Macroscopic Fluid Movement Lecture 6 PDF

SI2101 - LECTURE 6 Macroscopic uid movement Leo Quinlan, Cell Physiology Research Lab fl  Osmotic effects Osmolarity vs Tonicity What determines uid movement across capillary walls Understanding osmotic challenges LEARNING OUTCOMES FOR TODAY fl OS...

SI2101 - LECTURE 6 Macroscopic uid movement Leo Quinlan, Cell Physiology Research Lab fl  Osmotic effects Osmolarity vs Tonicity What determines uid movement across capillary walls Understanding osmotic challenges LEARNING OUTCOMES FOR TODAY fl OSMOTIC PRESSURE is generated by a solution when separated from another solution by a semi-permeable membrane. The solution must consist of a solvent (H2O) which is freely permeable and at least one solute which is not.  OSMOTIC EFFECTS Isosmotic Experiment Volume = 1 nL Volume = 1 nL Volume = 1 nL Place a cell in 300 mM Sucrose 300 mOsM 300 mOsM P P 300 mM Sucrose H2O H2O 300 mM Sucrose  OSMOTIC EFFECTS Isosmotic Experiment Volume = 1 nL Volume = 0 nL Place a cell in 300 mM Urea 300 mOsM 300 mOsM P P 300 mM Urea 300 mM H2O H2O Urea  OSMOLARITY TONICITY Concentration of solute Behavior of cells when placed in particles a solution Speci cally non permeable, Speci cally related to changes in dissociated particles cell volume OSMOLARITY VS TONICITY fi fi OSMOLARITY VS TONICITY 300 mM Sucrose 150 mM Sucrose 300 mM Urea Isosmotic Hypoosmotic Isosmotic No change in Increase in Increase in cell volume cell volume cell volume Isotonic Hypotonic Hypotonic Hypertonic = ???  There is a ready exchange of substances from the plasma to the ISF through thin walls of capillaries. Forces that govern this exchange are hydrostatic pressure and osmosis. PLASMA-INTERSTITIAL FLUID EXCHANGE  Capillary wall impermeable to plasma proteins Pressure in capillaries < arteries Arteriolar end approx. 35 mm Hg Venule end approx. 15 mm Hg. HYDROSTATIC PRESSURE AT THE CAPILLARY  Capillary wall permeable to water, not to plasma proteins, There is am osmotic pressure gradient Colloid Oncotic Pressure Plasma exerts about 28 mm Hg ISF only about 3 mm Hg. Net Oncotic Pressure approx. 25 mm Hg. OSMOTIC FORCES IN CAPILLARIES  HP causes uid to leave plasma, and oncotic pressure Venous pulls it back. Arterial fl STARLING FORCES The hydrostatic forces, gradually decrease over the length of the capillary, while the oncotic pressure remains constant. Edema is the accumulation of excess uid in the tissues. It is most common in the soft tissues of the extremities. Physiological causes of edema include water leakage from blood capillaries caused by the use of certain therapeutic drugs, by pregnancy, by localized injury, or by an allergic reaction. In the limbs, the symptoms of edema include swelling of the subcutaneous tissues, an increase in the normal size of the limb, and stretched, tight skin. DISORDERS OF FLUID BALANCE fl 45 PLASMA LOSS = PLASMA GAIN NO NET CHANGE 35 CAPILLARY PRESSURE ONCOTIC PRESSURE 25 15 ARTERIOLES VENULES 45 PREGNANCY PLASMA LOSS ≠ PLASMA GAIN NET LOSS FROM PLASMA NET GAIN TO ISF 35 EDEMA ONCOTIC PRESSURE 25 15 ARTERIOLES VENULES 45 STARVATION PLASMA LOSS ≠ PLASMA GAIN NET LOSS FROM PLASMA NET GAIN TO ISF 35 EDEMA ONCOTIC PRESSURE 25 15 ARTERIOLES VENULES Condition Example ECF Fluid ICF Fluid Volume Osmolarity Volume Osmolarity Hyposmotic Xs H20 expansion intake Hyposmotic Xs Salt contraction Loss Isosmotic expansion IV Infusion Isosmotic Haemorrhage contraction or Burns Hyper Drink Conc. expansion Saline Hyper Severe contraction Sweating  Osmotic effects Osmolarity vs Tonicity What determines uid movement across capillary walls Understanding osmotic challenges LEARNING OUTCOMES FOR TODAY fl