© 2009 Delmar, Cengage Learning

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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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/AccessoryOrgan 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

– 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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Gastric Juices• Enteroendocrine glands

– 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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Digestive Juices inthe 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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Large Intestine• Also called the colon• About 5 feet long• Ileum empties chyme through ileocecal

valveinto 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

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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