Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A red blood cell leaves a capillary in the big toe. Name, in order, the main vessels and the chambers of the heart it passes through until it is back in the big toe. How many times does it pass through the heart?
The heart has four chambers. The right side receives blood with little oxygen from the body and pumps it to the lungs. The left side receives oxygen-rich blood from the lungs and pumps it to the body. Valves stop backflow. In double circulation, the blood passes through the heart twice in each round of the body.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Back to the heart. The cell goes through veins into the vena cava, and then into the right atrium.
Step 2. To the lungs. It moves into the right ventricle, which pumps it through the pulmonary artery to the lungs. There it takes in oxygen.
Step 3. Back to the heart. It returns through the pulmonary veins to the left atrium, and moves into the left ventricle.
Step 4. To the toe. The left ventricle pumps it into the aorta. Smaller arteries carry it down the leg to the capillaries of the toe.
Answer: vena cava, right atrium, right ventricle, pulmonary artery, lungs, pulmonary veins, left atrium, left ventricle, aorta, arteries of the leg. It passes through the heart twice.
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