Aside from the pulmonary artery, arteries transport oxygenated blood at at high pressure away frmo the heart .In order to be able to perform this function, the lumen through which the blood flows is narrow and along with the elastic tissue that is found in two of the three layers of the arterial wall, this acts to withstand the high pressure. This ensures the rapid delivery of oxygen and nutrients like glocuse to the body tissues over the relatively large distance of the body.
The three tunica layers
The three tunica layers of the arterial wall are the:
- tunica intima, which consists of a thin layer of elastic tissue
- tunica media, which consists of a thick layer of smooth muscle
- tunica externa, which consists of a relatively thick layer of the fibrous protein called collagen, which provides strength to with stand the pressure and some elastic tissue to allow contractions and relaxions to take place.
Changes made to the blood by the arterioles
Arterioles decrease the pressue of the blood as capillaries cannot withstand the pressure. This would cause them to burst.
They also decrease the velocity so there is more time for efficient exchange by diffusion between the capilltaries and the tissues.
Under the control of the autonomic nervous system, the layer of smooth muscle in the artierole walls can be innervated to contract. This constricts the diameter fo the lumen of the arteriole, increasing resistance reducing the rate of flow of blood. This allows blood to be diverted away from some areas towards other areas where demand for oxygen is greater.
During a certain situation, the diameter of the lumen of the arterioles which branch off frmo the renal artery will constrict to reduce the blood lfow to the kidney.