Final answer:
Muscular or medium-sized arteries that deliver blood to specific organs are called distributing arteries. They have a thick tunica media for vasoconstriction and rely on smooth muscle and elastic fibers to adapt to the changes in blood flow and pressure.
Step-by-step explanation:
The arteries that are muscular or medium-sized and that deliver blood to specific organs are called distributing arteries. These arteries have a key role in vasoconstriction, which is the constriction of blood vessels to regulate blood flow and pressure. Distributing arteries have a thick tunica media, which is the middle layer of the artery, composed of smooth muscle and elastic fibers that allow for the regulation of the diameter of the blood vessel. The tunica media's muscle cells can respond to different stimuli, including the myogenic response, where constriction or dilation occurs in response to pressures related to blood flow. This adaptation ensures consistent flow to the capillary network. Additionally, the nervi vasorum are nerve fibers that stimulate muscular contractions to regulate blood flow.
These arteries start to branch from elastic arteries and transition as they carry blood further from the heart. A muscular artery can typically range from 0.1 mm to 10 mm in diameter and has a more substantial amount of smooth muscle and fewer elastic fibers compared to arteries closer to the heart. Since the blood pressure is lower at the point they carry blood to, the reduced elasticity is less of an issue for their function.