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  1. 1. Introduction to Gastrointestinal Physiology<br />The function of gastrointestinal (GI) system is to digest food and absorb nutrients, salts and water<br />Digestion is the process of breaking down food into components that can be absorbed<br />Absorption is the movement of nutrients, salts and water across the GI epithelium into blood or lymph<br />
  2. 2. Introduction to Gastrointestinal Physiology<br />Digestion requires the secretions of the GI system and motility, the activity of the muscle of the GI tract that mix and propel its content<br />Chemical factors and hormones some from the GI tract act on the hypothalamus, the CNS, regulate the caloric intake by stimulation or suppressing appetite<br />
  3. 3. Functions of the GI Tract<br /><ul><li>Motility:</li></ul>Movement of food through the GI tract.<br />Ingestion:<br />Taking food into the mouth.<br />Mastication:<br />Chewing the food and mixing it with saliva.<br />Deglutition:<br />Swallowing the food.<br />Peristalsis:<br />Rhythmic wave-like contractions that move food through GI tract.<br />
  4. 4. Functions of the GI Tract<br />Secretion:<br />Includes both exocrine and endocrine secretions.<br />Exocrine:<br />HCl, HC03-, bile, lipase, pepsin, amylase, and trypsin are secreted into the lumen of the GI tract.<br />Endocrine:<br />Stomach and small intestine secrete hormones to help regulate the GI system.<br />Gastrin, secretin, and somatostatin.<br />
  5. 5. Functions of the GI Tract<br />Digestion:<br />Breakdown of food particles into subunits (chemical structure change).<br />Absorption:<br />Process of the passage of digestion (chemical subunits) into the blood or lymph.<br />Storage and elimination:<br />Temporary storage and elimination of indigestible food.<br />
  6. 6. Digestive System (GI)<br />GI tract divided into:<br />Alimentary canal.<br />Accessory digestive organs.<br />GI tract is 30 ft long and extends from mouth to anus.<br />Insert fig. 18.2<br />
  7. 7. The wall of GI Tract has four layers<br />Composed of 4 parts:<br />Mucosa.<br />Submucosa.<br /><ul><li>Muscularis.
  8. 8. Serosa.</li></li></ul><li>
  9. 9. Mucosa<br />Lines the lumen of GI tract.<br />Consists of simple columnar epithelium. Forms the inner or luminal boundary<br />Lamina propria: <br />Thin layer of connective tissue carries blood and lymph vessels<br />Muscularis mucosae: <br />Thin layer of smooth muscle responsible moving the mucosal surface<br />Goblet cells:<br />Secrete mucus.<br />
  10. 10.
  11. 11. Submucosa<br />Thick, highly vascular layer of connective tissue.<br />Absorbed molecules enter the blood and lymphatic vessels.<br />Submucosal plexus <br />Provide autonomic nerve supply to the muscularis mucosae. <br />
  12. 12. Muscularis<br />Responsible for segmental contractions and peristaltic movement through the GI tract.<br />Inner circular layer of smooth muscle.<br />Outer longitudinal layer of smooth muscle.<br />Contractions of these layers move food through the tract; <br />Myenteric plexus located between the 2 muscle layers.<br />Major nerve supply to GI tract. <br />Fibers and ganglia from both sympathetic and parasympathetic nervous systems.<br />
  13. 13. Serosa<br />Binding and protective outer layer.<br />Consists of connective tissue <br />
  14. 14. Describe the features of red muscle fiber<br />Describe in steps the contraction and relaxation mechanism of smooth muscle cells<br />