You have probably seen blood in a film or filmstrip about blood, or even some fresh blood. But have you ever seen some preserved blood on a microscope slide?
Blood is a liquid with some small solid objects in it. The red blood cells carry oxygen. The white blood cells help the body to fight against infection and diseases. When the skin is cut, the platelets help to form a clot. This stops further bleeding.
The liquid part of the blood is called plasma. Plasma is water with lots of things dissolved in it, for example glucose.
The pump of you heart makes blood run in your blood vessels. One of the most important things that blood does is to carry things around the body. For example, it carries oxygen and glucose to the parts where they are needed. Blood also carries waste products away from the places where they are produced. This is why the blood and the blood vessels are called a transport system.
Here are some exercises for your heart to figure out how fit you are.
Use a box, chair or stool which is about 40-50 cm high for the physical exercise. Carry out the exercise like this. First, step up onto the box and stand on it with both legs straight. Then step down and stand on the floor with both legs straight. Step up and down like this for a total of four minutes. Do not try to go too fast. You should keep going at a steady rate of about one step up every two seconds. Step up and down, without stopping, for four minutes. Then sit down and rest.
Rest for exactly one minute. Then get your partner to take your pulse for 30 seconds. This is your first pulse reading. Write it down in your results table.
Rest for a further 30 seconds. Then get your partner to take your pulse for another 30 seconds. This is your second pulse reading. Write it down. Repeat the previous stage. This gives you a third pulse reading.
Work out your fitness score. Change over and let your partner do the fitness test.
We shall start with a couple of questions. Why do we have a heart? What does it do? What’s the pulse?
There are blood vessels all over the body. Some are easy to see, because they are close to the skin surface. Most blood vessels cannot be seen because they are buried deep among the muscles and other tissues. If you press your fingertips against some blood vessels you will feel a regular throbbing movement. This is called the pulse. Blood vessels which have a pulse are called arteries. They carry blood away from the heart. There are various places on the body where the pulse can be felt. The pulse is usually found on a person’s left wrist.
Each pulse throb is caused by a sudden rise in the pressure of the blood in the artery. What do you think causes this sudden rise in pressure of the blood in the artery? Okey, here’s another question: what makes the hot water move through the pipes and radiators of a modern central heating system?
Blood vessels are like pipes. The blood is like water. A pump is needed to move the blood through the blood vessels. This pump is the heart. Every time it beats, the heart forces blood out through the arteries. With each heartbeat there is a rise in pressure. This causes the arteries to swell, which is what you can feel at the pulse points. This explains why pulse rate is the same as heartbeat rate.
Your heart is the best pump ever made. In most people, the heart works all the time, without repair or servicing, for the whole of their lives. The speed at which it beats can be changed, in a few seconds, from about 70 to 140 beats per minute or more. Rates of 200 or more occur during violent exercise. Most important of all, the heart does not damage the blood as this passes through it. Blood is a delicate thing. No man has ever built a pump which is so gentle, so strong and so reliable. But the heart can go wrong if it is not looked after properly.