Small Intestine, Exocrine Pancreas and Liver

Question 1

3 parts of small intestine

Answer 1

duodenum
jejunum
ileum

Question 2

what substances does the small intestine receive

Answer 2

chyme - from stomach
pancreatic juice - from pancreas
bile - from liver and gallbladder

Question 3

what does the small intestine secrete

Answer 3

intestinal juice - succus entericus

Question 4

what does motility of the small intestine cause

Answer 4

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

Question 5

how is the surface area of small intestine increased

Answer 5

increased for absorption;
circular folds (of Kerckring)
villi
microvilli (brush border)

Question 6

describe segmentation in the digestive state

Answer 6

chopping moves chyme back and forth (very vigorous after a meal)
alternating contraction and relaxation of segments of circular muscle, movement is slow - allowing time for absorption
duodenum has more frequent segmentation contraction than the ileum

Question 7

how is segmentation initiated

Answer 7

by small intestine pacemaker cells, causing BER which is continuous
at threshold, this activates segmentation which in the duodenum is primarily due to distension by entering chyme

Question 8

how is strength of segmentation enhanced and decreased

Answer 8

enhanced - parasympathetic activity

decreased - sympathetic activity

Question 9

gastroileal reflex

Answer 9

segmentation in the empty ileum is triggered by gastrin from the stomach

Question 10

steps of mixing and propulsion of chyme

Answer 10

segmentation

peristalsis

Question 11

describe peristalsis in the interdigestive, or fasting, state

Answer 11

few localised contractions
migrating motor complex (MMC);
occurs between meals
strong peristaltic contraction slowly passing length of the intestine
clears small intestine of debris, mucus and sloughed epithelial cells between meals - housekeeper function

Question 12

how is peristalsis inhibited

Answer 12

by feeding and vagal activity

Question 13

how is peristalsis triggered

Answer 13

by motilin

Question 14

how is peristalsis suppressed

Answer 14

gastrin

CCK

Question 15

how does the small intestine secrete peptide hormones into the blood

Answer 15

from endocrine cells within the mucosa

Question 16

peptide hormones secreted by small intestine

Answer 16

gastrin
secretin 
CCK
GIP
GLP-1
motilin
ghrelin

Question 17

gastrin

Answer 17

from G cells of gastric antrum and duodenum
stimulates H+ secretion by gastric parietal cells
stimulates growth of gastric mucosa (trophic effect)

Question 18

secretin

Answer 18

from S cells of duodenum, released in response to H+ and fatty acids in lumen
promotes secretion of pancreatic and biliary and bicarbonate

Question 19

CCK

Answer 19

from I cells of duodenum and jejunum, released in response to monoglycerides, free fatty acids, amino acids, small peptides in 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 20

GIP

Answer 20

from K cells of duodenum and jejunum, released in response to glucose, amino acid and fatty acids
stimulates release of insulin from pancreatic β-cells (incretin action)
inhibits gastric emptying

Question 21

GLP-1

Answer 21

from L cells of the small intestine
stimulates insulin secretion
inhibits glucagon secretion from pancreatic α-cells
decreases gastric emptying and appetite

Question 22

motilin

Answer 22

from M cells of duodenum and jejunum, secreted during fasting state
initiates the migrating motor complex

Question 23

ghrelin

Answer 23

from Gr cells of the gastric antrum, small intestine and elsewhere (e.g. pancreas)
stimulates appetite

Question 24

what do peptide hormones (secreted from small intestine) act on

Answer 24

G-protein coupled receptors

Question 25

juice secretions of small intestine

Answer 25

Succus (juice) entericus (of the intestine) - composition varies throughout small intestine

Question 26

control mechanisms of juice secretions of small intestine

Answer 26

``` Distension/irritation gastrin CCK secretin parasympathetic nerve activity (all enhance) sympathetic nerve activity (decreases) ```

Question 27

contents of juice secreted by small intestine

Answer 27

lacks digestive enzymes contains; mucus from goblet cells aqueous salts from crypts of Lieberkuhn

Question 28

function of mucus in juice

Answer 28

protection | lubrication

Question 29

function of aqueous salts in juice

Answer 29

enzymatic digestion

Question 30

action of fluid secreted from pancreatic duct cells in duodenum

Answer 30

alkaline fluid neutralises acidic chyme entering the duodenum; provides optimum pH for pancreatic enzyme function protects mucosa from erosion by acid

Question 31

phases of control of pancreatic secretion

Answer 31

cephalic gastric intestinal (PP)

Question 32

cephalic phase of pancreatic secretion

Answer 32

mediated by vagal stimulation of mainly the acinar cells

Question 33

gastric phase of pancreatic secretion

Answer 33

gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells (5-10% total secretion)