C H A P T E R 4 3
Drugs affecting blood pressure
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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).
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
.
Vasomotor
centre
1
receptors
of heart
Sympathetic
ganglia
Adrenergic
nerve
terminals
Angiotensin II
receptor sites
Angiotensin II
receptor sites
Aldosterone
causes
sodium and
water retention
Adrenal gland
aldosterone
release
Capillary
endothelium
of lungs
Kidney
tubules
Renin
Converting enzyme
Angiotensin II
Angiotensin I
Angiotensinogen
Juxtaglomerular
cells that release renin
Alpha receptors
of vasculature
Vascular
smooth muscle
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.
