Nutrition and the Digestive System Chapter 16 Nutrition and the Digestive System

Introduction Digestion: breakdown of food into smaller, usable form Ingestion Peristalsis Digestion Absorption Defecation

General Organization

General Organization (cont’d.) Gastrointestinal tract Mouth, pharynx, esophagus, stomach, small intestine, large intestine Accessory organs Teeth, tongue, salivary glands, liver, gallbladder, pancreas

General Organization (cont’d.)

Histology Tunics (from the inside out) Mucosa: mucous membrane attached to thin layer of visceral muscle Submucosa: loose connective tissue Muscularis: skeletal or smooth muscle Adventitia: serous membrane made of connective and epithelial tissue Also called visceral peritoneum

The Mouth or Oral Cavity Functions Taste Mechanical breakdown of food Chemical digestion of carbohydrates Amylase

The Mouth or Oral Cavity (cont’d.) Structure Cavity lined with mucous membrane Cavity floor formed by tongue Cavity roof formed by hard and soft palate Cavity sides formed by cheeks Cavity opening guarded by lips

The Mouth or Oral Cavity (cont’d.) Functions of tongue Food manipulation, taste, speech Structure of tongue Skeletal muscle covered with mucous membrane Lingual frenulum Papillae Taste buds

The Mouth or Oral Cavity (cont’d.)

The Salivary Glands Pairs of salivary glands Saliva Parotid, submandibular, sublingual Saliva Is 99.5% water Has amylase, which digests carbohydrates Is buffered by bicarbonates and phosphates Has mucin to lubricate food Has lysozyme to destroy bacteria Needs Fig 8-1

The Salivary Glands (cont’d.)

Teeth Structure: crown, neck, root Crown covered in enamel Dentin: bonelike substance enclosing pulp cavity Cementum: covers root Periodontal ligament: anchors tooth

Teeth (cont’d.)

The Pharynx Common passageway for food and air Divisions Nasopharynx, oropharynx, laryngopharynx Function: begins swallowing (deglutition) Forms food bolus Air passageways close

The Esophagus Function Secrete mucus Transport food Peristalsis: smooth muscle contractions push food Lower esophageal sphincter Controls passage of food into stomach

The Stomach Functions: chemical and mechanical breakdown of food Parts Cardia, fundus, body, pylorus Gastric glands: secretory cells Zymogenic, parietal, mucous

The Stomach (cont’d.)

The Pancreas Functions Divisions Acini: digestive enzymes Islets of Langerhans: insulin and glucagon Divisions Head, body, tail

The Pancreas (cont’d.)

The Liver

The Liver Functions Produces heparin, prothrombin, thrombin Phagocytosis of bacteria and old blood cells Stores excess carbohydrates, minerals, and vitamins Converts toxins into less harmful substances Produces bile salts

The Gallbladder Pear-shaped sac Located in depression on surface of liver Stores and concentrates bile until needed Enters duodenum through common bile duct

The Small Intestine Function: absorption of digested food Divisions Duodenum: 10 inches Jejunum: 8 feet Ileum: 12 feet

The Small Intestine (cont’d.) Crypts of Lieberkuhn: secrete digestive enzymes Brunner’s glands: secrete alkaline mucus Chyme: digested contents of small intestine

The Small Intestine (cont’d.) Plicae: folds in the small intestine Villi: site of nutrient absorption Each villus is covered by microvilli Microvilli increase absorption area Villus contains arteriole, venule, capillary network, and lacteal

The Small Intestine (cont’d.)

The Large Intestine Reabsorption of water Manufacture and absorption of vitamins Formation and expulsion of feces

The Large Intestine (cont’d.) Cecum: pouchlike area Colon: ascending, transverse, descending Pouches called haustrae Rectum: terminates at the anus Anus: controlled by internal and external sphincter

The Large Intestine (cont’d.)

The Large Intestine (cont’d.) Mechanical movements Haustral churning Peristalsis: 3 to 12 contractions per minute Mass peristalsis

The Formation of the Feces Feces: semisolid mass originating from chyme Contain water, inorganic salts, epithelial cells, Escherichia coli Rectal distention initiates defecation reflex

Summary Described the major activities of the digestive system Discussed the major organs that are part of the digestive system Explained the functions of the liver Discussed the absorption of nutrients in the small intestine and the formation of feces in the large intestine