Explore Your Body - Microbe Magic

Your heart is a great big pump and the most important muscle in your body! It is part of your circulatory system and makes sure oxygen and nutrients travel where they are needed in your body and gets rid of any waste products. It does this by pumping blood from its chambers - the left side pumps blood from your lungs to the rest of your body while the right side pumps the blood from your body back to your lungs.

But what does your heart look like? It is a muscle about the size of your fist that sits behind your ribs on the left hand side of your torso, just between your lungs. It is made up of four different chambers, two on each side of your heart. On each side of your heart, the chamber at the top is called the atrium (if you are talking both top chambers, they are called the atria). Each chamber at the bottom of your heart is called a ventricle (or the ventricles if you are talking about both of them). The chambers at the left and right hand sides of your heart are separated by a very thick muscle called the septum.

Each atrium and ventricle has a job to do but also they work together as a team. The atria fill with blood that is returning from you body in your veins and pass it along to the ventricles. The very strong muscles in your heart pump the blood from your ventricles out through your arteries, to the rest of your body. As your ventricles squeeze out your blood, the atria fill up with blood again so the process starts again in a great big circle!

Your heart deals both with oxygenated blood (blood that has oxygen) and de-oxygenated blood (blood without any oxygen) but it does this on separate sides. The left side of your heart collects oxygenated blood from your lungs. This travels to your heart through your veins and into your left atrium. It is then is pumped away from your heart by your left ventricle and goes through your arteries to the cells in your body. The right side of your heart collects the deoxygenated blood from your body and pumps it to your lungs where it picks up oxygen in your lungs and is returned to your heart for the whole cycle to start again!

Like your veins, your heart has valves to stop blood flowing in the wrong direction. The valves are like little doors, once the blood goes through, they shut and stop the blood flowing backwards! The valves that separate the atria from the ventricles are called the mitral and the tri-cuspid valves. The valves that stop the blood from flowing back into your heart are called the aortic and pulmonary valves.

If you listen to your heart beat using a stethoscope, you would hear a lub-dub sound. This is made by the valves inside your heart opening and shutting as the blood flows through them. When the mitral and tricuspid valves open and close, you hear the ‘lub’ sound. When your blood leaves your heart, the aortic and pulmonary valves open and close, you hear the ‘dub’ sound. This is the sound of a healthy heart!

Heart beats are slower in adults than in children, about 60 - 70 times per minute in adults but up to 90 times per minute when you are younger. Did you know that you can measure how many times your heart beats? You can find your pulse (there is a cool pulse experiment on the Experiments page) by pressing down firmly on the side of your neck or the inside of your wrist with two fingers (you might have to try a couple of different places before you find this, but it is there!). Can you feel a pulse, like a light movement under your skin? This is the blood moving through a large artery just under your skin. You pulse rate is the same as your heart beat. Count how many pulses you have in a minute – this is your pulse and is the same as the number of times your heart beats in a minute! Try doing this when you are sitting still and then immediately after you have done some exercise. Do you feel your heart rate, your pulse, increase? This means your heart is getting a work out and staying healthy as it pumps blood around your body more quickly!

Do you know what makes your heart pump blood around your body all day, every day and every night? Your heart is an involuntary muscle, you cannot control it, it works all by itself. Your heart has a special group of cells that generate electrical signals. These signals cause electrical impulses in the right atrium of your heart, in the sino-atrial node. Your right atrium also has special fibres that spread the electrical impulses to the rest of your heart, making it contract (squeeze very tightly to pump out the blood) and you get a heart beat. You can measure this electric activity on an ECG – an electro-cardio-graph!

Your heart, like any muscle, needs to be exercised regularly to keep it healthy. You need to run around and make your heart make your heart beat quickly to give it a good workout every day! There are other things you can do to keep your heart healthy. Eat a healthy diet that doesn’t have too much fatty food, especially saturated fat (see the section on ‘Fats’ in the ‘Healthy living’ section of Microbe Magic) or trans fats. This means eating only a little animal fat (like butter or the fat on meat) and processed food (have a look at the label on food packets to check for trans fats). One of the most important things you can do is make sure you do not smoke. Smoking can damage your heart and the blood vessels of your circulatory system.

What happens if something goes wrong with your heart? The arteries in your heart can become clogged and break down. This can lead to a cardiac arrest, what you might know as a heart attack. This is very serious but it can be fixed. It is better to avoid a cardiac arrest in the first place though, and look after your heart!