Your heart's will to beat, to keep going, is incredibly strong. If the heart fails, so does everything else… Because it's your heart's job to deliver to every cell, to every nook and cranny of your body, the substance which keeps it alive - oxygen.
But how does the body do this? The hard graft of carrying oxygen is done by some of the smallest and most peculiar cells in your body. These red blood cells are well suited to the job of carrying oxygen around your body. Each red blood cell contains millions of haemoglobin proteins. They have a structure that oxygen likes to bind to. Haemoglobin is bulky, so there's not much space for anything else inside the red blood cells, which have to squeeze into tiny blood vessels. It means that red blood cells are unique amongst all your cells because to carry oxygen, they don't have a nucleus.
25 trillion red blood cells are pumped around the body, completing a circuit within a minute. Each cell makes a tortuous journey through wide arteries that surge like a river in full flood. Then branching off into smaller streams called arterioles. It's perfectly shaped to squeeze through tiny, slow-moving capillaries. And without a fat nucleus, it just about gets through. Here, in the smallest, narrowest vessels, our cell does the job it's built for… it releases its payload of oxygen into the tissues.
The reason that your body goes to such lengths to ensure a steady supply of oxygen is because oxygen is an essential ingredient in unlocking the energy you need to survive. Oxygen from the red blood cells passes into every other cell of your body. Here, there are hundreds of little powerhouses called mitochondria. They burn oxygen to release all the energy you need to live your life. But to do this, they need another ingredient which also comes via the bloodstream… food.
Food is mainly absorbed in the small intestine, which is covered in finger-like projections called villi and microvilli. They increase the surface area of your gut to that of a tennis court, so you can absorb as many nutrients as possible. If you eat a packet of crisps, for example, it is here that the crisps will be broken down into smaller and smaller particles until they are reduced to glucose, which is small enough to be absorbed into the bloodstream, ready to be transported to the mitochondria in your cells.
Over your lifetime, you will eat more than 50 tons of food, and take over 800 million breaths, which you will convert into enough energy to power a house for five years. And every mouthful and every breath has finished here, with your mitochondria using the energy released to get you through the day.
Video summary
This short film offers a look at respiration and a tour around the circulatory system and digestive system in the human body, through blood vessels and into mitochondria.
There is a detailed description of red blood cells and their journey around the body including the way that they are adapted to carry oxygen.
It also has up-close images of mitochondria and the villi inside the small intestine.
This short film is from the BBC series, Inside the Human Body.
Teacher Notes
Students could make models of red blood cells in capillaries or of mitochondria.
Alternatively, they could draw a journey to the mitochondria for two characters - an oxygen atom and a glucose molecule.
This short film will be relevant for teaching biology at KS3 and KS4/GCSE in England, Wales and Northern Ireland and National 4/5 in Scotland. Appears in AQA, OCR, EDEXCEL, CCEA, WJEC, SQA
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