5. 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.
6.
7. • 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
8. • 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.
REGULATION OF NORMAL BP
9.
10. • Factors released from the kidneys, adrenals, and myocardium
interact to influence vascular tone and to regulate blood
volume by adjusting sodium balance
11. 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.
12. – 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
13. – 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:
