DYNAMIC EQUILIBRIUM OF BODY FLUID

DENNY AGUSTININGSIH

In average young adult male:

% of body weightBody composition

18%Protein, & related substances

15%Fat

7%Mineral

60%Water

Body composition

Factors affecting body fluids Water intake & output Age:

- infant: 73%- elderly: 45%

Sex:- adult male: 60%- adult female: 40-50%

Body temperature healthy adult can sweat 1

liter/hr for 2 hrs (5% of body wt without problem)

perspire (1000cc wet sheet)

Every degree F = 75 ml increase/day in fluid needs

Obesity Climate Habits Level of physical activity

• solvent

• transportMain functions

• Give shape and form to the cells

• Regulate body temp.

• Joint lubricant

• Cushion body organs

• Maintain peak performance

Other functions

Body Fluid Compartments

Figure 5-13: Body fluid compartments

Total body water (TBW)‏

0.6 X body weight (men), 0.5xbody weight (women ?)‏

35L - 42L

Interstitial fluid

(ISF)‏

3/4 ECF

10.5L

Plasma

1/4

ECF

3.5 L

capillary wall

Extracellular fluid

(ECF)‏

0.2 X body weight

14L

Intracellular fluid

(ICF)‏

0.4 X body weight

28L

cell membrane

TranscellularwaterGI, kidney, sweattears, synovial, CSF

variable volume~ 1L

epithelial

layer

input

output

epithelial

Distribution of body water in an average 70 kg person

COMPOSITION OF BODY FLUIDS

Normal Ions and electrolytes Composition of the Body Fluids.

capillary wall plasma membrane

NaK

sodium pump ~ Na,K-ATPase:

Differences between ECF & ICF

ECFAnions:Cl- (108)

HCO3- (24)

Cations:

Na+ (142mmol/L)

K+ (4.2)

Mg2+ (0.8)

Nutrients:

O2, glucose, fatty acids, &

amino acids.

Wastes:

CO2, Urea, uric acid,

excess water, & ions.

ICFAnions:Cl- (4)

HCO3- (10)

Phosphate ions

Cations:

Na+ (14)

K+ (140)

Mg2+ (20)

Nutrients:

High concentrations of proteins.

Daily Water Gain and Loss

Copyright 2009, John Wiley & Sons, Inc.

HOMEOSTASIS

Claude Bernard (1878):

animals have 2 environtments- milieu exteriur : physically surrounds the whole

organism

- milieu interieur : surrounds the tissue and cells of the organism•organic liquid

•homeostasis

HOMEOSTASISParameters of the milieu interieur that must be

tightly controlled

– - core temperatures

– - levels of oxygen

– - glucose

– - potassium ions

– - calcium ions

– - hydrogen ions

Volume Contraction

Isotonic Hypertonic HypotonicE

CF

EC

F

ICF

EC

F

ICF

Osm

ola

lity

Volume Expansion

Isotonic Hypertonic Hypotonic

EC

F

ICF

EC

F

ICF

EC

F

ICF

Osm

ola

lity

From H. Valtin

ICF

PATHOPHYSIOLOGICAL CHANGES IN EXTRACELLULAR FLUID VOLUME

Changes in the osmolality of plasma lead to AVP secretionat a much lower threshold than they lead to thirst

Very small increases in AVP lead to very large changes in urine volume

Thus – the kidney is the first line of defense against cellular dehydration

Ongoing behavior is not disrupted by thirst unless the buffering effects of osmosis and antidiureses are insufficient

Osmotic homeostasis

• Dehydration produces a need for water

• Osmolality (expression of concentration) is the ratio of the amount of solute dissolved in a given weight of water: solute (osmoles)/water (kilograms)

• Body water can decrease as a result of deprivation or sweating, whereas solute can increase as a consequence of salt ingestion

• Either water decrease or solute increase leads to an increase in osmolality

Osmotic homeostasis

Excessive loss of H2O from ECF

1 2 3ECF osmotic pressure rises

Cells lose H2O to ECF by osmosis; cells shrink

Volume homeostasis

Hypovolemia triggers not only thirst, but also salt appetite

Blood volume is corrected only by replacing both water and salt

Drinking water alleviates thirst(by reducing plasma osmolality), but triggers salt appetite, whereas consuming salt triggers subsequent thirst (by increasing plasma osmolality)

Series of Events in Water Intoxication

Copyright 2009, John Wiley & Sons, Inc.