Digestion, Absorption, and Metabolism," discusses how food is digested, how nutrients form foods are absorbed into the body and transported to the cells where they are broken down to provide energy or used to synthesize structural or regulatory molecules, and finally how wastes are removed. This chapter provides an overview of metabolism that serves as a launching pad for the more detailed metabolism information presented in subsequent chapters.
the smallest unit of an element that still retains the properties of that element
a substance that cannot be broken down into products with different properties
the force that holds an atom together
a group of two or more atoms of the same or different elements bonded together
the smallest unit of life the basic structural and functional unit of plant and animal life
discrete structures composed of more than one tissue that perform a specialized function.
a group of organs that work together
chemical messengers that are produced in one location, released into the blood, and elicit responses at other locations in the body.
the process of breaking food into components small enough to be absorbed into the body
the process of taking substances into the interior of the body
body waste, including unabsorbed food residue, bacteria, mucus, and dead cells which is excreted from the gastrointestinal tract by passing through the anus.
a hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus in which digestion and absorption of nutrients occurs
the time between ingestion of food and the elimination of the solid waste from that food
the layer of tissue lining the GI tract and other body cavities
a viscous material produced by glands in the GI tract and other parts of the body. It acts to lubricate, moisten, and protect cells from harsh environments
a protein molecule that accelerates the rate of a chemical reaction without itself being changed
a watery fluid produced and secreted into the mouth by the salivary glands. It contains lubricants, enzymes, and other substances.
an enzyme secreted by the salivary glands that breaks down starch
an enzyme in saliva, tears, and sweat that is capable of destroying certain types of bacteria
a funnel-shaped opening that connects the nasal passages and mouth to the respiratory passages and esophagus. It is a common passageway for food and air and is responsible for swallowing.
a piece of elastic connective tissue at the back of the throat that covers the opening of the passageway to the lungs during swallowing.
a portion of the GI tract that extends from the pharynx to the stomach
coordinated muscular contractions that move food through the GI tract
a muscular valve that helps control the flow of materials in the GI tract
a mixture of partially digested food and stomach secretions
an inactive protein digesting enzyme produced by gastric glands and activated to pepsin by acid in the stomach
a protein digesting enzyme produced by the gastric glands. It is secreted in the gastric juice in an inactive form and activated by acid in the stomach
a hormone secreted by the stomach mucosa that stimulates the secretion of gastric juice
finger-like protrusions of the lining of the small intestine that participate in the digestion and absorption of nutrients
microvilli or brush border
minute brush-like projections on the mucosal cell membrane that increase the absorptive surface area in the small intestine
a small lymph vessel in the intestine that absorbs and transports the products of fat digestion.
rhythmic local constrictions of the intestine that mix food with digestive juices and speed absorption by repeatedly moving the food mass over the intestinal wall
starch digesting enzyme produced in the pancreas and released into the small intestine
a protein-digesting enzyme
a fat-digesting enzyme
a substance made in the liver and stored in the gallbladder. It is released into the small intestine to aid in fat digestion and absorption
the movement of substances from an area of higher concentration to an area of lower concentration. No energy is required.
the passive movement of water across a semipermeable membrane in a direction that will equalize the concentration of dissolved substances on both sides.
the movement of substances across a cell membrane from an area of lower concentration to an area of lower concentration with the aid of a carrier molecule. No energy is required.
a foreign substance (always a protein) that, when introduced into the body, stimulates an immune response
a protein produced by cells of the immune system that destroys or inactivates foreign substances in the body
a substance that causes an allergic reaction
gastroesophageal reflux disease (GERD)
a chronic condition in which acidic stomach contents leak back up into esophagus, causing pain and damaging the esophagus
an open sore in the lining of the stomach, esophagus, or small intenstine
enteral or tube-feeding
a method of feeding by providing a liquid diet directly to the stomach or intestine through a tube placed down the throat or through the wall of the GI tract
total parenteral nutrition (TPN)
a technique for nourishing an individual by providing all needed nutrients directly into the circulatory system.
an inflammation of the stomach lining that causes a reduction in the stomach acid and allows bacterial overgrowth
hepatic portal circulation
the system of blood vessels that collects nutrient-laden blood from the digestive organs and delivers it to the liver.
the system of vessels, organs, and tissues that drains excess fluid from the spaces between cells, transports fat-soluble substances from the digestive tract, and contributes to immune
a small, thin-walled blood vessel where the exchange of gases and nutrients between blood and body cells occurs.
a vessel that carries blood toward the heart
a vessel that carries blood away from the heart
hepatic portal vein
the vein that transports blood from the GI tract to the liver
the membrane that surrounds the cell contents
describes a membrane or barrier that will allow some substances to pass freely but will restrict the passage of others
the liquid found within cells
cellular organs that carry out specific metabolic functions
cellular organelle that is responsible for providing energy in the form of adenosine triphoshpate (ATP) for cellular activities.
a series of chemical rections inside a living organism that results in the transformation of one molecule into another
a small organic molecule (not a protein but sometimes a vitamin) that is necessary for the proper functioning of many enzymes
the biochemical reactions by which substances are broken down into simpler molecules releasing energy
ATP (adenosine triphosphate)
the high-energy molecule used by the body to perform energy requiring activities
energy-requiring biochemical reactions in which simpler molecules are combined to form more complex substances
the reactions that break down glucose, fatty acids, and amino acids in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP
a metabolic intermediate formed during the breakdown of glucose, fatty acids, and amino acids. It is a two-carbon compound attached to a molecule of CoA
citric acid cycle
also known as the Krebs cycle or the tricarboxylic acid cycle, this the stage of cellular respiration in which two carbons from acetyl-CoA are oxidize, producing two molecules of carbon dioxide
high-energy particle carrying a negative charge that orbits the nucleus of an atom
electron transport chain
the final stage of cellular respiration in which electrons are passsed down a chain of molecules to oxygen to form water and produce ATP
refers to a compound that has lost an electron or undergone a chemical reaction with oxygen
refers to a substance that has gained an electron
the functional unit of the kidney that performs the job of filtering the blood and maintaining fluid balance
a ball of capillaries in the nephron that filters blood during urine formation