lect 34 & 35- Lower GI Flashcards
what does the small intestine consists of
duodenum
jejunum
ileum
what are the layers of the intestinal wall of the small intestine (inside to outside)
mucosa with lamina propria and muscular is mucosa
submucosa
muscularis layers
serosa
define lacteal
single blind-ending central lymphatic vessel that is present at the core of a villus
what are the main histological characteristics of the duodenum
villi with spatulate or leaflike distal shape
deep crypts of lieberkuhn
brunner’s glands with ex. ducts in submucosa
define crypts of lieberkuhn
simple tubular glands within the intestinal mucosa that open between adjacent villi and extend to muscular is mucosa
what absorption are enterocytes involved in
absorption of proteins, carbs and lipids
what are the enzymes on the apical brush border of enterocytes important for
carbohydrate digestion
what do enterocytes produce and what is it necessary for
enteropeptidase (enterokinase) which is necessary for the activation of pancreatic zymogens and proenzymes
what are characteristics of paneth cells
basal crypt cells
prominent eosinophilic granules
produce lysozyme to control intestinal flora
what do you stain enteroendocrine cells with
chromium (chromaffin)
what do enteroendocrine cells produce
peptide hormones and serotonin
may produce paracrine or autocrine secretions
what are enteroendocrine cells analogous to
unicellular goblet cells
what are enteroendocrine cells formed from
endodermal stem cells in all regions of the GI tract
where are brunner glands found and what are they responsible for
found in submucosa of duodenum
responsible for formation of bicarbonate and mucus (necessary to neutralize gastric acid)
what are histological characteristics of jejunum
villi longer and narrow
crypts of lieberkuhn present
no glands in submucosa
what are histological characteristics of the ileum
villi longer and narrow
crypts of lieberkuhn present
no glands in submucosa
what type of epithelium is in the large intestine
simple columnar epithelium
crypts but no villi
what is the main functions of large intestine
secretion of mucus
absorption of fluid
formation of fecal mass
continuation of digestion initiated in small intestine
what is the prominent cell of the large intestine
goblet cell
what is the main function of the mucosa of the large intestine
absorption of water, sodium, vitamins and minerals
how do the fascicles of the outer longitudinal layer in the large intestine aggregate
aggregate into 3 spaced bands called taeniae coli
define appendix epiploica
aggregate of adipocytes surrounded by serosa
how are epithelial cells of the GI tract held together
by occluding junctions containing transmembrane proteins (claudins and occluding) which function to prevent paracellular transport
what do paneth cells secrete
lyozyme (increases perm. of bacteria by degrading peptidoglycan coat)
defensins: increase membrane perm. of target organism
TNF-alpha
what is TNF-alpha produced in response to
diverse infectious agents and tissue injury
what are the 2 layers of the mucosal layer
outer: contains microorganisms
inner: contains antimicrobial proteins that resist microbial penetration
where are toll-like receptors found
on surface of enterocytes
what do toll-like receptors do
recognize structurally conserved molecules broadly shared by pathogens but distinguishable from host molecule patterns (PAMPs)
what immunglobulin is most involved in the immune response system
IgA
where is the bulk of the body’s immune defenses centered
GALT
what are the components of GALT
transitory aggregations of lymphocytes, neutrophils and eosinophils
permanent structures: appendix, peyer’s patch, mesenteric lymph nodes
where are peyer’s patches located
under mucosal surface
what do HEVs facilitate
entrance of lymphocytes into lymphoid organs from the blood stream
what do specialized M (micro fold) cells do
sample particulate antigen and present it to antigen-presenting cells in the underlying lamina propria
what is IgA secreted and synthesized by
plasma cells in lamina propria of the gut
what is IgA linked to in the cell
secretory component that inhibits degradation of the sIgA by proteolytic enzymes in the GI lumen
how does secretory IgA function
functions by coating microorganisms, thus inhibiting microorganism binding to the epithelium
where are new cells formed in the esophagus and anus
in basal layer of stratified epithelium and migrate through sub-basal levels to be sloughed off into the lumen
where are new cells formed in the small intestine
in the crypts from undifferentiated cells
where is the proliferative compartment found in the large intestine
base of the crypts (because there are no villi)
where are stem cells found in the stomach
neck of the gastric gland
what do the stem cells in the stomach differentiate into
surface and neck mucus cells
enteroendocrine cells
parietal cells
chief cells
what does amylase do
hydrolyzes starch to form sugars. starch is hydrolyzed to disaccharides
where does the break down of disaccharides to monosaccharides occur
brush border of small intestine
what are monosaccharides absorbed by and what transporter is involved
enterocytes
Na+-dependent sugar glucose transporter-1 (SGLT-1)
where does digestion of proteins occur
stomach
what are proteins hydrolyzed to
peptides
what type of environment is required for pepsin to work
acidic environment
what enzymes secreted by the pancreas are involved in the polypeptide breakdown to peptides in the small intestine
trypsin, chymotrypsin, elastase, carboxypeptidase
what is the activation of pancreatic proteolytic enzymes initiated by
enteropeptidase (enterokinase) secreted by duodenal enterocytes
where does digestion of lipids begin
small intestine
what do lipids enter the small intestine as
triglyceride droplets
what does pancreatic lipid esterase do
splits cholesterol esters into cholesterol and fatty acids
what proteins are required for micelles to be passively absorbed across enterocyte apical plasma membrane
fatty acid binding proteins (FABPs) in apical membrane
where are chylomicrons enclosed
within membranes in golgi apparatus
how are proteins and carbohydrates entered into the blood vessels in the villi
transported to the liver via the hepatic portal system
what is the site of secretion of cholecystokinin and what are they secreted in response to
upper intestinal mucosa (duodenum)
secreted in response to gastric contents
what does cholecystokinin do
acts on pyloric sphincter to slow down emptying of stomach
stimulates bile release from gallbladder and secretion of pancreatic enzymes
competitive inhibitor of gastrins
what is the site of secretion of gastrin
pyloric-antral portion of stomach
what are the effects of gastrin
stimulates HCL production by gastric parietal cells, gastric motility, and release of insulin by pancreatic beta cells
promotes growth of gastric mucosa
what is the site of the secretion of secretin and what is it stimulated by
epithelial cells of duodenum and stimulated by acid contents of stomach
what are the targets and effects of secretin
enhances release of insulin by pancreatic beta cells
stimulates bicarbonate secretion by pancreas
