GI 2

2 types of secretory epithelium in pancreas

endocrine (islets) and exocrine

endocrine islets of pancreas

secrete insulin and glucagon

exocrine secretory epithelium of pancreas

secretes digestive enzymes and sodium bicarbonate

2 cell types of exocrine epithelium of pancreas

duct cells and acinar cells

pancreatic duct cells

make sodium bicarbonate

pancreatic acinar cells

make digestive enzymes

stimuli for exocrine pancreatic secretions

small intestine distension (long reflex), neural parasympathetic signals, and cck

pancreatic duct empties into duodenum via…

sphincter of oddi

sphincter of oddi

common b/w pancreatic and hepatic secretions, made of smooth muscle

are the digestive enzymes, secreted by acinar cells, in active form?

no. they are normally released as zymogens

what converts trypsinogen to trypsin

enteropeptidase (brush border enzyme)

what type of enzyme is trypsionogen?

protease

what enzyme, secreted by pancreas, activates other zymogens?

trypsinogen (active form is trypsin)

what are some enzymes secreted by pancreas which are already in active form?

pancreatic amylase, lipase, and colipase

there are high levels of carbonic anhydrase in the…

pancreas

how do the duct cells of pancreas produce sodium bicarbonate?

similar mechanism to lungs

how does CF alter pancreatic secretions

no CFTR channel→no saline produced→pancreatic duct gets clogged→bicarbonate and digestive enzymes cannot go in duodenum

what takes bile made in liver into gallbladder for storage

common hepatic duct

what takes bile from gallblader into small intestine?

common bile duct

what brings 25% of the liver’s blood to it?

hepatic artery

what brings 75% of the liver’s blood to it?

hepatic portal vein

non-enzymatic solution secreted from hepatocytes

bile

3 components of bile

bile salts, bile pigments, cholesterol

how are xenobiotics and drugs excreted

through bile, they empty into GI tract and end up in feces

hepatocytes cluster in

hexogonal hepatic lobules

what is in hepatic lobules, other than hepatocytes?

central vein and bile canaliculi

blood flow direction in hepatic lobule

from exterior (hepatic portal vein and artery) into central vein

• out to in

bile flow direction in hepatic lobule

from hepatocyte to bile canaliculi to common hepatic duct

• opposite to blood flow

what fills first, common hepatic duct or common bile duct?

common bile duct

can lipase get through bile layer by itself?

no

displaces bile salt layer so that lipase can enter emulsion

colipase

how many times per meal are bile salts recycled?

2-5

where in the small intestine is the bile salt recycling transporter located?

ileum

2 main types of ingested carbs

starch and sucrose, neither can be immediately digested

why do disaccharides have to be broken to monomers

no transporters exist for disaccharides

what are glucose polymers first broken down into and by what?

disaccarides, amylase (salivary and pancreatic)

facilitated diffusion on apical membrane via GLUT 5

fructose

secondary active transport (with sodium) on apical membrane on SGLT

glucose and galactose

exits basolateral membrane by diffusion through GLUT 2

glucose, fructose, and galactose

why does free glucose stay high in the enterocyte, despite glucose normally being turned to G6P to enter glycolysis?

enterocytes do not need glycolysis from glucose. instead they use glutamine for energy. this allows for basolateral transport to remain passive.

what’s easier to digest, plant or animal protein?

animal

enzyme that attacks peptide bonds in the middle of amino acid chain

endopeptidase

pepsin (stomach), trypsin and chymotrypsin (small intestine)

endopeptidase

enzyme that releases single amino acids from the end of a polypeptide chain one at a time

exopeptidases

which is the more common exopeptidase, aminopeptidase or carboxypeptidase?

carboxypeptidase

exopeptidase that is a brush border enzyme

aminopeptidase

exopeptidase that is released by pancreas

carboxypeptidase

how are peptides larger than 3 aa abosrbed

transcytosis if not broken down before (more rare)

how are single aa transported on basolateral side

Na exchange (passive)

how are single aa transported on apical side

Na cotransport (active)

how are di and tri peptides transported

H+ co transporter (oligopeptide transporter)

mineral absorption

active transport

is mineral absorption normally regulated?

no, except iron and calcium are

transporter for iron to exit enterocyte

ferroportin

hormone that regulates if ferroportin is in membrane

hepcidin

what triggers hepcidin to be made

increased iron levels in ECF

what causes removal of ferroportin

high hepcidin

what is the main way calcium is absorbed

paracellular absorption (not regulated)

what is the minor pathway that calcium is absorbed by?

transcellular pathway (regulated by vit D3)

where is most water absorbed

small intestine

what senses the types of foods you eat to vary the digestive response (secretion and motility)

enterocytes through GPCRs

primary influencer of intestinal motility

ENS neurons in myenteric plexus

releases motilin

Mo cells of duodenum, or possibly stimulated by high ph (due to decreased stomach acid)

accessory secretions of pancreas and liver are primarily regulated by…

long reflexes

secretin is secreted by

S cells

cck is released by

I cells

GIP is secreted by

K cells

GLP 1 is secreted by

L cells

pancreatic secretions beginning in cephalic and gastric phases is an example of what type of reflex

feedforward

can gastrin stimulate pancreatic acinar cells?

yes

what type of reflex is enteropancreatic reflex?

long reflex

what is enteropancreatic reflex triggered by

chyme entering small intestine

what stimulates s cells

H+

what acts on duct cell receptors causing them to secrete HCO3-

secretin

what stimulates I cells

mostly fatty acids (but also amino acids) being present in chyme

what acts on acinar cell receptors to stimulate enzyme secretion?

cck

what is the main goal of the enteropancreatic reflex?

to make duct cells of the pancreas release HCO3- and acinar cells release digestive enzymes

inhibition of gastric acid secretion, gastric motility, and gastric emptying

secondary role of secretin

what other enterogastrones work with secretin?

cck, GLP1, GIP

regulation of bile secretions and bile entry into small intestine from gallbladder

secondary role of cck

stimulation of K and I cells follows what pattern of feedback?

feedforward

stimulates insulin secretion

GIP and GLP 1

primary endocrine function of GIP and GLP 1

glucose homeostasis, but also inhibits gastric acid secretion and motility

found in duodenum and stimulated by carbs in small intestine

k cells and L cells

what do GLP 1 and GIP act on

beta cells of pancreas

what does hyperosmotic chyme do

inhibits gastric emptying

out of the 1.5 L that enters colon, how many L are absorbed?

1.4

separates ileum and cecum (large intestine)

ileocecal valve

as muscle contraction (caused by food) proceeds through ileum

ileocecal valve relaxes (this is gastroileal reflex: long reflex)

part of large intestine that secretes fluids (mostly mucus for lubrication)

intestinal glands

are there villi in the large intestine?

no