Salivation Flashcards
How much saliva is produced each day?
1.5 litres
What are the 3 functions of saliva?
- lubricate food
- protect oral mucosa - alkaline, bacteriostat, keeps mucosa moist, cleans teeth, high calcium concentration
- start carb digestion - alpha amylase digests alpha 1,4 bonds in amylose
What is xerostomia?
insufficient production of saliva => rapid degredation of mucosa and teeth
What are the overall features of saliva? (6)
- hypertonic
- bacteriostatic
- alkaline - neutralises acid produced by bacteria with higher than plasma concentration of bicarb
- contains electrolytes -higher than plasma concentration of iodide, potassium and calcium and lower than plasma concentration of Na+ and Cl-
- contains mucous
- contains amylase
What type of glands are salivary glands? What is their structure?
Exocrine glands that consist of acini (blind-ended tube) lined by acinar cells that is connected to a duct lined by duct cells.
What are the 3 different glands and what do they each secrete?
Parotid gland:
Serous gland that accounts for 25% of salivary secretio. Secretions are rich in enzymes with very little mucous
Submandibular gland:
Mixed mucus and serous gland of different acini and acinar cells opening into a common duct. Accounts for 70% of volume of saliva
Sub-lingual gland:
Mucous gland that produces very viscous secretion and accounts for 5% of overall saliva secretion
How is saliva hypertonic when they are no mechanisms in the body to actively add water as water addition/removal occurs by osmotic processes.
Fluid isotonic with plasma is concentrated - this is more concentrated than the end-result saliva. Solutes are then removed - namely Na and Cl and water can not follow down the osmotic gradient due to the tight gaps between duct cells => hypertonic
Low vs high flow rate saliva
low flow rate saliva is more hypotonic - allows more time for duct cells to modify and remove NaCl
high flow rate saliva is less hypotonic but more alkaline - duct cells have a limited modification rate and the mechanisms that stimulate saliva production also stimulate HCO3- secretion
Mechanism of acinar secretion
Acinar actively secrete Cl- into duct lumen and water and Na+ passively follow
Mechanism of ductal modification
Na/K/ATPase sets up concentration gradient for Na and K
Na/K/ATPase pumps Na from cell back into blood. Na is higher in lumen than in cells causing it to passively diffuse back into cells to be reabsorbed back into ECF.
Na/K/ATPase pumps K from blood into cells. K is higher in cells than in lumen which drives the expulsion of Cl- from duct cells into ecf. This sets up a Cl- gradient as there is a higher concentration of Cl- outside in the the duct lumen than inside the duct cells which drives HCO3- expulsion out into the lumen
Parasympathetic neural control of salivation
Afferent information from taste receptors in the tongue, mouth, chemical receptors in the nose etc is received by the medulla which stimulates the glands via the parasympathetic NS.
Parasympathetic control to the partoid gland occurs via CN IX and the otic ganglion, and to the submandibular and sublingual via CN VII and the submandibular ganglion.
This causes the glands to increase primary secretion by acinar cells and increases HCO3- secretion also.
Sympathetic neural control of salivation
Reduce blood flow to glands therefore reduce flow rate => increasing hypertonicity.
Also stimulates aldosterone release from the adrenal cortex which upregulates ENac and Na/K/ATPase, further facilitating removal of Na+ from saliva
