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1 Body Fluids Homeostasis of Body Fluids Maintained by: Osmoreceptors: specialized neurons in the hypothalamus that monitor the osmotic pressure of the blood, i.e. detect any changes in blood solute concentration (mainly Na + conc.) • Kidneys (Renin-Angiotensin-Aldosterone System (RAAS)) • Hormones (aldosterone) • pH regulators (electrolytes, buffers) Body Fluid Compartments • Constant fluid interchange between the 2 compartments High in K + , PO 4 -3 ++ High in Na + , Cl - Water Balance • Water intake = Water output • Fluids are transferred across semi-permeable membranes by diffusion or osmosis osmosis is the primary method of water movement • Conc. of solutes (mainly Na+) determines the direction of water, i.e. “where sodium goes, water follows” • Water loss   blood volume   BP The Importance of Water • Universal solvent • Transport medium • Necessary for metabolic reactions • % of body water as the amount of fat and age : What are the body routes of water loss? Characteristics of Electrolytes Cations = + ve ions Anions = - ve ions • Conduct electric current in solution • Important constituents of body fluid • Exist in the blood as • Include: Na + , K + , Ca ++ , PO 4 -3 , & Cl - • Other non-electrolytes such as are found in body fluids in very small amounts
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2 Functions of Electrolytes Homeostasis of body fluids Maintain acid/base balance Some are cofactors needed for enzyme activity Necessary for action potential propagation, and for the secretion of neurotransmitters in the synaptic clefts Electrolyte Balance The kidneys are the main regulators of electrolyte balance Cations Sodium (Na + ) major + ve ion in ECF – important in maintaining acid-base balance Potassium (K + ) major + ve ion in ICF – involved in cellular enzymes activities Calcium (Ca ++ ) most abundant mineral in the body – required for bone formation, blood clotting, muscle contractions and nerve impulses Anions Chloride (Cl - ) most abundant anion in ECF – essential for HCL formation Phosphate (PO 4 -3 ) – essential in carbohydrate metabolism, bone formation, and acid-base balance Electrolyte Disorders Hypernatremia : of Na + in body fluids, may be due to: ADH (as in diabetes insipidus); renal failure; dehydration; severe vomiting Hyponatremia : of Na + in body fluids, may be due to: aldosterone (as in Addison’s disease); water intoxication;
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This note was uploaded on 07/24/2010 for the course HP 320 taught by Professor Islam during the Spring '08 term at USC.

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