by: Destiny Smith

Facts
• The human heart’s mass is between 250 and 350 grams
• The human heart is about the size of a large fist
• The heart is one of the most important organs in the human body
• The heart is continuously pumping blood around our body through blood vessels
• The heart is located in your chest so it is well protected by your rib cage
• The heart is made up of four chambers, the left atrium, right atrium, left ventricle and right ventricle
• Blood going towards the heart is carried through veins
• Blood coming from the lungs to the left atrium is carried through the pulmonary veins
• Blood coming from the body to the right atrium is carried through the superior vena cava and inferior vena cava
• When your heart contracts it makes the chambers smaller and pushes blood into the blood vessels, after your heart relaxes again the chambers get bigger and are filled with blood coming back into the heart

Heart, arteries, veins, capillaries, platelets, blood vessels, plasma and lungs are all organs and body systems included in the circulatory system.

Main purpose of the circulatory system
The Circulatory System is responsible for transporting materials throughout the entire body. It transports nutrients, water, and oxygen to your billions of body cells and carries away wastes such as carbon dioxide that body cells produce. It is an amazing highway that travels through your entire body connecting all your body cells.

• An artery is a tube-like blood vessel that carries blood away from the heart
• Systemic arteries deliver oxygenated blood around the body
• Pulmonary arteries deliver deoxygenated blood to the lungs
• An arteriole is a smaller branch off an artery
• Blood flows through arteries at 30 cm per second in the main artery, down to 2 cm or less per second in the arterioles
• Arteries run alongside most of the veins that return blood to the heart
• The walls of arteries arc muscular and can expand or relax to control the blood flow
• Arteries have thicker, stronger walls than veins, and the pressure of the blood in them is a lot higher
• In old age the artery walls can become very stiff, this hardening of the arteries, called arteriosclerosis, can cut blood flow to the brain

• Veins carry de-oxygenated blood back to the heart, which gives them a dark blue/purple color
• Unlike arteries that need to have strong walls in order to withstand pressure from the heart, veins have thinner, more collapsible walls
• Veins contain a mechanism that prevents backflow, as they sometimes must transport blood against natural gravity