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The Digestive System

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The Digestive System The Digestive System Packet #8 1 Tuesday, October 25, 2016 Introduction Digestion begins in the mouth and ends at the intestine However, excretion occurs through the anus As food travels, different enzymes, secreted from different organs assist in the process of breaking down food. 2 Tuesday, October 25, 2016 A Look at the Major Organs and Enzymes of the Digestive System 3 Tuesday, October 25, 2016 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 Salivary Glands Salivary Glands Three pairs secrete into oral cavity Each pair has distinctive cellular organization And produces saliva with different properties Salivary Glands Produce 1.0–1.5 liters of saliva each day Saliva Saliva 99.4% water 0.6% includes Electrolytes (Na+, Cl-, and HCO3-) Buffers Glycoproteins (mucins) Antibodies Enzymes Waste products The Mouth The mouth is the opening through which food is taken in AND is the opening where teeth, salivary glands and the tongue are found. 7 Tuesday, October 25, 2016 The Mouth II • Teeth is involved in chewing. • Mastication • The tongue helps shape the food into a ball called the bolus. • Amylase, starts digestion and breaks down the polysaccharide amylose 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 Peristalsis Begins posterior to cricoid cartilage Is innervated by fibers from the esophageal plexus Swallowing Swallowing Also called deglutition Can be initiated voluntarily Proceeds automatically Is divided into three phases Buccal phase Pharyngeal phase Esophageal phase The Stomach The stomach is an enlarged, saclike structure that lies in the abdomen cavity. 11 Tuesday, October 25, 2016 Stomach Anatomy The Stomach Functions Digestion of food Secretion of gastric juice HCl Hydrochloric acid Digestion Pepsin Pepsin Rennin Secretion of Gastric Mucin Juice Rennin Secretion of gastric hormones and Functions of Secretion of Gastric intrinsic factors Stomach Hormones Intrinsic factor required for absorption Mucin of Vitamin B in small intestine. Regulation of Rate of 12 Movement of Food Regulation of the rate at which partially digested food is delivered to the small Absorption of Water and Dissolved intestine. Substances Absorption of small quantities of water and dissolved substances 13 Tuesday, October 25, 2016 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 Small Intestine I As acidic chyme is expelled from the stomach, it enters into the small intestine. 90% of absorption occurs within the small intestine. 17 Tuesday, October 25, 2016 Small Intestine II Small Intestine III Parts of Small Intestine Du·o·de·num [doo-uh-dee- nuhm] 10 inches long Receives thick partially digested food and acid from stomach. Acid is neutralized Bile received from gall bladder Digestive enzymes received from pancreas. 19 Tuesday, October 25, 2016 Small Intestine IV Parts of Small Intestine Je·ju·num [ji-joo-nuhm] 8.2 feet long Some digestion and absorption occurs here 20 Tuesday, October 25, 2016 Small Intestine V Parts of Small Intestine Il·e·um [il-ee-uhm] 11.48 feet long Final segment Absorption of vitamin B12 and re-absorption of bile salts. Ends at ileocecal valve Sphincter that controls flow from ileum to large intestine. 21 Tuesday, October 25, 2016 Small Intestine VI Intestinal Secretions Intestinal Movements Watery intestinal juice Chyme arrives in duodenum 1.8 liters per day enter intestinal Weak peristaltic contractions lumen move it slowly toward jejunum Moisten chyme Myenteric reflexes Assist in buffering acids Not under CNS control Keep digestive enzymes and Parasympathetic stimulation products of digestion in solution accelerates local peristalsis and segmentation The Large Intestine The Large Intestine Functions of the large intestine include: Absorption of water and certain electrolytes Bile salts reabsorbed in cecum and transported in blood to liver. Synthesis of certain vitamins by intestinal bacteria Vitamin K and certain B vitamins Compaction of intestinal contents into fecal matter. Temporary storage of waste (fecal matter) Elimination of waste from the body (defecation) 24 Tuesday, October 25, 2016 The Large Intestine II Role of Bacteria I Bacteria convert bilirubin to urobilinogens and stercobilinogens. Other bacterial cells break down peptides in fecal matter. Generates Ammonia Indole and skatole Hydrogen