January 07, ANIMALS Digestive System Stomach.notebook. The Stomach. (cardiac sphincter) bbbbbbbbbbbbbbbbbb

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1 (cardiac sphincter) bbbbbbbbbbbbbbbbbb 1

2 Location: thoracic cavity Physical description: a "J" shaped organ with muscular walls lined with folds it is the widest part of the digestive tract has 2 muscular valves called "sphincters" (at the top & bottom of the stomach) has a mucous lining Normal capacity: L Maximum capacity: 3 4 L Normal meal that provides a feeling of "fullness" is about 1L of food 2

3 The mass of chewed and moistened (by saliva) food that moves from the mouth into the esophagus to the stomach is called the bolus. When the bolus reaches the stomach its bathed in a liquid called gastric juice. Gastric juice is a mixture of hydrochloric acid, salts, enzymes, water and mucus that is produced by glands in the stomach to help digest food. Approximately every 20 seconds mixing waves combine the food with gastric juice to form chyme. Liquids empty from the stomach faster than solids, taking about 20 minutes. A mixed meal takes about 2 to 6 hours to be emptied. 3

4 Mechanical Digestion: Mechanical digestion in the stomach involves... Stomach Muscles (smooth muscle) churning food (mixing food with enzymes and acids) moving food (from stomach to the intestines) Sphincter muscles (valves) keep food from flowing in the wrong direction (a) Esophageal (Cardiac) Sphincter prevents stomach acids from flowing back up the esophagus (b) Pyloric Sphincter keeps food (chyme) in the stomach while acids and enzymes chemically digest it Mucus (lining) prevents the stomach from digesting itself 4

5 Chemical Digestion in the Stomach: Chemical digestion in the stomach involves gastric glands that secrete gastric juice a mixture of hydrochloric acid, salts, enzymes, water to help digest food, and mucus to protect the lining of the stomach HCl (Hydrochloric Acid) denatures (unfolds) protein into amino acids Pepsin a protease (enzyme) that breaks down protein into polypeptides which will be broken down into amino acids in the small intestine Digestive enzymes speed up the breaking down process by holding the large particle (substrate) in place and breaking bonds. The stomach does not usually break down the protein that make up its own cells because the pepsin is inactive until the hydrochloric acid is present. 5

6 The stomach lining produces chemicals used in digestion. (a) Lumen of the stomach which stores the food from a meal (b) Gastric pits from which mucus, enzymes and acid are secreted (c) Mucus secreting cells. Mucus protects the surface of the stomach from auto digestion (d) Parietal cells that produce HCl which kills microorganism that enter the digestive system (food & tracheal mucus). This also converts inactive pepsinogen to active pepsin (e) Chief cells: produces pepsinogen a protease enzyme 6

7 Interesting Facts about the Stomach: Powerful hydrochloric acid in the stomach helps break down the bolus into a liquid called chyme. HCl also kills most contaminating microorganisms. A thick mucus layer that lines the stomach walls prevents the stomach from digesting itself. When the mucus is limited, an ulcer (erosion of tissue) may form. Helicobacter story 7

8 In the 1980s, scientists began to notice the presence of curved bacteria, which later became known as H. pylori, in tissue samples taken from patients with peptic ulcers. Believing that bacteria could not survive in the harsh environment of the stomach, most researchers thought these mysterious bacteria had been carried into the stomach by contaminated food or might be another harmless species of bacteria similar to others found elsewhere in the gastrointestinal tract. In addition, they believed that peptic ulcers were mainly the result of stress or eating spicy food. However, Australian researchers Barry J. Marshall, M.D., and J. Robin Warren, M.D., were convinced that the bacteria were actually the cause of stomach ulcers. Frustrated by the lack of a good animal model of H. pylori infection and determined to prove this hypothesis, Marshall infected himself with the bacteria. He became ill, developed inflammation of the stomach, and was able to culture the bacteria from his own ulcers, thereby proving the microbe to be the cause of stomach ulcers. In 2005, Marshall and Warren were awarded the Nobel Prize in Medicine for their discovery of H. pylori and its role in peptic ulcer formation. 8