Small Intestine and Intestinal Pancreas

Question 1

what is the role of the small intestine

Answer 1

major site of digestion and absoprtion

Question 2

what are the three parts of the small intestine

Answer 2

duodenum - 25cm
jejunum - 2m
ileum - 2.5m

Question 3

What does the small intestine receive

Answer 3

pancreatic juices from pancreas via sphincter of Oddi
Bile from liver and gallbladder via sphincter of Oddi
chyme from stomach via pyloric sphincter

Question 4

What does motility involve in the small intestine

Answer 4

segmentation - mixing of chyme with digestive juice
peristalsis - slow propulsion of chyme in the aboral route
migrating motor complex - removal of undigested residues via ileocaecal valve

Question 5

what increases the surface area of the small intestine

Answer 5

circular folds - 3 fold
villi - 30 fold
microvilli with a brush border which increases SA 600 folds

Question 6

explain segmentation

Answer 6

alternating contraction and relaxation of circular muscle
rigorous after a meal
chopping moves chyme back and forth
Duodenum - due to chyme (12/min)
Jejunum - due to chyme (9/min)
Ileum - due to gastrin released from stomach = gastroileal reflex
sympathetic stimulation - increases segmentation rate
parasympathetic stimulation = decreases segmentation rate

Question 7

explain mitigating motor complex

Answer 7

slow strong peristaltic contraction from the stomach to ileocaecal valve
occurs between meals every 90-120 mins
clears small intestine of mucus and sloughed epithelial cells
inhibited by feeding or vagal stimulation
heightened by motilin
suppressed by CCK and gastrin

Question 8

explain gastrin

Answer 8

gastrin is released from G cells of gastric antrum and duodenum
–> increased H secretion into lumen

Question 9

explain secretin

Answer 9

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

Question 10

explain cholecystokinnin

Answer 10

released from I cells in duodenum and jejunum in response to free fatty acids, amino acids, monoglycerides, small particles
stops gastric emptying
secretion of pancreatic emptying
relax sphincter of Oddi and contract gallbladder
increases secretin

Question 11

explain the role of ghrelin

Answer 11

released from Gr cells of gastric mucosa and small intestine

stimulates apetite

Question 12

explain the role of motilin

Answer 12

released from M cells of duodenum and jejunum

initiates migrating motor complex

Question 13

explain glucose-like-peptide

Answer 13

from L cells of small intestine
stimulate insulin from pancreatic beta cells
inhibits glucagon from pancreatic alpha cells
decreases gastric emptying and appetite

Question 14

Glucose dependent insulin peptide

Answer 14

from K cells
inhibits gastric emptying
causes secretion of insulin from pancreatic beta cells

Question 15

what is succus enterious

Answer 15

juice of the small intestine approx 2l/day

Question 16

controlmechanisms of succus enterious

Answer 16

sympathetic and parasympathetic stimulation
gastrin
CCK
secretin
distension

Question 17

what does secretion lack

Answer 17

digetsive enzyme

Question 18

what does secretin contain

Answer 18

mucus = protein/ lubrication - via goblet cells

aqueous salts - digestive salts via Crypts of Liberkhun

Question 19

what do pancreatic enzymes include

Answer 19

endocrine - insulin and glucagon secreted in blood

exocrine - digestive enzymes (acinar cells) and NaHCO3- (duct cells)

Question 20

Duct cells secrete 1-2l of alkaline fluid into duodenum/day this

Answer 20

neutralises acidic chyme entering the duodenum

Question 21

Neutralising the acidic chyme –>

Answer 21

provides optimum pH for pancreatic function

protects the mucosa from erosion

Question 22

Pancreatic enzymes have the ability to

Answer 22

completely digest food in the absence of all other enzymes

Question 23

In acinar cells enzymes are stored in zymogen granules but when are they released

Answer 23

in response to increased intracellular calcium

Question 24

Explain in detail the downstream pathway from trpsin

Answer 24

In the duodenum trypsinogen is converted to trypsin in the presence of enteropeptidase (autocatalytic)
This then activates chymotrypsin from chymotrypsinogen
This then activates decarboxypeptidase A and B to caboxypeptidase A and B

Question 25

What is already activated in acinar cells

Answer 25

pancreatic amylase and pancreatic lipase

Question 26

what happens in response to acid in duodenal lumen

Answer 26

Secretin is released from S cells –> duct cells –> increased secretion of NaHCO3 in duodenum = neutralises

Question 27

what happens in response to fat and protein in duodenum

Answer 27

I cells release CCK which activates acinar cells to increase secretion of digestive enzymes