Physiology of Salivary gland

Physiology of Salivary gland

Saliva is a biological fluid which performs functions like bolus formation, secretion of enzymes, excretion of chemical substances etc.

We have 3 pairs of the major salivary gland and some minor salivary glands. Major salivary glands perform maximum involvement in salivary secretion.

Major salivary glands:

Major salivary glands include

1.     Parotid glands

2.     Submandibular glands

3.     Sublingual glands

On both side of our buccal cavity.

3 major salivary gland

Parotid glands:

They are the largest of all salivary glands. It is located on the lateral surface of oral cavity.

This gland communicates to the oral cavity by Stenson's duct in the upper 2nd molar tooth.

Submandibular glands:

These glands located in the submaxillary triangle and communicates through Wharton’s duct. It opens at the frenulum of the tongue by an opening called Caruncula sublingualis.

Sublingual glands:

The Smallest salivary gland located on the buccal mucosa at the floor of the oral cavity. This gland opens on small papillae under the tongue by Ducts of Rivinus or Bartholin’s duct.

Classification of salivary gland based on the secretion:

We can classify 3 types of salivary glands based on the type of salivary secretion.

1.    Serous glands

They are made of serous cells which secretes watery saliva. Eg, parotid and sublingual glands.

2.     Mucous glands

Made of mucous cells which secretes viscous saliva with reach in mucin. Eg, Minor salivary glands include buccal, lingual, and palatal glands.

3.     Mixed glands

These glands consist both mucous and serous cells. Eg, Submandibular and labial glands.

Structure of salivary gland:

Basically, salivary glands are racemose type (looks like a bunch of grapes). Salivary glands are made of acini. Acini determine the type of salivary secretion which contains mucous and/or serous cells. Followed by the cells It has a globular cavity which continues as a lumen to form intercalated duct. All the intercalated ducts connect to form intralobular duct followed by interlobular ducts. Interlobular ducts unite to form the main duct of the gland.

Saliva secretion:

       Saliva secretion is done by the stimulation of ANS (Parasympathetic and sympathetic fibres).

Simulation of parotid gland (Parasympathetic fibres):

It is done by the stimulation of the inferior salivatory nucleus in the upper medulla followed by Glossopharyngeal nerve (CN IX), Tympanic branch of the glossopharyngeal nerve, Tympanic plexus, Preganglionic fibre, Otic ganglion, Postganglionic fibre of auriculotemporal nerve (CN V) and finally reach the parotid gland.

Stimulation of Submandibular and sublingual glands (Parasympathetic fibres):

These glands are stimulated by the superior salivatory nucleus in pons followed by the intermedius of wrisberg nerve, geniculate ganglion, the preganglionic fibre of chorda tympani nerve [Motor branch of the facial nerve (CN VII)], the lingual nerve of the trigeminal nerve, Postganglionic fibres and finally reach both of the glands.

Stimulation of parasympathetic fibres cause saliva secretion with waterier by the activation of acinar cells. This stimulation is mediated by acetylcholine. Vasodilation will be there with less amount of organic substance in the saliva.

Stimulation of Sympathetic fibres:

Sympathetic fibres of salivary glands origin from the 1st and 2nd thoracic segment of the spinal cord in the lateral horns. Stimulation of sympathetic fibres cause increase saliva secretion with a large amount of mucus. Because of the activation of acinar cells and vasoconstriction. This stimulation is mediated by noradrenaline.

All these stimulations are initiated by unconditioned (Inborn reflex) and conditioned reflexes (In the presence of food).

Composition of saliva:

Normal Volume of salivary secretion is 1000 mL to 1500 mL per day.

Parotid glands 25%,

Submandibular glands 70%,

Sublingual glands 5%.

pH of saliva is 6.35 to 6.85.

Saliva is a mixture of 99.5% water and 0.5% solids.

Solid includes inorganic substance like Sodium, Potassium, Calcium, Bicarbonate, etc. and gases like Oxygen, Nitrogen and Carbon dioxide.

Water substance include enzymes like Amylase, Maltase, Lingual lipase, Lysozyme, Kallikrein, Carbonic anhydrase and other substance like Mucin, Albumin, IgA, Blood group Ag, etc.

Saliva function:

Mucin lubricate bolus,

Salivary enzyme-like amylase makes digestion easy,

Lysozyme, IgA and proline-rich protein in saliva act as antimicrobials,

It helps in the excretion of lead, thiocyanate and potassium iodide.


 

 

 

 

 

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