Even though it is negligible contribution to the osmotic pressure of the plasma, it is the only difference across the capillary membrane.The osmotic pressure exerted by plasma proteins amount to about 25 mmHg.It is similar to fluid separated by a semi-permiable membrane, the osmotic particle being the protein.The capillary pore permit all solutes in plasma except the cells and proteins.Larger molecules, albumin and other plasma proteins cannot pass through the pores Body Fluids.Water and water soluble substances such as sodium, chloride, bicarbonate and glucose pass through the pores.Lipid soluble substances including oxygen and carbon dioxide diffuse across the endothelium according to concentration gradient.Plasmalemmal vesicles also transport small amounts.Fluid and solutes pass freely through these pores.The capillaries have clefts between endothelial cells with diameter of 6-7 nm- smaller than albumin.Precapillarysphinctors determine the flow into specific capillaries which is determined by local metabolites.The exchange occurs through capillaries which lie between arteriol and venule.Many substances are transported across the membrane by facilitated diffusion, active transport, secondary active transport, pinocytosis, phagocytosis etc.The permeability to solutes is determined by fat solubility and mollicular size.The properties of the cell membrane determine the exchange.Osmolality of plasma (mOsm/L) = 2 (mEq/L) + 0.055 (mg/dL) + 0.36 (mg/dL) Body Fluids.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–.If the concentration increases, reactions are altered and if the volume increases beyond the limit- lyses or contents diffuse out.Cells swell when exposed to extracellular hypotonicity and shrink when exposed to extracellular hypertonicity because cell membrane is freely permiable to water.Osmotic pressure of 1 osmolar solution is 22.4 atmospheres = 17024 mmHg, plasma= 17024x0.290=4936 mmHg.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.The term tonicity is used to describe the osmolality of a solution relative to plasma- hypotonic, isotonic, hypertonic.Measured by the degree to which the freezing point is depressed.The osmolality is the number of osmoles per kilogram of solvent.The osmolarity is the number of osmoles per liter of solution (eg, plasma).Glucose- mole=Osmole, NaCl- 1 mole = 2 osmoles, Na2so4- 1 mole = 3 osmoles.Osmolar solution- 1 osmole in 1 liter.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.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.Permeability of the boundaries Body Fluids.Electrical gradient for charged particles.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.Molar solution contains one gram mole of a substance in one liter.The normality (N) of a solution is the number of gram equivalents in 1 liter.Gram equivalent is the weight of a substance that is chemically equivalent to 8.000 g of oxygen.One electrical equivalent (eq) is 1 mol of an ionized substance divided by its valence.A mole is the gram-molecular weight of a substance- NaCl- 23+35.5=58.5g.Extra cellular fluid-Inter cellular fluid.Muscles, bones, liver, spleen, brain….Carbon, oxygen, hydrogen, nitrogen, …….
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