Salivary Secretion Flashcards
Saliva composition, glands, secretions, and functions (non-specific)
- Is composed of water, electrolytes and mucins (glycoproteins). The most important proteins are enzymes - e.g. amylase and lipase.
- Specific salivary glands either produce largely mucins (submandibular and sublingual glands) or largely water (parotid glands). Buccal glands play a minor role.
- Facilitates swallowing by a lubricant action. It also allows sapid molecules to be dissolved so that they can be tasted.
- Has antibacterial actions via enzymes such as muramidase, a lysozyme which can kill certain bacteria. It also facilitates oral hygiene by washing away food particles upon which bacteria feed.
- Assists with normal speech.
Composition of saliva
A. Water
B. Inorganic constituents:
Bicarbonate (HCO3-), Sodium (Na+), Potassium (K+), Calcium (Ca2+) Phosphate (P), Chloride (Cl-)
C. Organic constituents:
- Mucoproteins: ABO blood group substances, mucins
- Enzymes: α-amylase, lingual lipase, ribonuclease, antibacterial agents (e.g., muramidase)
- Others: R-protein, epidermal growth factor
Zymogen granules
Serous acinar cells have zymogen granules containing salivary amylase and other proteins.
Is Saliva hypotonic or hypertonic? Why?
amount of fluid remains fairly constant but more Na+ and
Cl- leave than are replaced by K+ and HCO3-.
The net result of this is that saliva is hypotonic relative to plasma at all flow rates.
Acinus role in saliva production
In the acinus Na+ and Cl- enter the cell from the blood down the concentration gradient created by the Na+/K+ ATPase pump. Cl- diffuses into the duct lumen while the Na+ is pumped out of the cell via the Na+/K+ ATPasepump (this movement of 1 positive and one negative charge together ensures that the electrochemical gradient across the cell membrane is maintained). K+ and HCO3- diffuse passively into the lumen and are found to be present in amounts close to plasma levels.
Duct role in saliva production
In the duct the initial saliva is modified. Na+ leaves
the lumen down the concentration gradient created
by the Na+/K+-ATPase pump. Some Na+ is exchanged for K+. The inward movement of Cl- with Na+ maintains electrical neutrality. Some Cl- leaves in exchange for HCO3-.
Note: more Na+ and Cl- leave (are absorbed) than are replaced by K+ and HCO3- (secreted).
INFLUENCE OF FLOW RATE ON THE IONIC COMPOSITION OF SALIVA
The electrolyte composition of saliva changes as the flow rate increases:
The movement of K+ and HCO3- continues at about the same rate. The salivary HCO3- level rises only during the initial increase in flow (HCO3- secretion is stimulated by pharmacologic agents that stimulate flow) but K+ levels remain relatively unchanged at all flow rates.
The net result of these processes is that Na+ and Cl- levels in the saliva rise at all flow rates.
Autonomic nervous system and salivary secretion
Salivary secretion is exclusively under neural control by the autonomic nervous system and is increased by both sympathetic and parasympathetic stimulation.
In the duct cells both divisions of the a.n.s. increase the secretion of K+ and HCO3-.
In the acinar cells, neurotransmitters (acetylcholine, norepinephrine, substance P and VIP) act via cAMP or Ca2+ to increase the secretion of salivary amylase and the flow of saliva.
Parasympathetic stimulation can dilate blood vessels via release of kallikrein which acts on kininogen to release lysyl-bradykinin (kallidin), contributing to increased secretion.
MUMPS (also known as Infectious Parotitis)
results in inflammation of one or both parotid glands. This disease usually affects children.
SJOGREN’S SYNDROME
a chronic inflammatory autoimmune disease, found predominantly in older women, that is characterized by a dryness of mucous membranes and infiltration of the affected tissues by lymphocytes. In terms of the oral cavity it is associated with a decreased salivary secretion with or without parotid gland enlargement.
XEROSTOMIA
is a decreased salivary secretion (also known as “Dry Mouth”) which results in difficulty chewing and swallowing. In addition, speaking becomes difficult and the incidence of
dental caries increases. The latter problem is due to the loss of the flushing and bactericidal actions of saliva. Xerostomia may occur in as many as 30% of the elderly population. It is unclear whether this is due to an age-related decrease in salivary secretion; whether it is an accompanying side effect of other disease processes (e.g., rheumatoid arthritis); or whether it is due to the medications taken to treat such illnesses (e.g., antihypertensives, psychotropics or antidepressants). Many of these medications have muscarinic antagonist properties).
