BODY FLUIDS

FACTORS AFFECTING Total Body Water varies depending on body fat: infant: 73% male adult: 60% female adult: 40-50% effects of obesity Old age 45%

FLUID EXCHANGE BETWEEN BODY FLUID COMPARTMENTS FLUIDS and ELECTROLYTES FLUID EXCHANGE BETWEEN BODY FLUID COMPARTMENTS ICF ECF P ISF Osmotic Pressure Gradient Oncotic P (Colloid osmotic P) Capillary P (Hydrostatic P)

Control of Osmotic Pressure, Volume & Electrolyte Concentration FLUIDS and ELECTROLYTES Control of Osmotic Pressure, Volume & Electrolyte Concentration OBLIGATORY Reabsorption occurs in the proximal tubules 178 L/day of glomerular filtrate (80% reabsorbed) 2 to solute reabsorption independent of the water requirement FACULTATIVE Reabsorption occurs in the distal & collecting tubules independent of the active solute transport dependent of body’s need of water under the control of ADH

IMPORTANCE Maintaining ECF volume is critical to maintaining blood pressure ECF osmolarity is of primary importance in long-term regulation of ECF volume ECF osmolarity maintained mainly by NaCl balance:

FLUID COMPARTMENTS EXTRA CELLUAR INTRA CELLULAR FLUID FLUID PLASMA INTERSTITIAL FLUID TRANSCELLULAR FLUID CSF Intra ocular Pleural Peritoneal Synovial Digestive Secretions

VOLUME OF BODY FLUIDS IN 70 kg MAN TOTAL VOLUME 42 L INTRA CELLUAR FLUID 28 L(ROUGHLY 2/3 OF TBW) EXTRA CELLULAR FLUID 14 L(ROUGHLY 1/3 OF TBW) PLASMA 4 L (ROUGHLY ¼ OF ECF)

VOLUME MEASUREMENT OF VARIOUS FLUIDS COMPARTMETNS INTERSTITIAL FLUID ECF – Plasma Volume INTRACELLULAR FLUID TBW – ECF

TOTAL BODY WATER(TBW) 60% OF THE BODY WEIGHT IN ADULT MALE 50% OF THE BODY WEIGHT IN ADULT FEMALE

0.9% sodium chloride (NSS) Lactated Ringer’s sol’n Hypotonic FLUIDS and ELECTROLYTES IV FLUID REPLACEMENT THERAPY Types of Solutions Isotonic 0.9% sodium chloride (NSS) Lactated Ringer’s sol’n Hypotonic 5% dextrose and water (D5W) 0.45% sodium chloride 0.33% sodium chloride Hypertonic 3% NaCl Protein sol’ns Colloids Salt pour albumin Plasmanate, Dextran

Factors affecting ADH release

REGULATION OF FLUID INTAKE (THIRST) decreased salivation decreased blood volume increased blood osmotic pressure dry mouth and throat decreased blood pressure stimulation of hypothalamic osmoreceptors conscious awareness of thirst increased water intake stimulation of tactile receptors increased angiotensin II stimulation of hypothalamic thirst center

REGULATION OF FLUID OUTPUT dehydration ANTIDIURETIC HORMONE increased blood osmolarity stimulation of hypothalamic osmoreceptors rehydration secretion of ADH from posterior pituitary gland increased water reabsorption increased thirst ALDOSTERONE dehydration rehydration increased water reabsorption increased Na+ reabsorption increased aldosterone increased angiotensin II ATRIAL NATRIURETIC PEPTIDE increased blood volume decreased Na+ reabsorption decreased water reabsorption decreased blood volume stretch of right atrium secretion of ANP