Digestive System Question And Answers

Describe the composition and functions of saliva. Add a note on the regulation of salivary secretion. (or) Regulation of salivary secretion.
Answer:

Saliva:

• Saliva Composition:
  • Saliva constitutes of
    1. Water-99.5%
    2. Solids -0.5%
       1. Organic substances:
          1. Enzymes:
             • Ptyalin or amylase
             • Lysozyme
             • Kallikerin
             • Lingual lipase Maltase
             • Phosphatase
          2. Other:
          3. Proteins – mucin and albumin.
          4. Blood group antigens.
          5. IgA
          6. Free amino acids
          7. Urea, uric acid, creatinine, xanthine.
       2. Inorganic substances:

1. 1. 1. 1. • \(\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Ca}^{2+}\)
            • HCO3^–,PO₄^3-, bromide, F^–, CI^–
              

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Saliva Functions:

1. Lubrication of food:

• The saliva moistens and dissolves the food that enters in the mouth.
• Saliva also moistens the oral mucusa.
• Mucin present in saliva lubricates the food thus assists mastication and facilitates swallowing.

2. Appreciation of taste:

• Saliva serve as a solvent to dissolve the solid food substances.
• These dissolved particles stimulate the taste buds.

3. Digestive function:

1. Salivary amylase/ptyalin.
   • It is a carbohydrate splitting enzyme.
   • It acts in a neutral or slightly acidic medium
   • Amylase digest starch but not completely.
   • Major part of it is digested in stomach.
   • Amylase converts starch into dextrin and maltose.
2. Maltase.
   • It converts maltose into glucose.
3. Lingual lipase:
   • It converts triglycerides of milk fat into fatty acid and diacylglycerol.

4. Excretion:

• Saliva excretes substances like mercury, potassium iodide, lead and thiocyanate. Saliva also excretes certain viruses such as those causing rabies and mumps.

5. Cleansing action:

• Continuous secretion of saliva washes off the food residues, bacteria and desquamated epithelial cells.
• Mucin in saliva lubricates the oral mucosa and protects the mouth.

6. Regulation of water balance:

7. Regulation of pH balance:

• Proline rich proteins present in saliva binds to toxic substances like tannin and maintain oral pH at 7.0.
• At this pH, saliva is saturated with calcium which protects enamel.

8. Protective:

• Lysosyme kills some bacteria such as staphylococcus, streptococcus and brucella.
• IgA provides defence against bacteria and viruses.
• Lactoferrin – arrests bacterial multiplication.

9. Speech:

• Saliva moisten and lubricate the soft parts of mouth and lips and aids in speech.

Regulation of salivary secretion:

• Salivary glands are under the control of autonomic nervous system which includes both sympathetic and parasympathetic nerve.

2. Stimulation of sympathetic nerve includes 2 types of reflex.

1. Conditioned reflex.
   • Here salivary secretion increases by sight, smell, hearing or thought of food.
   • It is due to impulses arising from eyes, nose, ear, etc.
2. Unconditional reflex.
   • Here, salivary secretion increases when any substances is placed in the mouth.
   • This stimulates the sympathetic fibers.
   • These fibers activates the acinar cells and cause vasoconstriction to secrete noradrenaline.