Body Fluid Compartments

Sources of water intake

1) Ingested in form of liquid and food (2.1L)

2) Produced during metabolism (0.2L)

Total water intake

2.3L

Factors affecting water intake

Climate, habit and amount of physical activity

Sources of loss of water

1) Insensible loss (700ml) through skin and lungs (350ml each)

2) Fluid loss in sweat (100ml)

3) Water loss in feces (100ml)

4) Water loss in kidney (1400)

Insensible water loss through skin prevented by

Cholestrol filled cornified layer of skin (Incase of burns the layer is disrupted so leads to 3-5L body fluid loss)

Dryness in winter due to

Increased insensible water loss through lungs

Factors affecting fluid loss through sweat

Physical activity and temperature

Transcellular fluid

Synovial, peritoneal, pericardial, intraocular space fuids and CSF. It constitutes abt 1-2L

Body Fluid Distribution

¾ Intracellular fluid(40% body wt)

¼ Extracellular fluid(20% body wt)

Extracellular is further divided into interstitial fluid(11L), plasma(3L) and transcellular fluid

Factors affecting the contribution of fluids to body weight

Age, gender and degree of obesity

Body fluid contribution more in

1) males or females

2) Newborns or old people

3) Skinny or obese

1) Men

2) Newborns

3) Skinny

Higher protein in interstitial fluid or plasma

Protein

Blood Volume

Plasma(3L)+ RBC(2L)= 5L

Hematocrit

Fraction of blood composed of RBCs

Normal hematocrit

0.40 in males n 0.36 in females

Donnan effect

More positive charge in plasma than interstitial fluid

Composition of intracellular fluids

K+, Mg++, Na+(very little), PO4 3- n organic anions, protein, little cl- n HCO3-

Composition of Extracellular fluid

Na+, Ca2+, K+ a little

Dye to measure total body water

Radioactive water, heavy water, antipyrine

Dye for Measurement of Extracellular fluid volume

Radioactive Na, radioactive chloride, radioactive iothalamate, thiosulphate kon, inulin

Intracellular fluids Volume

Calculated

Volume(intracellular fluid= Total body fluid-extracellular fluid

Dye for Measurement of plasma volume

Serum albumin labelled with radioactive iodine, Evans blue dye

Interstitial fluid volume

Extracellular fluid volume - plasma volume

Blood Volume

Blood Volume= Plasma volume/(1-hematocrit)

RBC labelled with radioactive materials like radioactive chromium

Osmosis

Net diffusion of water across a selectively permeable membrane from a region of high water concentration to that has lower water concentration

Osmoles

The number of osmotically active particles

Osmolality

Number of osmoles per kilogram of solvent(water)

Osmolarity

Number of osmoles per litre of solution

Higher osmotic pressure(20mm Hg greater) and osmolarity(1 higher) in plasma due to

Plasma proteins