Ch 5 Membrane dynamics

Ch 5 Membrane dynamics - Chapter 5 Membrane Dynamics MASS...

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Chapter 5: Membrane Dynamics MASS BALANCE AND HOMEOSTASIS The body is an open system that exchanges heat and minerals with the outside environment - To maintain a state of homeostasis, the body utilizes the principle of mass balance o Which says that if the amount of a substance in the body is to remain constant, any gain must be offset by an equal loss i.e., to maintain constant body concentration, water gain must be offset by water loss other substances whose concentrations are maintained through mass balance include oxygen and carbon dioxide, salts, and hydrogen ions (pH) - law of mass balance: o total amount of substance x in the body = intake + production - excretion – metabolism - to maintain mass balance the body must take part in: o excretion the elimination of material from the body, usually takes place through the urine, feces, lungs, or skin i.e., CO 2 produced during metabolism is excreted by the lungs, many xenobiotics ( xenos, a foreigner) that enter the body, such as drugs or artificial food additives, are excreted by the liver and kidneys o Metabolism A second option to maintain mass balance i.e., nutrients that enter the body become the starting substrates in metabolic pathways converts the original nutrient to a different substance but in doing so creates a new mass balance disturbance by adding more metabolite to the body EXCRETION CLEARS SUBSTANCES FROM THE BODY Clearance - the rate at which a molecule disappears from the body by excretion, metabolism, or both - hepatocytes, metabolize many different types of molecules, including hormones and drugs
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Chapter 5: Membrane Dynamics o the resulting metabolites may be secreted into the intestine for excretion in the feces or released into the blood for excretion by the kidneys - saliva, sweat, breast milk, and hair also contain solutes that have been cleared from the body - salivary secretion of the hormone called cortisol provides a simple noninvasive source of hormone for monitoring chronic stress - drug and alcohol excreted into breast milk are important because a breast-feeding infant will ingest these substances - hair analysis can be used to test for arsenic in the body - the lungs clear volatile lipid-soluble materials from the blood when these substances pass into the airways and are expelled during breathing o i.e., garlic breath, and ethanol are cleared by the lungs HOMEOSTASIS DOES NOT MEAN EQUILIBRIUM Homeostasis - is the stability of the body’s internal environment, or in other words, the stability of the extracellular fluid o the reason for this is that we are able to monitor the composition of the extracellular fluid by withdrawing blood and analyzing its fluid matrix, the plasma o also, cells maintain cellular homeostasis - the composition of both body compartments is relative stable o individual solutes in the two compartments are not in equilibrium Osmotic equilibrium - water is essentially the only molecule that moves freely between cells and the ECF
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This note was uploaded on 04/07/2008 for the course BIOL 425 taught by Professor Tondi during the Spring '08 term at George Mason.

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Ch 5 Membrane dynamics - Chapter 5 Membrane Dynamics MASS...

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