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Unformatted text preview: CHAPTER 27 FLU I DS & ELECTROLYTES Body fluid consists of body water and its dissolved substances, and makes up 55-60% of the body weight on average. 1. Intracellular fluid--inside cells (2/3 of total) 2. Extracellular fluid--all other body fluids (1/3 total) a. Plasma--20%--liquid part of blood b. Interstitial fluid--80%--mostly between cells, also includes: c. Also: Lymph Pericardial fluid Cerebrospinal fluid Peritoneal fluid GI tract fluids Glomerular filtrate Synovial fluids Fluids of the eye Pleural fluid Fluids of the ear Body fluids are separated into compartments by selectively permeable membranes, the plasma membranes of cells and blood vessel walls. Molecules are constantly moving from one compartment to another, but in homeostasis the total volume in each compartment remains fairly constant. Fluid balance--the body contains the required total amount of water and the water is properly distributed in the various compartments. Since water moves from one compartment to another mainly by osmosis, fluid balance requires electrolyte balance. Typical daily fluid intake: Daily output Ingested liquids 1600 ml Kidneys 1500 ml Water in food 700 ml Skin 600 ml Metabolic water 200 ml Lungs 300 ml 2500 ml GI Tract 100 ml 2500 ml Normally intake and output balance in every 24-hour period. If water output exceeds intake, even for a brief period, dehydration results. REGULATION OF WATER INTAKE Thirst is the major regulator. We feel thirst for 3 reasons: Increased blood osmotic Decreased flow of Decreased blood pressure saliva volume All stimulate thirst center of hypothalamus We drink water and get immediate wetting of the oral mucosa, distention of the stomach and then, and absorption occurs, increased blood volume and lowered blood osmotic pressure. All of these effects inhibit the thirst center. REGULATION OF OUTPUT 1. Angiotensin I I and aldosterone increase the reabsorption of Na+ in the CCT and collecting tubule. since water follows Na+, these hormones also promote increased reabsorption of water. If water output exceeds intake, these 2 hormones are secreted. If water intake is high, the hormones are inhibited. 2. ADH regulates water reabsorption by changing the permeability of tubule cells. 3. Atrial natriuretic peptide is secreted to increase water and Na+ loss when blood volume rises. 4. Dehydration leads to decreased blood volume and decreased blood pressure. The glomerular filtration rate (GFR) therefore falls and urine output decreases. 5. Vomiting and diarrhea or increased loss through the skin can lead to dehydration. In dehydration, water first leaves the extracellular fluids, but the increased concentration of solutes in plasma soon causes fluid loss from interstitial fluid and inside cells to follow....
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This note was uploaded on 07/26/2011 for the course BSC 1094 taught by Professor Porter during the Fall '11 term at Edison State College.

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