Saliva, Mastication and Deglutition

What are the principal salivary glands?

Parotid, submandibular and sublingual

What are the types of salivary secretion?

1) Serous, secreted from serous cells and contains a amylase

2) Mucous, secreted from mucus cells and contains mucin

What is the composition of saliva?

Volume of saliva is 800 - 1500 ml/day

PH 7

What are the components of saliva?

Composed of 99% water, and 1% solids.

Inorganic solids = Na, K, Cl, HCO3, thiocyanate.

Organic = Mucin, enzymes, a amylase lysozyme, and Ig A

What is the mechanism of salivary secretion?

Its a rapid process under nervous control only, increased by sym. and parasym. stimulation.

What are the phases of salivary secretion?

1) Cephalic = Occur before food enters mouth, caused by conditioned reflex which is acquired (smelling or seeing food) causing salivation

2) Buccal = Occur when food in mouth, caused by unconditioned reflex which is inherent, not acquired, no need for training or intact cerebral cortex.

3) Gastrointestinal phase = oesphago salivary reflex and gastro salivary reflex. Unconditioned reflexes.

What are the functions of saliva?

1) Starch digestion due to a amylase

2) Solvent for food particles

3) Diluting medium for irritant particles

4) Lubricant that facilitate swallowing

5) Keeps mouth cavity wet for speech

6) Keeps PH about 7, prevent acidity that dissolves Ca and cause dental caries.

7) Oral hygiene, saliva flow washes away bacteria and contains Ig A defending against pathogens

What is the definition of deglutition? (swallowing)

The act of passage of masticated food from the mouth to the stomach.

Name and explain the phases of deglutition

1) Buccal phase:

• It's the only voluntary stage.

• When the food is masticated & mixed with saliva, the tongue moves upward & backward → forcing the bolus of food into the pharynx

2) Pharyngeal phase:

• It's an involuntary stage.

• Presence of food into the pharynx stimulates the swallowing receptors which send afferent impulses to the swallowing centre in the medulla via the 5 , 9 & 10 cranial nerves.

• The swallowing centre send efferent impulses via the 5 , 9, 10 & 12 the CNS

3) Esophageal stage:

• It's involuntary & consists of passage of food from the oesphagus to the stomach.

What does the pharyngeal phase lead to?

• Elevation of the soft palate to close the posterior nasal cavity.

• The tongue remains in contact with the hard palate so the food can't regurgitate to the mouth.

• Approximation of the palatopharyngeal folds allowing only passage of the properly masticated food only.

• Approximation of the vocal cords.

• The epiglottis swings over the opening of the larynx to cover it.

• The larynx is elevated upward & anteriorly.

• The upward & anterior movement of the larynx initiates:

a) relaxation of the upper oesphageal sphincter so food enters the oesphagus

b) contraction of the superior constrictor ms. which spreads down as a peristaltic wave along the oesphagus.

c) relaxation of the lower oesphageal sphincter & upper stomach.

Define esophagus

It is a muscular tube about 20 cm length.

It's muscles are:

• Striated in the upper third.

• Smooth in the lower third.

• Striated & smooth the middle third.

both smooth and striated muscles are supplied by vagal fibers

List the espohageal sphincters

1) Upper oesphageal sphincter

2) Lower oesphageal sphincter

What is the site of the UES and its state during rest and swallowing?

Site:

• It lies at the pharyngeoesopheal junction

During rest:

• Tonically contracted to prevent entrance of air to stomach during respiration

During swallowing:

• Relaxes to allow passage of food, then recontracts

What is the site of the LES and its state during rest and swallowing?

Site:

• Lies at the gastro-oesphageal junction

During rest:

• Tonically contracted to prevent regurgitation of acidic gastric contents into esophagus

During swallowing:

• Relaxes to allow passage of food, then recontracts

What are the factors that reduce LES tone and cause heartburn?

• Foods like tea, coffee, chocolate and fats

• Smoking

• Prostaglandins