Humans have a double circulatory system because blood moves through the heart twice (pulmonary and systemic circulation)
Allows lots of oxygenated blood to be transported quickly
Pulmonary circulation - The right side of the heart and blood vessels carries deoxygenated blood from your heart to the lungs and back again
Systemic circulation - The left side of the heart pumps oxygenated blood to every part of the body that uses oxygen
Artery structure:
Thick layers of muscle in walls to allow them to stretch to withstand the high blood pressure
Elastic fibres to recoil back into their original shape
Small lume to help maintain high blood pressure
Artery function:
Carry blood with high oxygen away from the heart to the organs or body
Vein structure:
Thinner muscular and elastic walls than arteries because blood is under low pressure
Larger lumen as well
Valves to prevent back flow of blood
Vein function:
Carry blood with low oxygen from organs towards the heart
Capillary structure:
Very thin walls (one cell thick) to make sure there is a short diffusion distance for oxygen
Capillary structure:
Very narrow lumens which only allow one red blood cell to pass through at a time - slows blood flow to increase the time that oxygen and glucose can diffuse into cells
Capillary function:
Capillaries connect arteries and veins
Found close to all cells where substances easily diffuse between the blood and cells