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Body Fluids. Prof. K. Sivapalan. Body Composition. Carbon, oxygen, hydrogen, nitrogen, ……. Muscles, bones, liver, spleen, brain…. Water 60 %. Protein 18-20 % Fat: M-15 %, F- 25 % Carbohydrate 2 % Minerals. Body Fat. Structural fat [6-7%] and storage fat Lean body mass

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Body fluids

Body Fluids

Prof. K. Sivapalan

Body composition
Body Composition

  • Carbon, oxygen, hydrogen, nitrogen, …….

  • Muscles, bones, liver, spleen, brain….

  • Water 60 %.

  • Protein 18-20 %

  • Fat: M-15 %, F- 25 %

  • Carbohydrate 2 %

  • Minerals.

Body Fluids

Body fat
Body Fat

  • Structural fat [6-7%] and storage fat

  • Lean body mass

  • Body mass index-

    • Weight in Kg/height in M2

Body Fluids

Fluid compartments
Fluid Compartments

  • Intra cellular fluid

  • Extra cellular fluid-Inter cellular fluid

    • Tissue fluid

    • Plasma

    • Transcellular fluids

Body Fluids

Major components
Major Components

Body Fluids

Definitions solutions
Definitions - Solutions

  • A mole is the gram-molecular weight of a substance- NaCl- 23+35.5=58.5g

  • One electrical equivalent (eq) is 1 mol of an ionized substance divided by its valence.

  • Gram equivalent is the weight of a substance that is chemically equivalent to 8.000 g of oxygen

  • The normality (N) of a solution is the number of gram equivalents in 1 liter

  • Molar solution contains one gram mole of a substance in one liter.

Body Fluids


  • Diffusion is the process by which a gas or a substance in a solution expands, because of the motion of its particles, to fill all the available volume.

  • The rate depends on ,

    • Concentration [chemical] gradient

    • Electrical gradient for charged particles

    • Cross-sectional area

    • Distance

    • Permeability of the boundaries

Body Fluids


  • Diffusion of solvent molecules into a region in which there is a higher concentration of a solute to which the membrane is impermeable—is called osmosis.

  • P=nRT/V [n is the number of particles, R is the gas constant, T is the absolute temperature, and V is the volume]

  • One osmole (Osm) equals the gram-molecular weight of a substance divided by the number of freely moving particles that each molecule liberates in solution

  • Osmolar solution- 1 osmole in 1 liter [op-22.4 atmosphears]

  • Glucose- mole=Osmole, NaCl- 1 mole = 2 osmoles, Na2so4- 1 mole = 3 osmoles.

Body Fluids

Osmolality tonisity
Osmolality - Tonisity

  • The osmolarity is the number of osmoles per liter of solution (eg, plasma)

  • The osmolality is the number of osmoles per kilogram of solvent.

  • Measured by the degree to which the freezing point is depressed [1.86 ºC]

  • Osmolality of plasma is 290 mOsm/L

  • The term tonicity is used to describe the osmolality of a solution relative to plasma- hypotonic, isotonic, hypertonic.

  • Osmotic Pressure is the pressure exerted by the solution when separated from water by semi-permiable membrane or the pressure required to prevent net movement of water into the solution.

  • Osmotic pressure of 1 osmolar solution is 22.4 atmospheres = 17024 mmHg, plasma= 17024x0.290=4936 mmHg.

Body Fluids

Importance of osmolality
Importance of Osmolality

  • Cells swell when exposed to extracellular hypotonicity and shrink when exposed to extracellular hypertonicity because cell membrane is freely permiable to water. [Fragility test for red cells]

  • If the concentration increases, reactions are altered and if the volume increases beyond the limit- lyses or contents diffuse out.

  • All but about 20 of the 290 mOsm in each liter of normal plasma are contributed by Na+ and its accompanying anions, principally Cl– and HCO3–.

  • Osmolality of plasma (mOsm/L) = 2[Na+] (mEq/L) + 0.055[Glucose] (mg/dL) + 0.36[Blood Urea Nitrogen] (mg/dL)

Body Fluids

Exchange between icf and ecf
Exchange Between ICF and ECF

  • The properties of the cell membrane determine the exchange.

  • Water is freely permeable

  • The permeability to solutes is determined by fat solubility and mollicular size.

  • Many substances are transported across the membrane by facilitated diffusion, active transport, secondary active transport, pinocytosis, phagocytosis etc.

Body Fluids


Body Fluids

Exchange between blood and tissues
Exchange Between Blood and Tissues

  • The exchange occurs through capillaries which lie between arteriol and venule.

  • Precapillarysphinctors determine the flow into specific capillaries which is determined by local metabolites.

  • The capillaries have clefts between endothelial cells [slit-pores] with diameter of 6-7 nm- smaller than albumin.

  • Fluid and solutes pass freely through these pores.

