The primary function of<unk>  is to increase blood flow in the body to tissues that need it most. This is often in response to a localized need for oxygen but can occur when the tissue in question is not receiving enough glucose, lipids, or other nutrients. Localized tissues have multiple ways to increase blood flow, including releasing vasodilators, primarily adenosine, into the local interstitial fluid, which diffuses to capillary beds, provoking local<unk> . Some physiologists have suggested that it is the lack of oxygen itself that causes capillary beds to vasodilate by the smooth muscle hypoxia of the vessels in the region. This latter hypothesis is posited due to the presence of precapillary sphincters in capillary beds. These approaches to the mechanism of<unk>  are not mutually exclusive.<unk>  and arterial resistance<unk>  directly affects the relationship between mean arterial pressure, cardiac output, and total peripheral resistance (TPR).<unk>  occurs in the time phase of cardiac systole, whereas vasoconstriction follows in the opposite time phase of cardiac diastole. Cardiac output (blood flow measured in volume per unit time) is computed by multiplying the heart rate (in beats per minute) and the stroke volume (the volume of blood ejected during ventricular systole). TPR depends on several factors, including the length of the vessel, the viscosity of blood (determined by hematocrit) and the diameter of the blood vessel. The latter is the most important variable in determining resistance, with the TPR changing by the fourth power of the radius. An increase in either of these physiological components (cardiac output or TPR) causes a rise in the mean arterial pressure.<unk>  works to decrease TPR and blood pressure through relaxation of smooth muscle cells in the tunica media layer of large arteries and smaller arterioles.<unk>  occurs in superficial blood vessels of warm-blooded animals when their ambient environment is hot; this process diverts the flow of heated blood to the skin of the animal, where heat can be more easily released to the atmosphere. The opposite physiological process is vasoconstriction. These processes are naturally modulated by local paracrine agents from endothelial cells (e.g., nitric oxide, bradykinin, potassium ions, and adenosine), as well as an organism's autonomic nervous system and adrenal glands, both of which secrete catecholamines such as norepinephrine and epinephrine, respectively.
Vasodilation
Vasoconstriction
Osteostimulation
Vasoactivity
Cytostasis
Cardioprotection
Lymphangiogenesis
Vascular recruitment