Small Intestine and Intestinal Pancreas Flashcards
what is the role of the small intestine
major site of digestion and absoprtion
what are the three parts of the small intestine
duodenum - 25cm
jejunum - 2m
ileum - 2.5m
What does the small intestine receive
pancreatic juices from pancreas via sphincter of Oddi
Bile from liver and gallbladder via sphincter of Oddi
chyme from stomach via pyloric sphincter
What does motility involve in the small intestine
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
what increases the surface area of the small intestine
circular folds - 3 fold
villi - 30 fold
microvilli with a brush border which increases SA 600 folds
explain segmentation
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
explain mitigating motor complex
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
explain gastrin
gastrin is released from G cells of gastric antrum and duodenum
–> increased H secretion into lumen
explain secretin
released from S cells in response to H and fatty acids in lumen
promotes secretion of pancreatic and biliary bicarbonate
explain cholecystokinnin
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
explain the role of ghrelin
released from Gr cells of gastric mucosa and small intestine
stimulates apetite
explain the role of motilin
released from M cells of duodenum and jejunum
initiates migrating motor complex
explain glucose-like-peptide
from L cells of small intestine
stimulate insulin from pancreatic beta cells
inhibits glucagon from pancreatic alpha cells
decreases gastric emptying and appetite
Glucose dependent insulin peptide
from K cells
inhibits gastric emptying
causes secretion of insulin from pancreatic beta cells
what is succus enterious
juice of the small intestine approx 2l/day
controlmechanisms of succus enterious
sympathetic and parasympathetic stimulation gastrin CCK secretin distension
what does secretion lack
digetsive enzyme
what does secretin contain
mucus = protein/ lubrication - via goblet cells
aqueous salts - digestive salts via Crypts of Liberkhun
what do pancreatic enzymes include
endocrine - insulin and glucagon secreted in blood
exocrine - digestive enzymes (acinar cells) and NaHCO3- (duct cells)
Duct cells secrete 1-2l of alkaline fluid into duodenum/day this
neutralises acidic chyme entering the duodenum
Neutralising the acidic chyme –>
provides optimum pH for pancreatic function
protects the mucosa from erosion
Pancreatic enzymes have the ability to
completely digest food in the absence of all other enzymes
In acinar cells enzymes are stored in zymogen granules but when are they released
in response to increased intracellular calcium
Explain in detail the downstream pathway from trpsin
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
What is already activated in acinar cells
pancreatic amylase and pancreatic lipase
what happens in response to acid in duodenal lumen
Secretin is released from S cells –> duct cells –> increased secretion of NaHCO3 in duodenum = neutralises
what happens in response to fat and protein in duodenum
I cells release CCK which activates acinar cells to increase secretion of digestive enzymes
