autoregulation of blood flow

Autoregulation of blood flow

Intrinsic ability of an organ to maintain constant blood flow despite changes in perfusion pressure, can be short term or long term.

Myogenic tone

Vascular smooth muscle contraction when stretched, leading to vasoconstriction to maintain constant blood flow, known as the Bayliss Effect.

Endothelial mediators

Vasoconstrictor - Endothelin; Vasodilators - Nitric Oxide (NO), prostacyclins.

Nitric oxide biosynthesis

Substrate - L-Arginine; Enzyme - Endothelial Nitric Oxide Synthase (eNOS).

eNOS reaction

Converts L-arginine to nitric oxide (NO) and L-citrulline, requiring oxygen (O₂) and NADPH.

Nitric oxide diffusion

NO diffuses from endothelial cells to nearby vascular smooth muscle cells.

Nitric oxide activation

Activates guanylyl cyclase in vascular smooth muscle cells.

Guanylyl cyclase activation

Converts GTP to cGMP (cyclic guanosine monophosphate).

cGMP effects

Triggers smooth muscle relaxation, activates PKG, phosphorylates target proteins, decreases intracellular calcium levels, reduces sensitivity of contractile proteins to calcium.

Nitric oxide effect

Causes vasodilation, decreases vascular resistance, increases blood flow.

Active hyperemia

Increased metabolic activity of tissue producing vasodilators, leading to increased blood flow.

Adenosine vasodilation

Breakdown product of ATP causing vasodilation.

Reactive hyperemia

Decreased tissue blood flow due to occlusion followed by release of metabolic vasodilators.

Inflammatory hyperemia

Active process from increased arterial blood inflow due to inflammatory mediators like histamine, bradykinin, prostanoids, neuropeptides.

Triple response of the skin - Red Line

Caused by histamine-induced vasodilation.

Triple response of the skin - Flare

Mediated by axon reflex releasing neuropeptides causing vasodilation.

Neurogenic inflammation

Inflammation mediated by nerve-induced release of neuropeptides leading to vasodilation and redness.

Triple response of the skin - Wheal

Localized swelling due to increased capillary and venule permeability, caused by histamine and other inflammatory mediators.