Secretions from Salivary Glands & Stomach Flashcards
what’s triggered by anticipation of food?
autonomic and endocrine reflexes
acts to prepare GI tract
what are the three phases of salivary gland secretion?
cephalic
gastric
intestinal
what’s the cephalic phase of saliva secretion?
food anticipation
what’s the gastric phase of salivary secretion?
mechanical stim of oral cavity and stomach
what’s the intestinal phase of saliva secretion?
regulation of stomach emptying and digestion/absorption in SI
what glands produce saliva?
parotid, mandibular, lingual, buccal
what is the major source of water and bicarb to a cattle rumen?
SALIVA
what’s saliva made of?
mostly water
som electrolytes
salivary protein
urea (ruminants)
saliva functions
solvent for molecules to stimulate taste buds, food lube, keeps mouth clean, has buffer/lysozymes/antitoxic
salivary glands are ___ glands
acinar
what are acini?
secretory units
fluid is secreted into the lumen of acini and is ___ on the way through intercalated and striated ducts
modified
what is a salivary mucocele?
painless swelling of neck or in oral cavity
caused by saliva collection from a damaged salivary gland/duct
what creates hypotonic saliva?
iso-osmotic secretion by acini cells and selected reabsorption by duct cells
how do acini cells release proteins and mucus?
exocytosis
what do acini cells secrete?
Cl-, bicarb, K+, Na+, water
duct cells ___ Na+ and Cl- in exchange for H+ and bicarb
reabsorb
__ is recycled for K+
H+
saliva osmolarity is determined by ___
flow rate
saliva is ___ at low flow rates
hypotonic
at high flow rates, ___ concentration increases in saliva.
electrolyte
what happens to saliva in relation to plasma during high flow rates?
saliva becomes isotonic in relation to plasma
protein concentration ___ affected by saliva flow rate
IS NOT
saliva from different glands varies in ___ concentration
protein
serous means more ___
protein
mucous means ___
more glycoproteins aka proteins with oligosaccharide chains
parotid gland consists of…
serous cells providing protein to saliva
sublingual, submandibular glands contain…
mix of mucus and serous cells
what is ptyaline (alpha amylase)?
initiates starch digestion in pigs and humans
NOT carnivore/horse
where is lingual lipase most frequently present?
young animals on milk diet
what does lingual lipase do?
initiates hydrolysis of triglycerides into diacylglyceride and free FA
in ruminants and herbivores, saliva consists of ___ and ___ proteins
lysozymes
antitoxic protein
what are the antibacterial effects of lysozymes?
hydrolytic enzymes
*loss of peptidoglycan integrity results in rapid cell lysis in hypo-osmotic environment
what are tannins?
phenolic compounds made by plants as defense mechanism against herbivores
creates bitter taste to reduce tasteness
has NEGATIVE GI tract effect
tannins cause a ___ of food intake, ___ in ruminal protein degradation, and ___ digestive enzymes by binding and forming insoluble complexes
REDUCTION/INHIBIT
which species likely has a bigger parotid gland?
browser»_space; grazer
how is tannin neutralized?
parotid glands producing proline rich proteins
browsers eat plant material with ___ tannin concentrations. they have ___ parotid glands than grazers
higher, larger
explain the buffer function of saliva in ruminants
buffers rumen fluid
microbial activity constantly produces VFA, which is buffered by bicarb from saliva.
ruminant saliva pH 8, has NO enzymes
what are the four components of gastric juice?
HCl
pepsinogen
mucus
intrinsic factor
what does the HCl do in gastric juice?
reduces pH of stomach, activates pepsinogen, aids in protein digestion, kills bacteria
what does pepsinogen do i gastric juice?
inactive/active digests protein
what does mucus do in gastric juice?
protects gastric mucosa from corrosive actions of HCl
what does the intrinsic factor do in gastric juice?
necessary for absorption of vitamin B12 in ileum
which species have glandular mucosa in stomach?
dog, cat
which species have non-glandular mucosa in stomach?
horse, rats
the epithelium in the glandular region contains what type of cells?
parietal
chief
enteroendocrine
what do chief cells do?
pepsinogen -> pepsin
what do surface mucus cells do?
produce thick, tenacious mucus, protective function against acid and mechanical damage
what do mucus neck cells do?
thin mucus
progenitor cells
can do mitosis
what doe D cells, G cells, ECL cells do?
produce hormones that regulate gastric secretion and motility
what do parietal cells secrete? what pumps are used?
H+ and Cl-
H+ via…ATP pumps, exchange H+ against K+
Cl- via…passive movement down electrogenic gradient
where is HCl formed in stomach?
gastric lumen
what is Cl- exchanged for on basolateral membrane?
bicarb
what is the “alkaline tide”?
Cl- exchanged for bicarb
HCO3-/Cl- exchange on basolateral side to bring in Cl- and cause alkaline tide (temporary pH increase in blood)
explain neural control of HCl secretion
PNS and ENS activate parietal cells via M3 receptors
explain endocrine control of HCl secretion
secretion of GASTRIN from G cells binds to CCK-B receptors
secretion of HISTAMINE from ECL binds to H2 receptors
what is histamine released in response to?
gastrin
what is gastrin released in response to?
small peptides and AA in stomach
distension of stomach
vagal stimulation
what are the two mechanisms that mediate activation of H-K ATPase and therefore HCl stimulation?
- by the PNS (ACh) and by gastrin through G protein coupled receptors, which stimulates IP3/DAG which increases Ca2+ concentration
- by histamine receptors that mediate elevation of cAMP concentration
Ca2+ and cAMP ___ the proton pump
stimulate
what is the main control of reducing parietal cell activation?
pH
measured by G cells
pH < 2 triggers negative feedback
the absence of food causes ____ of HCl production
downregulation
what two hormones cause the downregulation of HCl production?
somatostatin and prostaglandin
what is the gastric mucosal barrier?
protects stomach epithelial lining against acidic environment
what happens if the gastric mucosal barrier is broken?
acid could then diffuse across mucosa and damage the stomach wall
what are the three components of the gastric mucosal barrier?
compact epithelial lining
gastric mucus covering
bicarb secreted by surface epithelial cells which creates neutral micro-environment
what is a gastric ulcer?
localized area of erosion
due to improper mucus layer
causes = defect in mucosal barrier, HCl hypersecretion, heliobacter pylori
what are the therapeutic approaches for gastric ulcers?
reduce acid production (via vagotomy, drugs)
stimulate re-epithelization
antibiotics for helicobacter
what is pepsinogen produced/secreted by?
chief cells
how is pepsinogen stored in chief cells?
stored in zymogen granules, released by exocytosis
why is pepsin released as a proenzyme?
prevent AUTODIGESTION
proenzyme is converted to active pepsin by HCl in stomach lumen
what is the function of pepsin?
cleaves proteins to peptides at aromatic links
digests 10-20% of proteins in a meal
explain the stimulation of pepsinogen
