Chapter 24: The Digestive System
• Functions of the Digestive System
o Ingesting: taking food into mouth
o Secretion: release of water, acid,
... [Show More] buffers, and enzymes into lumen of GI tract.
o Mixing and propulsion: churning and movement of food through GI tract.
o Digestion: mechanical and chemical breakdown of food
o Absorption: passage of digestion products from GI tract into blood and lymph
o Defecation: elimination of feces from GI tract.
• Overview of the Digestive System
o Digestive System: consist of a group of organs that break down the food we eat into smaller molecules that can be use by body cells.
o Gastrointestinal (GI) tract organs (alimentary canal): it is a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities.
▪ Organs include: mouth, most of pharynx, esophagus, stomach, small intestine, large intestine, rectum
o Accessory digestive organs: includes teeth, tongue, salivary glands, liver, gallbladder, and pancreas
o GI tract organs breaks down the food and help in digestion and accessory digestive organs provides enzymes and hormones as well as buffers and ions that line the tract break down the food chemically.
• Digestive Processes- 6 basic processes
o Ingestion: involves taking foods and liquids into the mouth (eating)
o Secretion: everyday the cells within the walls of the GI tract and accessory digestive organs secrete total of about 7 liters of water, acid, buffers, and enzymes into the lumen of the tract. In this process saliva moisten dry food and contain salivary amylase which is a digestive enzyme that begins the digestion of carbohydrates.
o Mobility (mixing and propulsion): alternating contractions and relaxations of smooth muscle in the walls of GI tract mix food and secretions and move them towards the anus. This capability of the GI tract to mix and move material along its length is called mobility.
o Digestion: which is the process of breaking down ingested food into small molecules that can be used by body cells. mechanical digestion: the physical breakdown of large pieces of food into smaller pieces. The teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food to further assist the process, as a result, food molecules become dissolved and thoroughly mixed with digestive enzymes. Chemical digestion: begins in the moth with salivary amylase in saliva splitting complex carbohydrates into simple form. During the process the large carbohydrate, lipid, protein, and nucleic acid molecules in food split into smaller molecules by hydrolysis. Digestive enzymes produced by the salivary gland, tongue, stomach, pancreas, and small intestine catalyze these catabolic reactions.
o Absorption: the movement of the products of digestion from the lumen of the GI tract into blood or lymph. Once absorbed, these substances circulate the cells throughout the body. A few substances in food can be absorbed without undergoing digestion. These include vitamins, ions, cholesterol, and water.
o Defecation: removes indigestible substance from the body so that they do not accumulate inside the gut. The eliminated material is called feces or stool. The timing of defecation is controlled voluntarily by the conscious part of the brain but must be accomplished on a regular basis to prevent a backup if indigestible materials.
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