What are the major types of blood vessels in the human body?

The human circulatory system comprises three major types of blood vessels, each serving distinct functions in transporting blood throughout the body. These are:

1. Arteries

• Function: Carry oxygenated blood away from the heart to the tissues (except the pulmonary arteries, which carry deoxygenated blood to the lungs).
• Structure:
  • Thick, elastic walls to withstand high pressure from the heart.
  • Narrow lumen to maintain blood flow under pressure.
• Major Examples:
  • Aorta: The largest artery, distributing oxygenated blood from the heart to the rest of the body.
  • Coronary arteries: Supply blood to the heart muscle itself.

2. Veins

• Function: Return deoxygenated blood back to the heart (except pulmonary veins, which carry oxygenated blood from the lungs to the heart).
• Structure:
  • Thinner walls than arteries, as blood pressure is lower.
  • Larger lumen for easier blood flow.
  • Contain valves to prevent backflow of blood due to low pressure.
• Major Examples:
  • Superior and Inferior Vena Cava: Bring deoxygenated blood from the upper and lower body to the heart.
  • Jugular veins: Drain blood from the head and neck.

3. Capillaries

• Function: Facilitate the exchange of oxygen, nutrients, carbon dioxide, and waste products between the blood and tissues.
• Structure:
  • Extremely thin walls (one cell layer thick) to allow for efficient diffusion.
  • Smallest blood vessels, connecting arteries to veins.
• Key Role: Form networks called capillary beds in tissues for nutrient and gas exchange.