What’s bradykinin?
Bradykinin is a hormone, which means that it contributes to the communication between cells. It has a similar effect to histamine. In contrast to steroid hormones such as cortisol, for example, it is made up of amino acids strung together, in this case 9 different amino acids.
The biological half-life is just 15 seconds. Bradykinin is one of the kinins which are tissue hormones, i.e. they do not act systemically in the whole body but locally. Especially in the inflammatory process, bradykinin plays an important role by dilating the nearby arteries and veins so that white blood cells can enter the inflamed area to defend against pathogens. Bradykinin also increases the sensation of pain in the inflamed area.
Task, function and effect of bradykinin
The main function of bradykinin is to contribute to the development of inflammation in an injured area. This is necessary to enable rapid healing and to combat any pathogens that may occur in the best possible way. In the case of an injury, a special hormone receptor (B2 receptor) is incorporated into the cell walls from nearby blood vessels, to which bradykinin specifically binds.
This binding leads to a relaxation of the vascular muscles and thus to an expansion. As a result, the local blood pressure drops, but at the same time there is increased blood circulation, which is noticeable in the form of redness and an increased temperature. In addition, the permeability of the vascular wall increases, allowing white blood cells to enter the injured area to defend against intruders.
It also has a mobility-increasing effect on these blood cells so that they can move better through the connective tissue. In addition, fluid escapes from the vessel into the tissue, causing the swelling of an inflammation. In addition, bradykinin binds to another hormone receptor (B1-receptor), which is formed by injured tissue, thereby locally increasing the sensation of pain.
For this reason, inflamed skin areas are particularly sensitive to pain or even hurt without irritation. Besides these easily detectable effects, bradykinin has several other effects. For example, it causes a narrowing of the bronchial tubes by stimulating the bronchial musculature.
If this happens excessively, it can lead to a dry cough. Bradykinin also causes contraction of the smooth muscles in the gastrointestinal tract and uterus. In the kidney, bradykinin causes increased diuresis (urine production) with loss of sodium.
Bradykinin also plays a role in blood clotting: it is activated by factor XII from the coagulation cascade and contributes to the release of the tissue plasminogen activator, which activates the enzyme plasmin. This ensures that a thrombus is broken down again after it has fulfilled its function. Due to its vasodilatory effect, it also plays a role in temperature regulation: more heat is released to the outside world through a dilated vessel than through a narrow one. Bradykinin also plays a role in allergic reactions in that foreign substances that are actually harmless are perceived as dangerous and cause, for example, narrowing of the bronchial tubes or swelling of the skin. Bradykinin is broken down by various enzymes contained in the blood.
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