بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم

2. The digestive system consists of: Alimentary canal from mouth to the anal canal . Associated glands: salivary gland, liver, pancreases. Accessory organs: tongue, teeth, muscle of mastication etc …. Digestive system By prof.Dr.sobhy el-kafafy

4. The main physiological function of GIT are: Digestion. Absorption. Secretion of digestive juice. Immune function. Endocrine function.

5. Salivary secretion • Three pairs of main salivary glands. • Parotid, submandibular and sublingual • Many small glands in the buccal mucosa.

7. Composition of saliva: • The volume: 1000 – 1500 ml/day • Colourless, viscous fluid, slightly acidic pH 6.6-7.1, it is hypotonic • 99.5% water. • 0.2% inorganic constituents. • 0.3% organic constituents.

8. Inorganic constituents: • NaCl and KCL. • Na2 H CO3: NaH2 CO3 and NaH2PO4: Na2HPO4. • Calcium salts as Ca bicarbonate and phosphate. • - Tartar. • - Salivary calculi. • Potassium thiocyanate, it has bactericidal action. • Organic constituents: • Ptyalin (α-amylase), lysozyme and lingual lipase. • Albumin, globulins and mucus,.

9. Salivary amylase: Hydrolyses cooked starch to polysaccharides. • Lysozyme: has antibacterial action. • Types of salivary gland:

10. Moistening of food. Cleaning of the mouth by: mechanical wash. antibacterial action by lysozyme. the bactericidal effect by thiocyanante. antibodies. Functions of saliva:

11. 3. facilitation of speech. 4. digestion of starch. 5. it dissolves food materials to facilitate taste sensation. 6. water balance. 7. buffering action for acids and alkalis.

12. 8. Neutralization of the excessive cold or hot food. 9. Body temperature regulation. 10. Excretion of iodides and mercury.

13. Control of salivary secretion Nervousmechanism only: 2 types of reflexes: The inborn (unconditioned) reflex. Acquired (conditioned) reflex. 1- Unconditioned reflexes: (inborn, do not depend on previous training)

14. 2-Conditioned reflex: acquired, depend on training and pervious experience (Pavlov experiment).

16. Mastication (chewing) Mastication is the mechanical processing of food, breaking it into pieces by grinding and mixing it with saliva, ready to swallow. Mastication is started voluntarily but continue as an involuntary reflex.

17. Deglutition (swallowing) Deglutition is the transfer of food from the mouth to the stomach. Start of deglutition is voluntary, but it is completed by reflex actions (involuntary)

18. Phases of deglutition: The first phase: Voluntary during which passage of the bolus of food through the anterior pillars of the fauces takes place.

19. The second phase: It is involuntary, very rapid, takes about 1-2 seconds. This phase passes by the following sequences of events: 1- The posterior pillars of the fauces shut off the mouth.

20. 2- Protective reflexes prevent the passage of food into the larynx by: Elevation of the soft palate. Elevation of the larynx and closure of its opening (glottis) by epiglottis and approximation of the vocal cords. Inhibition of respiration (reflex apnea).

21. The third phase: Passage of food along the esophagus to the stomach occurs, it is involuntary.

23. The stomach

24. The functions of the stomach are: • Storage of large quantities of food. • Mixing of food with gastric secretions. • Regulation of the rate of evacuation of chime. • The acidic gastric juice facilitates the absorption of calcium and iron.

25. Digestive function. • Release intrinsic factor for vit. B12 absorption. • Secretion of mucin, which is protective for the mucosa.

26. The gastric glands are composed of different types of cells: • The mucous neck cells, which secrete mucin. • The chief or pepticcells secret digestive enzyme (pepsin). • The parietal or oxyntic cells secret HCl, and intrinsic factor.

28. Composition of gastric secretion: About 3 liters/day, pH 1-2 approximately Constituents: water 99% Enzymes pepsin, gelatinase. Lipase Cations Na+, K+, Mg++, Ca++ Anions Cl- ,HPO-, SO4- HCl 0.4% Mucin Intrinsic factor

29. Functions of HCl: • Activation of pepsinogen. • gives the optimum pH needed for its action. • Antibacterial action. • Absorption of calcium and iron. • Hydrolysis of some food. • Stimulate the release of secretin H.

30. Function of the enzymes: Pepsin: - optimum pH = 2.0 pepsin converts proteins into acid metaproteins, proteoses, and peptones. - pepsionogen is activated by HCl to pepsin, any minute amounts of pepsin formed can activate the rest of pepsinogen to pepsin.

