09 April 2006

Your blood

Maybe we find the colour red so vibrant and dramatic because it’s the colour of life itself: the bloodstream, flowing throughout the body and nourishing its billions of cells.

Maybe we find the colour red so vibrant and dramatic because it’s the colour of life itself: the bloodstream, flowing throughout the body and nourishing its billions of cells.

It’s also likely no coincidence that we associate red with danger, given that the sight of blood means injury.

What is blood?
Blood is a rich, diverse substance, made up of cells and other useful bits floating in solution. The cell part consists of red blood cells (RBCs), which carry oxygen and give blood its crimson hue; white blood cells, whose main task is to fight infection; and platelets, cell ‘pieces’ vital in the clotting process.

The yellowish fluid in which these cellular parts are suspended is called plasma. It is 90% water but also contains nutrients, proteins, hormones and waste products.

What does blood do for you?
If the blood vessels are like a system of river channels, then blood is the ‘river of life’ itself, carrying oxygen and nutrients to the cells and carting off their waste products. But this river also carries special defenders to fight invaders, and has the means to stop leaks from its banks.


Nutrition and waste removal
The red blood cells are primarily responsible for transporting oxygen from the lungs to the cells. The RBCs contain haemoglobin, a protein specially designed to carry the oxygen, and release it wherever cells are oxygen-hungry. The RBCs are also the main carrier of the cellular waste product carbon dioxide, which they transport back to the lungs.

Red blood cells, which have a definitive shape - like plump discs compressed at their centres (a bit like a hockey puck) – are nonetheless incredibly flexible, which they demonstrate as they squeeze single file through the capillaries, the tiniest vessels leading to and from the cells.

The white blood cells circulate in the bloodstream so they can access areas of infection and fight intruder germs, as well as cancerous cells. White blood cells can move in and out of the bloodstream to reach affected tissues. The blood contains far fewer white than red cells, although the body can increase production of white blood cells to fight infection.

Sealing leaks
When a blood vessel breaks, platelets gather and help close off the leak. Proteins called clotting factors also help to form a solid plug to prevent bleeding inside and on the surfaces of our bodies.

When large blood vessels break, clotting may not be enough. That’s when medical intervention comes in handy, with dressings or stitches to help control bleeding. And, if you’ve lost dangerous amounts of blood, a transfusion may be necessary.

How does the body make more blood?
The blood is constantly replenishing itself. Blood cells are produced primarily in the bone marrow (soft tissue inside the bones). As children, most of our bones produce blood. As we age this function is relegated to just certain parts of the skeleton.

The life of a red blood cell is about four months, white blood cells a few days to months, and platelets about nine days. Each day, you produce new red blood cells to replace those that die or are lost from the body. The body contains more red blood cells than any other type: the ratio is about 600 RBCs for each white blood cell and 40 platelets.

What can you do for your blood?
Give it! OK, that sounds more like ‘what your blood can do for other people’, but actually, the more of us with healthy blood who donate, the more there’ll be available in the blood banks – and the more likely you’ll have ready, safe access to a transfusion should you need it one day.

Blood: did you know?

  • There may be something to the expression ‘red-blooded male’: men average 5,200,000 red blood cells per cubic millimeter, while it’s 4,600,000 per cubic millimetre for women.
  • The adult body contains about 5 litres of blood, which makes up 7 to 8 percent of your total weight.
  • Plasma is normally a clear, pale yellow, but after a high-fat meal it can actually appear milky.


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