How does the heart work?

By Zoë Gamble

Something I’ll never forget is doing human dissection in my second year of university. Walking into the dissection room for the first time, we were confronted with six bodies on six metal tables, and a very distinctive smell. Our first incision was straight down the middle of the chest, and over the next few months we dissected different parts of the cadavers.

A fascinating organ to dissect is the heart. In real life, our hearts look completely different to the image we normally think of as being ‘heart shaped’.

hearts

 

 

 

 

 

 

 

 

 

 

The heart is a muscular organ, working constantly to pump blood around our bodies. It is made up of four chambers; the right and left atria, and the right and left ventricles. These actually make two distinct pumps and the blood cannot flow freely between them.

The journey through the heart

The right atrium receives blood into the heart. In diagrams like the one below, this is the one on the top left of the image. This blood is deoxygenated as it has supplied it’s oxygen to where it is needed by our tissues and organs. It enters the right atrium of the heart via two large veins, the superior and inferior vena cava.

From the right atrium, the blood travels down into the right ventricle through the tricuspid valve. Valves in the heart prevent blood from flowing backwards.

From the right ventricle, the blood is pumped upwards to the lungs through the pulmonary arteries, passing through the pulmonary valve.

Diagram of the human heart

CC BY-SA

In the lungs, our blood picks up oxygen, which we call oxygenated blood. The contraction of the right ventricle is not strong enough to send the oxygenated blood all around the body after the lungs, so the oxygenated blood needs to return to the heart for another pump.

Entering the heart through the pulmonary veins, oxygenated blood comes into the left atrium. Continuing down through the mitral valve, it passes to the left ventricle.

From the diagram above, you can see that the muscle of the left ventricle (pictured in pink) is thicker than that of the right ventricle. This is because of the additional force needed to pump blood around the whole body rather than just the lungs.

From the left ventricle, blood passes through the aortic valve, and exits the heart via the aorta. The aorta is a very important blood vessel, accommodating high pressure blood from the heart. The aorta has elastic properties, allowing it to expand as higher pressure blood passes through, then contract passively.

From the aorta, the blood travels through smaller arteries and capillaries to reach all parts of our body. Returning through veins, the now deoxygenated blood returns to the vena cava, and the journey begins again.

To the anatomy student however, colourful diagrams of the heart are just the beginning. Trying to learn parts of the heart from diagrams is a far cry away from reality. You can imagine the difficulty trying to pinpoint key features of the heart below!

Dissected pig’s heart. By Theleftorium CC BY-SA

 

I did not, as you have probably guessed, become a heart surgeon. Eventually the smell of the preserving chemicals in the dissection room was too much for me! I became a science communicator instead, telling other people about all the cool things I’d learned like how our hearts work!

For a video of how our hearts work, check out this one I made for the BBC Bitesize website for KS2:

bitesize_circulation

 

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Posted in Biology