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Skip to 0 minutes and 5 seconds Now we’ll talk about the function of the circulatory system. The function of the circulatory system is to transport the blood cells and the substances dissolved within the blood around the body. This includes the transport of oxygen to the tissues and the transport of carbon dioxide from the tissues back to the lungs to be exhaled. Each cell in our body needs oxygen in order to function. We need the oxygen to generate energy. And in that process, we also generate carbon dioxide as a waste product, and this needs to be transported back to the lungs to be removed. When we breathe in, air enters in through the nose and mouth where it becomes filtered and warmed.

Skip to 0 minutes and 51 seconds It then travels down the trachea, or windpipe, and divides into the two bronchi, one to the left lung and one to the right lung. The bronchi are like branches of a tree. As the branches divide, they get smaller and smaller, eventually becoming the bronchioles. At the end of the bronchioles, you have the small tiny sacs known as alveoli, and this is where we have the transport of oxygen and carbon dioxide from the air within the alveoli into the tiny blood supply surrounding them. Like most substances, oxygen moves from areas of higher concentration to areas of lower concentration by a process called diffusion. You can imagine it being like all the passengers on a bus.

Skip to 1 minute and 36 seconds Imagine they’re all sat all on the lower deck. Given the opportunity, half the passengers will move upstairs to the quieter area. This is like the process of diffusion. Oxygen moves from the crowded air in the alveoli into the less crowded area in the blood. It then travels through the blood system to the tissues. And again, it moves from the blood into the even less crowded area in the tissues. In the tissues, the oxygen is used, and carbon dioxide is produced, and carbon dioxide also follows its diffusion gradient, moving from areas of high concentration to areas of low concentration. The carbon dioxide moves from the higher concentration in the active tissues into the lower area of concentration in the blood.

Skip to 2 minutes and 25 seconds It then travels back to the lungs, and again, it moves from the slightly higher concentration in the blood to the even lower concentration in the air in the alveoli and is breathed out through the lungs. Thus, the function of the circulatory system is to provide a transport network for the blood from the lungs to the tissues and back again.

Function of the circulatory system

Watch Dr Natasha Barrett explain the function of the circulatory system, which pumps the blood around the body transporting oxygen and carbon dioxide.

You can download the Week 1 supplement, which contains additional images and descriptions to help you understand the topics covered in this video.

Why do you think the deoxygenated blood goes back to the heart and not straight to the lungs?

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This video is from the free online course:

Heart Health: A Beginner's Guide to Cardiovascular Disease

University of Reading