sulfide The Large Intestine III Role of Bacteria II Bacteria feed on indigestible carbohydrates Complex polysaccharides Produces flatus (intestinal gas) The Large Intestine The large intestine has three major areas. Colon Colon Rectum Large Rectum Anus Intestine Anus The Colon I The colon has five main parts Cecum Ce·cum Stores materials and begins Ascending compaction Colon Has the appendix attached A lymphoid organ Transverse Colon Ascending Colon Colon Ascends along the right lateral and posterior wall of the Descending peritoneal cavity, to the inferior Colon surface of the liver and bends right at the right colic flexure. Sigmoid Colon 28 Tuesday, October 25, 2016 The Colon II The colon has five main parts Cecum Transverse colon Crosses abdomen from right Ascending to left Colon Descending Colon Transverse Colon Proceeds inferiorly along the Colon left side Located in the Descending retroperitoneal cavity and is Colon firmly attached to the Sigmoid abdomen wall. Colon 29 Tuesday, October 25, 2016 The Colon III The colon has five main Cecum parts Ascending Sigmoid colon Colon S shaped segment Transverse Colon 6 inches long Colon Lies posterior to the urinary Descending bladder. Colon Empties into the rectum. Sigmoid Colon 30 Tuesday, October 25, 2016 The Rectum 6 inches long Expandable for temporary storage of feces. Movement of fecal matter into the rectum triggers the urge to defecate. Contains the anal canal Last portion of the rectum Contains small longitudinal folds called anal columns. The Anus Also called the anal orifice The exit of the anal canal Has keratinized epidermis like skin. Movements of the Large Intestine Gastroileal & gastroenteric Movements from transverse reflexes colon through rest of large Move materials into cecum while you eat intestine results from powerful Movement from cecum to peristaltic contractions (mass transverse colon is very slow, movements) allowing hours for water absorption Distension of the rectal wall Peristaltic waves move material triggers defecation reflex along length of colon Two positive feedback loops Segmentation movements Both loops triggered by stretch (haustral churning) mix contents receptors in rectum of adjacent haustra Accessory Organs of the Digestive System 34 Tuesday, October 25, 2016 Liver Liver I Largest gland in the body that is located in the right upper abdominal cavity Composed of hepatocytes. Involved in synthesis, storage, detoxification, excretion and metabolism Blood, leaving the absorptive surfaces of the digestive tract, enters the hepatic portal system and flows into the liver. Liver extracts nutrients and toxins Liver removes and stores excess 36 Tuesday, October 25, 2016 nutrients. Liver II Synthesis Bile salts Plasma proteins Storage Glucose (glycogen) Fat-soluble vitamins A, D, E, K Vitamin B12 Liver III Detoxification Changes toxic substances into substances that can be more easily eliminated from the body—generally through the kidneys Excretion Bilirubin Cholesterol Drugs Liver IV Metabolism Carbohydrates Proteins The liver can make a number of amino acids Fats Fatty acids can be broken down to synthesize cholesterol and phospholipids Liver V Phagocytosis Kupffer cells can phagocytose bacteria and other substances. Accessory Organ II Gall Bladder Gall Bladder Pear-shaped sac attached to the underside of the liver. Posterior surface of the liver’s right lobe. Bile, produced in the liver, is stored in the gall bladder Bile, once concentrated, is released, upon stimulation of the hormone CCK {cholecystokinin}, into the small intestine {duodenum}. 42 Tuesday, October 25, 2016 Accessory Organ III Pancreas Pancreas Accessory organ located just posterior to the stomach. Lies from the duodenum toward spleen. Bound to the wall of the abdominal cavity. 44 Tuesday, October 25, 2016 Pancreas II Endocrine cells of the pancreatic islets: Secrete insulin and glucagon into bloodstream Exocrine cells: Acinar cells and epithelial cells of duct system Secrete pancreatic juice Digestive enzymes that are used in the duodenum during digestion. 45 Tuesday, October 25, 2016 Enzymes of the Digestive System 46 Tuesday, October 25, 2016 Overview I Enzymes of the Digestive System 48 Tuesday, October 25, 2016 Diseases of the Digestive System 49 Tuesday, October 25, 2016 Diseases of Digestive System Chart 50 Tuesday, October 25, 2016 Review 51 Tuesday, October 25, 2016.
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