Microcirculation
Encyclopedia
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
, 3. tissue fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
(swelling or edema), 4. delivery of oxygen and other nutrients and removal of CO2 and other metabolic waste products, and 5. body temperature. The microcirculation also has an important role in inflammation.
Most vessels of the microcirculation are lined by flattened cells, the endothelium
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
and many are surrounded by contractile cells the smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
or pericytes. The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the plasma between the blood and the tissues. The endothelium also produce molecules that discourage the blood from clotting unless there is a leak. The smooth muscle cells can contract and decrease the size of the arterioles and thereby regulate blood flow and blood pressure.
Flow
Flow is determined by the diameter and the length of the vessels of the microcirculation. The Hagen–Poiseuille equation predicts the flow of blood through the vessels.Capillary Exchange of Water
The Starling equation is an equation that describes the roles of hydrostatic and osmoticOsmotic pressure
Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane....
forces (the so-called Starling forces) in the movement of fluid across capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
endothelium
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
.