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THE MICROCIRCULATION. MAIN CONCEPTS Guido E. Santacana Ph.D. Professor Dept. of Physiology
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MICROCIRCULATION STRUCTURE LAW OF LAPLACE TRANSCAPILLARY EXCHANGE STARLING’S HYPOTHESIS LYMPHATICS
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Structure of the Microcirculation Smooth muscle Arteriole Venule Metarteriole Capillary Endothelial cells Precapillary sphincters
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Ultrastructure of a Capillary Lumen Intracellular channels Endothelial cell 1 Endothelial cell 2 Basement membrane Nucleus Intercellular cleft 5-10 m
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LAW OF LAPLACE T = P x r/wt Tension = Pressure x Radius / wall thickness Why do the capillaries in our feet don’t just burst from the pressure (about 100mmHg)?
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How does Laplace Work?
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Less wall tension with smaller radius?
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FLOW AND DIFFUSION LIMITED TRANSPORT PARTICLE SIZE AND FLOW CELL FLOW LIMITED PARTICLE SIZE & DISTANCE CELL DIFFUSION LIMITED
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REFLECTION COEFFICIENT oncotic pressure = o RT (Ci - Co) water=0 albumin=1 RT= gas and temperature constants Ci= concentration inside Co= concentration outside REFLECTION COEFFICIENT = ACTUAL OSMOTIC FLOW/ THEORETICAL
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CAPILLARY FILTRATION HYDROSTATIC FORCES OSMOTIC FORCES ARTERIAL PRESSURE VENOUS PRESSURE PRE-POST CAPILLARY RES. INTERSTITIAL FLUID PRESSURE ONCOTIC PRESSURE ALBUMIN BALANCE STARLING’S HYPOTHESIS Qf = k (Pc + i) - (Pi + p)
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Graphic Representation of Capillary Filtration
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Capillary Filtration in Various Clinical Conditions A B C D
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What I cannot forget about Microcirculation Four Forces known as Starling Forces Determine Fluid Movement Across the Capillary Membranes. Pc= Capillary Pressure Tends to move fluid out of the capillary Pi= Interstitial Fluid Pressure Tends to move fluid into the capillary. Πc = Plasma Colloid Osmotic Pressure Tends to cause Osmosis of fluid into capillary. Πi = Interstitial fluid colloid osmotic pressure Tends to cause osmosis of fluid out of the capillary. Net Filtration Pressure = Pnet= ((Pc-Pi) – (Πc- Πi))
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More things that I cannot forget about the microcirculation EDEMA or excess fluid outflow into the interstitium is commonly caused by : Capillary Pressure ( Pc ; Heart Failure) Plasma Proteins ( Πc ; Nephrotic Syndrome, liver failure) Capillary Permeability ( Kf ; Toxins, infections, burns) Interstitial Fluid Colloid Osmotic Pressure ( Πi; lymphatic blockage) Net Fluid Flow = Pnet (Kf)
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Pitting Edema of the Feet A Pit forms where the skin is pressured. It may remain there for a few minutes
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The Lymphatic System
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Elephantiasis or Lymphatic Filariasis
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