How does noradrenaline result in rise of systolic blood pressure even when the cardiac output is decreasing?
Noradrenaline, also known as norepinephrine, is a hormone and neurotransmitter that plays a crucial role in regulating blood pressure. When released by sympathetic nerve fibers, it can cause vasoconstriction (narrowing of blood vessels) and increase the heart rate, both of which contribute to the rise in systolic blood pressure.
Even if the cardiac output (the volume of blood pumped by the heart per minute) is decreasing, the vasoconstrictive effect of noradrenaline on blood vessels can compensate for the reduced cardiac output by constricting the arteries. This constriction increases the resistance against which the heart pumps blood, resulting in a rise in systolic blood pressure.
Additionally, noradrenaline acts on the heart by binding to receptors called beta-1 adrenergic receptors located on the heart muscle cells. This stimulation increases the strength of the heart’s contractions, known as contractility, which helps to maintain sufficient blood flow to vital organs and tissues despite the decreasing cardiac output.
In summary, noradrenaline, through its vasoconstrictive effect and stimulation of the heart’s contractility, can elevate systolic blood pressure even when the cardiac output is decreasing.
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