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BLOOD VESSELS
The cardiovascular system transports and distributes blood throughout the body carrying materials such as: oxygen, nutrients, hormones and waste products.
Arteries : carry blood away from the heart to other organs.
Arterioles : a small artery that delivers blood to a capillary.
Capillary : branches of arterioles, and the site of substance(s) exchange between blood and body tissues.
Venules : groups of capillaries within tissue that reunite to form small veins.
Veins : blood vessels that convey blood from tissues back towards the heart.
Heart → Arteries → Arterioles → Capillaries → Tissues → Venules → Veins → Heart
Structure of a Blood Vessel
1) Tunica Interna (Intima)
Innermost layer and the lining of a blood vessel with direct contact with the blood as it flows through the lumen (interior opening of the vessel). Innermost layer is simple squamous epithelium called Endothelium . Endothelium lines the entire cardiovascular system (heart and blood vessels) Next layer is the Basement Membrane (superficial to the endothelium) consisting of a framework of collagen fibres with significant tensile strength. Outermost layer is Internal Elastic Lamina which is a thin layer of elastic fibres with a variable window-like openings giving it a “swiss-cheese” look. These openings facilitate diffusion of materials through the tunica interna to the next thicker layer – Tunica Media
2) Tunica Media
Middle, muscular connective tissue layer composed of smooth muscle cells that regulate the diameter of the lumen; and many elastic fibres. Smooth muscle cells regulate blood flow, blood pressure, and prevents blood loss when a vessel is injured. Smooth muscle also helps to produce the elastic fibres of the tunica media allowing for vessel stretch and recoil. Most variable layer structurally among various vessel types
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