Woody’s Valentine’s Day
Woody wanted to draw a heart for Valentines Day, but he wasn’t sure just what a heart looked like. Confused, Woody asked his teacher, “What a real heart looked like?”
“That’s
a very good question, Woody,” said his teacher. “Even though we draw
a heart like this for a Valentine (the teacher drew a heart like this
on the black board 
.
“Real hearts don’t look anything like this drawing. A heart is made of very strong muscles that pump the blood around the body. Blood delivers oxygen and food to the body’s cells and takes waste products away. In mammals, like you and I,” continued Woody’s teacher, “our blood makes two round trips through the heart. On the first trip the oxygen-poor blood from the cells is pumped from the right side of the heart into the lungs where it picks up oxygen, then, on the second trip, oxygen-rich blood from the lungs enters the left side of the heart and is pumped throughout the body.”
“Then does the heart just have two sides?” asked Woody. “Actually, Woody,” answered his teacher, “the heart has four chambers. The top chambers are called atriums and the lower chambers are called ventricles. The left and right sides of the heart are divided by the band of muscle called the septum. Each time the heart beats the right atrium fills with oxygen-poor blood and the left atrium fills with oxygen-rich blood from the lungs. Then these chambers contract to push the blood through valves into the ventricles. Then the ventricles contract and push the blood through more valves the right ventricle pushes blood to the lungs, the left pushes blood into a big blood vessel called the aorta, which takes the blood around the body.
“The ventricles have much stronger muscles than the atriums, which is why your heart beats with a ‘lub-dub.’ But this is only true for mammals and birds, other animals have fewer chambers to their hearts, and some don’t have any hearts at all.”
“Wow,” laughed Woody. “I bet they have trouble drawing Valentine’s Day cards!”