How do salivary secretions protect the body?
they include buffers to neutralize acidic materials
wash out any unwanted materials
have ABX capability via lysosome and lactoferrin
How do salivary secretions aid in digestion?
it includes a-amylase which contributes to 70% of hydrolysis of starch to produce maltose via breaking a1,4-glucosdase bonds
and contains lingual lipase (which starts lipid digestion)
What are the three main salivary glands?
parotid (serous cells)
submandibular and sublingual (serous and mucus cells)
What is the difference beween serous and mucus cells?
serous fluid only contains electrolytes and protein while mucus fluid contains mucus
Acinar cells secrete the electrolytes, water, and proteins (initial saliva- similar to plasma) which are propelled via the myoepithelial cells into the intercalated ducts. The cuboidal cells of the intercalated cells also propell the initial saliva into the striated ducts.
Striated ducts are lined by columnar cells, the composition of the saliva changes
What is the vasculature to the salivary glands?
Very high blood flow from branches from the external carotid a., which flows opposite to salivary flow and capillaries, surround acini and non-acinar regions
What is the innervation to salivary glands?
parasym via the facial glosspharyngeal nn. and autonomic ganglia and sympathetics via the superior cervical ganglion both contribute to gland secretions
Note that the osmolarity, composition, and pH vary with flow rate
WIth lower flow rates, there is more time for NaCl to be absorbed into the striated ducts as it passed through the acinar system and it becomes more hypotonic. With higher flow rates, the composition of the saliva is similar to whats produced in the acinus
Describe electrolyte exchange from the acinus to the striated duct openings
Initially, I-, Na+, Cl- and HCO3- are secreted into the acinus (so that its composition is similar to plasma) and as it enter the striated ducts K+(active) and more HCO3- is added and Na+ (active), Cl-, and H2O are lost (absorbed)
Why does the osmolarity of fluid decrease along the length of the striated ducts?
the water re-asborption is very slow and cannot match the Na and Cl reabsorption
What other products are secreted in the acinus into saliva?
lysozyme and lactoferrin
blood group substances
What part of saliva secretions is active?
Cl- into the acinus lumen because it is coupled to a K/Na ATPase on the basolateral membrane. So blocking this ATPase will cause Cl- to not be secreted and reduce saliva.
How does Cl- enter the acinus epithelium to produce the gradient that drives movement into the lumen passively?
a Na/K/2Cl transporter on the basolateral membrane AND
a basolateral Cl/HCO3- exchanger
BOTH of these require a Na gradient so Cl- is linked to Na/KTPase
How does Na+ enter the acinus lumen to enter intiial saliva?
paracellular mechanisms via tight-junctions and Cldn2
How does water enter the acinus lumen to enter intiial saliva?
How is Na+ reabsorbed from the acinus lumen in the striated ducts?
There is a much higher conc. of Na+ in the lumen leading to passive reabsorption of Na+ which is then returned to blood via a NaKATPase pump on the basolateral side. The K that then enters the acinus epithelium passively diffuses into the lumen via gradient
How is Cl- reabsorbed from the acinus lumen in the striated ducts?
it passively diffuses to maintain the electrochemical gradient after Na leaves the lumen or via exchange with HCO3- on the luminal membrane and passively into blood on the basolateral side.
The HCO3- needed for this enters the acinus epithelium via a co-transport mechanism with Na+
T or F. There is no known hormonal regulation of saliva
T. Only para- and sympathetic stimulation
How does the parasym system regulate saliva secretions?
mainly by increasing blood flow and production of kallikrein and thus bradykinin (a vasodilator)
Saliva output in terms of sympathetic input
The dip is due to transient vasocontriction (via a receptors) and the longterm increase is due to constriction of the myoepithelial cells via B receptors
How else can salivary secretion be mediated?
centrally via inputs such as smell, taste, nausea which stimulate the salivary nucleus of the medulla to signal via CN IX and X to release Ach to cause increased secretion via a Gq mechanism as well as sympathetics from T1-T3
What things inhibit the salivary nucleus of the medulla?
fatigue, sleep, fear, dehydration
What are the main salivary gland tumors?
-Pleomorphic adenoma (50%) (mixed benign tumor)
-Mucoepidermoid carcinoma (15%)
-Warthin tumor (5-10%) (benign)
What are these?
Pleomorphic adenomas, which show great histologic variation. These are most commonly found in middle aged females
How do pleomorphic adenomas present?
typically as slow growing, painless, movable, firm masses. Rarely, carcinomas can arise in longstanding pleomorphic adenomas, which is marked by sudden rapid growth
Histological variation of pleomorphic adenomas
•benign tumors that consist of a mixture of ductal (epithelial) and myoepithelial cells, and therefore they show both epithelial and mesenchymal differentiation.
•They reveal epithelial elements dispersed throughout the matrix along with varying degrees of myxoid, hyaline, chondroid (cartilaginous), and even osseous tissue.
What is this?
A warthin tumor
Describe warthin tumors
These are benign salivary tumors common in middle-aged males and especially SMOKERS. They are found almost exclusively in the parotid glands, can be bilateral, and are painless
How do Warthin tumors appear histologically?
They are marked by epithelial and lymphoid elements
•Note the follicular germinal center beneath the epithelium
Cystic spaces separate lobules of neoplastic epithelium consisting of a double layer of eosinophilic epithelial cells based on a reactive lymphoid stroma