An electrical system controls your heart and uses electrical signals to contract the heart's walls. When the walls contract, blood is pumped into your circulatory system. Inlet and outlet valves in your heart chambers ensure that blood flows in the right direction.

Your heart is vital to your health and nearly everything that goes on in your body. Without the heart's pumping action, blood can't move throughout your body.

Your blood carries the oxygen and nutrients that your organs need to work well. Blood also carries carbon dioxide (a waste product) to your lungs so you can breathe it out.

A healthy heart supplies your body with the right amount of blood at the rate needed to work well. If disease or injury weakens your heart, your body's organs won't receive enough blood to work normally.

through the

trachea or 

windpipe, which separates into two branches, called

bronchial tubes or bronchi

, one entering each lung. The bronchi subdivide

many times inside the lungs, analogous to the branching pattern of grapes, finally

becoming hairlike tubes called

 bronchioles In the last part of the terminal

bronchioles are tiny bubble-like bunch of structures called

alveoli or airsacs
When you breathe in, or

, the diaphragm muscle contracts. Inhaling moves

the diaphragm down and expands the chest cavity. Simultaneously, the ribs move up and

increase the size of the chest cavity. There is now more space and less air pressure inside

the lungs. Air pushes in from the outside where there is a higher air pressure. It pushes into

the lungs where there is a lower air pressure. When you breathe out, or

, the

diaphragm muscle relaxes. The diaphragm and ribs return to their original place. The chest

cavity returns to its original size. There is now less space and greater air pressure inside the

lungs. It pushes the air outside where there is lower air pressure.
The following are the three major

, with their roles:

1.

Heart–

 pumps the blood throughout the body

2.

Blood vessel–

 carries the blood throughout the body 

 Arteries -

 carry oxygenated blood away from the heart to the cells,tissues and organs of the body Veins - carry deoxygenated blood to the heart Capillaries - the smallest blood vessels in the body, connecting thesmallest arteries to the smallest veins - the actual site where gases and nutrients are exchanged3.Blood  – carries the materials throughout the body

The heart is divided into four chambers. The upper chambers are termed atria, and the interatrial septum constitutes the division between them. The lower chambers are termed ventricles, and are divided by the interventricular septum.

Left atrium. The upper right chamber of the heart. The left atrium receives oxygenated blood from the lungs and pumps it down into the left ventricle which delivers it to the body.

Right atrium. The right upper chamber of the heart. The right atrium receives deoxygenated blood from the body through the vena cava and pumps it into the right ventricle which then sends it to the lungs to be oxygenated.

Left ventricle. The left lower chamber of the heart that receives blood from the left atrium and pumps it out under high pressure through the aorta to the body.

Right ventricle. The lower right chamber of the heart that receives deoxygenated blood from the right atrium and pumps it under low pressure into the lungs via the pulmonary artery.