Human_Physiology_Notes - Chapter 5 Membrane Dynamics Law of...

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Chapter 5 “Membrane Dynamics” Law of Mass Balance: if the amount of a substance in the body is to remain constant, any gain must be offset by an equal loss Total amount (or load) of substance X in the body = intake + production – excretion –metabolism Materials either enter the body by various routes or are produced through metabolism Materials leave the body either by excretion or by metabolism Excretion: the elimination of material from the body, and it usually takes place through the urine, feces, lungs, or skin Metabolite: the general term for any product created in a metabolic pathway Clearance: the rate at which a molecule disappears from the body by excretion, metabolism, or both The kidney clears solutes from the body The liver is involved in clearing materials, especially xenobiotics Lungs clear lipid soluble material from the blood when these substances pass into the airways and are expelled during breathing Mass Flow: the rate of intake, production, or output of X Mass flow (amount of X/ min) = concentration (amount X/ vol) * volume flow (vol/ min) Osmotic Equilibrium: when the total amount of solute per volume fluid is equal on the two sides of a cell membrane Chemical Disequilibrium: when the major solutes are more concentrated in one of the two body compartments than in the other Sodium, chloride, calcium, and bicarbonate (HCO 3 - ) ions are more concentrated in extracellular fluid than in intracellular fluid, whereas potassium ions are more concentrated inside the cell The body as a whole is electrically neutral The intracellular and extracellular compartments are in: o Osmotic equilibrium o Chemical disequilibrium o Electrical disequilibrium Selectively Permeable: the lipid and protein composition of a given cell membrane determines which molecules will enter the cell and which will leave Permeable: if a membrane allows a substance to pass through it, the membrane is permeable to that substance Impermeable: if a membrane does not allow a substance to pass, the membrane is said to be impermeable to that substance Some molecules such as water, oxygen, carbon dioxide and lipids move easily across most cell membranes while ions, most polar molecules and very large molecules have difficulty entering the cell Passive Transport: does not require the input of energy; uses kinetic energy which is possessed by all molecules Active Transport: requires the input of energy from some outside source, such as ATP Diffusion: the movement of molecules from an area of higher concentration of molecule to an area of lower concentration of the molecules. Diffusion has the following 7 properties: 1. Diffusion is a passive process.
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Human_Physiology_Notes - Chapter 5 Membrane Dynamics Law of...

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