I.DIGESTION is the MECHANICAL(changes size of food) and CHEMICAL(changes chemical composition) breakdown of food. II. Processes of the digestive system:

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I. DIGESTION is the MECHANICAL(changes size of food) and CHEMICAL(changes chemical composition) breakdown of food.



II. Processes of the digestive system: Mechanical and chemical digestion, ingestion, propulsion, absorption, and defecation.

III. The digestive system is made up of the ALIMENTARY CANAL and accessory organs.

A. The alimentary canal is an 8 meter long tube made up of the mouth, pharynx, esophagus, stomach, small and large intestine, and anal canal.

B. The accessory organs are the gall bladder, salivary glands, liver, and pancreas.

IV. Structure and movements of the tube.



A. 4-layered wall: Mucous membrane (or MUCOSA), SUBMUCOSA, MUSCULAR LAYER, and SEROSA (Or serous layer).

1. Mucosa: Composition - epithelial and some connective and smooth tissue. It has enfolding and may contain glands. Function - absorption, protection and secretion.

2. Submucosa: Composition - loose connective tissue, blood vessels, lymphatic vessels, and nerves. Function - nourishes surrounding tissue and transports absorbed materials.



3. Muscular layer: Composition - Smooth muscle fibers arranged in circular and longitudinal groups. Function - movements of the tube and its contents.

4. Serosa: Composition - Epithelium, connective tissue. Function - Protection and lubrication.

B. Two types of movements: Mixing and propelling.



1. Mixing occurs when smooth muscles in small segments of the tube contract rhythmically.

2. Propulsion - peristalsis

V. Stops along the way

A. The mouth



•Performs mechanical digestion (chewing) and mixes food with saliva for chemical digestion.•Cheeks - pads of fat that help with chewing.•Lips - contain sensory receptors that judge temperature and consistency of foods.

•Tongue - covered with mucous membranes; connected to floor of mouth by lingual frenulum; muscles mix food with saliva and move food toward pharynx; covered with PAPILLAE (taste buds/provide friction); the root of the tongue is anchored to the hyoid bone





•PALATE - roof of oral cavity; hard anterior and soft posterior part; uvula moves upward during swallowing to prevent food from entering the nasal cavity; PALATINE tonsils composed of lymphatic tissue lie at the back of the mouth on either side of the tongue; PHARYNGEAL tonsils (also called ADENOIDS) are behind them and may be surgically removed.

•Teeth - hardest body structures; kind of like bone, but with extra proteins; adapted to handle different kinds of food

B. The Salivary Glands

• Secrete saliva to moisten food and begin chemical digestion

• Solvent allows food tasting

• Scattered through tongue, palate, and cheeks

• Glands have both sereous cells (secrete digestive enzymes) and mucous cells (mucous make food easier to swallow)

•Parotid, submandibular, and sublingual glands



C. Pharynx

• Constrictor muscles allow for swallowing.

• Swallowed food is called a bolus.

• Swallowing begins as a voluntary action, but becomes involuntary.

D. Esophagus

• 25 cm long collapsible muscular tube

• Lined with mucous cells

• The lower esophageal sphincter is located where the esophagus joins the stomach. It remains contracted (except during peristalsis) to prevent regurgitation.





E. Stomach

• J-shaped pouch-like organ that holds over a liter; thick folds (RUGGAE) of mucosal and submucosal tissue; mixes food with gastric juices; begins digesting proteins; limited absorption

•The PYLORIC SPHINCTER controls emptying of the stomach

•Gastric secretions - gastric glands are lined with goblet cells, parietal cells (release HCl), and chief cells (release digestive enzymes)

•Gastric absorption - the stomach absorbs some water, certain salts and lipid-soluble drugs, and alcohol.

•Mixing and emptying - Food enters the stomach causing the stomach to enlarge while the muscles hold their tone (eating too much spikes pressure and signals pain receptors); food is mixed with gastric juices to form a liquid called chyme; stomach contractions push cyme (5-15 ml at a time) through the pyloric sphincter



F. The Pancreas

• Secretes pancreatic juice full of enzymes that digest carbohydrates, fats, proteins, and nucleic acids.

• The head of the pancreas is in the first portion of the small intestine (DUODENUM)

• The pancreatic duct connects with the duodenum.

G. The Liver

• The largest internal organ located inferior to the diaphragm.

• Composed of large right lobe, smaller left lobe, and two even smaller lobes. QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

•Functional units, called HEPATIC LOBULES, are filled with blood vessels. BILE CANALS receive secretions from hepatic cells. Many canals merge to form the HEPATIC DUCT.

•Liver functions - carbohydrate metabolism and maintenance of blood sugar; oxidizing fatty acids; making lipoproteins, phospholipids, and cholesterol; converting carbs and proteins into fats; making urea; converting amino acids; storing vitamins, nutrients, and blood; destroying damaged blood cells; removing toxins from the body (alcohol, drugs, etc.); making bile

•Bile - a yellowish green liquid made of water, bile salts, bile pigments, cholesterol, and electrolytes. Bile salts are the only substances with digestive properties. It absorbs fat-soluble vitamins and cholesterol and breaks down fat globules.

H. The Gallbladder

• Pear-shaped sac located in a depression

in the liver.

• Stores bile

• Its CYSTIC DUCT joins with the joins with hepatic duct to form the COMMON BILE DUCT.

I. Small Intestine

• Fills abdominal cavity - in cadavers it is 18-20 ft long, but only 1/2 that in living people.



•Parts - DUODENUM (small attached first part), Jejunum (unattached portion), Ileum (joins with jejunum); the Jejunum and Ileum are covered by a serous membrane called the MESENTARY. It

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I.DIGESTION is the MECHANICAL(changes size of food) and CHEMICAL(changes chemical composition) breakdown of food. II. Processes of the digestive system: