Rao 4 - Salivary Secretions Flashcards
What are the 3 primary functions of salivary secretions?
- Lubrication
- Protects
- Digestion
What are the protective functions of Saliva?
- HCO3- neutralizes any acid washed up by the stomach
- Washes out pepsin and acid
- Antibiotic action with Lysozyme, Lactoferrin, and IgA
What role does saliva play in digestion?
1. alpha-Amylase degrades 70% of starch before it is inactivated
2. Salivary Lipase is also present with hydrolysis beginning in the stomach and remains active throughout the entire GI tract
** Not affected by Bile Salts, Fatty Acids, or Lecithin**
How much saliva is secreted by the salivary glands each day?
1 L per day is excreted, this is the highest secretion per unit weight in the entire GI tract
What are the 3 primary Salivary Glands?
• How much does each gland contribute to the total amount of secretions?
25% of secretions:
Parotid
75% of secretions:
Submandibular
Sublingual
What type of secretions come from the parotid gland?
• What is contained in these secretions?
Parotid = SEROUS GLAND
Serous Secretions = H2O, ion, and Enzymes
Enzymes = Amylase, Lipase, Lactoferrin, Lysozyme
**Note: High Protein production means lots of ER and Protein containing granules in the cytoplasm
How do mucinous cells appear?
• what is secreted from them?
Mucinous cells appear like goblet cells
• Fluid Secreted contains Mucin and Glycoproteins
What are the 3 parts to the Salivary Gland?
Acinus, Intercalated Duct, and Striated Duct
• These are surrounded by myoepithelial cells
How does the initial solution secreted by Acinar Cells change as it moves from acinus to striated duct?
• How are Na, Cl, HCO3, and K affected?
As fluid moves from the acinus to the striated duct the fluid goes from **ISOosmolar to HYPOosmolar
there is a net ABSORPTION of Na/Cl back into the ducts and net SECRETION of HCO3-, K+ also increases**
What is the effect of Sympathetic, Parasympathetic, and Hormonal Stimuli on salivary gland excretion?
BOTH Sympathetic (minor) and Parasympathetic (major) increase secretions from the salivary glands
Hormones have NO effect on salivary gland secretions
What are the products of alpha amylase working on startch?
Maltose
Maltriose
Limit Dextrans
Describe the blood flow across the salivary gland.
Blood is supplied from vessels branching off of the external carotid that flow in the OPPOSITE direction as saliva.
1st: Capillary Bed surrounding the Striated and Intercalated Ducts is hit
2nd: Blood travels through PORTAL vessels to…
3rd: A second capillary bed surrounding the Acinus is supplied
What is the primary ion in Acinar Transport?
• Ductal Transport?
• Are these ions absorbed or excreted?
Acinar transport centers around the SECRETION of Cl- by NKATPase (Ouabain) dependent mechanisms
Ductal transport centers around ABSORPTION of Na+ by NKATPase (Ouabain) dependent mechanisms
What channels and transporters are located on the basal side of Acinar Cells?
• Which are most important to assuring that Cl- get exported from the cell?
-
Na/K/2Cl cotransporter - increases intracellular Cl- to push it through to the lumen
**Inhibition of this channel leads to a 65% reduction in salivary excretions -
Na/H Exchanger - allows for H+ efflux so that Carbonic Anhydrase can continue to produce H+ and HCO3 to operate the HCO3/Cl exchanger and increase Cl- concetration in the cell
**Inhibition of this channel leads to a 35% reduction in salivary excretions - HCO3/Cl Exchanger - imports Cl- to increas intracellular Cl-
- Na/K ATPase - this is what makes the entire process of Cl- transport ACTIVE, because Na+ gradient is required for steps 1. and 2.
- K+ channel allows K+ OUT of the cell (down its gradient) so that Na/K ATPase can continue to run
What channels and transporters are located on the Apical side of Acinar Cells?
• Which are most important to assuring that Cl- get exported from the cell?
- Cl and HCO3- channels allow passive diffusion out of the cell into gland lumen
- Cl- Channel - allows Cl- to flow by itself down electrochemical gradient
- AQP5 - allows for equilibration of H2O between cell and lumen (what leads to the acinar secretions being isotonic)
What molecules are allowed to move paracellularly in the acinar cells?
H20
Na+ via Cldn2
What channels and transporters are located on the Basal side of Ductal Cells?
• Which are most important to assuring that Na+ get imported into the cell and into the blood?
- N/K ATPase exports Na+ from the cell into the blood - makes the process Ouabain dependent
- Na/HCO3 Exchanger imports HCO3- by letting Na+ flow into the cell down its gradient
- Cl- channel allows Cl- to re-enter the blood
What channels and transporters are located on the Apical side of Ductal Cells?
• Which are most important to assuring that Na+ get imported into the cell and into the blood?
- CFTR - cAMP activated HCO3 exporter puts HCO3 into the lumen of the striated duct
- HCO3/Cl exhanger - pulls Cl- back into the cell and pushes HCO3- into the salivary secretions
- Cl Channel - allows Cl- to flow back into the ductal cell and into the blood down its concentration gradient
4/5. K+ and Na+ channels are ALDOSTERONE regulated and allow for K+ and Na+ to flow back down their gradients (so that K+ EXITS the cell into saliva and Na is absorbed into the cell and blood)
What molecule can travel paracellularly between Ductal Cells?
Cl-
How does the composition of Saliva change with flow rate?
• What are the primary components?
• Explain this change.
Low Flow Rate:
• K+ is High, Na and Cl are Low, and HCO3- is relatively same
**This occurs because K+ has more time to leak out of aldosterone dependent K channels; Cl- is absorbed into Ductal Cells in Exchange for HCO3-; Na+ has more time to flow DOWN its gradient and leak INTO cells via aldosterone dependent Na channels
High Flow Rate:
• K+ is slightly lower, Na+ and Cl- are high, and HCO3- is relatively the same
***This occurs because there is little contact with the ductal cells that are responsible for changing the electrolyte composition as shown above
What are the two broad functions of sympathetic and parasympathetic stimulation that lead to increased salivary secretions?
- *1. Myoepithelial Contraction
2. Regulating Blood Flow**
What stimuli increase and decrease the parasympathetic stimulation of salivation?
Increase Parasympathetic Response:
• Conditioned Responses: Food, Nausea, Smell
Decreased Parasympathetic Response:
• Dehydration, Fear, Sleep
What preganglionic nerves carry efferent information from central stimuli?
CN VII - Facial n.
CN IX - Glossopharyngeal
How does parasympathetic stimulation lead to vasodilation to increase salivary output?
Ach acts to increase vasodilation (don’t know how? maybe M3 stimulated cGMP creation)
Increased Cellular metabolism as a result of Ach stimulation leads to Kallikrien release that cleaves Kininogen to Bradykin which acts as a vasodilator
