Body Fluids Prof. K. Sivapalan. June 20132 Body Composition Body Fluids.
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Transcript of Body Fluids Prof. K. Sivapalan. June 20132 Body Composition Body Fluids.
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Body Fluids
Prof. K. Sivapalan
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Body FluidsJune 2013 2
Body Composition
• Carbon, oxygen, hydrogen, nitrogen, …….
• Muscles, bones, liver, spleen, brain….
• Water 60 %.
• Protein 18-20 %
• Fat: M-15 %, F- 25 %
• Carbohydrate 2 %
• Minerals.
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Body Fluids 3
Body Fat
• Structural fat [6-7%] and storage fat
• Lean body mass
• Body mass index-
– Weight in Kg/height in M2
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Body Fluids 4
Fluid Compartments
• Intra cellular fluid
• Extra cellular fluid-Inter cellular fluid
– Tissue fluid
– Plasma
– Transcellular fluids
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Body Fluids 5June 2013
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Body Fluids 6June 2013
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Body Fluids 7
Major Components
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Body Fluids 8June 2013
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Body Fluids 9
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.
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Body Fluids 10June 2013
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Body Fluids 11
Diffusion
• 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
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Body Fluids 12
Osmosis
• 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.
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Body Fluids 13
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.
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Body Fluids 14
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)
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Body Fluids 15
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.
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Body Fluids 16
TRANSPORT ACROSS MEMBRANE
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Body Fluids 17
PINOCYTOSIS
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Body Fluids 18
• The exchange occurs through capillaries which lie between arteriol and venule.
• Precapillary sphinctors 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.
Exchange Between Blood and Tissues
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Body Fluids 19
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
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Body Fluids 20
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
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Body Fluids 21
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].
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Body Fluids 22
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
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Body Fluids 23
Role of Lymphatics
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• 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.
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Body Fluids 24
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.
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Body Fluids 25
Summary of Microcirculation
• Filtration at the arteriolar end
• Re-absorption at venular end
• Balance fluid and proteins drained by lymphatics.
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Body Fluids 26
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.
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Body Fluids 27
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.
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Body Fluids 28
Measurement of Total Body Water
• Radioactive water (tritium, 3H2O) or heavy water (deuterium, 2H2O) can be used to measure total body water.
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Body Fluids 29
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
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Body Fluids 30
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.
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Body Fluids 31
Measurement of Body Fluid Volumes
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Body Fluids 32
Fluid Balance- ml/day
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