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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. Capillary fluid movement may occur as a result of three processes: * diffusion * filtration * pinocytosis Starling's equation only refers to fluid movement across the capillary membrane that occurs as a result of filtration. In the glomerular capillaries, there is a net fluid filtration of 125 ml/min (about 180 litres/day). In the rest of the body's capillaries, there is a total net transcapillary fluid movement of 20 ml/min (about 28.8 litres/day) as a result of filtration. This is several orders of magnitude lower than the total diffusional water flux at the capillary membrane, as that is about 80,000 litres/day. The Starling equation was formulated in 1896 by the British physiologist Ernest Starling, also known for the Frank–Starling law of the heart. ==The equation== The Starling equation reads as follows: : where: * is the net fluid movement between compartments. * is the net driving force, * * ''P''c is the capillary hydrostatic pressure * * ''P''i is the interstitial hydrostatic pressure * * ''π''c is the capillary oncotic pressure * * ''π''i is the interstitial oncotic pressure * * ''K''f is the filtration coefficient – a proportionality constant * * ''σ'' is the reflection coefficient By convention, outward force is defined as positive, and inward force is defined as negative. The solution to the equation is known as the net filtration or net fluid movement (''J''''v''). If positive, fluid will tend to ''leave'' the capillary (filtration). If negative, fluid will tend to ''enter'' the capillary (absorption). This equation has a number of important physiologic implications, especially when pathologic processes grossly alter one or more of the variables. Note that previously it was believed that at steady state the arterial capillaries filter fluid and the venous capillaries reabsorb it, as shown by the diagram. Though many physiology textbooks still use this misconception, modern evidence shows that in most cases venular blood pressure exceeds the opposing pressure, thus maintaining a positive outward force. This indicates that capillaries are normally in a state of filtration along their entire length.〔Levick J.R., Introduction to Cardiovascular Physiology. Oxford Press, 2003, pp. 179–180.〕 Pressures are often measured in millimetres of mercury (mmHg), and the filtration coefficient in millilitres per minute per millimetre of mercury (ml·min−1·mmHg−1). In essence the equation says that the net filtration (''J''''v'') is proportional to the net driving force. The first four variables in the list above are the forces that contribute to the net driving force. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Starling equation」の詳細全文を読む スポンサード リンク
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