IT CIRCULATES

• The circulatory system is the transport system of the human body. Your body is like a map filled with passageways of different sizes that are filled with blood. Arteries and veins are the body’s largest blood vessels. Arteries carry oxygen-rich blood away from the lungs and back through the heart so it can be delivered to all the cells of the body. Veins carry carbon dioxide wastes back to the heart and through the lungs so they can be exhaled. Capillaries are the tiniest blood vessels. They are especially helpful in the lungs, where the gas exchanges take place in microscopic, air sacs called alveoli that look like grape clusters under the microscope.
• At the very center of the circulatory system is the heart. Your heart is about the same size as your fist, but it is made of muscle. It’s job is to pump your blood through all those blood vessels. It never stops working, even when you are sleeping. It is the strongest muscle in your body. Your heart has four chambers, or spaces inside it: the left and right ventricle, and the left and right atrium. Each chamber is separated by a valve that only lets blood flow in one direction. The opening and closing of the valves is what you can hear through a stethoscope when you visit the doctor. The blood being pushed through the valves is what you can feel as your pulse.
• Blood looks like a simple red liquid when you have a cut or a scrape. That’s only because your eyes cannot see what is going on inside the blood at the microscopic level. The reason blood looks red to us is because it contains an iron-rich substance called hemoglobin. Hemoglobin is what allows blood to hold on to oxygen and carry it around the body. Hemoglobin is found in disc-shaped cells called red blood cells. There are also white blood cells in our blood. They are larger than red blood cells, and are important because they help us fight disease. Platelets, another kind of cell found in our blood, help us form scabs when we are injured so we don’t lose too much blood. All of these cells float in a liquid called plasma. Plasma also carries sugar to cells, and waste products away from cells.

Name:__________________________________

Answer the following questions based on the reading passage. Don’t forget to go back to the passage whenever necessary to find or confirm your answers.

1)   What is the function of the white blood cells?

2)   How alike arteries and veins alike?

3)   Based on other information in the passage, what gases can you infer are being exchanged in the alveoli? 

4)   What is the main idea of this passage?

  5)   Based on what you have read about red blood cells, what mineral is essential to include in your diet? Why?