Microcirculation

Microcirculation is blood flow through arterioles, capillaries, and venules, where exchange between blood and surrounding tissues occurs.

Arterioles: Small arteries that regulate blood flow into capillary beds by changing their diameter. Their constriction and dilation control how much blood enters each tissue bed.
Blood flow: The movement of blood through the circulatory system driven by pressure differences. Microcirculation is the tissue-level part of this broader movement.
Tissue perfusion: The delivery of blood through a tissue's vascular network. Perfusion describes the practical outcome of microvascular blood flow.
Macrocirculation: Blood flow through larger arteries and veins that transport blood between the heart and organs. It contrasts organ-scale transport with exchange in small vessels.
Capillaries: Microscopic blood vessels with thin walls that enable exchange between blood and tissues. Their thin endothelial walls form the principal exchange surface.
Blood pressure: The force exerted by circulating blood against vessel walls. Pressure gradients propel blood through arterioles, capillaries, and venules.
Laser Doppler flowmetry: A technique that estimates microvascular blood flow from Doppler shifts in laser light scattered by moving cells. It measures changes in superficial microvascular flow in clinical and research settings.
Lymphatic system: A network of vessels and organs that returns interstitial fluid to the bloodstream and supports immune functions. It removes fluid and proteins that leave blood vessels but are not directly carried by venous blood.
Venules: Small vessels that collect blood leaving capillary beds and carry it toward veins. They drain capillary beds and also participate in fluid and immune-cell movement.
Hematocrit: The proportion of blood volume occupied by red blood cells. Red-cell concentration affects blood viscosity and flow through narrow vessels.

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