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%

FLUIDS and ELECTROLYTES

FLUID EXCHANGE BETWEEN BODY FLUID COMPARTMENTS

Osmotic Pressure Gradient

Oncotic P (Colloid osmotic P)

Capillary P (Hydrostatic P)

ICF ECF

P ISF

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 FLUID

INTRA CELLULAR FLUID

INTERSTITIAL FLUIDPLASMA TRANSCELLULAR

FLUID

CSFIntra ocular

PleuralPeritonealSynovial

Digestive Secretions

VOLUME OF BODY FLUIDS IN 70 kg MAN

TOTAL VOLUME 42 L

INTRA CELLUAR FLUID28 L(ROUGHLY 2/3 OF TBW)

EXTRA CELLULAR FLUID14 L(ROUGHLY 1/3 OF TBW)

PLASMA4 L (ROUGHLY ¼ OF ECF)

VOLUME MEASUREMENT OF VARIOUS FLUIDS COMPARTMETNS

INTERSTITIAL FLUIDECF – Plasma Volume

INTRACELLULAR FLUIDTBW – ECF

TOTAL BODY WATER(TBW)

• 60% OF THE BODY WEIGHT IN ADULT MALE

• 50% OF THE BODY WEIGHT IN ADULT FEMALE

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