Digestive System Human Anatomy & Physiology PDF

DIGESTIVE Human Anatomy & Physiology SYSTEM University of Washington PMT DIGESTIVE SYSTEM FUNCTION Acquires nutrients from environment Anabolism -Uses raw materials to synthesize essential compounds (complex molecules) from simpler one, which requires energy and re...

DIGESTIVE Human Anatomy & Physiology SYSTEM University of Washington PMT DIGESTIVE SYSTEM FUNCTION Acquires nutrients from environment Anabolism -Uses raw materials to synthesize essential compounds (complex molecules) from simpler one, which requires energy and reducing power. Catabolism -Decomposes substances to provide energy cells need to function DIGESTIVE (GI) TRACT ACTIONS OF DIGESTIVE (GI) TRACT Ingestion Occurs when Secretion  Release of water acids, material enters buffers, enzymes & salts via the mouth by epithelium of GI tract and glandular organs Mechanical Processing Absorption Crushing /  Movement of organic substrates, electrolytes, Shearing – makes vitamins & water across material easier to digestive epithelium move through the tract Excretion  Removal of waste Digestion products from body Chemical fluids breakdown of  MOVEMENT OF DIGESTIVE MATERIALS By muscular layers of digestive tract Along digestive tract: Has rhythmic cycles of activities (PERISTALSIS) Consists of waves of muscular contractions Move a bolus along the length of the tract PERISTALSIS FUNCTIONS OF ORAL CAVITY Sensory analysis  Of material before swallowing Mechanical processing  Through actions of teeth, tongue, and palatal surfaces Lubrication  Mixing with mucus and salivary gland secretions Limited digestion  Of carbohydrates and lipids  ESOPHAGUS A hollow muscular tube About 25 cm (10 in.) long and 2 cm (0.80 in.) wide Conveys solid food and liquids to the stomach  STOMACH FUNCTION Major Functions of the Stomach Storage of ingested food Mechanical breakdown of ingested food Disruption of chemical bonds in food material by acid and enzymes Production of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine  DIGESTION IN THE STOMACH Stomach performs preliminary digestion of proteins by pepsin –Some digestion of carbohydrates (by salivary amylase) –Lipids (by lingual lipase) Stomach contents –Become more fluid –pH approaches 2.0 –Pepsin activity increases –Protein disassembly begins Although digestion occurs in the stomach, nutrients are not absorbed there  SMALL INTESTINE 90% of absorption occurs in the small intestine SMALL INTESTINE The Duodenum  The segment of small intestine closest to stomach  25 cm (10 in.) long  “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver  Functions of the duodenum  To receive chyme from stomach  To neutralize acids before they can damage SMALL INTESTINE The Jejunum Is the middle segment of small intestine 2.5 meters (8.2 ft) long Is the location of most Chemical digestion Nutrient absorption SMALL INTESTINE The Ileum The final segment of small intestine 3.5 meters (11.48 ft) long Ends at the ileocecal valve, a sphincter that controls flow of material from the ileum into the large intestine SMALL INTESTINE Intestinal Secretions Intestinal  Watery intestinal Movements juice Chyme arrives in  1.8 liters per day duodenum enter intestinal lumen Weak peristaltic  Moisten chyme contractions  Assist in buffering move it slowly acids toward jejunum  Keep digestive VILLI tiny, finger-like projections that line the small intestine and help absorb nutrients and water: RUGAE Gastric rugae, also known as gastric folds, are coiled tissue sections in the stomach that allow it to expand and increase its surface area.  PANCREAS Lies posterior to stomach  From duodenum toward spleen Functions of the Pancreas 1.Endocrine cells of the pancreatic islets:  Secrete insulin and glucagon into bloodstream 2.Exocrine cells:  Secrete pancreatic juice  PANCREAS Pancreatic Enzymes  Pancreatic alpha-amylase  Breaks down starches  Similar to salivary amylase  Pancreatic lipase  Breaks down complex lipids  Releases products (e.g., fatty acids) that are easily absorbed LIVER LIVER Hepatocytes  Are liver cells  Adjust circulating levels of nutrients through selective absorption and secretion  Many Kupffer cells (resident liver macrophages and play a critical role in maintaining liver function) are located LIVER FUNCTION The Physiology of the Liver 1. Metabolic regulation 2. Hematological regulation 3. Bile production LIVER GALLBLADDER Is a pear-shaped, muscular sac Stores and concentrates bile prior to excretion into small intestine GALLBLADDER Functions of the Gallbladder Stores bile Releases bile into duodenum LARGE INTESTINE Is horseshoe shaped Extends from end of ileum to anus Lies inferior to stomach and liver Frames the small intestine Also called large bowel Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide  LARGE INTESTINE FUNCTIONS Reabsorption of water Compaction of intestinal contents into feces Absorption of important vitamins produced by bacteria Storage of fecal material prior to defecation  PARTS OF LARGE INTESTINE The Cecum  Is an expanded pouch  Receives material arriving from the ileum  Stores materials and begins compaction Appendix  Also called vermiform appendix  Is a slender, hollow appendage about 9 cm (3.6 in.) long  Is dominated by lymphoid nodules (a lymphoid organ) PARTS OF LARGE INTESTINE The Colon Has a larger diameter and thinner wall than small intestine The wall of the colon  Forms a series of pouches (haustra) Haustra permit expansion and elongation of colon PARTS OF COLON Ascending Colon Transverse Colon Descending Colon Sigmoid Colon PARTS OF COLON PARTS OF LARGE INTESTINE The Rectum  Forms last 15 cm (6 in.) of digestive tract  Is an expandable organ for temporary storage of feces  Movement of fecal material into rectum triggers urge to defecate The anal canal is the last portion of the rectum  Contains small longitudinal folds called anal columns Anus  Also called anal orifice  Is exit of the anal canal  Has keratinized epidermis like skin PHYSIOLOGY OF THE LARGE INTESTINE Absorption in the Large Intestine  Reabsorption of water  Reabsorption of bile salts  In the cecum  Transported in blood to liver  Absorption of vitamins produced by bacteria  Absorption of organic wastes PHYSIOLOGY OF THE LARGE INTESTINE Three Vitamins Produced in the Large Intestine 1. Vitamin K (fat soluble):  Required by liver for synthesizing four clotting factors, including prothrombin 2. Biotin (water soluble):  Important in glucose metabolism 3. Pantothenic acid: B5 (water soluble):  Required in manufacture of steroid hormones and some neurotransmitters PHYSIOLOGY OF THE LARGE INTESTINE Organic Wastes  Bacteria break down peptides in feces and generate: Ammonia, hydrogen sulfide  Bacteria feed on indigestible carbohydrates (complex polysaccharides)  Produce flatus, or intestinal gas, in large intestine DIGESTION Digestive system handles each nutrient differently Large organic molecules Must be digested before absorption can occur Water, electrolytes, and vitamins Can be absorbed without processing  DIGESTION Water Absorption Cells cannot actively absorb or secrete water All movement of water across lining of digestive tract Involves passive water flow down osmotic gradients