Microcirculation: Difference between revisions
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**The difference in concentration of the substances in the blood and in the interstitum drives the flow of substances across the capillary bed. | **The difference in concentration of the substances in the blood and in the interstitum drives the flow of substances across the capillary bed. | ||
==Starling's | ==Starling's Law== | ||
{{Main|Starling equation}} | {{Main|Starling equation}} | ||
* The Starling equation is an equation that illustrates the role of [[hydrostatic pressure|hydrostatic]] and [[oncotic pressure|oncotic]] forces (the so-called '''Starling forces''') in the movement of fluid across [[capillary|capillary membranes]]. | * The Starling equation is an equation that illustrates the role of [[hydrostatic pressure|hydrostatic]] and [[oncotic pressure|oncotic]] forces (the so-called '''Starling forces''') in the movement of fluid across [[capillary|capillary membranes]]. |
Revision as of 18:00, 25 October 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
- The microcirculation is the blood flow through blood vessels smaller than 100 µm (i.e. arterioles, capillaries, and venules).
- The main functions of the microcirculation are transporting blood cells and substances to/from the tissues, and as body coolant in thermoregulation processes.
- It also contributes to tissues color and stiffness.
- Diffusion is the capillary exchange of substances across the endothelial cells membranes.
Determinants of Capillary Exchange
- 1- Surface area of the capillary bed
- It is dependent on the metabolic activity of the tissue.
- 2- Permeability of the capillary bed
- It is dependent on the characteristic of each organ, for example the brain is relatively impermeable to most substances whereas the kidneys have very high permeability.
- 3- Free diffusion coefficient of the substances to be exchanged
- It is dependent on the substance size, charge and lipid solubility.
- 4- Concentration of the substances to be exchanged
- The difference in concentration of the substances in the blood and in the interstitum drives the flow of substances across the capillary bed.
Starling's Law
- The Starling equation is an equation that illustrates the role of hydrostatic and oncotic forces (the so-called Starling forces) in the movement of fluid across capillary membranes.
- According to Starling's equation, the movement of fluid depends on six variables:
- Capillary hydrostatic pressure ( Pc )
- Interstitial hydrostatic pressure ( Pi )
- Capillary oncotic pressure ( πc )
- Interstitial oncotic pressure ( πi )
- Filtration coefficient ( Kf )
- Reflection coefficient ( σ )
- Starling's equation is the following:
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