2.  There are three main types of blood vessels in the mammalian circulatory sys: 1. Arteries (smaller ones are called arterioles) 2. Veins (smaller ones are called venules) 3. Capillaries  As vessels get smaller, friction increases and blood pressure decreases  Blood pressure is highest in arteries since they are just coming from the heart Arteries are buried deep in our body for protection  if artery’s cut, you’ll bleed to death

3. VEIN CAPILLARY ARTERY ARTERIOLE

4. ARTERIE S CAPILLARIESVEINS DIRECTION OF FLOW Away from heart Between arterioles and venules Toward the heart WALLSElastic and thicker than veins 1 cell thick for easy diffusion Less elastic and greater capacity VALVESAbsent Present

5.  There are one-way valves in veins which point in the direction of blood flow  They prevent the flow of blood away from the heart  The contraction of skeletal muscles squeezes the veins, forcing the blood to move toward the heart  Varicose veins: chronic condition involving damaged valves.