lecture 16-GI secretory functions, digestion, absorption Flashcards
what are the functions of saliva
initial starch digestion and initial triglyceride digestion. lubrication of food and protection of mouth and esophagus
describe the composition of saliva at lowest flow rates
lowest osmolarity. lowest sodium, chloride and bicarbonate ion concentrations, highest potassium ion concentrations
describe the composition of saliva at high flow rates
composition closest to that of plasma
describe the first stage of salivary secretion of ions
occurs in acini, secretion contains ptyalin (alpha-amylase), composition is isotonic with ionic concentration similar to plasma
describe the second stage of salivary secretion of ions
occurs in salivary ducts, active reabsorption of sodium and secretion of potassium ions, active/passive secretion of bicarbonate ions
what cranial nerves regulate salivary secretion
cranial nerves VII and IX
what factors increase saliva production
food in mouth, smells, conditioned reflexes, nausea
what factors decrease saliva production
sleep, dehydration, fear, anticholinergic drugs
name secretory cell types in gastric glands
mucous neck cells, chief (peptic) cells, parietal (oxyntic) cells
describe the direct way that vagal stimulation increases gastric secretions
CN X innervates parietal cells (stimulates H+ secretion directly), utilizes Ach and muscarinic receptor
describe the indirect way that vagal stimulation increases gastric secretions
CNX innervates G cells, stimulates gastrin secretion, gastrin stimulates secretion of H+, neurotransmitter is GRP
what is the second messenger for histamine stimulation
cAMP
what is the second messenger for gastrin stimulation
on parietal cell: IP3/Ca++
what does somatostatin inhibit
gastric H2 secretions
describe the direct way that somatostatin inhibits gastric H secretions
somatostatin binds to receptors on parietal cell that are coupled to adenyl cyclase via a Gi protein (antagonistic to stimulatory action of histamine)
describe the indirect way that somatostatin inhibits gastric H secretions
inhibits the release of histamine and gastrin
describe the role of prostaglandins in gastric secretions
inhibits gastric H2 secretions by activating Gi protein, inhibiting adenyl cyclase
describe the gastric phase of gastric secretion
local nervous secretory reflexes, vagal reflexes, gastrin-histamine stimulation
describe the intestinal phase of gastric secretion
nervous and hormonal mechanisms
what is the trypsin inhibitor secreted by
glandular cells
what is the digest enzymes for carbohydrates
pancreatic amylase
what is the digestive enzymes for fat
pancreatic lipase, cholesterol esterase, phospholipase
decrease pancreatic secretions at low flow rates
isotonic fluid composed mostly of sodium and chloride ions
describe pancreatic secretions at high flow rates
isotonic fluid composed mostly of sodium and bicarbonate ions
describe acinar cells
produce small volume of pancreatic secretion composed mainly of sodium and chloride ions
describe ductal cells
secrete bicarbonate ion and reabsorb chloride ion via a chloride-bicarbonate exchange mechanism. ducts are permeable to water (so water moves into ducts to make secretion isotonic)
how does acetylcholine effect pancreatic secretions
stimulates enzyme secretion by acinar cells and potentials effect of secretin
what does CCK do in regulation of pancreatic secretions
causes dramatic increase in secretion of pancreatic enzymes. potentiates effect of secretin on ductal cells to stimulate bicarbonate secretion
what does secretin do in regulation of pancreatic secretions
stimulates release of large amounts of sodium bicarbonate by ductal cells
what causes the release of enzymes into acini
vagal stimulation
what factor stimulates the release of bile from the gallbladder
presence of fatty food in duodenum
what are bile acids conjugated with
glycine or taurine
CCK in blood stream causes___
gallbladder contraction and relaxation of sphincter of Oddi
what causes gallstones
too much absorption of water from bile,
too much absorption of bile acids from bile,
too much cholesterol in bile,
inflammation of epithelium
what are condensations reactions used for
to remove hydrogen ions and hydroxyl ions from building blocks in order to allow the bonding of monomers into polymers
what is the role of hydrolysis reactions
incorporating water molecules in such a way that polymers are broken down into monomers
how does absorption of fructose occur
entirely by facilitated diffusion in small intestine
what does lactase break lactose down into
glucose and galactose
