chapter14 - Cells Exist in Tightly Controlled Environment...

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Cells Exist in Tightly Controlled Environment in ECF Homeostasis of ECF maintains life support fluid of cells Fluids + substances must be tightly controlled We don’t have a “storage” place for H 2 O, but most other substances have some storage capacity Dietary excesses stored + deficiencies supplied by stored supply It’s a balance btwn input + output Input = Output Maintain Stable Balance in ECF “+” balance = input > output “-“ balance = input < output Input of substances into plasma is poorly controlled or not controlled (eating habits = variable) Compensatory adjustments occur on output side of urinary excretion - Salts + acids kept w/in narrow, homeostatic ranges 1 st Place Imbalance Exist is Plasma then Interstitial Area Main components of acid/base balances = 2 O Fluid + acid/base balance = intimately connected Body H 2 O is Divided into 2 Basic Compartments Majority of body water is contained in ICF inside cells (60%) 40% = ECF ECF divided into interstitial (80%) and vascular (20%) - Interstitial = bathes cells - Vascular = transport medium Body H 2 O is Distributed btwn ECF and ICF Compartments H 2 O = most abundant substance in body Amount varies in different tissues (Overall amount = constant) There are minor ECF compartments = lymph, joints, eyes, digestive tract, + digestive compartment - Not really involved in exchange of fluids Plasma + Interstitial Fluid have Similar Composition ECF + ICF have markedly different composition Barrier btwn plasma + interstitial fluid = blood vessel walls Most substances (not plasma proteins) are exchanged btwn these 2 compartments through cap walls Barrier btwn ECF + ICF = cellular plasma membrane Membrane = selectively permable Differences btwn Solutes in ICF + ECF Many cellular proteins remain in cells More Na is in ECF More K is in ICF More Cl + bicarbonate ions are in ECF More P ions are in ICF Cell membranes are freely permeable to H 2 O - H 2 O will move by osmosis ECF = Intermediary btwn Cells + External Environment All external substances must pass through EFC (plasma + interstitial fluid) before reaching cells Control vol of H 2 O + solute conc. = vital to life Fluid, Osmolarity, + BP = Controlled Plasma Regulation regulates vol of interstitial fluid Regulation of ECF vol + regulation of osmolarity = closely related Rgulation of ECF vol maintain BP Na has “H 2 O-holding” power - Less Na in ECF H 2 O loss in this compartment - Controls H 2 O vol in ECF Regulation of ECF osmolarity = important to maintain constant cell volume Fluid, Osmolarity, + BP = Inter-Related Baroreceptor reflex mechanisms control BP, along w/ temporary or automatic shifts btwn plasma + interstitial fluid (short-term regulation) Also long-term regulation mechanism for BP - Involves removing or retaining fluid + electrolytes)
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chapter14 - Cells Exist in Tightly Controlled Environment...

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