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Chapter 18 Digestive System
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Objective Describe the general function of the digestive system
List the structures and the functions of the digestive system Describe the action of the enzymes on carbohydrates, fats and protein Trace food from the beginning of the digestive process to the end Describe common disorders of the digestive system Define the key words that relate to this chapter
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The Digestive System
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Digestive System Food must be converted by physical and chemical changes before it can be used by the cells; this process is called digestion Enzymes Chemical substances that promote chemical reactions in living things Alimentary canal Accessory organs
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Layers of the Digestive System
Mucosa Innermost lining Submucosa Circular muscle Longitudinal muscle
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Lining of the Digestive System
Peritoneum Two-layered membrane Parietal (lines the abdominal cavity) Visceral (covers the outside of each organ in the abdominal cavity Specialized layers Mesentery (attaches to the posterior wall of the abdominal cavity and the small intestines) Greater omentum (contains large amounts of fat and hangs over the abdominal organs like a protective apron)
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Functions of the Digestive System
Break down food physically Change food chemically Absorb the nutrients Eliminate the waste products of digestion
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Organs of Digestion Mouth (oral or buccal cavity)
Functions Receive food by ingestion Break food into small particles by mastication Mix food with saliva Tongue/accessory organ of digestion The tongue and its muscles are attached to the floor of the mouth, helping in both chewing and swallowing Salivary glands Functions of saliva Cleansing action on the teeth Moistens and lubricates food during mastication and swallowing Dissolves certain molecules so that foods can be tasted Begins the chemical digestion of starches
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Teeth/Accessory Organ of Digestion
Gingivae or gums Support and protect the teeth Teeth Food chewed or masticated Deciduous and permanent teeth Structure of the tooth Crown Neck Root Pulp cavity
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Esophagus Muscular tube to transport swallowed food to stomach
Muscles in the upper third are voluntary and lower portion is smooth muscle, or involuntary
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Stomach Divided into 3 portions Sphincters
Fundus (upper part) Body or great curvature (middle section) Pylorus (lower portion) Sphincters Cardiac sphincter Pyloric sphincter Four layers of the stomach wall
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The Stomach
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Gastric Juices Enteroendocrine glands Parietal cells Chief type cells
Secrete gastrin Parietal cells Produce HCL and intrinsic factor Chief type cells Produce pepsinogen Mucus cells Secrete alkaline mucus
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Small Intestine About 20 feet long Same four layers as the stomach
Divided into 3 sections Duodenum Jejunum Ileum Functions Finishes the process of digestion Absorbs the nutrients Passes the residue on to the large intestine
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Small Intestine
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Digestive Juices in the Small Intestine
Enzymes, secretin, and cholecystokinin Pancreatic juices Protease or trypsin Amylase or amylopsin Lipase or steapsin Bile Intestinal juices Maltase, lactase, sucrase Peptidase Steapsin
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Absorption in the Small Intestine
Villi Makes absorption possible Each villi contains a network of blood and lymph capillaries Digested portion passes through the villi into the bloodstream and lacteals Undigested portion passes on to the large intestine
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Accessory Organs of Digestion
Pancreas Functions both as an exocrine and as an endocrine Liver Functions Manufactures bile Produce and store glucose in the form of glycogen Detoxify harmful substances Manufacture blood proteins necessary for blood clotting Store vitamins A, D and B complex Converts ammonia into urea Break down hormones no longer useful Remove worn-out red blood cells from circulation and recycle the iron content Gallbladder Function is to store and concentrate bile when it is not needed by the body
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Pancreas, Liver, Gallbladder
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Large Intestine Also called the colon About 5 feet long
Ileum empties chyme through ileocecal valve into large intestine Regions of the large intestine Cecum and appendix Ascending, transverse, and descending colon Sigmoid colon Anal canal Functions Absorption of fluid and electrolytes and the elimination of waste products
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General Overview of Digestion
Mouth Bolus Pharynx Swallowing, or deglutition Esophagus Peristalsis Stomach The action of gastric juices is helped by the chuming of the stomach walls Semiliquid food is called chyme Small intestine Process of digestion is completed and absorption occurs Digestion of protein, fats and carbohydrates Absorption of nutrients Large intestine water absorption bacterial action fecal formation gas formation and defecation
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Action in the Large Intestine
Absorption Bacterial action Gas formation Fecal formation Defecation
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Effects of Aging Decrease sensory ability of taste buds
Reduction of saliva Loss of teeth Slowing peristalsis
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Metabolism Within the cells, nutrients are changed into energy
Aerobic metabolism Anaerobic metabolism Thyroid hormones
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Disorders – Digestive System
Stomatitis Gingivitis Periodontal disease Gastroesophageal reflux disease (GERD) Hiatal hernia Heartburn Pyloric stenosis Gastritis Gastroenteritis Enteritis Ulcer Inflammatory bowel disease (IBD) Appendicitis Hepatitis
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Disorders – Digestive System
Cirrhosis Cholecystitis Gallstones Pancreatitis Diverticulosis Hemorrhoids Diarrhea Constipation
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