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