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Renal Objectives - BODY FLUID COMPARTMENTS AND OSMOSIS...

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BODY FLUID COMPARTMENTS AND OSMOSIS VERSUS TONICITY 1. Name the five major body fluid compartments and give the size of each as a percentage of an individual's body weight. Total Body Water = 60% Intracellular Fluid = 40% Extracellular Fluid = 20% o Interstitial Fluid = 16% o Plasma = 4% 2. Define whole body balance. Describe what is meant by positive balance and negative balance. Whole body balance means that inputs equal outputs and TBW remains constant Positive balance means that inputs are GREATER than outputs and TBW increases Negative balance means that inputs are LESS than outputs and TBW decreases 3. Describe normal whole body water balance and understand how the body responds to disturbances of water intake. Normal whole body water balance: the outputs balance out the inputs o Inputs Metabolism 3500 mL Food 1000 mL Drink 1200 mL Total: 2550 mL o Outputs Kidneys 1500 mL Biggest contributor Insensible water loss (skin, lungs) 900 mL Sweat 50 mL GI (with feces) 100 mL Total: 2550 mL If you were starving (no food or water; don’t count metabolism because it’s negligible) o Inputs 0 mL o Outputs Kidney 500 mL OBLIGATORY water loss Only the kidney changed its output Body NOT in balance though Insensible 900 mL Sweat 50 mL GI 100 mL If you drank over 15 liters in 1 day (Primary Polydipsia) o Inputs 15 L o Outputs Kidneys 15-20 L of urine Water diuresis urine would be very dilute Kidney able to balance out the (extremely large) input!! Insensible 900 mL Sweat 50 mL GI 100 mL
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4. Name the two driving forces for water movement across cell membranes. Hydrostatic pressure gradient – water moves from high to low pressure Osmotic pressure gradient – water moves from low to high osmolarity (solute concentration) 5. Define osmolarity and osmotic pressure. Osmolarity is a function of the NUMBER OF PARTICLES in solution, NOT the molecular size or chemical identity o Higher osmolarity means LOWER fluid content o Equal to number of particles per mole times concentration Osmotic pressure is the amount of pressure that must be applied to a solution to prevent the net flow of water into it o Greater osmolarity causes greater osmotic pressure o Lower water concentration means higher osmotic pressure 6. Define isotonic, hypertonic, and hypotonic solutions using red blood cells as an example. Isotonic – RBC would have same concentration of NON-penetrating particles as a 0.9% NaCl solution o NO volume change would occur Hypertonic – the RBC would be in a solution that is more concentrated in NON-penetrating solute o Water diffuses down its concentration gradient OUT of the RBC o The cell will shrink Hypotonic – the RBC would be in a solution that is LESS concentrated in NON-penetrating particles o Water diffuses down its concentration gradient INTO the cell o The cell will lyse (burst) 7. Describe the volume and osmolarity changes in the ECF and ICF compartments when an individual ingest pure water, NaCl or saline.
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