THE HUMAN DIGESTIVE SYSTEM

1. THE HUMAN DIGESTIVE SYSTEM

4. Food passes through the digestive tube in the following order Oral cavity pharynx esophagus (mouth) (throat) (gullet) Stomach small large intestine intestine Rectum anus

5. HUMAN DIGESTIVE SYSTEM • Liver, pancreas and salivary glands lie outside of the digestive tract and they are called as accessory organs. • Food is never found within the alimentary canal itself. • These organs aid digestion by the secretion of digestive fluids.

7. THE MOUTH AND PHARYNX • Mechanical breakdown and chemical digestion occur. • Chunks of food are bitten of with the teeth and ground into pieces small enough to swallow • The tongue moves and shapes the food mass in the mouth • Saliva is secreted into the mouth by three pairs of salivary glands

9. TYPESOFSALIVA Thin, watery secretion that wets the food Thicker, mucuous secretion that acts as a lubricant and causes the food particles to stick together to form a food mass (bolus)

10. Saliva also contains a digestive enzyme called salivary amylase . (This enzyme breaks down starch, which is a polysacharide, into maltose, which is a disaccharide.) • When the food has been chewed sufficiently , it is pushed by the tongue to the back of the throat, or pharynx. This starts the automatic swallowing reflex, which forces the food into the esophagus, the tube leading to the stomach. • To prevent food and liquids from entering the larynx, it is automatically closed off during swallowing by a flap of tissue called epiglottis. • At the same time, breathing stops momentarily and passageways to the nose, ears and mouth are blocked

11. THE ESOPHAGUS • The esophagus is a tube through which food passes from pharynx to the stomach. • Beginning in the esophagus, the movement of food down the digestive tube is aided by alternate waves of relaxation and contraction in the muscular walls of the alimentary canal. This is called peristalsis.

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13. THE ESOPHAGUS • Where the esophagus opens into the stomach , there is a ring of muscle called sphincter. There are two sphincters to isolate the stomach. Cardiac sphincter is located between the esophagus and the stomach Pyloric sphincter is located between the stomach and the intestine

15. When the wave of peristalsis reaches the sphincter, it relaxes and opens, and the food (bolus) enters the stomach. • During vomitting, a wave of peristalsis passes upward -reverse peristalsis- causing the cardiac sphincter to open, and the contents of the stomach to be “thrown up”

17. THE STOMACH • The stomach is thick-walled muscular sac. • Food is stored temporarily in the stomach. • Mechanical breakdown and the partial digestion of protein occur. • Churning of the stomach causes mechanical break down and helps the mixing of the food with its secretions.

19. GLANDS OF THE STOMACH • Pyloric glands • Secretes mucus • Mucus protects the lining of the stomach from being digested • Gastric glands • Secretes gastric juice(pH 1.5 to 2.5) • GASTRIC JUICE • Pepsinogen • Inactive form of pepsin and activated by HCl • Breaks down large protein molecules into shorter chains of a.a called polypeptides. • HCl • HCl kills the bacteria that are swallowed with food • Activates pepsinogen

20. GLANDS OF THE STOMACH

21. GLANDS OF THE STOMACH

25. THE STOMACH The breakdown of starch by salivary amylase which begins in the mouth, continues for some time after the food mass reaches the stomach. Gradually however, the low pH of the acid in the stomach inactivates this enzyme and starch breakdown.

26. THE STOMACH There are three mechanisms involved in stimulating the flow of gastric juice. • The thought, sight, smell or taste of food stimulates the brain to send messages to the gastric glands, causing them to secrete moderate amounts of gastric juice

27. THE STOMACH 2. Food touching the lining of the stomach stimulates the secretion of moderate amounts gastric juice. 3. When a food mass enters the stomach, it stretches the stomach wall. The streching of the stomach wall, as well as the presence of proteins, caffeine, alcohol and certain other substances, stimulates the lining of the stomach to secrete a hormone called gastrin directly into the blood. Gastrin further stimulates the gastric glands in the stomach to secrete large amounts of gastric juice.

28. THE STOMACH • Liquids pass through the stomach in 20 minutes or less. • Solids on the other hand, must first be reduced to a thin, soupy liquid called chyme

29. THESMALLINTESTINE pyloric sphincter 6.5 meters in length chyme 2.5 cm in diameter duodenum jejenum ileum Most of the digestion takes place • FUNCTIONS OF THE SMALL INTESTINE: • Most of the chemical digestion takes place and completed in it • It is the site of absorption

31. THESMALLINTESTINE It has a number of structural features that increase the surface area for absorbtion. • It is very long • Its lining has many folds • The lining is covered with millions of finger-like projections which are called villi • The epithelial cells that make up the intestinal lining have brush borders. In the brush borders, the membranes of cells that face into the intestinal opening have tiny projections called microvilli that further increase the surface area of the cells.

36. Within each villus , there is a network of blood capillaries and in the center of it there is a lacteal. Fatty acids and glycerol are absorbed into tiny lacteals of the lymphatic system.

37. THESMALLINTESTINE • Absorption involves both diffusion and active transport. • When food is present, the small intestine is in constant motion. This peristaltic movements have four effect: • They squeeze chyme through the intestine • They mix the chyme with the digestive enzymes • They break down food particles mechanically • They speed up absorption of digestive end products by bringing the intestinal contents into contact with intestinal wall.

39. Chyme from the stomach is mixed with Pancreatic juice from pancreas Intestinal juice from glands in the wall of the intestine Bile from the liver *** Fluids in the small intestine are generally alkaline

40. PANCREAS • Pancreas is located in the abdominal cavity between stomach and duodenum. • It is both endocrine and exocrine gland. • It secretes insulin and glucagon form the Islets of Langerhans • pH of pancreatic juice is 8.5

43. PANCREATIC JUICE • When the acidic chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete two hormones CHOLECYSTOKININ SECRETIN stimulates Pancreas to secrete pancreatic juice and pancreatic enzymes pass throuh the pancreatic duct onto the ampulla of vater in the duodenum part of the small intestine

46. PANCREATIC JUICE • Enzymes • Amylase • Proteases • Lipase • Bicarbonate ions • Converts the acidic chyme into alkaline solution • Chyme is neutralised by HCO3- and turns into alkaline solution. • H+ + HCO3 - H2 CO3 Alkaline because medium of intestine is basic Acid from stomach Bicarbonate from liver and pancreas

47. ENZYMES OF PANCREATIC JUICE • Pancreatic Amylase: • Starch + water maltose + dextrin amylase 2. Proteases Trypsin Trypsinogen trypsin (inactive) (active) chymotrypsin anterokinase They continue the break down of large protein molecules into amino acids begun in the stomach Trypsin and chymotrypsin Polypeptides + water peptide + amino acids

48. ENZYMES OF PANCREATIC JUICE 3. Lipase lipase lipid fatty acids + glycerol 4 . Nucleases Nucleic acids nucleotides

49. Digestion in small intestine (pancreatic juice) cells in intestinal lining Acidic chyme to secrete hormones Secretin and cholecystokinin stimulate Pancreas to secrete Pancreatic juice Pancreatic duct given to Small intestine