Small Intestine, Exocrine Pancreas and Liver Flashcards
3 parts of small intestine
duodenum
jejunum
ileum
what substances does the small intestine receive
chyme - from stomach
pancreatic juice - from pancreas
bile - from liver and gallbladder
what does the small intestine secrete
intestinal juice - succus entericus
what does motility of the small intestine cause
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)
how is the surface area of small intestine increased
increased for absorption;
circular folds (of Kerckring)
villi
microvilli (brush border)
describe segmentation in the digestive state
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
how is segmentation initiated
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
how is strength of segmentation enhanced and decreased
enhanced - parasympathetic activity
decreased - sympathetic activity
gastroileal reflex
segmentation in the empty ileum is triggered by gastrin from the stomach
steps of mixing and propulsion of chyme
segmentation
peristalsis
describe peristalsis in the interdigestive, or fasting, state
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
how is peristalsis inhibited
by feeding and vagal activity
how is peristalsis triggered
by motilin
how is peristalsis suppressed
gastrin
CCK
how does the small intestine secrete peptide hormones into the blood
from endocrine cells within the mucosa
peptide hormones secreted by small intestine
gastrin secretin CCK GIP GLP-1 motilin ghrelin
gastrin
from G cells of gastric antrum and duodenum
stimulates H+ secretion by gastric parietal cells
stimulates growth of gastric mucosa (trophic effect)
secretin
from S cells of duodenum, released in response to H+ and fatty acids in lumen
promotes secretion of pancreatic and biliary and bicarbonate
CCK
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
GIP
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
GLP-1
from L cells of the small intestine
stimulates insulin secretion
inhibits glucagon secretion from pancreatic α-cells
decreases gastric emptying and appetite
motilin
from M cells of duodenum and jejunum, secreted during fasting state
initiates the migrating motor complex
ghrelin
from Gr cells of the gastric antrum, small intestine and elsewhere (e.g. pancreas)
stimulates appetite
what do peptide hormones (secreted from small intestine) act on
G-protein coupled receptors
juice secretions of small intestine
Succus (juice) entericus (of the intestine) - composition varies throughout small intestine
control mechanisms of juice secretions of small intestine
Distension/irritation gastrin CCK secretin parasympathetic nerve activity (all enhance) sympathetic nerve activity (decreases)
contents of juice secreted by small intestine
lacks digestive enzymes
contains;
mucus from goblet cells
aqueous salts from crypts of Lieberkuhn
function of mucus in juice
protection
lubrication
function of aqueous salts in juice
enzymatic digestion
action of fluid secreted from pancreatic duct cells in duodenum
alkaline fluid neutralises acidic chyme entering the duodenum;
provides optimum pH for pancreatic enzyme function
protects mucosa from erosion by acid
phases of control of pancreatic secretion
cephalic
gastric
intestinal (PP)
cephalic phase of pancreatic secretion
mediated by vagal stimulation of mainly the acinar cells
gastric phase of pancreatic secretion
gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells (5-10% total secretion)
