Physiology Salivary Secretion
in the striated duct, important ionic exchanges occur to modify the composition of saliva. what are these changes?
1. Na+ is actively reabsorbed and K+ is secreted into saliva 2. Ca2+ is secreted into saliva 3. Cl- is reabsorbed and HCO3= is secreted into saliva 4. water is retained (hypo-osmolar)
what are the 4 unique properties of saliva?
1. large volume related to mass of glands 2. hypo-osmolar 3. K+ concentration is high 4. contains enzymes, lactoferrin, lysozyme
what are functions of saliva?
1. lubrication (facilitates swallowing) 2. protection (buffer to acid, washes out particles of acid/pepsin, antibiotic via lysozyme, lactoferrin, IgA) 3. digestion (amylase, and lingual lipase)
saliva's 3 functions = lubrication, protection, digestion. what are the factors responsible for lubricating ingested material to facilitate swallowing?
1. mucus 2. water
what are the 3 clinical conditions associated by defective salivary secretion?
1. xerostomia- no saliva 2. Sjogren's- atrophy of glands 3. CF- reduced fluid and bicarbonate due to defective CFTR
how is salivary secretion regulated?
ANS Parasympathetic- facial/glossopharyngeal nerves (major influence) Sympathetic- superior cervical ganglion control blood flow and contraction of myoepithelial cells
saliva's 3 functions = lubrication, protection, digestion. what are the factors responsible for digestion?
a-amylase can break down alpha 1-4 glycosidic bonds in carbs/starch lingual lipase- lipid hydrolysis
saliva's 3 functions = lubrication, protection, digestion. a-amylase can break down alpha 1-4 glycosidic bonds in carbs/starch lingual lipase- lipid hydrolysis where are these enzymes active and why?
a-amylase works at pH 7 and is inactivated in stomach lingual lipase are active throughout GI tract
the functional unit of salivary gland = salivon and consists of a round acinus, narrow intercalated duct, wide striated duct. what cells make up each part?
acinus- monolayer of polygonal cells that secrete initial saliva intercalated duct- cuboidal cells striated duct- columnar cells
salivary osmolality depends on flow rate. how and why?
at higher flow rate, saliva = more similar to plasma bc less time for ionic exchanges
where does blood supply to salivon come from? how is blood drained?
external carotid (flows opposite to salivary flow) *capillaries surround acinar regions and non acinar regions non-acinar capillaries drain into portal venules that join acinar capillaries and second set of venules drain into systemic circulation
saliva's 3 functions = lubrication, protection, digestion. what are the factors responsible for protective functions of saliva?
functions = buffer, washing away, and antibiotic buffer- bicarbonate that neutralizes acid in pharynx and esophagus due to reflux from stomach antibiotic- lysozyme and lactoferrin kill bacteria in mouth IgA = active against viruses and bacteria
blood flow per unit weight of salivary tissue is 20 times greater than other tissues. why?
high rate of salivary secretion
salivary secretion is regulated by both PSYM and SYM via control of blood flow and contraction of myoepithelial cells. how does PSYM regulate salivary secretion?
major component of regulation 1. vasodilation of surround blood vessels/ production of kallikrein that produces bradykinin vasodilator 2. contraction of myoepithelial cells
salivary secretion is regulated by both PSYM and SYM via control of blood flow and contraction of myoepithelial cells. how does SYM regulate salivary secretion?
minor component of regulation biphasic response that initially decreases secretion bc of vasoconstriction mediated by a-adrenergic direct stimulation of myoepithelial cells to contract via NE and cAMP b-adrenergic
myoepithelial cells surround both the acinus and the intercalated duct of the salivon and generate contractile force to propel saliva out. what are myoepithelial cells regulated by?
neural inputs
salivary glands include the parotid and submandibular and sublingual. what are the secretions of each and how much do the secretions of each gland contribute to the daily output of saliva?
parotid- serous, watery, amylase containing secretion 25% submandibular, sublingual- serous and mucus, 75%
the saliva secreted by the acinus = initial saliva that moves into the intercalated duct. what is initial saliva like in composition?
plasma
what is the functional unit of a salivary gland and what does it consist of?
salivon round acinus, narrow intercalated duct, wide striated duct
what are the properties of saliva secretion? (rate, osmolarity, regulation)
secreted at high rate 1L/day hypo-osmolar (watery) regulated by both symp and parasym
regulation of salivary secretion is centrally regulated. what reflexes and body response stimulate or inhibit salivary nucleus of medulla?
stimulate- smell, taste, pressure, nausea inhibit- fear, sleep, fatigue, dehydration
the saliva secreted by the acinus = initial saliva that moves into the intercalated duct. initial saliva is like plasma in composition. where in the salivon do important ionic exchanges occur to modify the composition of saliva?
striated duct
what prevents back diffusion of salivary constituents?
tight junctions in epithelium
what are constituents of saliva?
water, electrolytes, protein
