39. ARTERY AND VEIN

Arteries and veins are blood vessels with a shared three-layered structure (tunica intima, media, adventitia) but distinct, specialized anatomy for transporting blood. Arteries are thick-walled, elastic vessels with narrow lumens designed to carry oxygenated blood under high pressure away from the heart, while veins are thinner, less muscular vessels with wide lumens and valves, transporting deoxygenated blood back to the heart at low pressure

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Anatomical Structure Comparison

Both vessel types consist of three layers, known as tunics, but differ in composition: 

• Tunica Intima (Innermost layer): Composed of endothelium. Arteries have an internal elastic membrane for flexibility, whereas veins generally lack this.
• Tunica Media (Middle layer): Contains smooth muscle and elastic fibers. This layer is significantly thicker and more muscular in arteries to withstand high blood pressure. Veins have a much thinner tunica media.
• Tunica Adventitia/Externa (Outermost layer): Composed of collagenous connective tissue. In veins, this layer is often thicker to support the vessel. 

Key Differences

• Function: Arteries carry blood away from the heart (typically oxygenated); veins carry blood toward the heart (typically deoxygenated).
• Valves: Veins contain one-way valves to prevent backflow (especially in the limbs), while arteries lack valves.
• Pressure & Wall Structure: Arteries operate under high pressure, resulting in rigid, thick, and elastic walls. Veins operate under low pressure, resulting in thin, collapsible, and less muscular walls.
• Lumen Size: Veins have a wider, larger lumen compared to the narrow lumen of arteries. 

Specialized Components

• Arteries: The aorta is the largest artery, taking blood directly from the left ventricle.
• Veins: The vena cava is the largest vein, returning blood to the heart.
• Exceptions: Pulmonary arteries carry deoxygenated blood to the lungs, and pulmonary veins carry oxygenated blood to the heart. 

Location in the Body

• Arteries: Generally located deeper within muscles for protection.
• Veins: Often located closer to the surface of the body, appearing bluish.