salivary gastric ....

• Salivary, Gastric and Pancreatic (exocrine) Secretions


  Secretions from the salivary glands, stomach, and pancreas
• Learning Outcomes


  1. Describe the properties, composition & function of saliva<|>2. Explain the regulation of salivary secretion<|>3. Describe the properties, composition & function of gastric juice<|>4. Explain the regulation of gastric secretion<|>5. Describe the properties, composition & function of pancreatic juice<|>6. Explain the regulation of pancreatic secretion

  
• Properties, composition & function of

  • Saliva
  • Gastric juice
  • Pancreatic juice
• Saliva


  Slightly acidic pH 6.75 to 7<|>1000 to 1500ml daily
• Gastric juice


  Acidic 1.5 ≈ 3<|>2000ml daily
• Pancreatic juice


  Alkaline ≈ pH8<|>1200 to 1500ml daily
• Composition of Saliva


  • Mainly H2O-hypo-osmotic, electrolytes (Na, K, CI, PO4, HCO3-) and salivary amylase, protein mucin, lysozymes and IgA
• Composition of Gastric juice

  • Digestive enzymes pepsin and rennin, hydrochloric acid, and mucus
• Composition of Pancreatic juice

  • Mainly H2O, enzymes (pancreatic proteases) and bicarbonate
• Functions of Saliva

  • Digestive-carbohydrate in mouth via salivary amylase
  • Protective-antibacterial action via lysozyme
  • Stimulate taste bud-saliva serve as solvent for molecules
  • Facilitate swallowing via mucus
• Functions of Gastric juice

  • Digestive- proteolytic and lipolytic via pepsin
  • Hemopoietic-intrinsic factor is essential for absorption of vitamin B12
  • Protective-mucus derived from mucous cells and epithelial cell; against mechanical injury, self-digestion of stomach wall, acid injury by neutralizing HCL
• Functions of Pancreatic juice

  • Digestive- carbohydrate digestion, Lipolytic, proteolytic function
  • Activation of zymogen
  • Alkaline solution bicarbonate irons neutralized the acid in chyme
  • Brush-border Enteropeptidase
• Salivary glands


  Three major salivary glands

  
• Regulation of Salivary Secretion

  1. Autonomic influence

  2. Unconditioned reflex

  3. Conditioned reflex

  
• Autonomic influence on salivary secretion

  Parasympathetic - dominant role, produces abundant flow of watery saliva rich in enzymes<|>Sympathetic - produces much smaller volume of thick saliva secretion rich in mucus

  
• Unconditioned reflex


  1. Stimulation through presence of substance in mouth

  2. Stimulation of nerve endings in the oral cavity

  3. Efferent vagal nerve impulses

  4. More saliva is produced

  
• Conditioned reflex


  1. Stimulation through the sight, smell, hearing and/or thought of food

  2. New neuronal circuits develop between the receptors of special senses, cerebral cortex, and salivary center

  3. Efferent vagal nerve impulses

  4. More saliva is produced

  
• Phases of Gastric Secretion

  1. Cephalic Phase

  2. Gastric Phase

  3. Intestinal Phase
• Cephalic Phase


  Factors arising before the food ever reaches the stomach<|>Stimulus arises from the head region<|>Conditioned and unconditioned reflexes<|>Secretion of gastric juice starts before food enters the stomach<|>Direct vagal stimulation and gastrin release
• Gastric Phase


  Stimulation by the presence of food bolus in stomach<|>Involvement of vagal and enteric nerve

  
• Intestinal Phase


  Stimulation by the presence of chyme in the small intestine<|>Largely hormonal<|>Stimulatory effects-gastrin, inhibitory effects- secretin, GIP, cholycystokinin
• Dual function of pancreas

  • Endocrine - islets of Langerhans, hormone production (insulin and glucagon)
  • Exocrine - secretion of digestive juice (pancreatic juice)
• Pancreatic juice


  Secreted via pancreatic duct<|>Contains pancreatic enzymes: proteolytic enzymes, pancreatic amylase, pancreatic lipase<|>Aqueous alkaline solution: NaHCO3, sodium bicarbonate
• Proteolytic Function of Pancreatic Secretion

  Trypsinogen must remain inactive within the pancreas to prevent proteolytic enzymes from digesting the cells<|>Pancreatic tissue also produce trypsin inhibitor to block trypsin's actions
• Regulation of pancreatic juice secretion

  1. Cephalic Phase

  2. Gastric Phase

  3. Intestinal Phase
• Cephalic Phase


  Sight, smell, hearing, thought of food stimulate secretion via conditioned reflex

  
• Gastric Phase


  Bolus in stomach (stomach distention) stimulates secretion via unconditioned reflex
• Intestinal Phase


  Chyme in intestine stimulates secretion of hormones secretin and cholecystokinin
• Functions of important digestive hormones

  • Secretin - Stimulates pancreatic duct cells to produce NaHCO3, inhibits gastric emptying and secretion
  • Gastrin - Stimulates secretion of gastric juice
  • Gastric Inhibitory Polypeptide (GIP) - Stimulates insulin release, inhibits gastric secretion and motility
  • Cholecystokinin - Stimulates pancreatic enzyme secretion, causes gallbladder contraction, inhibits gastric motility and secretion