physiology of the small intestine and exocrine pancreas

Question 1

what are the 3 parts of the small intestine

Answer 1

duodenum
jejunum
ileum

Question 2

what does the small intestine receive

Answer 2

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

Question 3

what does the small intestine secrete

Answer 3

intestinal juice ie succus enteric

Question 4

what does motility in the small intestine cause

Answer 4

> 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)

Question 5

how is the surface area increased in the small intestine

Answer 5

by: circular folds (Kerkring), villi and microvilli

Question 6

what is segmentation

Answer 6

mixing of chyme with digestive juices in digestive state

Question 7

how does segmentation work

Answer 7

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

Question 8

what initiates segmentation

Answer 8

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

Question 9

what has the most segmentation contractions - duodenum or ileum ?

Answer 9

duodenum = 12
ileum = 9 

per minute

Question 10

how can segmentation be enhanced/reduced

Answer 10

via parasympathetic and sympathetic activity

Question 11

what triggers segementation in an empty ileum

Answer 11

triggered by gastrin from the stomach

Question 12

how does peristalsis in the inter digestive state occur as

Answer 12

> a few localised contractions

>the migrating motor complex (MMC)

Question 13

features of the MMC

Answer 13

> 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

Question 14

what does the small intestine secrete into the blood

Answer 14

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

Question 15

gastrin

Answer 15

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

Question 16

secretin

Answer 16

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

Question 17

CCK

Answer 17

> 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

Question 18

GIP

Answer 18

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

Question 19

GLP-1

Answer 19

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

Question 20

motilin

Answer 20

> is secreted during the fasting state

>initiates the migrating motor complex

Question 21

ghrelin

Answer 21

> stimulates appetite

Question 22

what are the control mechanisms of the secretion of intestinal juice

Answer 22

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

Question 23

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

Answer 23

mucus

aqueous salt

Question 24

what does the endocrine pancreas secrete

Answer 24

insulin and glucagon - secreted to blood

Question 25

what does the exocrine pancreas secrete

Answer 25

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

Question 26

what are duct cells

Answer 26

>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

Question 27

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

Answer 27

>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

Question 28

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

Answer 28

>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

Question 29

what can pancreatic enzymes do

Answer 29

can completely digest food in the absence of all other enzymes

Question 30

what are the pancreatic enzymes and where are they stored

Answer 30

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

Question 31

where is enterokinase stored

Answer 31

mucosal cells of duodenum

Question 32

what does enterokinase cleave

Answer 32

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

Question 33

what are the three phases of control of pancreatic secretion

Answer 33

cephalic gastric intestinal