About the Heart and Blood Vessels

The heart is the hardest working muscle in the human body. Located almost in the center of the chest, the heart of a child is about the size of his/her fist. During an average lifetime, the human heart will beat more than three billion times - pumping an amount of blood that equals about one million barrels. The heart is always working, 24 hours a day, seven days a week - even while we are sleeping.
 
A child's heart works just as hard as an adult's heart. In fact, a baby' s heart may beat up to 190 times a minute, while an adult's heart usually beats between 60 and 100 times a minute. The rate at which the heart pumps gradually slows down from birth to adolescence.
 
The cardiovascular system, composed of the heart and blood vessels,  is responsible for circulating blood throughout the body. A healthy cardiovascular system is vital to supplying the body with oxygen and nutrients.

How the heart works:

The heart is a large, hollow, muscular organ that pumps blood filled with oxygen and nutrients through the blood vessels to the body tissues. It is made up of:

• four chambers (two atria and two ventricles) that receive blood (the atria) from the body and pump out blood (the ventricles).
  
  • The right atrium receives blood from the body, which is low in oxygen and high in carbon dioxide.
  • The right ventricle pumps the blood from the right atrium into the lungs to provide it with oxygen and remove carbon dioxide.
  • The left atrium receives blood from the lungs, which is rich in oxygen.
  • The left ventricle pumps the blood from the left atrium into the body, supplying all organs with blood.
    
    
• four valves to prevent backward flow of blood: the aortic, pulmonary, mitral, and tricuspid valves. Each valve is designed to allow the forward flow of blood and prevent the backward flow.
  
  
• blood vessels that bring blood to the lungs, where oxygen enters the bloodstream, and then to the body.
  
  
  • The inferior and superior venae cavae bring oxygen-poor (blue) blood from the body into the right atrium.
    
    
  • The pulmonary artery channels oxygen-poor (blue) blood from the right ventricle into the lungs, where oxygen enters the bloodstream.
    
    
  • The pulmonary veins bring oxygen-rich (red) blood to the left atrium.
    
    
  • The aorta channels oxygen-rich (red) blood to the body.
    
    
  • An electrical system stimulates contraction of the heart muscle.

A network of arteries and veins also carry blood throughout the body.

• Arteries transport blood from the heart to the body tissues.
• Veins carry blood back to the heart.

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