Bayliss effect – function, task & diseases


Bayliss effect

Of the Bayliss effect Keeps the blood flow to organs such as the brain and kidneys constant despite daily fluctuations in blood pressure. At elevated pressures, vasoconstriction of the vascular muscular system is initiated by the effect. Disruption of the Bayliss effect leads to persistent hyperemia and edema formation in the extracellular space.

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What is the Bayliss effect??

Blood pressure values ​​are subject to fluctuations day after day. Despite these fluctuations, the organ perfusion must be maintained constant. The Bayliss effect contributes to the constant maintenance of organ perfusion. This myogenic autoregulation was described for the first time by the British physiologist Bayliss and corresponds to a contraction reaction of the blood vessels, which, in the context of local control in the blood circulation, maintains the constancy of the blood flow to organs and tissues.

The blood vessels are equipped with smooth muscles. In blood pressure changes, the vascular muscle cells respond to the new situation by either contracting or relaxing. The molecular cause of the Bayliss effect is the activation of mechano-sensitive receptors within the blood vessels. The Bayliss effect ultimately corresponds to a variant of circulatory regulation that is independent of the autonomic nervous system and its nerve fibers. While the effect on the kidneys, gastrointestinal tract and brain can be demonstrated, the phenomenon does not seem to matter to the skin and lungs.

function & task

As soon as the mechanoreceptors in the vessels register lower blood pressure values ​​again and thus register a decreasing supply of blood supply, a vasodilatation is initiated. The musculature of the vessels relaxes again to their basal tone. In this way, the Bayliss effect keeps the blood flow in the kidneys, the gastrointestinal tract and the brain largely constant and regulates the values ​​in these body areas relatively autonomously.

Efficiency is shown by the Bayliss effect at systolic blood pressure values ​​of 100 to 200 mmHg. The effect is based on molecular mechanisms. Bayliss-effect arteries and arterioles carry mechano-sensitive cation channels in their walls. When these cation channels are opened, calcium ions enter the muscle cells and form a complex with the protein calmodulin.

Upon binding to a complex, the enzyme myosin light chain kinase is activated. If phosphorylation takes place in the sense of an interconversion of this kinase, the motor protein myosin II is thereby activated. This motor protein allows the contraction of vascular smooth muscle cells.

For every muscle contraction, the myosin and atkin filaments in the muscle must slide into each other. Myosin II is involved in this movement as it is responsible for the binding site to the muscles’ atkin filament.

The Bayliss effect is a type of circulatory regulation that works independently of vegetative innervation of the blood vessels. Even if the vegetative connection is cut off by a transection of the supplying nerves, the Bayliss effect thus remains. The mechanism can be blocked exclusively by the use of spasmolytics such as papaverine, which induce relaxation of the vascular muscle cells.

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Diseases & complaints

The abolition of the Bayliss effect may result in the passage of fluid into individual organ structures due to the resulting hyperemia of a particular coverage area. In this way extracellular edema can develop. Edema is preceded by the escape of fluid from the vessels, which eventually accumulates in the interstitial space. Edema formation is always preceded by a change in fluid movement between the interstitium and the capillaries. The laws of the Starling equation play a major role in fluid leakage.

In addition to the hydrostatic pressure of the blood capillaries, the difference in oncotic vessel pressure between capillaries and interstitial space plays a role. The hydrostatic and oncotic pressure act against each other. While hydrostatic pressure causes the escape of water into the interstitial space, the oncotic pressure binds fluid within the capillaries. The two forces are usually approximately in balance.

Edema can only develop in the context of deviating pressures, which no longer keep the balance. Such abnormal pressure values ​​occur, for example, with the failure of the Bayliss effect. Since the ion channel TRPC6 in particular is involved in the Bayliss effect, among other things, mutations of the gene coding for it can cause disturbances of the effect. In the meantime, rare hereditary diseases of the kidneys, for example, have been attributed to a mutation in the TRPM6 gene. Mutations can alter the protein in the ion channel so much that it no longer works. A magnesium deficiency and a disturbed calcium supply within the cells is the result.

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