T Mean arterial pressure toward normal

Figure 3-16. Role of the baroreceptor reflex in the cardiovascular response to hemorrhage. TPR=total peripheral resistance.

(2) It causes vasoconstriction of the arterioles, thereby increasing TPR and mean arterial pressure.

2. Example: response of the renin-angiotensin-aldosterone system to acute blood loss (Figure 3-17)

C. Other regulation of arterial blood pressure 1. Cerebral ischemia a. When the brain is ischemic, the concentrations of carbon dioxide (C02) and hydrogen (H+) in brain tissue increase.

b. Chemoreceptors in the vasomotor center respond by increasing both sympathetic and parasympathetic outflow.

- Ventricular contractility and TPR are increased, but heart rate is decreased (bcause of an overriding parasympathetic influence).

Acute hemorrhage

i

1 Arterial

pressure

I Renal perfusion pressure t Renin release from juxtaglomerular cells t Conversion of angiotensinogen to angiotensin I (plasma)

t Conversion of angiotensin I to angiotensin II (lung)

t Conversion of angiotensin I to angiotensin II (lung)

t Salt and water reabsorption

Figure 3-17. Role of the renin-angiotensin-aldosterone system in the cardiovascular response to hemorrhage.

TPR = total peripheral resistance.

Figure 3-17. Role of the renin-angiotensin-aldosterone system in the cardiovascular response to hemorrhage.

TPR = total peripheral resistance.

- Because of increased TPR and peripheral vasoconstriction, blood flow to other organs (e.g., kidneys) is significantly reduced in an attempt to preserve blood flow to the brain. -Mean arterial pressure can increase to life-threatening levels.

c. The Cushing reaction is an example of the response to cerebral ischemia. Increases in intracranial pressure cause compression of the cerebral blood vessels and cerebral ischemia. The response is as described above—elevation of mean arterial pressure (sympathetic in crease in contractility and TPR), with simultaneous decrease in heart rate (parasympathetic).

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