 ml of ileocecal material (indigestible residues, unabsorbed biliary components, unabsorbed fluid) per day

4

what is entry into the large intestine permitted by?

gastroilial reflex through the ileocecal sphincter

5

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

6

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

7

what are the patterns of motility in the large intestine?

-Haustration (non-propulsive segmentation)
-Peristaltic propulsive movements (mass movement)
-Defaecation

8

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)

9

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

10

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