Blood circulation

The supply of organs or parts of organs with blood is called blood flow or perfusion (exact hemoperfusion ) . It is supplied via arteries and drained via veins (and lymph vessels ). This serves to supply tissues with oxygen , nutrients and other vital blood components as well as the removal of metabolic products and carbon dioxide . Organ perfusion can be maintained artificially. As reperfusion re-flow is an organ after temporary interruption of blood supply (z. B. after embolism ), respectively.

Disorders of various causes are called circulatory disorders and can cause acute and chronic impairment of various organ and tissue functions and, in the extreme case, lead to the destruction of the areas of the organs with poor blood supply.

quantification

Also referred to as perfusion (in the sense of a quantifiable variable ) is the volume of blood that flows through an organ or, more generally, through biological tissue of the mass per unit of time . Depending on the reference variable, the physical unit of perfusion is either (related to an organ such as the kidneys): ${\displaystyle \Delta V}$ ${\displaystyle \Delta t}$ ${\displaystyle m}$

${\displaystyle \left[{\frac {\Delta V}{\Delta t}}\right]={\frac {\text{ml}}{\text{min}}}}$

or (based on regional blood flow, also referred to as specific perfusion):

${\displaystyle \left[{\frac {\Delta V}{m\cdot \Delta t}}\right]={\frac {\text{ml}}{{\text{g}}\cdot {\text{min}}}}}$.

The (total) blood flow to the kidneys of an adult is, for example, approx. 1200 ml / min; the specific perfusion is approximately 4 ml / (g · min). The total blood flow of an organ can be also as the ratio of the pressure drop between the arterial ( ) and venous pressure ( ) and the vascular resistance of the organ, so as to describe. ${\displaystyle \Delta p=p_{\text{a}}-p_{\text{v}}}$ ${\displaystyle p_{\text{a}}}$ ${\displaystyle p_{\text{v}}}$ ${\displaystyle R}$ ${\displaystyle \Delta p/R}$

The (specific) perfusion can be measured with various imaging methods such as perfusion MRT , perfusion CT or nuclear medicine methods.

Blood flow variability

There is a rest blood flow from a maximum possible blood flow (or perfusion reserve distinguished). The individual organs are supplied with blood to varying degrees: At rest, the kidneys receive the relatively largest proportion of blood (in relation to their weight), with maximum blood flow these are the muscles (skeletal and heart muscles) and the skin . The need-based adjustment of the blood flow is guaranteed by complex control mechanisms .

pregnancy

In pregnancy , the blood flow to the increased uterus (via the uterine arteries. ) Of 50 at the beginning to 500-750 ml / min at the end of pregnancy, which ultimately (in a proportion of 10-15 percent of the maternal maternal ) cardiac output (HMV) corresponds ( uterine or maternoplacental blood flow ). The driving force here is the maternal blood pressure, while the fetal blood pressure enables the so-called fetoplacental blood flow . Of the 250–400 ml / min of the fetal HMV, around 50–60 percent flow into the umbilical arteries ( Aa. Umbilicales ).

Individual evidence

1. ↑ Frans van den Berg (Ed.): Applied Physiology 2: Understanding Organ Systems . 2nd Edition. Georg-Thieme-Verlag, Stuttgart 2005, ISBN 3-13-117082-4 , p. 126 . ( limited preview in Google Book search)
2. ↑ Robert F. Schmidt, Florian Lang, Gerhard Thews (ed.): Physiology of humans: With pathophysiology . 29th edition. Springer, Berlin Heidelberg New York 2005, ISBN 3-540-21882-3 , pp. 809 . ( limited preview in Google Book search)
3. ^ Péter Bálint: Normal and pathological physiology of the kidneys . VEB People and Health, Berlin 1969, p. 69-70 . ( limited preview in Google Book search)
4. ^ Rainer Klinke, Stefan Silbernagl (ed.): Textbook of Physiology . 4th edition. Georg Thieme, Stuttgart, New York, ISBN 3-13-796004-5 , pp. 169 ff .
5. ^ H. Steiner, KTM Schneider: Doppler sonography in obstetrics and gynecology: guidelines for practice . Springer, 2007, ISBN 3-540-72370-6 , pp. 10 ff . ( limited preview in Google Book search).