salivary and gastric secretions Flashcards
what secretions are added to the lumen of the GI tract (exocrine)
saliva
gastric acid and secretions
pancreatic secretions
bile
describe the characteristics of saliva
high bicarbonate
high potassium
hypotonic
contains alpha amylase and lingual lipase
1 L per day
what factors increase salivary secretion
primarily parasympathetic but also sympathetic
No hormonal control
what factors decrease secretion
sleep
dehydration
atropine
what is the function of saliva
Initial digestion of starches and lipids
Dilution and buffering of ingested foods
Lubrication of ingested foods with mucous (mucin)
describe the function of the parotid glands
• Serous cells secreting an aqueous fluid composed of water,
ions and enzymes
very high blood flow
what makes up mucin
glycoprotein for lubrication
what do acinar cells produce
an initial
isotonic saliva composed of
water, ions, enzymes and
mucus
what do myoepithelial cells do
stimulated by neural input to eject saliva
what do ductal cells do
modify the initial
saliva by altering electrolyte
concentrations
how is saliva modified
– Absorption of Na+ and Cl- – Secretion of K+ and HCO- 3 – Becausemore NaCl is absorbed than KHCO3 secreted there is net absorption of solute so hypotonic – Low water permeability of ductal cells means that the final saliva is hypotonic
what substances are secreted by the acinar cells
amylase Lingual lipase-digestion of lipids Mucus-lubricant Kallikrein enzymatic cleavage of kininogen to bradykinin (potent vasodilator)
how does neural stimulation affect the salivary glands
increased saliva
production, HCO-
3 production, enzyme secretion and
myoepithelial cell contraction
what substances digest protein
HCl and pepsinogen
what is the function of intrinsic factor
vitamin B12 absorption in the ileum
what is the function of mucus
protects mucosa and lubrications
what increases secretion of HCl
gastrin
what increases and decreases secretion of pepsinogen
acetylcholine
chyme in duodenum
what increases secretion of intrinsic factor
histamine and parasympathetic NS
what decreases secretion of intrinsic factor
Somatostatin
Atropine
Cimetidine
Omeprazole
where are stomach parietal cells found
body
where are chief cells found
body
where are G cells found
antrum
what are invaginations of the stomach called
gastric glands
they increase surface area
describe the layers of the stomach (inside to out)
mucosa and epithelia lamina propria muscularis mucosae submucosa muscularis externa
also submucosal plexus and myenteric plexus
name the cells in an oxyntic (gastric) gland
surface epithelium
mucous neck cells
parietal cells
peptic/chief cells
what cells release HCl and intrinsic factor
oxyntic/ parietal cells
what cells release pepsinogen
chief cells aka peptic cells
what pH is the stomach
1-2
what is responsible for conversion of pepsinogen to pepsin
low pH
what is carbonic anhydrase
CO2 + H2O > carbonic acid
how is HCl secreted through the apical membrane
– H+ is secreted into the lumen via the H+-K+ ATPase
– Cl- follows by diffusion through an apical channel
describe the events at the basolateral surface in order to secrete HCl
bicarbonate ion is exchanged for Cl- via an exchanger (no ATP needed)
Na+ is swapped for K+ using ATP
what is the cephalic phase of HCl release
30% of secretion
– Smell, taste, chewing, swallowing, conditioned reflex
in anticipation of food
- Direct stimulation of the parietal cells by the vagus
- Indirect stimulation of the parietal cells by gastrin
what peptide stimulates gastrin release from G cells
Vagal gastrin releasing peptide (GRP)
this enters the circulation and stimulates parietal cells
what causes the gastric phase of HCl secretion
60% of secretion
– Distension of the stomach and the presence of
breakdown products of proteins, amino acids and
small peptides in the stomach
how does distension lead to HCl release
– direct vagal stimulation of parietal cells
– indirect stimulation via gastrin
– local reflexes in the antrumthat stimulate gastrin
release
what neurotransmitter is responsible for vagal activation of parietal cells via the direct pathway
ACh
what is the indirect vagal pathway
Vagal stimulated release of gastrin fromG cells (byGRP neuropeptide transmitter )
how do amino acids and peptides stimulate Hcl release
they cause gastrin to be released
what is the intestinal phase of HCl secretion
10% of secretion
– presence of breakdown products of proteins in the
duodenum
what messengers are used in vagal stimulation of parietal cells
ACh and IP3/ Ca2+
muscarinic 3 receptors on parietal cells
how does histamine stimulate Hcl secretion
secreted by Enterochromaffin
like cells (ECL) in the
gastric mucosa
Diffuses to and
binds to H2
receptors on
parietal cells
second messenger is cyclic AMP
what receptors does gastrin bind to on parietal cells
CCKB
receptors
IP3/Ca2+ is the second messenger
what does somatostatin do
inhibits Hcl secretion
– Direct pathway – binds to receptors on parietal cells and
inhibits adenylate cyclase via Gi protein
– Indirect pathway – inhibits histamine release from ECL
cells and gastrin release from G cells
what causes secretion of pepsinogen from chief and mucous cells
vagal stimulation and H+ triggers local reflexes which stimulate chief cells
what causes pernicious anaemia
lack of intrinsic factor
what cells release mucoprotein containing intrinsic factor
parietal cells
what is a gastrinoma
a tumor in the pancreas or duodenum that secretes excess of gastrin leading to ulceration in the duodenum, stomach and the small intestine. There is hypersecretion of the HCl acid into the duodenum, which causes the ulcers.
also causes hypertrophy and inactivation of pancreatic lipases
how many lumbar veins are there
4 joining the IVC and one joining the common iliac
what do the sublingual glands produce
mucus
what is cimetidine
histamine 2 antagonist that inhibits stomach acid production
used in heart burn and peptic ulcers
what is omeprazole
PPI
GERD and peptic ulcers not heartburn
what is zollinger ellison syndrome
gastrin secreting tumour in the pancreas
what is the difference between pepsin and trypsin
pepsin is produced in the stomach and trypsin is made in the pancreas
where does omeprazole act
H/K atp ase
where does cimetidine act
H2 receptors
where is pepsinogen secreted from
cheif cells
