Capillaries are a network of very small blood vessels that pass through all the tissues in the body and form the connection between the arteries and the veins. Arterioles, the smallest arteries in the body, contract or relax to regulate blood flow into the capillaries. If they are constricted, transport of oxygen and nutrients into the tissues can be reduced, affecting vital organs, muscles and blood flow to the extremities (characterised by, for example, cold hands and feet). This can be transitory and may be a result of mental or physical stress, dehydration, the use of nicotine or excessive caffeine.
In some cases, arteriole constriction can be a consequence of ageing, chronic inflammation, poor diet or lifestyle choices. Over time, this can contribute to the onset of arteriosclerosis (thickening and stiffening of the arterial walls) and the build-up of fatty deposits in the arteries, both of which restrict blood flow.