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GI > physiology of the small intestine and exocrine pancreas > Flashcards

physiology of the small intestine and exocrine pancreas Flashcards

1
Q

what are the 3 parts of the small intestine

A

duodenum
jejunum
ileum

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2
Q

what does the small intestine receive

A

chyme from the stomach
pancreatic juice from the pancreas
bile from the liver and gall bladder

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3
Q

what does the small intestine secrete

A

intestinal juice ie succus enteric

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4
Q

what does motility in the small intestine cause

A

> mixing of chyme with digestive juices (segmentation)
slow propulsion of the chyme aborally (peristalsis)
removal of undigested residues to the large intestine via the ileocaecal valve (the migrating motor complex)

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5
Q

how is the surface area increased in the small intestine

A

by: circular folds (Kerkring), villi and microvilli

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6
Q

what is segmentation

A

mixing of chyme with digestive juices in digestive state

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7
Q

how does segmentation work

A

chopping moves chyme back and forth - this is particularly vigorous after a meal (almost none between meals)
>due to the alternation contraction and relaxation of segments of circular muscle

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8
Q

what initiates segmentation

A

small intestine pacemaker cells causing the BER (basic electrical rhythm?) which is continuous
>at threshold this activates segmentation which in the duodenum is primarily due to distension by entering chyme

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9
Q

what has the most segmentation contractions - duodenum or ileum ?

A 
duodenum = 12
ileum = 9

per minute

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10
Q

how can segmentation be enhanced/reduced

A

via parasympathetic and sympathetic activity

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11
Q

what triggers segementation in an empty ileum

A

triggered by gastrin from the stomach

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12
Q

how does peristalsis in the inter digestive state occur as

A

> a few localised contractions

>the migrating motor complex (MMC)

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13
Q

features of the MMC

A

> it occurs between meals every 90-120mins
strong peristaltic contraction slowly passing length of the intestine (stomach to the ileocaecal valve)
clears small intestine of debris, mucus and sloughed epithelial cells ‘housekeeper function’
inhibited by feeding and vagal activity
triggered by motilin, suppressed by gastrin and CCK

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14
Q

what does the small intestine secrete into the blood

A 
succus entericus and various peptide hormones (from endocrine cells in the mucosa)
>gastrin
>secretin
>cholecystokinin CCK
>gastric inhibitory peptide GIP 
>GLP-1 glucagon like peptide-1
>motilin
>ghrelin
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15
Q

gastrin

A

from G cells of gastric antrum and duodenum
>stimulates hydrogen ion secretion by gastric parietal cells
>stimulates growth of gastric mucosa

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16
Q

secretin

A

> released in response to hydrogen ions and fatty acids in lumen
promotes secretion of pancreatic and biliary bicarbonate

17
Q

CCK

A

> released in response to monoglycerides, free fatty acids, amino acids, and small peptides in the lumen
inhibits gastric emptying
causes secretion of pancreatic enzymes required for digestion
stimulates relaxation of sphincter of Oddi and contraction of gall bladder to eject bile into duodenum
potentiates the action of secretin

18
Q

GIP

A

> released in response to glucose, amino acids and fatty acids
stimulates release of insulin from pancreatic B-cells (Incretin action)
inhibits gastric emptying

19
Q

GLP-1

A

> stimulates insulin secretion
inhibits glucagon secretion from pancreatic alpha-cells
decreased gastric emptying and appetite

20
Q

motilin

A

> is secreted during the fasting state

>initiates the migrating motor complex

21
Q

ghrelin

A

> stimulates appetite

22
Q

what are the control mechanisms of the secretion of intestinal juice

A

> distension/irritation, gastrin, CCK, secretin, parasympathetic nerve activity enhance secretion
sympathetic nerve activity decreases secretion

23
Q

secretion of intestinal juice lacks digestive enzymes - what does it contain

A

mucus

aqueous salt

24
Q

what does the endocrine pancreas secrete

A

insulin and glucagon - secreted to blood

25
Q

what does the exocrine pancreas secrete

A

digestive enzymes (acinar cells), aqueous sodium bicarbonate solution (duct cells) and these are secreted to the duodenum collectively as pancreatic juice

26
Q

what are duct cells

A

> they secrete alkaline fluid into the duodenum per day
they neutralise acidic chyme entering the duodenum
-provides optimum pH for pancreatic enzyme function
-protects the mucosa from erosion by acid

27
Q

duct cells - what is going on at the apical membrane facing the lumen

A

> bicarbonate secretion occurs via a calcium/bicarbonate exchanger in the lumen is needed for exchange
CFTR is a chloride channel that provides an important fraction of the luminal chlorine needed for chlorine/bicarbonate exchange - activated by secretin

28
Q

duct cells - what is going on at the basolateral membrane facing the interstitium

A

> the sodium/chloride contransporter provides some of the bicarbonate required for its secretion across the apical membrane
sodium/potassium ATPase maintains the electrochemical gradients of sodium and potassium ions
sodium/hydrogen exchanger contributes to the export of hydrogen ions liberated by dissociation of carbonic acid
proton pump contributes to export of hydrogen ions liberated by dissociation of carbonic acid

29
Q

what can pancreatic enzymes do

A

can completely digest food in the absence of all other enzymes

30
Q

what are the pancreatic enzymes and where are they stored

A
  1. trypsinogen chymotrypsinogen procarboxypeptidase A and B
    pancreatic amylase
    pancreatic lipase
  2. stored in zymogen granules of acinar cells and are released as a result of elevated calcium ions
31
Q

where is enterokinase stored

A

mucosal cells of duodenum

32
Q

what does enterokinase cleave

A

> trysinogen to trypsin
chymotrypsinogen to chymotrypsin
procarboxypeptidase A and B to carboxypeptidase A and B

33
Q

what are the three phases of control of pancreatic secretion

A

cephalic
gastric
intestinal

GI (39 decks)

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