Venules and veins

• venules — tiny veins which connect capillaries to large veins
• veins have a larger diameter and thinner walls than arteries so have a larger lumen
• veins contain valves to prevent back flow of blood
• the pressure is lowest in the veins
• velocity of blood increases again due to a decrease in the total cross sectional area compared with the carpillaries
• most blood stored in veins - largest cross sectional area
• skeletal muscles around veins contract, squeezing them, returning blood to the heart
• return blood from the organs to the heart - carry deoxygenated blood apart from the pulmonary veins which take oxygenated blood from lungs to the heart