Saliva: Difference between revisions
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Saliva is secreted by the parotid, submandibular, sublingual and buccal [[Salivary glands|salivary glands]]. The | Saliva is secreted by the parotid, submandibular, sublingual and buccal [[Salivary glands|salivary glands]]. The aqueous component is formed by primary secretion of a solution similar to [[Extracellular Fluid|extracellular fluid]]. This is modified as it passes along the gland ducts, with removal of Na<sup>+</sup> and Cl<sup>-</sup>, and addition of K<sup>+</sup> and HCO<sub>3</sub><sup>-</sup>. Bicarbonate makes saliva alkaline and helps buffer the acid in food, protecting against dental caries. | ||
The main organic components of saliva are: | The main organic components of saliva are: | ||
*[[Mucus|Mucus]], for lubrication in eating and speech. | *[[Mucus|Mucus]], for lubrication in eating and speech. | ||
*[[Amylase|Amylase]], which digests starch at alkaline pH. | *[[Amylase|Amylase]], which digests starch at alkaline pH. | ||
*[[Lysozyme|Lysozyme]], which has antibacterial actions and protects against oral infection. | *[[Lysozyme|Lysozyme]], which has antibacterial actions and protects against oral infection. | ||
Secretion of saliva is reflexly stimulated via the salivary nuclei in the medulla oblongata in response to: | Secretion of saliva is reflexly stimulated via the salivary nuclei in the medulla oblongata in response to: | ||
*Stimulation of chemoreceptors and mechanoreceptors in the mouth. | *Stimulation of chemoreceptors and mechanoreceptors in the mouth. | ||
*Activity in higher centres of the [[Central nervous system|central nervous system]] | *Activity in higher centres of the [[Central nervous system|central nervous system]] (CNS), e.g., smelling food or thinking about food. | ||
The efferent limb of the reflex is parasympathetic and follows cranial nerves VII and IX to reach the glands. Parasympathetic stimulation favours a rapid flow of enzyme-rich saliva. Drugs which block parasympathetic neurotransmission produce a dry mouth by inhibiting salivation | The efferent limb of the reflex is parasympathetic and follows cranial nerves VII and IX to reach the glands. Parasympathetic stimulation favours a rapid flow of enzyme-rich saliva. Drugs which block parasympathetic neurotransmission produce a dry mouth by inhibiting salivation<ref>J G Mcgeown et al. 2007, Physiology, Third Edition Master Medicine, Philadelphia PA, Churchill Livingstone Elsevier Limited</ref>. | ||
There are 3 pairs of glands that are responsible for secreting 90% of saliva: | |||
*Parotid glands - Serous and Amylase | |||
*Sublingual and Submandibular glands - a mixed secretion of serous and mucous | |||
*10% are secreted from minor glands - mucous and mucins | |||
In total, an average person would secrete around 1.5 litres per day<ref>Piper M. Treuting, Suzanne M. Dintzis, in Comparative Anatomy and Histology, 2012</ref>. | |||
=== '''References''' === | === '''References''' === | ||
<references /> | <references /> | ||
Latest revision as of 10:42, 23 October 2018
Saliva is secreted by the parotid, submandibular, sublingual and buccal salivary glands. The aqueous component is formed by primary secretion of a solution similar to extracellular fluid. This is modified as it passes along the gland ducts, with removal of Na+ and Cl-, and addition of K+ and HCO3-. Bicarbonate makes saliva alkaline and helps buffer the acid in food, protecting against dental caries.
The main organic components of saliva are:
- Mucus, for lubrication in eating and speech.
- Amylase, which digests starch at alkaline pH.
- Lysozyme, which has antibacterial actions and protects against oral infection.
Secretion of saliva is reflexly stimulated via the salivary nuclei in the medulla oblongata in response to:
- Stimulation of chemoreceptors and mechanoreceptors in the mouth.
- Activity in higher centres of the central nervous system (CNS), e.g., smelling food or thinking about food.
The efferent limb of the reflex is parasympathetic and follows cranial nerves VII and IX to reach the glands. Parasympathetic stimulation favours a rapid flow of enzyme-rich saliva. Drugs which block parasympathetic neurotransmission produce a dry mouth by inhibiting salivation[1].
There are 3 pairs of glands that are responsible for secreting 90% of saliva:
- Parotid glands - Serous and Amylase
- Sublingual and Submandibular glands - a mixed secretion of serous and mucous
- 10% are secreted from minor glands - mucous and mucins
In total, an average person would secrete around 1.5 litres per day[2].