Blood Vessels Blood circulates inside the blood vessels which form a closed transport system called the vascular system. The vascular system consists of: Arteries –large vessels moving blood away from the heart Arterioles – smaller vessels that feed capillary beds Capillary Beds – vessels that supply tissues and facilitate gas exchange Venules – small vessels that drain capillary beds Veins – larger vessels that return blood to the heart

Microscopic Anatomy of Blood Vessels The walls of blood vessels have three coats or tunics. Tunica intima: lines the interior of the vessel and consists of endothelium Tunica media: bulky middle coat of vessel made of smooth muscle and elastic tissue Tunica externa: outermost tunic composed of fibrous connective tissue that supports and protects the vessels.

Differences Between Vessels Differences between arteries, veins and capillaries: Walls of arteries are much thicker than veins Veins have valves that prevent backflow that could occur due to low pressure Capillaries have transparent walls that are only one cell thick to allow for gas exchange

Capillary Beds Capillary beds are the networks of tiny capillaries that provide oxygen and nutrients to tissues. Capillary beds consists of two types of vessels: Vascular Shunt: vessel that directly connects arteriole and venule at opposite ends True Capillaries: actual exchange vessels

Major Arteries The aorta is the largest artery in the body. The aorta is approximately the size of a garden hose and exits the heart at the left ventricle. The aorta branches into different major arteries to supply the tissues of the body. Many of those arteries are named either for the organs they serve, the area of the body they are in or the bone they follow.

Major Veins Veins tend to be more superficial and more easily palpated. Most deep veins follow the pathways of the arteries and are named accordingly. All the veins converge into the venae cavae which enters the right atrium. Veins from the head and arms enter the superior vena cava. Veins from the lower body empty into the inferior vena cava.