31. Gastric lipase: It is a lipolytic enzyme. (weak). Mucin: Protection for the stomach wall,lubrication of food transport and neutralization of HCl. Intrensic factor: It is a glycoprotein necessary for absorption of (Vit. B12).

32. Regulation of gastric secretion Gastric secretion is regulated by both nervous and hormonal mechanisms. Nervous mechanism: • Conditioned reflexes: Stimulus: is seeing, hearing, smelling, .… (primary center is the cerebral cortex) • Unconditioned reflexes: Stimulus: is presence of food in the mouth.

33. Hormonal control: gastricand intestinalphase. a. gastric: (gastrin H) GastrinH:Stimulus for its release from the pylorus is: • distension of the stomach by food. • secretagogues: vegetables extracts, peptones, and alcohol.

34. b. Intestinal phase: Intestinal gastrinH: Secreted from duodenum in response to: • distension of the intestine. • chemical stimuli. Gastrin H. increases gastric secretion and motility.

35. Regulation of stomach emptying: 1- Gastric factors: • Volume of the gastric contents. • Gastrin hormone. 2- Duodenal factors: • Enterogastric reflex. • Hormonal factors: -Cholecystokinin H.-Secretin H.

36. Vomiting Definition: It is outward expulsion of the gastric contents through the oral cavity. Mechanisms of vomiting: steps: • Contraction of the diaphragm, anterior abdominal wall muscles and the pelvic floor, this leads to rise of the intra-abdominal pressure.

37. Relaxation of body and funds of the stomach and esophageal sphincters. • Contraction of the pyloric portion of the stomach. • The protective reflexes that prevent passage of vomitus in respiratory passage.

38. Causes of vomiting: The causes of vomiting can be grouped into: 1- Central causes: • Direct stimulation of the vomiting centre as: increased intracreanial pressure. • Indirect stimulation of vomiting centre by certain substances circulating in the blood as: - exogenous drugs: tartar emetic, emetine, morphine,… - endogenous toxins: blood urea,….

39. 2- Peripheral causes: by afferent impulses from: - G.I.T. tract: from the pharynx to the colon. - Affection of other abdominal organs: kidneys,… - Extrabdominal organs: cardiac, vestibular apparatus,…. 3- Psychogenic vomiting: Without any organic diseases or by conditioned reflexes

40. Pancreatic secretion • The exocrine pancreatic secretion is considered as the most important source for the digestive enzymes. • Digesting the three major types of food. • It is the most alkaline juice in the human body pH is 8.3 (bicarbonate)

41. Anatomy of the pancreas

43. Composition of pancreatic secretion • 1200ml/day pH is 8.3. the main enzymes are: 1- Proteolytic enzymes: ProenzymeActive enzyme Enterokinase - Trypsinogentrypsin trypsin • Chymotrypsinogenchymotrypsin trypsin - Procarboxypolypeptidascarboxypolypeptidase.

44. 2- Pancreatic amylase: hydrolyses of uncooked and cooked starches, glycogen and carbohydrates to form disaccharides. Chloride ions serve as a coenzyme. 3-Lipolytic enzymes: pancreatic lipaseis the main enzyme for digestion of fat (neutral fat into glycerol and fatty acid), and cholesterol esterasefor hydrolysis of cholesterol esters.

45. Other constituents of pancreatic juice: -Water - Cations as Na+, K+, Ca+, Mg+. -Anions as HCO-3, CL-, SO-4, HPO-4 . -Albumin and globulin.

46. Regulation of pancreatic secretion: Both nervous and hormonal mechanisms hormonal regulation is the more important 1- Nervous regulation: - by both conditioned and unconditioned reflexes, - nervous type of secretion is rich in enzymes but deficient in alkali and water.

47. 2- Hormonal regulation: A. Secretin H: • presences of acidchime in the duodenum, release and activate secretin H. • copious pancreatic secretion very alkaline poor in enzymes. Importance of secretin H: • secretin H. stimulates alkaline pancreatic secretion for neutralization of Hcl. • bicarbonate secretion provide the suitable pH for the enzyme.

48. Extrapancreatic action of secretin H. • stimulation of bile secretion form the livers (choleretic). • increase the intestinal movements. • inhibit gastric motility and secretion.

49. B. Cholecystokinin H: (C.C.K.) - released from the mucosa of the upper small intestine. - stimulus is digestive products of protein and fats. - Cholecystokinin pancreatic secretion rich in enzymes and poor in bicarbonates.

50. Extra pancreatic action of C.C.K. - Evacuation of gall bladder. (cholagouge) - Increase intestinal movements. - Inhibit gastric motility and secretion