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Skip to 0 minutes and 9 seconds Part one of this practical involves a demonstration. Obviously, it wouldn’t be safe or feasible for you to work with human blood at home, so I’m going to demonstrate this for you. Earlier today, we obtained some blood from some of our volunteers. Here, I have some whole blood. You can see that it’s red and liquid.

Skip to 0 minutes and 33 seconds The average adult human has five litres of blood in their body. It’s about the same volume as this bottle.

Skip to 0 minutes and 43 seconds If we take the blood and allow the blood cells to settle to the bottom, the blood separates into layers. At the bottom of the tube, we end up with the cells. And we can see here the cells in the blood make up about 45% of the volume. Above the red blood cells, we have a very thin layer of white blood cells. So we can see that there are many, many more red cells than there are white blood cells. Above the cells, we have the yellow straw coloured liquid. This is the plasma, and it also contains the tiny platelets floating within it.

Skip to 1 minute and 27 seconds If we take this plasma, and we centrifuge it once more, so we spin it so the cells fall to the bottom, we end up with a yellow liquid known as plasma. So now, it has no cells in it whatsoever. Plasma is the liquid part of blood. It contains salts and sugars and transports the proteins around the body. We also then have the platelets. This is a suspension of platelets. Platelets are tiny cells and when they’re in their resting state, they form this pearlescent sheen.

Skip to 2 minutes and 13 seconds When we activate the platelets, they send out their spiny protrusions to stick together, and hopefully, we’ll see that happening.

Demonstration of how blood clots: An overview

In this video, Dr Natasha Barrett gives an overview of the different layers of blood that occur when it separates.

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This video is from the free online course:

Heart Health: A Beginner's Guide to Cardiovascular Disease

University of Reading