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BIOL 2P93 (93)

Overview of Renal System

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Jenny Janke

Overview of Renal System-- Guggino I. Functions of the human kidney a. Main function: maintain volume and solute concentration in extracellular fluid b. Also, excretes substances, makes glucose, NH , and 3ormones II. Control of fluid compartments a. Fluid is compartmentalized in the human body - Intracellular fluid: holds about 2/3 of body fluid - Extracellular fluid: holds about 1/3 of body fluid 1. Interstitial fluid (ISF)—between cells & outside of bloodstream, ultrafiltrate of plasma but doesn’t contain many proteins 2. Intravascular fluid (IVF)—includes plasma & RBC 3. Transcellular fluids (TCF)—special glandular secretions (tears) b. Statistics: - Body composed of ~60% water - 20-25% total cardiac output is blood sent to kidney - ~180 L are filtered thru kidney (enter bowman’s capsule) but only 1-1.5 L are excreted per day c. Water is freely exchangeable among all body compartments, but distribution is controlled: - By solute concentration, ie osmotic pressure (a colligative property) - By hydrostatic pressure—pressure created by H2O presence - Means of solute migration: 1. permeability 2. transporters 3. ion pumps (a transporter) and membrane potential d. Solute distribution - ICF & ECF have different ion distributions 1. ICF—high [K], high [protein] & [inorganic/organic phosphate] 2. ECF—high [Na], high [Cl] - ISF is different from IVF 1. ISF has very little protein 2. ISF has different [divalent cations] (b/c they normally bind to proteins rather than dissolve freely) e. Regulation of Cell Volume (ICF) - Reason: allows conduction in nerve/mm cells, all cells are permeable to H2O, prevents overfilling/drying up - Na/K pumps—pump 3Na out for every 2K into cell; key in maintaining composition of ICF & controlling cell volume - When pumps stop cells swell! - Healthy cells are capable of controlling their own internal [solutes] by taking up/letting out different ions f. Control of ECF Volume - Intake from GI tract (eating/drinking), Outflow via kidney & sweat - Epithelia—determine composition of ECF by matching in & outflow III. Homeostasis (control theory) a. Terms - Steady State—when total body H2O & electrolyte content are constant - Homeostasis—preservation of a constant internal environment - Set Point—optimal composition (condition for functioning) that is rigorously maintained & regulated by body - Sensors—evaluate magnitude of components (& change) in the internal environment - Mediators—re
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