  • Plasmalemmal vesicles also transport small amounts.

Body Fluids

Diffusion in capillaries
Diffusion in Capillaries

  • Lipid soluble substances including oxygen and carbon dioxide diffuse across the endothelium according to concentration gradient.

  • Water and water soluble substances such as sodium, chloride, bicarbonate and glucose pass through the pores.

  • Larger molecules, albumin and other plasma proteins cannot pass through the pores

Body Fluids

Colloid osmotic pressure
Colloid Osmotic Pressure

  • The capillary pore permit all solutes in plasma except the cells and proteins.

  • It is similar to fluid separated by a semi-permiable membrane, the osmotic particle being the protein.

  • The osmotic pressure exerted by plasma proteins amount to about 25 mmHg.

  • Even though it is negligible contribution to the osmotic pressure of the plasma, it is the only difference across the capillary membrane.

  • It is named colloid osmotic pressure or oncotic pressure.

  • As the largest number of protein molecules are albumin, it is responsible for the colloid osmotic pressure

Body Fluids

Starling forces for capillary exchange
Starling Forces forCapillary Exchange

  • Pressure of the blood in the arteriolar end of the capillaries is 30 mm Hg.

  • It reduces progressively towards the venous end and becomes 10 mmHg.

  • Colloid osmotic pressure is 25 mmHg at the arteriolar end and becomes 28 mm Hg as concentration increases.

  • Tissue pressure is slightly negative [-3 mm Hg] probably due to lymphatic suction.

  • As some protein molecules escape into the tissue fluid, it also has mild colloid pressure [8 mm Hg].

Body Fluids

Starling equilibrium for capillary exchange
Starling Equilibrium forCapillary Exchange

  • At the arteriolar end:

    • Hydrostatic [blood] pressure= 30 mmHg

    • Plasma Colloid osmotic pressure= -25 mmHg

    • Tissue Colloid osmotic pressure= 8 mmHg

    • Tissue pressure= -3 mmHg

  • At the Venular end

    • Hydrostatic [blood] pressure= 10 mmHg

    • Plasma Colloid osmotic pressure= -28 mmHg

    • Tissue Colloid osmotic pressure= 8 mmHg

    • Tissue pressure= -3 mmHg

Body Fluids

Role of lymphatics
Role of Lymphatics

  • Allmost all tissues have lymphatics channels which coalase and open into superior venacava through thoracic duct [2-3 liters / day].

  • Exceptions include the superficial portions of the skin, the central nervous system, the endomysium of muscles, and the bones.

  • Lymphatic channels originate in the tissues as blind ended tube.

Body Fluids

Formation of lymph
Formation of Lymph

  • Lymphatic capillaries are made of endothelial cells which are attached to connective tissue through anchoring filaments.

  • The edge of one endothelial cell overlaps the adjacent cell so that the edge forms a minute valve that opens to the interior of the lymphatic capillary.

  • The lymphatics contract periodically and the valves prevent back flow and push the contents forwards.

  • This permits sucking of excess tissue fluid along with the protein and other large particles.

Body Fluids

Summary of microcirculation
Summary of Microcirculation

  • Filtration at the arteriolar end

  • Re-absorption at venular end

  • Balance fluid and proteins drained by lymphatics.

Body Fluids

Estimation of fluid volumes
Estimation of Fluid Volumes

  • The volume of a fluid compartment in the body can be measured by placing an indicator substance in the compartment,

  • allowing it to disperse evenly throughout the compartment’s fluid,

  • and then analyzing the extent to which the substance becomes diluted.

Body Fluids

Conditions for indicator dilution principle
Conditions for Indicator Dilution Principle

  • This method can be used to measure the volume of virtually any compartment in the body as long as :

  • (1) the indicator disperses evenly throughout the compartment,

  • (2) the indicator disperses only in the compartment that is being measured, and

  • (3) the indicator is not metabolized or excreted.

  • Several substances can be used to measure the volume of each of the different body fluids.

Body Fluids

Measurement of total body water
Measurement of Total Body Water

  • Radioactive water (tritium, 3H2O) or heavy water (deuterium, 2H2O) can be used to measure total body water.

Body Fluids

Measurement of extracellular fluid volume
Measurement of Extracellular Fluid Volume.

  • substances that disperse in the plasma and interstitial fluid but do not readily permeate the cell membrane are used.

  • They include radioactive sodium, radioactive chloride, radioactive iothalamate, thiosulfate ion, and inulin

Body Fluids

Measurement of plasma volume
Measurement of Plasma Volume

  • Substance used should not penetrate capillary membranes but remains in the vascular system after injection.

  • One of the most commonly used substances for measuring plasma volume is serum albumin labeled with radioactive iodine (125I-albumin).

  • Also, dyes that avidly bind to the plasma proteins, such as Evans blue dye (also called T-1824), can be used.

Body Fluids