1. ORAL CAVITY SALIVA SECRETION SWALLOWING
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. SWALLOWING
Swallowing mean moving the food from the mouth through esophagus into the stomach.
Swallowing is all or none reflex.
Swallowing is initiated when a bolus or chewed food or liquid is voluntarily forced by the tongue to the back of mouth into the pharynx.

22. SWALLOWING
Pharyngeal pressure receptors send afferent impulses to the swallowing center located in the medulla of brain stem.
Swallowing center activates the muscles involved in swallowing.
Swallowing is initiated voluntarily but once began, it can not be stopped.

23. SWALLOWING Swallowing has three stages: 1. Oral Stage - voluntary
2. Pharyngeal Stage – involuntary
3. Esophageal Stage – involuntary
Oropharyngeal Stage
It last for 1 to 2 second and consist of moving the bolus from the mouth through the pharynx into the esophagus.

25. SWALLOWING Oropharyngeal Stage {cont}
When bolus [food] enters the pharynx, it is directed into the esophagus and prevented from entering the trachea or nasal passages.
Food is prevented from entering the nasal passages by elevation of soft palate and uvula sealing off the nasal passages from the pharynx so that food does not enter the nose.

26. SWALLOWING Oropharyngeal Stage {cont}
Food is prevented from entering the trachea by elevation of larynx and tight closure of vocal cords across the laryngeal opening or glottis.
Epiglottis – cartilaginous tissue prevents the food from entering the trachea.

27. SWALLOWING
During swallowing, respiration ceases, as respiratory passages are sealed off and swallowing center briefly inhibits the respiratory center in medulla.

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

29. THANK YOU