Cardiovascular Physiology — Integrated Pressure Control

Renal–body fluid system for arterial pressure control

dominant system in long-term pressure control

pressure diuresis

pressure natriuresis

renal urinary output curve

at 50 mm Hg

at 100 mm Hg

at 200 mm Hg

equilibrium point & infinite feedback gain principle

determinants of long-term arterial pressure level

shifting the curve

changing intake level of salt and water

failure of total peripheral resistance to elevate long-term arterial pressure

changes in TPR does not affect long-term arterial pressure level

renal function curve must be altered to have long-term changes in arterial pressure

changing renal vascular resistance does lead to long-term changes in arterial pressure

increased fluid volume can elevate arterial pressure

increase in cardiac output

increase in TPR

P = CO × TPR

sodium (NaCl) is a major determinant of ECFV

stimulation of thirst

increase in ADH secretion

chronic hypertension

values

mean arterial pressure > 100 mm Hg

135/90

mean arterial pressure > 170 mm Hg

250/130

effects

increased cardiac workload

cerebral infarcts — strokes

kidney failure

Renin-angiotensin system

production of renin

juxtaglomerular (JG) cells — modified afferent arteriolar smooth muscle

prorenin

release of renin

angiotensinogen → angiotensin I (a decapeptide)

action of ACE of pulmonary endothelial cells

angiotensin I → angiotensin II (an octapeptide)

actions of angiotensin II

vasoconstriction → ↑ TPR → ↑ arterial pressure

renal effects:  retention of salt & water

direct action shifts renal function curve to right

promotion of adrenocortical aldosterone secretion

effect of sodium intake

RAS important in maintaining normal arterial pressure

renal effects:  retention of salt & water

as Na intake is increased, renin levels fall to near 0

as Na intake is decreased, renin levels increase significantly

Factors which decrease renal excretory function & increase BP

angiotensin II
aldosterone
sympathetic nervous activity
endothelin

Factors which increase renal excretory function & reduce BP

atrial natriuretic peptide
nitric oxide
dopamine

Different forms of hypertension

primary (essential) hypertension

↑ CO & ↑ TPR

↑ sympathetic activity

↑ angiotensin II & aldosterone levels

impaired renal-pressure natriuresis mechanism

treatment

renal vasodilators

natriuretic or diuretic drugs

renovascular hypertension

sleep apnea & neurogenic hypertension

chronic renal disease

hyperaldosteronism

pheochromocytoma

pregnancy-induced hypertension (preeclampsia)

exogenous substances

alcohol
steroids
sympathomimetics

↑ sympathetic activity

↑ angiotensin II & aldosterone levels

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