ORAL CAVITY & SALIVA SECRETION Lecture 2 Dr. Zahoor Ali Shaikh
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.
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.
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.
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.
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.
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
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.
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.
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-.
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].
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
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.
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
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.
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.
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].
WHAT YOU SHOULD KNOW FROM THIS LECTURE • Oral Cavity • Saliva • Salivary Glands • Composition of Saliva • Functions of Saliva • Salivary Secretion • Neural Control • XEROSTOMIA