GI Tract Part 2 Flashcards
where are goblet cells located
interspersed among enterocytes
what do goblet cells synthesize and what is it stored in
mucinogen stored in membrane bound granules
what does mucinogen (mucus) do
lubricates and protects epithelium
where are actively dividing stem cells located
at base of crypts
where do actively dividing stem cells migrate as they mature
up villus, mature and are shed
how often is the entire epithelial lining replaced
every 3-5 days
where are paneth cells found
at the base of crypts
what do paneth cells contain and what do they produce
large eospinophilic granules that produce antibacterial proteins called defensins and enzymes including lysozyme
what do A cells secrete
glucagon
what do K cells secrete
GIP
where is MALT located
lamina propria and submucosa of small intestine
what are M cells
squamoid enterocytes modified for Ag sampling and uptake of macromolecules
what are Peyer’s patches
dome shaped areas grossly visible on surface of mucosa and project into lumen
what is the duodenum characterized by
Brunner’s glands in submucosa
what do Brunner’s glands contain
large numbers of highly convoluted branches, tubuloalveolar submucosal glands
what do brunner’s glands do
secrete mucus and zymogens
what is the main function of the duodenum
neutralize gastric acid and pepsin
what assists the duodenum in its function
pancreas and gallbladder
what do the pancreatic duct and bile duct empty into
duodenum at major duodenal papulla
what does chyme from the stomach stimulate the release of
secretin and CCK from APUD cells
what do secretin and CCK promote
section of exocrine pancreas
describe the ph of pancreatic secretions and why
highly alkaline due to bicarbonate
what does CCK stimulate
contraction of bladder and release of bile acids
what do bile acids do
act as emulsifying agents for digestion of lipids to form micelles
what do pancreatic secretions contain
proteolytic enzymes trypsin and chymotrypsin for digestion of proteins, and amylase and lipase
what are enzymes in pancreatic secretions secreted as
inactive precursors (zymogens) such as trypsinogen and chymotrypsinogen
why are enzymes secreted as inactive precursors
to prevent autolysis
what is trypsin activated by
enterokinase
what does trypsin activate
chymotrypsin
what are the two steps in the digestion process
luminal digestion and membrane digestion
what does luminal digestion involve
mixing of chyme with pancreatic enzymes that results in molecular breakdown
what does membrane digestion involve
enzymes of glycocalyx on plasma membrane of enterocytes
what do enterocytes synthesize
enzymes and carrier proteins for absorption of carbohydrates and amino acids
what enzymes do enterocytes synthesize
peptidases, peptide hydrolases, disaccharidases,
what are proteins initially denatured by and hydrolyzed by
denatured by HCl from parietal cells and hydrolyzed by pepsin into polypeptide fragments
what continutes to breakdown proteins
pancreatic enzymes which results in small peptide fragments (AAs) that are absorbed by enterocytes via active transport by carrier proteins
what are the types of carbohydrates
poly-, oligo-, and disaccharides
what hydrolyzes starch to disaccharides
salivary and pancreatic amylase
what are disaccharides further broken down into
monosaccharides
what are examples of disaccharides? monosaccharides?
disaccharides: sucrose, lactose, maltose, isomaltose
monosaccharides: glucose, galactose and fructose
what are monosaccharides and AAs absorbed by
enterocytes lining villi, transported across epithelium, enter capillaries within lamina propria -> portal vein to liver for storage
what are lipids and what are they emulsified by
triglycerides from diet, emulsified by bile acids
what are lipids further broken down into
monoglycerides and fatty acids by pancreatic lipase to form extracellular micelles
what are micelles absorbed by
enterocytes then re-synthesized into triglycerides within enterocytes and coated with proteins and phospholipids to form intracellular chylomicrons
where are chylomicrons transported
across enterocytes to lacteals
what are lacteals
blind ended lymph vessels within lamina propria of villi
where are chylomicrons eventually carried to
thoracic duct and general circulation
what does the large intestine include
cecum, appendix, ascending, transverse, descending and sigmoid colon, and rectum
what does the large intestine lack
villi and plicae circulares
what is the appendix
small, blind ended sac distal to ileo cecal junction
what does the appendix contain
large amounts of submucosal MALT
what is the primary function of the colon
water and electrolyte resporption
-also produces mucus for elimination of undigested food and waste
what does the colon contain
large numbers of goblet cells in epithelium and colonic glands in submucosa
what does the colon not have
brunner’s glands, villi, plicae circulares
what is the mucosal epithelium in the colon similar to
small intestine but paneth cells are generally absent in adults
what does the MALT not form in large intestine
Peyers patches
are lacteals present in the lamina propria of the colon
NO
where does epithelial replacement occur in the colon
from stem cells at the base of glandular crypts
what type of bacteria is common in the colon
commensal bacteria
describe the outer longitudinal muscle layer in muscularis externa of the colon
reduced or incomplete- forms 3 longitudinal strips called taenia coli
what are taenia coli responsible for
formation of haustra
what are polyps
adenomas
- any mass arising from the wall of the colon that protrudes into the lumen
what is the most common sign of polyps
rectal bleeding
what is colon cancer
adenocarcinoma
what decreases colon cancer risk
increased fiber in diet which decreased transit time and increases GI motility
describe the rectum
short dilated terminal portion of large intestine
what does the rectum contain
transverse rectal folds and large numbers of mucus glands
what is the transition of mucosa at anal canal
simple columnar epithelium to stratified squamous epithelium
what does the anal canal contain
longitudinal folds called anal columns
where are anal glands located
extend into submucosa and muscularis externa
describe the type of glands anal glands are
branched, straight, tubular glands that secrete mucus
what is the external anal sphincter made of? internal?
external: skeletal muscle
internal: smooth muscle
what are occasional enlargement and irritation of submucosal veins called
hemorrhoids
what is the anus
external opening, exit of GI tract
