McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 3 Drugs affecting blood pressure

Renin–angiotensin–aldosterone system Another compensatory system is activated when the blood pressure within the kidneys falls. Because the kidneys require a constant perfusion to function properly, they have a compensatory mechanism to help ensure that blood flow is maintained. This mechanism is called the renin–angiotensin–aldosterone system .

a generalised vasoconstriction, which increases total peripheral resistance and blood pressure. These increases should raise pressure in the system, which restores blood flow to the brain and stimulates the baroreceptors. The stimulation of the baroreceptors leads to a decrease in stimulatory impulses from the medulla, and the blood pressure falls back within normal limits (Figure 43.1).

Vasomotor centre

1 receptors of heart

Sympathetic ganglia

Adrenergic nerve terminals

Alpha receptors of vasculature

Vascular smooth muscle

Angiotensin II receptor sites

Aldosterone causes sodium and water retention

Adrenal gland aldosterone release

Kidney tubules

Angiotensin II receptor sites

Capillary endothelium of lungs

Juxtaglomerular cells that release renin

Converting enzyme

Renin

Angiotensin II

Angiotensin I

Angiotensinogen

FIGURE 43.1  Control of blood pressure. The vasomotor centre in the medulla responds to stimuli from aortic and carotid baroreceptors to cause sympathetic stimulation. The kidneys release renin to activate the renin–angiotensin system, causing vasoconstriction and increased blood volume.