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The DIGESTIVE System

The DIGESTIVE System. Digestion. The breaking down of large food molecules into molecules small enough to be used by the body’s cells for growth, repair, and energy production Digestive Processes: Ingestion - Movement (Propulsion) Digestion - Absorption Mechanical Digestion

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The DIGESTIVE System

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  1. The DIGESTIVE System

  2. Digestion • The breaking down of large food molecules into molecules small enough to be used by the body’s cells for growth, repair, and energy production • Digestive Processes: • Ingestion - Movement (Propulsion) • Digestion - Absorption • Mechanical Digestion • Chemical Digestion • Defecation

  3. Ingestion Taking food into the body (EATING).

  4. Movement (Propulsion) Passage of food through the alimentary canal.

  5. Digestion • The breaking down of food by both mechanical and chemical means • Mechanical Digestion - various movements of the alimentary canal that aid in chemical digestion. • grinding of teeth to soften food • churning of food by smooth muscles to mix with digestive enzymes • Chemical Digestion –a series of catabolic reactions that break down large molecules into smaller molecules.

  6. Absorption The passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for distribution to body cells.

  7. Defecation The elimination of indigestible substances from the alimentary canal.

  8. Gastrointestinal Tract (Alimentary Canal) • A continuous tube running through the ventral body cavity extending from the mouth to the anus. • Organs of the Gastrointestinal Tract • mouth - pharynx - esophagus • stomach - small intestine - lg. intestine • Accessory Organs of the G.I.. Tract • teeth - tongue • salivary glands - liver • gallbladder - pancreas

  9. Glands and Organs of the Digestive System

  10. Mouth(Oral or Buccal Cavity) • Cheeks • Lips (Labia) • Vestibule • Hard Palate • Soft Palate • Uvula • Tongue • Papillae • Lingual Frenulum

  11. Oral Cavity

  12. Salivary Glands • Paired accessory structures that lie outside the oral cavity. • Secrete their product (saliva) into ducts that empty into the mouth. • Parotid Glands – underneath the ears • Parotid (Stensen’s) ducts • Submandibular Glands - under the mandible • Submandibular (Wharton’s) ducts • Sublingual Glands - under the tongue • Lesser Sublingual (Rivinus’s) ducts

  13. Salivary Glands

  14. Saliva • Fluid secreted by the salivary glands • 99.5% water • 0.5% solutes • chlorides - bicarbonates - sodium • potassium - phosphates - urea • uric acid - globulin -mucin • serum albumin • Salivary amylase - digestive enzyme • begins carbohydrate digestion in the mouth • Lysozyme - destroys bacteria in the mouth

  15. Teeth • Accessory structures of the digestive system • Deciduous teeth (baby teeth) - 20 • Permanent teeth - 32 • Incisors (8) - 4 on top, 4 on bottom • chisel shaped - front of mouth • Canines (4) - 2 on top, 2 on bottom • sharp pointed tearing teeth • Premolars (8) - 4 on top, 4 on bottom • Molars (12) - 6 on top, 6 on bottom • broad, flat, crushing teeth

  16. Teeth

  17. Portions of the Tooth • Crown - exposed portion of the tooth above the gum line. • Neck - constricted junction line in the tooth between the crown and the root. • Root(s) - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae.

  18. Tooth Structures

  19. Composition of Teeth • Enamel - outermost covering of the crown; protects the tooth from wear and tear. • the hardest substance in the body • Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity. • Pulp Cavity - large cavity enclosed by the dentin that is filled with pulp. • Cementum - a bone-like substance which helps anchor the root.

  20. Periodontal Ligament • Dense fibrous connective tissue attached to the socket walls and the cemental surface of the roots of the teeth. • Anchors teeth in position. • Serves as a shock absorber when chewing.

  21. Digestion in the Mouth • Mechanical Digestion • Chewing (Mastication) • Tongue manipulates the food. • Teeth grind up the food and mix it with saliva. • The result of mechanical digestion is a soft flexible mass of food called a BOLUS. • Chemical Digestion • Salivary amylase initiates the breakdown of carbohydrates. • Only chemical digestion in the mouth.

  22. Swallowing (Deglutition) • Moving food from the mouth to the stomach. • Voluntary Stage - bolus is moved through the FAUCES into the oropharynx. • Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus. • Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach.

  23. Swallowing

  24. Deglutition

  25. Esophagus • Muscular tube inferior to the trachea. • Approximately 10 inches long. • Does not participate in digestive processes. • It is a transport corridor for food. • Food is pushed through the esophagus and into the stomach by peristaltic action. • esophageal hiatus - opening in the diaphragm for the esophagus

  26. Lining of the Esophagus

  27. Stomach • J-shaped enlargement of the alimentary canal inferior to the diaphragm. • Superior portion - continuation of the esophagus. • Inferior portion empties into the duodenum. • Position and size of the stomach varies with individuals.

