Lecture 4: Salivary and Gastric Secretions Flashcards
What are the three major salivary glands?
Parotid glands
Submandibular glands
Sublingual glands
What kind of cells and fluid are in the parotid gland?
Serious cells; aqueous fluid
What does the secretions of the parotid gland contain?
Water, ions, enzymes
What cells do sublingual and submandibular glands contain?
Mixed glands with serous and mucous cells (mucin glycoproteins)
What gland is special to the dog and cat?
Zygomatic gland
In the structure of a salivary gland, each “grape” in the bunch of grapes is an
Acinus
Salivary glands are lined with what kind of cells
Acinar cells
Acinar cells produce what? (vague)
Initial saliva
What does initial saliva contain?
Water, ions, enzymes, mucous
Which duct does initial saliva pass through first?
Intercalated duct
What duct does saliva pass through second?
Striated duct
What kind of cells line the striated duct?
Ductal cells
What is the function of ductal cells?
Modify saliva (alter concentration of ions)
What kind of cells contract and eject saliva due to neural stimulation?
Myoepithelial
What kind of innervation do acinar and ductal cells have?
PNS and SNS
Which innervation typically dominates acinar and ductal cells?
PNS
How is blood flow impacted when saliva production is stimulated?
Increases
Name the components of saliva
Water, electrolytes, amylase (some species), lingual lipase, kallikrein, mucus
What is the function of kallikrein?
Regulates local vasodilation association with secretion
Saliva is ________ compared with plasma
Hypotonic
What is the first step of saliva formation?
Formation of isotonic solution by acinar cells
What is the second step of saliva formation?
Modification of solution by ductal cells to become hypotonic
Saliva has increased ____ and _____, lower ____ and ____ compared to plasma
Increased potassium and bicarb
Lower Na and Cl
What are the two transporters involved in saliva modification?
Luminal membrane and basolateral membrane
Name the luminal membrane transporters
Na+/H+ Exchange
Cl-/HCO3- Exchange
H+/K+ Exchange
Name the basolateral membrane transporters
Na+/K+ ATPase
Cl- Channels
Absorption of Na+ and Cl- into the blood = _____ concentrations in saliva
Low
Ductal cells are ___________ to water
Impermeable
When Na + Cl reabsorbed, what happens to water (ductal cells)
Stays, because ductal cells impermeable
Which cells secrete organic components?
Acinar
Alpha amylase in pigs and humans is responsible for
Starch digestion
Lingual lipase is responsible for
Lipid digestion
What is the function of mucin glycoproteins?
Mucous, lubricant
At what flow rates does saliva resemble plasma?
High flow rates, 4 mL/min
At what flow rates is saliva hypotonic when compared to plasma?
Low, <1 mL/min
Final saliva is typically hypertonic or hypotonic?
Hypotonic
Final composition of saliva depends on contact time with
Ductal cells
Why does saliva resemble plasma at high flow rates?
Less time to modify saliva
Concentration of what is lowest at low flow rates and highest at high flow rates?
HCO3
Secretion of what is selectively stimulated when production is stimulated?
HCO3
Salivary secretion is exclusively under
Neural control
Salivary secretion is stimulated by what ANS
Parasympathetic and sympathetic
Where is saliva formation PNS innervation located
On facial and glossopharyngeal nerves
How do food, smell, nausea effect PNS activity on saliva formation?
Increase
How do fear, sleep, dehydration effect PNS activity on saliva formation?
Decrease
Postglanglionic neurons of PNS release what
Ach
The Ach released by postganglionic neurons of PNS act on which receptors?
Muscarinic on acinar and ductal cells
Postanglionic neurons of SNS release what?
NE
NE binds to which receptors in saliva formation?
Beta-adrenergic on acinar and ductal cells
When SNS postganglionic NE binds to beta-adrenergic receptors on acinar and ductal cells, what happens?
Increased saliva secretions
List the components of gastric juice
HCl, pepsinogen, intrinsic factor, mucus
What two components of gastric juice initiate protein digestion?
HCl and pepsinogen
What is the purpose of intrinsic factor in gastric juice?
Essential for absorption of Vitamin B12 in ileum
What is the purpose of mucus in gastric juice?
Protects gastric mucosa from HCl and lubricates
What gastric glands are located in the body of the stomach?
Oxyntic glands
Name the cells located in oxyntic glands
Epithelial, mucous neck cells, parietal cells, chief cells
Where are epithelial cells of oxyntic glands lining?
Opening of oxyntic glands
What is function of mucous neck cells in oxyntic glands?
Secrete mucous
What is the function of parietal cells?
Secrete HCl and intrinsic factor
What is the purpose of chief cells?
Secrete pepsinogen
Need to be activated
What glands are located in the antrum of the stomach?
Pyloric glands (deeper)
Name the cells found in pyloric glands
G cells, mucous neck cells
What is the function of mucous neck cells in pyloric glands?
Secrete mucous, bicarb, pepsinogen
What is the purpose of G cells in pyloric glands?
Secrete gastrin into circulation
HCl is secreted by which cells?
Parietal
Apical membrane has which channels?
H+/K+ ATPase and Cl- Channels
Basolateral membrane has which channels?
Na/K ATPase and Cl/HCO3 exchangers
Carbonic anhydrase is contained by which cells?
Parietal
H+ goes to where via what transporter?
Lumen via H+/K+ ATPase
HCO3 is absorbed into where via what transporter?
Blood via HCO3/Cl exchanger
What follows H+ into the lumen and through what transporter?
Cl follows H+ into lumen via Cl- channels
What is responsible for the “alkaline tide” in gastric venous blood after a meal?
HCO3
What will happen to absorbed bicarbonate in the alkaline tide?
Will be secreted back into GIT via pancreatic secretions
During HCl secretion there is a net secretion of what and net absorption of what?
Net secretion of HCl
Net absorption of HCO3
What three substances stimulate H+ secretion?
Histamine, ACh, Gastrin
Where is histamine released and by what?
ECL cells in gastric mucosa
What does histamine bind to/what cells are involved?
H2 receptors on parietal cells
What is the second messenger for Histamine?
cAMP
What is ACh released by?
Vagus nerves innervating gastric mucosa
What does ACh bind/what cells involved?
Muscarinic receptors in parietal cells
What are the second messengers for ACh?
IP3/Ca2+
What is gastrin secreted by and where?
G cells in stomach antrum
What does gastrin bind/what cells involved?
CCKB receptors on parietal cells
What are the second messengers involved with gastrin?
IP3/Ca2+
Define potentiation in relation to histamine
Strong interaction with either ACh or Gastrin
Gives strongest response to stimulate H+
Potentiation general definition
Sum of 2 stimuli cause a greater response than the sum of indifivdual responses
Drugs can have ______________ effects due to potentiation
Greater than expected
Omeprazole is a non-competitive inhibitor of what?
H+-K+ ATPase transporter
Irreversibly blocks and avoids H+ secretion