Blood Vessels

• Arteries carry blood away from the heart.
• Arteries have a narrow lumen which decreases volume and increases pressure, enabling blood to be carried to all areas of the body.
• Arteries have lots of smooth muscle and elastic tissue; smooth muscle contracts, forcing blood through the artery at high pressures. Elastic tissue recoils, maintaining the pressure.
• Veins carry blood to the heart.
• Veins have a wide lumen which carries blood at a low pressure.
• Veins contain only some smooth muscle and elastic tissue to allow for muscle contraction and elastic recoil as blood flows at a lower pressure than an artery - this prevents damage to the vein.
• Endothelium cells that line the lumen provide a smooth surface for smooth blood flow.
• The lumen is the space that the blood travel through. It is the space between the endothelium and the muscle layer.
• Capillaries are the site of gas exchange.
• Capillaries have a one cell thick endothelium for rapid diffusion.
• Capillaries have a high surface area to volume ratio (SA:V) for rapid diffusion.
• Capillaries have a narrow lumen which allow for rapid diffusion.
• The low pressure in the capillaries prevents them from bursting.
• Blood vessels have three layers: tunica intima, tunica media, and tunica adventitia.
• Tunica intima consists of an inner lining called the endothelium, which is smooth and allows for easy flow of blood.
• Veins have pocket valves which prevent the backflow of blood.
• Veins have skeletal muscles which squeeze the vein to return the blood back to the heart.
• Arterioles carry blood from artery to capillary bed. They reduce blood pressure between the arteries and the capillaries to prevent damage to capillaries.
• Venules collect blood from capillary beds and return blood to veins.
• Artery -> arteriole -> Capillaries -> Venule -> Vein -> Heart