24-1 Chapter 24: Water, Electrolyte, and Acid-Base Balance
24-2 Water, Electrolyte and Acid-Base Balance
24-3 Water Balance •Total body water for 150 lb. male = 40L •Fluid compartments –65% intracellular fluid –35% extracellular fluid •25% tissue fluid •8% blood plasma, lymph •2% transcellular fluid (CSF, synovial fluid)
24-4 Water Movement in Fluid Compartments•Electrolytes play principle role in water distribution and total water content
24-5 Water Gain •Preformed water –ingested in food and drink •Metabolic water –by-product of aerobic metabolism and dehydration synthesis
24-6 Water Loss •Routes of loss –urine, feces, expired breath, sweat, cutaneous transpiration •Loss varies greatly with environment and activity –respiratory loss ↑: with cold, dry air or heavy work –perspiration loss ↑: with hot, humid air or heavy work •Insensible water loss –breath and cutaneous transpiration •Obligatory water loss –breath, cutaneous transpiration, sweat, feces, minimum urine output (400 ml/day)
24-7 Fluid Balance
24-8 Regulation of Fluid Intake •Dehydration –↓blood volume and pressure –↑blood osmolarity •Thirst mechanisms –stimulation of thirst center (in hypothalamus) •angiotensin II: produced in response to ↓BP •ADH: produced in response to ↑blood osmolarity •hypothalamic osmoreceptors: signal in response to ↑ECF osmolarity –inhibition of salivation •thirst center sends sympathetic signals to salivary glands
24-9 Satiation Mechanisms •Short term (30 to 45 min), fast acting –cooling and moistening of mouth –distension of stomach and intestine •Long term inhibition of thirst –rehydration of blood (↓blood osmolarity) •stops osmoreceptor response, ↑capillary filtration, ↑saliva
24-10 Dehydration, Thirst, and Rehydration
24-11 Regulation of Output •Controlling Na+reabsorption (changes volume) –as Na+is reabsorbed or excreted, water follows •Action of antidiuretic hormone (ADH)(changesconcentrationofurine) –ADH secretion (as well as thirst center)stimulated by hypothalamic osmoreceptors in responsetodehydration –aquaporins synthesized in response to ADH •membrane proteins in renal collecting ducts to channel water back into renal medulla, Na+is still excreted –effects: slows ↓in water volume and↑osmolarity
24-12 Secretion and Effects of ADH
24-13 Disorders of Water Balance •Fluid deficiency –volume depletion (hypovolemia) •total body water ↓, osmolarity normal •hemorrhage, severe burns, chronic vomiting or diarrhea –dehydration •total body water ↓, osmolarity rises •lack of drinking water, diabetes, profuse sweating, diuretics •infants more vulnerable –high metabolic rate demands high urine excretion, kidneys cannot concentrate urine effectively, greater ratio of body surface to mass •affects all fluid compartments –most serious effects •circulatory shock, neurological dysfunction, infant mortality
24-14 Water Loss & Fluid Balance
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