ORAL CAVITY & SALIVA SECRETION

1. ORAL CAVITY & SALIVA SECRETION Lecture 2 Dr. Zahoor Ali Shaikh

2. ORAL CAVITY • Entry to GIT is through the mouth or oral cavity. • In mouth, we have: LIPS • These are muscular, help to keep the food in mouth. • Lips have non-digestive function also e.g. help in speech, have sensory receptors.

3. ORAL CAVITY PALATE • It forms the roof of the oral cavity and separates the mouth from the nasal passages. • Palate allows breathing and chewing to take place at the same time. • At the end of palate, there is UVULA. • NOTE – During swallowing one has to stop breathing.

4. ORAL CAVITY TONGUE • It forms the floor of the oral cavity, it is composed of voluntarily controlled skeletal muscles. • Movements of tongue help in guiding food within the mouth. • Tongue plays important role in speech. • Taste buds [e.g. sweet, bitter] are located at the tongue.

5. ORAL CAVITY PHARYNX • It is the cavity at the throat. • It acts common path for both digestive system [mouth and esophagus for food] and respiratory system [link between nasal passages and trachea for air]. • In the side walls of pharynx are tonsils, lymphoid tissues, part of body’s defense.

6. ORAL CAVITY TEETH • Teeth are responsible for process of mastication or chewing. • Teeth are embedded in jaw bones. • Chewing helps in breaking the food into smaller pieces to facilitate swallowing and increase food surface area where salivary enzymes can act. • Chewing helps to mix food with saliva.

7. SALIVA • It is secretion produced by salivary glands. • Daily secretion about 1000ml– 1500ml • There are 3 pairs of salivary glands which produce saliva, they lie outside oral cavity and discharge saliva through ducts in the mouth. They are: • i). Parotid Glands • ii). Submandibular Glands • iii). Sublingual Glands

10. COMPOSITION OF SALIVA • Water – 99.5% • Electrolyte & Protein – 0.5% • pH – 7 • Salivary protein are amylase, mucus, lysozyme. • Saliva contains two major types of protein secretion: • 1. Serous secretion – contains α-amylase [ptyalin] enzyme for digesting starch. • 2. Mucus secretion – that contains mucin for protection and lubrication.

11. COMPOSITION OF SALIVA • Parotid gland secrete serous type of secretion. • Submandibular gland secrete both i.e. serous and mucus secretion. • Sublingual Glands secrete mainly mucus.

12. COMPOSITION OF SALIVA • Saliva is secreted in the acini is nearly isotonic to the plasma. • During passage through the ducts, the composition of saliva is modified as Na+ and Cl- are absorbed and K+ and HCO3 are secreted. • The ducts are relatively impermeable to water. • Therefore, saliva that reaches the mouth is HYPOTONIC, rich in K+, but depleted of Na+ and Cl-.

13. FUNCTIONS OF SALIVA 1.Helps in digestion of carbohydrates in mouth through action of salivary amylase, an enzyme that breaks polysaccharide into maltose [disaccharide]. 2. Helps in swallowing by providing lubrication due to presence of mucus. 3. Anti-bacterial action due to presence of lysozyme, an enzyme that destroys bacteria. 4.Acts as solvent for molecules that stimulate taste-buds [present on the tongue].

14. FUNCTIONS OF SALIVA 5.Helps in speech [it is difficult to talk when mouth is dry]. 6. Helps in oral hygiene by keeping mouth and teeth clean. 7. Saliva is rich in bicarbonates which neutralizes acids in food. 8. Prevents dental caries. 9. Saliva contain IGA

15. SALIVA • Is Saliva essential for digestion? • Not essential for digestion because enzymes produced by pancreas and small intestine can complete food digestion even in the absence of salivary secretion. • CLINICAL • Decreased salivary secretion is called ‘XEROSTOMIA’. It causes dryness of mouth, therefore, difficulty in chewing, swallowing, speech, increase in dental caries.

16. SALIVARY SECRETION • Salivary secretion increased with different stimuli. • It is maximum with lemon [4 to 5ml/min]. • There is continuous basal secretion of saliva [0.5ml/min] due to stimulation of parasympathetic nerve ending to salivary glands. • Salivary secretion is increased by: • (i). Simple Reflex • (ii). Conditioned Reflex

18. SALIVARY SECRETION (i).Simple Salivary Reflex • When we take food, chemoreceptors and pressure receptors in oral cavity are stimulated. • Afferent nerve carry impulse to salivary center in Medulla [brain stem], it send impulse via autonomic nerves to salivary glands and increase salivary secretion. (ii).Conditioned Reflex • It occurs without taking food, but just thinking, seeing, smelling of food. • Reflex occurs through cerebral cortex to stimulate medullary salivary center.

19. Control of Salivary Secretion • Both parasympathetic and sympathetic ANS supply salivary glands and increase salivary secretion. • The quantity, characteristic, and mechanism of saliva production by parasympathetic and sympathetic are different.

20. Control of Salivary Secretion • Parasympathetic – produces increased amount of watery saliva rich in enzymes. • Sympathetic – produces small increase of thick saliva, rich in mucus. • IMPORTANT – control of salivary secretion is NEURAL only [other digestive secretion are regulated by nervous system and hormones].

21. WHAT YOU SHOULD KNOW FROM THIS LECTURE • Oral Cavity • Saliva • Salivary Glands • Composition of Saliva • Functions of Saliva • Salivary Secretion • Neural Control • XEROSTOMIA

22. THANK YOU