Blood Vascular System

Blood Vascular System

• The blood vascular system consists of the heart, arterial side, and venous side.
• The arterial side includes the aorta, distributing arteries, arterioles, and arterio-venous connections (capillaries).
• The venous side includes the superior and inferior vena cava, collecting veins, venules, and small venules that end at the arterio-venous connection.

Layers of the Blood Vessel Wall

• The wall of the blood vascular system is formed of three main layers: tunica intima, tunica media, and tunica adventitia.
• Tunica intima is the innermost layer, formed of simple squamous epithelium (endothelium) and a sub-endothelial layer of areolar connective tissue.
• Internal elastic lamina is the most external component of tunica intima, preventing complete occlusion of vessels during contraction.
• Tunica media is the middle layer, formed of circularly arranged smooth muscles, a variable amount of connective tissue, and external elastic lamina.
• Tunica adventitia is the outermost layer, formed of areolar connective tissue containing blood vessels (Vasa vasorum) and nerves.

Characteristics of the Aorta

• The aorta is a long, elastic artery with a wide lumen.
• It has a very thick elastic wall.
• The intima is thick, consisting of endothelium, subendothelium, and an unapparent internal elastic lamina.
• The media is very thick, formed of circularly arranged perforated elastic lamina with smooth muscle fibers in between, and an unapparent external elastic lamina.
• The adventitia is thin, formed of fibro-elastic connective tissue containing Vasa vasorum and nerves.

Medium-Sized Artery

• It has a thick wall but a narrow lumen.
• It has no valve in its lumen.
• The intima is thick and folded, consisting of endothelium, subendothelium, and an internal elastic lamina.
• The media is thick, consisting of circularly arranged smooth muscle fibers with some elastic fibers and an external elastic lamina.
• The adventitia is thin, containing elastic fibers and nerves.

Medium-Sized Vein

• It has a thin wall but a wide lumen.
• Valves may be present in some veins.
• The intima is thin, not folded, and has no internal elastic lamina.
• The media is thin, with no external elastic lamina.
• The adventitia is thick, rich in collagen fibers, with Vasa vasorum and nerve fibers.

Comparison of Medium-Sized Artery and Vein

• The wall of the medium-sized artery is thicker, while the wall of the medium-sized vein is thinner.
• The lumen of the medium-sized artery is narrower, while the lumen of the medium-sized vein is wider.
• The intima of the medium-sized artery is thicker, while the intima of the medium-sized vein is thinner.
• The internal elastic lamina is present in the medium-sized artery but absent in the medium-sized vein.
• The media of the medium-sized artery is thicker, with elastic fibers and smooth muscles, while the media of the medium-sized vein is thinner, with fewer elastic fibers.
• The adventitia of the medium-sized artery is thinner, with more elastic fibers, while the adventitia of the medium-sized vein is thicker, with more collagenous fibers and Vasa vasorum.
• Valves are absent in the medium-sized artery but may be present in the medium-sized vein.

Basilar Artery

• It supplies the brain tissue.
• It has a thin wall, thin intima, thin media, and thin adventitia.
• It has a well-developed internal elastic lamina.