The Circulatory System

• The circulatory system is an important system of human body whose main components are the heart,the blood,and the blood vessels.
• The heart is really a muscle and has the size of your clenched fist.
• It is located a little to the left of the middle of the chest,under the ribcage and between the lungs.
• A fibrous tissue or sac,called the pericardium,encloses and protects the heart.
• The heart has four chambers.The upper half is composed of the right and left atria while the other half is composed of the right and left ventricle.
• The atria are the chambers that fill with the blood returning to the heart from the lungs and body.
• The ventricles squeeze,pumping out the blood to the body and lungs.
• A muscular wall,called the septum, separates the right and left chambers.
• Valves separate the atria from the ventricles.There are four valves that aid in the flow of blood.
• Two of the heart valves are the mitral valve and the tricuspid valve.
• The other two are called the aortic valve and pulmonary valve
• The mitral valve is located between the left atrium and left ventricle.
• The tricuspid valve is located between the right atrium and right ventricle.
• Aortic valve: A valve that prevents backflow of blood into the left ventricle.
• Pulmonary valve: Valve between the left atrium and the left ventricle.
• Systole - Contraction phase where the heart pumps out blood to the body or lungs.
• Diastole - Relaxation phase where the heart fills with blood from the veins.
• The blood that leaves and returns to your heart move through many tubes called the blood vessels.
• There are three kinds of blood vessels according to their functions:the arteries,the veins and the capillaries.
• Blood vessels that carry the blood away from the heart are arteries.
• As the arteries move away from the heart they divide into thinner arteries called arterioles.
• The arteries have three layers:

  The endothelium is the inside layer and provides a smooth lining for the blood to flow through the artery.

  The media is the middle part which is made up of a layer of muscle and the elastic tissue allowing it to expand and contract.

  The adventitia is the tough covering protects the artery.