cellular function demands the composition of the intracellular and

Cellular function demands the composition of the

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cellular function demands the composition of the intracellular and extracellular fluid compartments be narrowly controlled - volume which ions and compounds are present individual and collective concentration, i.e., osomolarity Three types of homeostatic balance Water balance Electrolyte balance Acid–base balance Balances maintained by collective action of urinary , respiratory, digestive, integumentary, endocrine, nervous, cardiovascular and lymphatic systems 24-45
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Fluid Compartments within the Body - 70 kg male Total Fluid 40 L
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24-47 Movement of H 2 O Between Major Fluid Compartments Osmosis from one compartment to another determined by relative solute concentration in each compartment If electrolytes, esp. Na shift H 2 O shifts Digestive tract Bloodstream Bloodstream Tissue fluid Lymph Intracellular fluid
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24-48 Typical Water Intake vs. Output Water Balance In = Out Water is not stored. Metabolic water: 200 mL aerobic metabolism and dehydration synthesis Insensible water loss Sensible water loss Preformed water: 2,300 mL food and drink Obligatory water loss unavoidable expired air, cutaneous transpiration, sweat, fecal moisture, minimum urine output, 400 mL
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24-49 Dehydration Thirst Rehydration Sensitivity to Osmolarity vs. Plasma Volume 2%-3% plasma osmolarity sense of thirst, whereas , 10%-15% blood loss sense of thirst Thirst inhibits Salivation, via sympathetic signals from thirst center to salivary glands Dehydration : blood vol. and BP or blood osmolarity Thirst is main factor that drives fluid intake INHIBITION OF THIRST Short Term; prevents over-drinking Cooling/moistening of mouth quenches thirst stomach & small intestine distension Long Term: intestinal H 2 O absorption plasma osmolarity Stops osmoreceptor response capillary filtration and saliva production ('watery') mouth not as dry
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24-50 Regulation of Fluid Output Only significantly control H 2 O output = regulation of urine volume Kidneys cannot replace H 2 O or electrolytes - instead decrease loss until H 2 O or electrolytes can be ingested HOW? Control mechanisms of water output Change urine volume linked to regulation of Na + reabsorption As Na + is reabsorbed or excreted, water follows. H 2 O output is slowed through action of ADH
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24-51 Action of Antidiuretic Hormone (ADH) Dehydration hypothalamic osmoreceptors posterior pitutiary release ADH ADH Collecting Duct synthesize and insert Aquaporins (H 2 O channels) into apical membrane H 2 O reabsorption/diffusion into renal medulla urine volume Na + still excreted urine osmolarity ADH System - Negative Feedback plasma osmolarity OR volume ADH secretion H 2 O reabsorption plasma osmolarity & volume then ADH secretion plasma osmolarity OR volume, inhibits ADH release CD reabsorbs less H 2 O Urine output trends reversed plasma volume
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24-52 Sodium Homeostasis Na + principal cation in ECF; Na + (Cl - ) account for 90-95% ECF osmolarity Na + deficiency rare; primary concern is excretion of excess dietary Na + Kidney - primary organ that regulates Na + excretion and Na +
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