Arteries and Arterioles

• thick and muscular elastic walls to withstand high pressure blood pumped from heart by contraction of ventricles
• elastic layer allows expansion and recoil of arteries which smooths surges of blood flow
• endothelium folded to allow expansion and to maintain pressure
• tough but stretchable allowing contraction and dilation
• blood surges can be felt as a pulse where arteries pass close to the surface of the skin or over bone
• Carry oxygenated blood away from the heart and towards the organs —apart from the pulmonary artery which carries deoxygenated blood away from heart to lungs
• arterioles — regulate flow by contracting muscle layers so blood is restricted through certain vessels (vasoconstriction) or relaxing smooth muscle layers so blow flow increases ( vasodilation )