Anatomy of Blood Vessels PDF

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Anatomy of Blood Vessels...

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Anatomy of Blood Vessels •

Blood vessels can be categorized into arteries, arterioles, veins, venules, and capillaries.

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Arteries and veins have walls composed of 3 layers: § The tunica intima composed of a single layer of endothelial cells, § The tunica media made of smooth muscle, § The tunica adventitia composed of white fibrous connective tissue. Arteries have walls made of these 3 coats or tunics surrounding a hollow core known as a lumen through which blood flows.

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Arteries are thicker and stronger than veins with 2 major properties: § Elasticity § Contractility This is necessary b/c when the 2 ventricles of the heart contract, they inject a large amount of blood into the large aorta and pulmonary trunk. These arteries must be able to expand to accommodate the extra blood. Then while the ventricles relax, the elastic recoil of the arteries pushes the blood forward.

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Most parts of our body receive branches from more than one artery. In these areas, the distal ends of these branches unite to form one artery going into the organ.

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The junction of two or more blood vessels is called an anastomosis.

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Arterioles are small arteries that deliver blood to capillaries.

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Capillaries are microscopic vessels made of simple squamous epithelial cells, one cell layer thick, called endothelium. § They are found in close proximity to nearly every cell of the body. § They connect arterioles to venules. § Their primary critical function is to permit the exchange of nutrients and oxygen and waste and carbon dioxide between the blood and the tissue cells of the body. § Their unique wall structure of a single cell layer allows this to occur by diffusion. § A substance in the blood must pass through the plasma membrane of just one cell to reach the tissue cell and vice versa. § This vital exchange occurs only through capillary walls.

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Venules are small vessels that connect capillaries to veins. § They collect blood from capillaries and drain it into veins.

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Veins are made of the same 3 coats or tunics as arteries but have less elastic tissue and smooth muscle but more white fibrous connective tissue in the outer layer or adventitia. § They also are capable of distention to adapt to variations of blood volume and blood pressure. § Veins also contain valves that ensure blood flow in one direction, toward the heart.

Anatomy of Blood Vessels •

There is another term that will be encountered when reading about blood vessels. That term is vascular or venous sinuses. § These should not be confused with cavities in bones, which are also called sinuses. § Venous sinuses are veins with thin walls....