Blood Vessels

Study Notes

The tunica interna (intima) is the innermost layer of blood vessels.
It's composed of a thin layer of endothelium, which is a specialized, single layer of epithelial cells.
The endothelium is supported by a basement membrane and a thin layer of connective tissue, known as the subendothelial layer.
The endothelium plays a crucial role in maintaining blood flow by preventing clotting and promoting vasodilation (widening of blood vessels).
It also interacts with blood components and contributes to the regulation of blood pressure.

Elastic arteries are large arteries like the aorta and its major branches.
They function as pressure reservoirs, expanding as blood is pumped from the heart and then recoiling to maintain smooth blood flow throughout the cardiac cycle.
They have a thick, elastic wall that allows them to withstand the high pressure of blood ejected from the heart.
Muscular arteries are medium-sized arteries that distribute blood to specific organs and tissues.
Compared to elastic arteries, they have relatively thinner walls but contain a thick layer of smooth muscle in their tunica media.
The smooth muscle allows them to constrict or dilate to regulate blood flow based on the body's needs.

Arterioles act as "resistance vessels" controlling blood flow into capillary beds.
They are the smallest arteries, characterized by a thin wall and smooth muscle that surrounds the tunica intima.
Their contraction and relaxation change blood vessel diameter, directly influencing resistance and thus blood flow.
Vasodilation of arterioles reduces resistance and increases blood flow to tissues, while vasoconstriction increases resistance and reduces blood flow.

Arterioles have a single layer of endothelial cells lining the lumen.
They possess a thin layer of smooth muscle surrounding the internal elastic lamina, which allows for regulation of blood flow.
A thin layer of connective tissue surrounds the tunica media.

Delivery of oxygen and nutrients: Arteries, arterioles, and capillaries transport oxygenated blood and nutrients from the heart to tissues throughout the body.
Removal of carbon dioxide and waste products: Veins carry deoxygenated blood and waste products back to the heart for excretion.
Regulation of blood pressure: Blood vessels contribute to controlling blood pressure through vasodilation and vasoconstriction, influencing the overall circulatory system.
Maintenance of body temperature: Blood vessels can aid in thermoregulation by constricting to conserve heat or dilating to release heat.
Protection against infections: The endothelial lining of blood vessels acts as a barrier against pathogens and helps regulate immune system activity.