Secretory Function of GIT Salivary secretion Gastric juice secretion Pancreatic juice Biliary secretion 14-Nov-18 salivary secretion

Salivary Secretion Functions of saliva Salivary glands Composition of saliva Secretory process Control mechanism 14-Nov-18 salivary secretion

Functions of Saliva Moisten and lubricate food Dissolve food Digestion Taste buds can be stimulated Digestion Salivary amylase Oral health Washes food particles Prevent dental carries Lysozymes – antibacterial 14-Nov-18 salivary secretion

Salivary Glands Parotid gland Serous gland Watery secretion Protein – salivary amylase Electrolytes Produces 20% of total saliva 14-Nov-18 salivary secretion

Salivary Glands Submandibular glands Mixed glands Secrete both mucus and serous secretions Electrolytes, mucus, protein Produce 70% of total saliva 14-Nov-18 salivary secretion

Salivary Glands Sublingual Others Mucous Secrete mucus Produces 5% of total saliva Others Bucal glands, lingual Minor produce mucus Produce 5% of total saliva 14-Nov-18 salivary secretion

Physiological Anatomy Secretory function of salivary gland Salivon Acinus Duct system Arterial blood supply (counter current) 14-Nov-18 salivary secretion

Functional unit of salivary gland Acinar capillaries Acinus Blood flow Intercalated ducts Duct capillaries Interlobular ducts Excretory duct Salivary flow 14-Nov-18 salivary secretion

Composition of Saliva Electrolyte Na+, K+, HCO3-, Cl- Urea, Iodide Water Saliva is hypotonic in comparison to plasma Contain higher potassium & bicarbonate Lower sodium and chloride 14-Nov-18 salivary secretion

Composition Proteins Volume of saliva = 500 to 1500 ml/24 hrs Enzymes (ptyalin, lingual lipase) Plasma proteins “R” proteins – cobalmin binding Mucin – glycoprotein lubricate food Volume of saliva = 500 to 1500 ml/24 hrs 14-Nov-18 salivary secretion

Composition Composition of saliva changes with rate of secretion At low rate of secretion Osmolarity is very low; As low as 50 mOsm/l At maximum rate Composition approaches that of plasma 300 mOsm/l 14-Nov-18 salivary secretion

Secretory Process Saliva secretion involves two processes Primary secretion by acinus Secondary modification by salivary ducts 14-Nov-18 salivary secretion

Primary Process Acinus secrete primary secretion that contain Na+, Cl-, H2O, HCO3-, protein, mucin Acinus secrete primary secretion that contain Protein, mucin, electrolyte, water in conc. Similar to that of ECF Ultra-filtrate of plasma 14-Nov-18 salivary secretion

Primary Process Protein Mucin Serum protein (0.1 to 0.5 gm/dl) Na+, Cl-, H2O, HCO3-, protein, mucin Protein Serum protein (0.1 to 0.5 gm/dl) Immunoglobin A Salivary α amylase Mucin Glycoprotein, mucopolysaccharide Blood group specific 14-Nov-18 salivary secretion

Secondary Modification Na+, Cl-, H2O, HCO3-, protein, mucin As the primary secretion flows through the duct system Secretion of some substances in the duct HCO3- , K+, Cl-, Urea, Iodide Reabsorption of materials from the duct Na+ HCO3-, urea, Iodide Na+ K+ Cl- Na+, Cl-, H2O, HCO3-, proteins, Urea, Iodide ,K+ 14-Nov-18 salivary secretion

Secondary Modification Na+, Cl-, H2O, HCO3-, protein, mucin Under resting condition Conc. Of Na+ = 15 mEq/l About 1/10 that of plasma Conc. Of K+ = 30 mEq/l About 7 times that of plasma HCO3-, urea, Iodide Na+ K+ Cl- Na+, Cl-, H2O, HCO3-, proteins, Urea, Iodide ,K+ 14-Nov-18 salivary secretion

Secondary Modification Na+, Cl-, H2O, HCO3-, protein, mucin Conc. Of HCO3- = 50 to 70 mEq/L About 2 to 3 times that of plasma pH 5.45 to 6.06 HCO3-, urea, Iodide Na+ K+ Cl- Na+, Cl-, H2O, HCO3-, proteins, Urea, Iodide ,K+ 14-Nov-18 salivary secretion

Secondary Modification Na+, Cl-, H2O, HCO3-, protein, mucin During maximal stimulation Increased rate of formation of primary secretion Rapid flow of fluid Little modification Electrolyte Na+, Cl- rises to about ½ to 2/3rd that of plasma K+ conc. Falls HCO3- conc. Rises PH 6.0 to 7.4 HCO3-, urea, Iodide Na+ K+ Cl- Na+, Cl-, H2O, HCO3-, proteins, Urea, Iodide ,K+ 14-Nov-18 salivary secretion

Secondary Modification Na+, Cl-, H2O, HCO3-, protein, mucin Aldosterone increase Na+ re-absorption K+ secretion HCO3-, urea, Iodide Na+ K+ Cl- Na+, Cl-, H2O, HCO3-, proteins, Urea, Iodide ,K+ 14-Nov-18 salivary secretion

14-Nov-18 salivary secretion

Control of Salivary Secretion Controlled by ANS Parasympathetic Cause gland cells to secrete large volume of watery fluid High in electrolytes Low in protein There is profound vasodilatation Due to release of VIP A co-transmitter with Ach Atropine block Ach block Ach Reduces saliva secretion 14-Nov-18 salivary secretion

Control of salivary secretion Sympathetic Causes gland cells to secrete small volume of fluid High concentration of mucus 14-Nov-18 salivary secretion

 -  IX  VII Higher centers Salivary nucleus Fear, sleep, fatigue, dehydration Thought, Sight, Smell, taste,  Appetite center Salivary nucleus IX  Parotid VII Stomach, Intestine Sublingual Submandibular 14-Nov-18 salivary secretion