The DIGESTIVE System Digestion The breaking down of

The DIGESTIVE System

Digestion • • The breaking down of large food molecules into molecules small enough to be used by the body’s cells for growth, repair, and energy production Digestive Processes: – Ingestion – Digestion • • - Movement (Propulsion) - Absorption Mechanical Digestion Chemical Digestion – Defecation

Ingestion Taking food into the body (EATING).

Movement (Propulsion) Passage of food through the Gastrointestinal (GI) tract.

Digestion • • The breaking down of food by both mechanical and chemical means Mechanical Digestion - various movements of the alimentary canal that aid in chemical digestion. – grinding of teeth to soften food – churning of food by smooth muscles to mix with digestive enzymes (Stomach) • Chemical Digestion –a series of catabolic reactions that break down large molecules into smaller molecules.

Absorption The passage of digested food from the GI tract into the cardiovascular and lymphatic systems for distribution to body cells.

Defecation The elimination of indigestible substances from the GI tract

Gastrointestinal Tract • • A continuous tube running through the ventral body cavity extending from the mouth to the anus. Organs of the Gastrointestinal Tract – mouth - pharynx – stomach - small intestine • - esophagus - lg. intestine Accessory Organs of the G. I. . Tract – – – teeth - tongue salivary glands - liver gallbladder - pancreas

• Glands and Organs of the Digestive System

Mouth (Oral or Buccal Cavity) • • • Cheeks Lips (Labia) Hard Palate Soft Palate Tongue

Oral Cavity

Salivary Glands • • Paired accessory structures that lie outside the oral cavity. Secrete their product (saliva) into ducts that empty into the mouth.

Saliva • • • Fluid secreted by the salivary glands 99. 5% water 0. 5% solutes – chlorides - bicarbonates - sodium – potassium - phosphates - urea – uric acid - globulin -mucin – serum albumin • Salivary amylase - digestive enzyme – begins carbohydrate digestion in the mouth

Teeth • • Accessory structures of the digestive system Deciduous teeth (baby teeth) - 20 Permanent teeth - 32 Incisors (8) - 4 on top, 4 on bottom – chisel shaped - front of mouth • Canines (4) - 2 on top, 2 on bottom – sharp pointed tearing teeth • • Premolars (8) - 4 on top, 4 on bottom Molars (12) - 6 on top, 6 on bottom – broad, flat, crushing teeth

Teeth

Portions of the Tooth • • • Crown - exposed portion of the tooth above the gum line. Neck - constricted junction line in the tooth between the crown and the root. Root(s) - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae.

Tooth Structures

Composition of Teeth • Enamel - outermost covering of the crown; protects the tooth from wear and tear. – the hardest substance in the body • • • Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity. Pulp Cavity - large cavity enclosed by the dentin that is filled with pulp. Cementum - a bone-like substance which helps anchor the root.

Digestion in the Mouth • Mechanical Digestion – Chewing (Mastication) • • Tongue manipulates the food. Teeth grind up the food and mix it with saliva. The result of mechanical digestion is a soft flexible mass of food called a BOLUS. Chemical Digestion – Salivary amylase initiates the breakdown of carbohydrates. – Only chemical digestion in the mouth.

Swallowing • • Moving food from the mouth to the stomach. Voluntary Stage - bolus is moved into the oropharynx. Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus. Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach.

Swallowing

Swallowing

Esophagus • • • Muscular tube inferior to the trachea. Approximately 10 inches long. Does not participate in digestive processes. It is a transport corridor food. Food is pushed through the esophagus and into the stomach by peristaltic action.

Stomach • • J-shaped enlargement of the alimentary canal inferior to the diaphragm. Superior portion - continuation of the esophagus. Inferior portion empties into the duodenum. Position and size of the stomach varies with individuals.

Structures of the Stomach

Stomach Structures

Mechanical Digestion in the Stomach • • Several minutes after food enters, the stomach generates mixing waves that churns the food inside –MACERATION. Food mixes with gastric juices and is converted into a thin liquid called CHYME.

Absorption in the Stomach • • Does not participate in the absorption of food molecules into the blood. However, can absorb some substances through the stomach wall. – – – water weak glucose concentrations electrolytes certain drugs (aspirin) alcohol

Pancreatic Juice • Alkaline mixture of fluid and digestive enzymes Pancreatic Digestive Enzymes: – Pancreatic Amylase - CHO digestion – Pancreatic Lipase - Fat digestion

Liver • • Located just under the diaphragm on the right side of the body. Largest organ of the abdominopelvic cavity. Weighs about 1. 4 kgs (3 lbs). Nicknamed the chemical factory of the body.

Liver and Pancreas

Functions of the Liver • • Metabolism of CHO, fats, and proteins Removal of drugs and hormones Excretion of bile Synthesis of bile salts Storage of vitamins, minerals, and food molecules Phagocytosis of old, worn out RBCs and WBCs Activation of Vitamin D

The Gallbladder • • • A pear shaped sac about 7 - 10 cm long. Located on the bottom surface of the liver. Stores and concentrates bile until needed by the small intestine

Gallbladder

The Small Intestine • Duodenum - the beginning of the small intestine. Is attached to the stomach. – first 12 to 14 inches • Jejunum - the portion of the small intestine after the duodenum. – normally about 8 ft. long • Ileum - the final portion of the small intestine. – about 12 ft. long – ileocecal valve

The Small Intestine

Chemical Digestion of the Small Intestine • • • Very complex process with a series of chemical events that results in the breakdown of carbohydrates, fats, and proteins. Result of the collective effort of pancreatic juice, bile, and intestinal juice. Results in absorption - passage of digested nutrients into the blood or lymph.

Absorption in the Small Intestine • 90% of absorption takes place within the small intestine. – other 10% occurs in the stomach and large intestine

Mechanical Digestion of the Small Intestine • • Segmentation - localized contraction of muscles of the small intestine in areas containing food Peristalsis - rhythmical contraction of muscles of the small intestines that propels chyme through the intestinal tract

The Large Intestine • • • About 1. 5 m (5 ft) in length. Cecum - beginning of the large intestine Colon - large tube-like portion of large intestine – Ascending Colon – Descending Colon • • Rectum Anal Canal --->Anus - Transverse Colon - Sigmoid Colon

Large Intestine Structures

Functions of the Large Intestine • • • Completes absorption Reabsorption of water Manufacture certain vitamins Formation of feces Expulsion of feces from the body

Mechanical Digestion in the Large Intestine • Peristalsis - rhythmical contraction of the colon that moves the contents along through the length of the colon.

Chemical Digestion in the Large Intestine • • • last stage of digestion Digestion due to bacterial action in the large intestine bacteria ferment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gas also converts any remaining proteins into amino acids absorbs any remaining water and electrolytes

Feces Formation in the Intestine • • Large by the time chyme has remained in the large intestine for 3 - 10 hours it has become a solid or semi-solid and is known as FECES consists of water, inorganic salts, epithelial cells, products from bacterial decomposition, and indigestible parts of food

Defecation • • • The emptying of the rectum. Diarrhea - frequent defecation of liquid feces. Constipation - infrequent or difficult defecation. Stools are hard and dry.