Blood vessels - Arteries, Veins & Capillaries

Blood vessels form a vital network in the circulatory system, transporting blood throughout the body to deliver oxygen and nutrients and remove waste products.
There are three main types: arteries, veins, and capillaries.

Function:
- Arteries carry oxygen-rich blood away from the heart (except the pulmonary artery) and withstand high pressure from the heart’s contractions.
- They branch into smaller arterioles, which connect to capillaries
Structure:
- Thick, muscular walls with three layers: tunica intima (inner), tunica media (middle, with smooth muscle and elastic fibers), and tunica adventitia (outer).
Key Features:
- Aorta: The largest artery, originating from the left ventricle.
- Arteries help regulate blood pressure through contraction and relaxation of smooth muscle.

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Function:
- Veins return oxygen-poor blood to the heart (except the pulmonary veins, which carry oxygen-rich blood).
- They contain valves that prevent backflow and rely on skeletal muscle contractions to aid blood flow, especially against gravity.
Structure:
- Thinner walls than arteries, with fewer smooth muscle cells and elastic fibers. Like arteries, they have three layers but less pronounced tunica media.
- Valves throughout their length help prevent backflow.
Key Features:
- Superior and Inferior Vena Cavae: The largest veins, delivering blood to the heart’s right atrium.

Function:
- Capillaries facilitate the exchange of oxygen, nutrients, and waste between the blood and tissues.
- Oxygen-rich blood releases oxygen to the tissues, while carbon dioxide and waste products are picked up for removal.
Structure:
- Smallest blood vessels, with walls made up of a single layer of endothelial cells.
- Their thin walls allow for efficient gas and nutrient exchange.
Key Features:
- Capillaries connect arterioles to venules and form a vast network throughout the body to regulate blood flow.

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