[citation needed] In addition to these blood vessels, the microcirculation also includes lymphatic capillaries and collecting ducts.

The main functions of the microcirculation are the delivery of oxygen and nutrients and the removal of carbon dioxide (CO2).

The vessels on the arterial side of the microcirculation are called the arterioles, which are well innervated, are surrounded by smooth muscle cells, and are 10-50 μm in diameter.

Their function is to regulate blood flow before it enters the capillaries and venules by the contraction and relaxation of the smooth muscle found on their walls.

[citation needed] In addition to these blood vessels, the microcirculation also includes lymphatic capillaries and collecting ducts.

The main functions of the microcirculation are the delivery of oxygen and nutrients and the removal of carbon dioxide (CO2).

Distension of the vessels due to increased blood pressure is a fundamental stimulus for muscle contraction in arteriolar walls.

Other hormones (catecholamine, renin-angiotensin, vasopressin, and atrial natriuretic peptide) circulate in the bloodstream and can have an effect on the microcirculation causing vasodilation or vasoconstriction.

The endothelium begins to control muscle tone and arteriolar blood flow tissue.

This dynamic displacement of materials between the interstitial fluid and the blood is named capillary exchange.

[5] These substances pass through capillaries through three different systems or mechanisms: diffusion, bulk flow, and transcytosis or vesicular transport.

[5] The minimum number of un-absorbable plasma proteins that exit capillaries enter lymphatic circulation for returning later on to those blood vessels.

[8] Glucose, amino acids, oxygen (O2) and other molecules exit capillaries by diffusion to reach the organism's tissues.

Contrarily, carbon dioxide (CO2) and other wastes leave tissues and enter capillaries by the same process but in reverse.

Lipids, which are transported by proteins, are too large to cross the capillary walls by diffusion, and have to rely on the other two methods.

[7] When the flow of substances goes from the bloodstream or the capillary to the interstitial space or interstitium, the process is called filtration.

Finally, these materials exit by exocytosis, the process by which vesicles go out from a cell to the interstitial space.