REGULATION OF NORMAL BLOOD

PRESSURE

BLOOD PRESSURE

• The pressure exerted by the blood against the walls of the

blood vessels, especially the arteries.

BLOOD PRESSURE

CARDIAC OUTPUT

PERIPHERAL RESISTANCE

STROKE VOLUME

HEART RATE

BLOOD PRESSURE

NORMAL BLOOD PRESSURE

SYSTOLIC BP:100-140 mmHg

DIASTOLIC BP:60-90 mmHg

AVERAGE BP:120/80 mmHg

REGULATION OF NORMAL BP

• CARDIAC OUTPUT• Influenced by many genetic, environmental and demographic

factors.

• Stroke volume depends on filling pressure, which is regulated

through sodium homeostasis and its effect on blood volume.

• Heart rate and myocardial contractility are regulated by ß-

adrenergic systems.

REGULATION OF NORMAL BP

• PERIPHERAL VASCULAR RESISTANCE:

• Determined by functional and anatomic changes in small

arteries and arterioles. Affected by neural and hormonal

factors.

• Vascular tone is regulated by vasoconstrictors (angiotensin II,

catecholamines, and endothelin) and vasodilators (kinins,

prostaglandins,and NO).

REGULATION OF NORMAL BP

• Resistance vessels also exhibit autoregulation, whereby

increased blood flow induces vasoconstriction to protect

tissues against hyperperfusion.

• Finally, blood pressure is fine-tuned by tissue pH and hypoxia

to accommodate local metabolic demands.

• Factors released from the kidneys, adrenals, and myocardium

interact to influence vascular tone and to regulate blood

volume by adjusting sodium balance

ROLE OF KIDNEY

• Renin-angiotensin system:

– Renin: fall in BP renin is secreted by the juxtaglomerular cells

and released into the blood circulation.

It cleaves plasma angiotensinogen to angiotensin I, which is

then converted to angiotensin II by angiotensin converting

enzyme.

– Angiotensin II raises BP by increasing both peripheral

resistance (vasoconstriction) and blood volume (by stimulating

secretion of aldosterone by the adrenal medulla, and increase

reabsorption of sodium in distal tubules).

• Antihypertensive substances: The kidney also produces

substances which cause vasodilatation and have

antihypertensive effect. These include prostaglandins and

nitric oxide (NO). They counterbalance the vasoconstriction

produced by angiotensin II.

ROLE OF KIDNEY

– When blood volume is reduced, GFR falls → increased

reabsorption of sodium by PCT→ conserves sodium and expands

blood volume

– When blood volume increased, natriuretic factors (natriuretic

peptides) are secreted by atrial and ventricular myocardium.

They inhibit sodium reabsorption in distal tubules and cause

excretion of sodium and diuresis. Natriuretic peptides also cause

vasodilation and may be considered as endogenous inhibitors of

the renin-angiotensin system.

SODIUM HOMEOSTASIS AND BLOOD VOLUME:

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