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active transport[ak´tiv trans´port]
the movement of ions or molecules across cell membranes and epithelial layers, usually against a concentration gradient, as a direct result of the expenditure of metabolic energy. For example, under normal circumstances more potassium ions are present within the cell and more sodium ions are present extracellularly. The process of maintaining these normal differences in electrolytic composition between the intracellular and extracellular fluids is active transport. The process differs from passive transport, simple diffusion, and osmosis in that it requires the expenditure of metabolic energy.
the passage of ions or molecules across a cell membrane, not by passive diffusion but by an energy-consuming process at the expense of catabolic processes proceeding within the cell; in active transport, movement takes place against an electrochemical gradient.
The movement of a chemical substance through a gradient of concentration or electrical potential in the direction opposite to normal diffusion, requiring the expenditure of energy: active transport across a cell membrane.
the movement of materials across the membranes and epithelial layers of a cell by means of chemical activity that allows the cell to admit otherwise impermeable molecules against a concentration gradient. Expediting active transport are carrier molecules within the cell that bind and enclose themselves to incoming molecules. Active transport is the means by which the cell absorbs glucose and other substances needed to sustain life and health. Certain enzymes play a role in active transport, providing a chemical "pump" that typically uses adenosine triphosphate (ATP) to help move substances through the plasma membrane. Compare osmosis, passive transport.
Active TransportThe transportation across membranes by a membrane-bound protein complex of ions, nutrients or other molecules against a concentration gradient, which requires hydrolysis of high-energy phosphate bonds—e.g., ATP.
ac·tive trans·port(ak'tiv trans'pōrt)
The passage of ions or molecules across a cell membrane, not by passive diffusion but by an energy-consuming process against an electrochemical gradient.
active transportThe movement of dissolved substances across a membrane in the direction opposite to that of normal diffusion. Active transport operates against gradients of chemical concentration, electrical charge or electrochemical state. It requires the expenditure of energy.
active transportmovement of a substance from a region of low concentration to another of higher concentration, i.e. against the CONCENTRATION GRADIENT. Such transport typically occurs in cell membranes, which are thought to contain carriers which move molecules from one side of the membrane to the other. Since these processes involve movement up a free-energy gradient, they require the expenditure of energy from the breakdown of ATP and are therefore sensitive to factors affecting metabolism (temperature, oxygen, pH, etc.). Compare DIFFUSION. See ACTIVE ABSORPTION.
A process by which particles (e.g. ions, molecules) are transported across cell membranes, against, in almost all instances, the concentration gradient. It requires energy, which is provided by the metabolism of carbohydrates, proteins or lipids and cellular energy, which is obtained from splitting adenosine triphosphate (ATP).(Example: the sodium/ potassium pump that keeps sodium ions out of a cell and potassium ions in). When this process results in a compound being released, it is termed 'secretion'. This process is one of the mechanisms by which aqueous humour is produced in the ciliary body. See action potential; ultrafiltration.
ac·tive trans·port(ak'tiv trans'pōrt)
Passage of ions or molecules across a cell membrane by an energy-consuming process at the expense of catabolic processes proceeding within the cell.
the drugs or chemicals in a pharmaceutical preparation that exert an effect pharmacologically; as distinct from the inert fillers, wetting agents and other excipients also often included.
that region of a protein, usually an enzyme, that binds to another molecule such as the substrate of the enzyme.
the movement of ions or molecules assisted by a carrier protein across the cell membranes and epithelial layers, usually against a concentration gradient, resulting directly from the expenditure of metabolic energy. For example, under normal circumstances more potassium ions are present within the cell and more sodium ions extracellularly. The process of maintaining these normal differences in electrolytic composition between the intracellular fluids is active transport. The process differs from simple diffusion or osmosis in that it requires the expenditure of metabolic energy.
1. movement of materials in biological systems, particularly into and out of cells and across epithelial layers.
see active transport.
death during transportation, e.g. porcine stress syndrome.
see paratenic host.
see transport medium.
membrane transport proteins
specific proteins associated with the plasma membrane of cells that are responsible for transferring solutes including ions, sugars, amino acids, nucleotides and many metabolites across cell membranes.
see exertional rhabdomyolysis.
stress imposed by lack of access to water and feed, physical exhaustion caused by standing for long periods, heat stress, aggression by other animals.
see transit tetany.