Introduction Autoregulation is a mechanism that ensures constant blood flow to organs, despite changing resistance (perfusion pressures) in the blood vessels 2 hypotheses explain autoregulation myogenic hypothesis metabolic hypothesis recall that blood flow (Q) = (change in pressure [P])/resistance (R) Hypotheses of Autoregulation Myogenic hypothesis when the vascular smooth muscle is stretched (like when arterial pressure is increased), the smooth muscle contracts (increases resistance) when there is an increase in blood pressure, the myogenic reflex causes smooth muscle contraction in order to maintain flow Metabolic hypothesis O2 delivery to a tissue is matched to O2 consumption of that tissue this is accomplished by changing the resistance (and blood flow) of the arterioles metabolic activity causes tissues to produce metabolites, including vasodilators CO2, H+, K+, lactate, and adenosine ↑ metabolic demand → ↑ O2 demand → vasodilation → ↓ resistance this results in ↑ blood flow Autoregulation of Organs Organ Factors Determining Autoregulation Heart Local metabolites pO2, adenosine, pCO2, and NO Brain Local metabolites pCO2 andpH Kidneys Myogenic hypothesis tubuloglomerular feedback Lungs Local metabolites pO2→ vasoconstriction Skeletal muscles Local metabolites lactate,K+, and adenosine Skin Sympathetic innervation Organ-Specific Autoregulation Heart most sensitive to pO2, adenosine, pCO2, and NO adenosine results in coronary vasodilation ↑ myocardial contractility → ↑ O2 demand and consumption → vasodilation → ↑ blood flow Brain most sensitive to pCO2 and pH ↑ pCO2 → ↓ pH → vasodilation→ ↑ blood flow to remove excess CO2 Kidneys myogenic hypothesis tubuloglomerular feedback ↑ renal arteriole pressure → ↑ blood flow login to view 1 more bullet ↑ GFR increases delivery of solute and water to juxtaglomerular apparatus (JGA) login to view 3 more bullets Lungs most sensitive to low pO2, which causes vasoconstriction NOT vasodilation login to view 2 more bullets Skeletal muscles most sensitive to vasoactive metabolites during exercise (e.g., lactate, K+, and adenosine) sympathetic innervation at rest login to view 1 more bullet Skin most sensitive to sympathetic innervation ↓ body temperature → α1 receptors vasoconstrict login to view 1 more bullet ↑ body temperature → inhibition of cutaneous vasoconstriction login to view 1 more bullet plays a major role in the regulation of body temperature