Secretions of the GI Tract and Panceas Flashcards
functions of saliva
initial digestion of starches and lipids
dilution and buffering of ingested food
lubrication of ingested food with mucus
parotid glands
largest of the salivary structure
located near the angle of the jaw and the ear
composed of serous cells
secrete fluids composed of water, ions, and enzymes (rich in amylase)
secrete 25% of the daily output of saliva
submaxillary glands and sublingual glands
composed of serous and mucous cells
secrete aqueous fluid and mucin glycoprotein for lubrication
secrete most of the rest of 75% of daily output saliva
salivary galnd
ectodermal in origin
has the appearance of a bunch of grapes
similar features as the exocrine pancreas
the blood supplied to the salivary glands is distributed by carotid artery
acinus - blind end
acinar cells secrete initial saliva
myoepithelial cells
rest on the basement membrane of acinar cells
contain an actinomycin
have motile extensions
when stimulated by neural input, contract to eject saliva into the mouth
intercalated duct
contains myoepithelial cells
saliva in the intercalated duct is similar in ionic composition to plasma
striated duct
lined by columnar epithelial cells (ductal cells)
ductal cells modify the initial saliva to produce the final saliva (hypotonic)
ductal cells alter the concentration of various electrolytes
composition of saliva
water, electrolytes, alpha amylase, lingual lipase, killikrein, and mucose
increased K and HCO3
decreased N and Cl
alpha amylase
begins initial digestion of carbohydrates
lingual lipase
beings initial digestion of lipids
killikrein
protease involved in the production of bradykinin (vasodilator)
mechanism of salivary secretion
formation of isotonic plasma like solution by acinar cells
modification of the isotonic solution by the ductal cells
cystic fibrosis
pt. lack the Cl transporter
salivary Ca Na and protein are elevated
flow rate and ion composition of saliva
increased - saliva resembles plasma and initial saliva
decreased - saliva has lower concentrations of Na and Cl and higher K
parasympathetic inn of salivary glands
presynaptic n originate at facial and glossopharyngeal n
postsynaptic fibers in autonomic ganglia innervate individual glands
sympathetic inn of salivary glands
preganglionic n originate at the cervical ganglion
postganglionic fibers extend to the glands in the periarterial spaces
HCl
with peptin will initiate the process of protein digestion
needed for the conversion of pepsinogen to the enxyme pepsin
kills a large number of bacteria that enter the stomach
pepsinogen
inactive precursor to peptin
mucus
lines the wall of the stomach and protects it from damage
acts as lubricant
together with HCO neutralized acid and maintains the surface of the mucosa at a neural pH
intrinsic factor
required for the absorption of vit B12 in the ileum
indispensable component
water
medium for the action of HCl and enzymes
solubilizes much of the ingested material
ocyntic gland
located in the proximal 80% of the stomach (body and fundus)
secretes acid
pyloric gland
located in the distal 20% of the stomach (antrum)
synthesizes and release gastrin
parietal cells
intrinsic factor and HCl
chief cells
pepsinogen
G cells
gastrin
mucus cells
mucus, HCO3, and pepsinogen
histamine regulation of HCl
stimulation of HCl secretion
released form ECL cells
binds to H2 R on parietal cells leads to cAMP which will activate H/K ATPase
Ach regulation of HCl
stimulation of HCl secretion
released from vagus n
binds to M3 mAChR on parietal cells leads to IP3 and Ca2 release which stimulates H/K ATPase
stimulation of ECL cells
gastrin regulation of HCl
stimulates HCl secretion
secreted by G cells
binds to CCKB R on parietal cells leads to IP3 and Ca2 leading to stimulation of H/K ATPase
stimulation of ECL cells
somatostatin regulation of HCl
inhibits HCL secretion
secreted by detla cells
binds to SSTR2 R on parietal cells which inhibits adenylate cyclase
inhibits histamine and gastrin
vagus n and HCl secretion
direct pathway - stimulation of parietal cells
indirect pathway - stimulation of G cells
cephalic phase
30% of HCl secreted in response to meal
brain tells stomach to prepare for receipt of meal
vagus n. - fxn through direct and indirect pathways to lead to release of HCl
gastric phase
60% of the total HCl secreted in response to meal
distention of the stomach and presence of breakdown of proteins, amino acids, and small peptides
activation of mechanoR leads to stimulation of the vagus n, local stimulation of G cells
intestine phase
less than 10% of the total HCl secreted in response to meal
distention of SI stimulates acid secretion
digested protein stimulate acid secretion via direct effect on parietal cells through gastrin relase
gastric juice secretion rate
low - solution of NaCl
high - more H than Na
more H, K , and Cl and less Na than plasma
non parietal gastric secretion
basal alkaline secretion of constant and low volume
make of Na, Cl, and K at same concentration as K
HCO3is secreted at a concentration of 30 mEq/L
parietal gastric secretion
hyperosmotic
150-160 mEq H/L and 10-20 mEq/L
Cl is the only anion present
as secretion rate increases the concentration of electrolytes begin to approach those of pure parietal cell secretion
regulation of gastrin release
stimulated by GRP which is released though stimulation of vagus n
inhibited by somatostatin
works through negative feedback
pepsinogen secretion
secreted by chief cells and mucus cells in the oxyntic glands
needs to be converted into pepsin by H
vagus n stimulation is the most important stimulus for pepsinogen secretion
H will trigger the release of pepsinogen
function of pepsin
converts more pepsinogen to pepsin splits interior peptide linkages pH 1.8 to 3.5 reversible inactivated at pH greater than 5 irreversible inactivated at pH 7-8
intrinsic factor
secreted by parietal cells
combines with B12 to make a complex which allows the absorption of B12
no secretion leads to pernicious anemia
growth of gastic mucosa
epithelium secretes HCO3 and mucus to form gel like mucosal barrier (neck cells - mucus and epithelial cells - HCO3)
protects the gastric mucosal epithelium against HCl and pepsin
factors that protect gastric mucosa
HCO3, mucus, prostaglandins, mucosal blood flow and GF
factors that damage gastric mucosa
acid, pepsin, NSAIDs, H pylori, aspirin, bile and stress
peptic ulcer diseases
H. pylori infections and NSAID use
loss of protective mucosal barrier, excessive H and pepsin secretion
gastric ulcers
because of mucosal barrier defect
caused by H. pylori
urease converts urea to NH3 which alkalinizes the local environment which lets the bacteria live
duodenal ulcers
H secretory rates are higher than normal
H. pylori inhibits somatostatin
zollinger-ellison syndrome
duodenal ulcers
tumor in the panceas secretes large quantities of gastrin
exocrine panceas
secretes aqueous solution containing HCO3 and enzymatic secretion
acinus - secrete enzymatic portion
ducts - secrete HCO3
inn of exocrine pancreas
sympathetic- celiac and superior mesenteric plexuses (inhibit)
parasympathetic - vagus n (activates)
secretion rate of pancreatic juices
increased - high HCO3 and Cl lowest
decreased - high Cl and HCO3 lowest