  28. Anatomy of the Stomach • Cardia (cardiac region, cardiac sphincter) - area of the stomach that surrounds the lower esophageal sphincter. • Fundus - rounded, superior portion of the stomach to the left of the cardia. • Body - large central portion of the stomach • Lesser Curvature - Greater Curvature • Pylorus - narrow, inferior region of the stomach. • pyloric sphincter - opening from the stomach to the duodenum

  29. Structures of the Stomach

  30. Stomach Structures

  31. Histology of the Stomach • Composed of the same four tissue layers as the rest of the alimentary canal. • When the stomach is empty, the mucosa lie in large folds called RUGAE. • Mucosa contains millions of tiny openings called gastric pits that open into gastric glands of the lamina propria layer. • secretes digestive enzymes and a fluid called gastric juice (2-3 liter per day).

  32. Histology of the Stomach

  33. Secretory Cells of the Gastric Glands • Zymogenic (Chief) Cells • Digestive enzymes • Pepsinogen (activated by HCl) • Pepsin – enzyme which digests proteins. • Parietal Cells • HCl • Intrinsic Factor (absorption of Vitamin B12) • Goblet Cells • Secrete mucus to protect the stomach mucosa from the acidic environment.

  34. Gastric Gland

  35. GastricGland

  36. Mechanical Digestion in the Stomach • Several minutes after food enters, the stomach generates mixing waves that churns the food inside –MACERATION. • Food mixes with gastric juices and is converted into a thin liquid called CHYME.

  37. Chemical Digestion in the Stomach • Cephalic Phase - reflexes initiated by sensory receptors in the head. • sight - smell - taste • thought of food • Gastric Phase - sensory receptors in the G.I. tract and stomach initiate nervous and hormonal chemical digestive processes. • Intestinal Phase – Movement of chyme into the duodenum to complete digestion.

  38. Absorption in the Stomach • Does not participate in the absorption of food molecules into the blood. • However, can absorb some substances through the stomach wall. • water • weak glucose concentrations • electrolytes • certain drugs (aspirin) • alcohol

  39. Pancreas • Oblong gland that lies posterior to the greater curvature of the stomach. • Connected by ducts to the duodenum. • Composed of clusters of glandular epithelial cells. • Two main types of Pancreatic Cells: • Pancreatic Islets-Islets of Langerhans (1%) • Hormones: insulin, glucagon, somatostatin • Acini Cells (99%) • Digestive pancreatic enzymes

  40. Pancreas

  41. Pancreatic Juice • Alkaline mixture of fluid and digestive enzymes from the acini cells. • Pancreatic Digestive Enzymes: • Pancreatic Amylase - CHO digestion • Pancreatic Lipase - Fat digestion • Chymotrypsin-Trypsin-Carboxypeptidase - Protein digestion • Nucleases - Nucleic Acid digestion • Regulated by the intestinal hormones: Secretin and Cholecystokinin.

  42. Liver • Located just under the diaphragm on the right side of the body. • Largest organ of the abdominopelvic cavity. • Weighs about 1.4 kgs (3 lbs). • Nicknamed the chemical factory of the body. • Completely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum.

  43. Anatomy of the Liver • Right Lobe - largest lobe of the liver. • Located on the lateral-right side of the body • Caudate Lobe - posterior portion of right lobe • Quadrate Lobe - inferior portion of right lobe • Left Lobe - smaller, medial lobe of the liver. • Falciform Ligament - separates the right and left lobes of the liver and anchors it to the diaphragm and anterior abdominal wall.

  44. Liver and Pancreas

  45. Lobules of the Liver • Smaller functional units of the liver. • Hepatocytes in the lobules produce and secrete a yellowish, brownish, or olive green liquid called BILE (1 quart daily). • Composed of bile salts and pigments, lecithin, and several ions. • pH of 7.6 - 8.6. • Excretory product and digestive secretion. • Assists in the breakdown of fat molecules (Emulsification). • Principle bile pigment is bilirubin.

  46. Functions of the Liver • Metabolism of CHO, fats, and proteins • Removal of drugs and hormones • Excretion of bile • Synthesis of bile salts • Storage of vitamins, minerals, and food molecules • Phagocytosis of old, worn out RBCs and WBCs • Activation of Vitamin D

  47. The Gallbladder • A pear shaped sac about 7 - 10 cm long. • Located on the bottom surface of the liver. • Stores and concentrates bile until needed by the small intestine for the emulsification of fat.

  48. Gallbladder

  49. Bile Pathway

  50. The Small Intestine • Duodenum - the beginning of the small intestine. Is attached to the stomach. • first 12 to 14 inches • Jejunum - the portion of the small intestine after the duodenum. • normally about 8 ft. long • Ileum - the final portion of the small intestine. • about 12 ft. long • ileocecal valve

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