Blood: Where Does It Come From? Where Does It Go?

The average adult human has about ten pints of blood in their body.
For having such a large amount of  blood, we rarely stop to think about it. We know that our blood carries oxygen and nutrients to our cells, cleans and clots wounds and helps us fight diseases (through the white blood cells), but how much do we really know about it?

Firstly, we need to think about what composes our blood, and where it comes from. Blood is made up of four parts: red blood cells, white blood cells, plasma and platelets.

  • Red Blood Cells

Red blood cells are the part of the blood that carries oxygen to and away from our cells. These round cells are biconcave-shaped, having a bowl-like depression on each side. Red blood cells are produced by the body’s red bone marrow and usually have a lifespan of about 120 days. Fun fact for blood donors: the red blood cells are fully replaced within 56 days following a blood donation. When they become too old and need replaced, the cells are removed from the blood by the macrophages in the liver and spleen.

  • White Blood Cells

The disease-fighting part of our blood – white blood cells, also referred to as leukocytes – are made in the white bone marrow of the body. Usually, there are about 7,000 white blood cells in a microliter of blood. When fighting an illness, however, that number increases. Believe it or not, there are actually six main types of white blood cells (neutrophils, eosinophils,
basophils, bands, monocytes and lymphocytes), with each fighting different kinds of bacterial or parasitic infections. The white blood cells usually only have a lifespan of 13 to 20 days before they are destroyed by our lymphatic system.

  • Plasma

Plasma is the fluid part of the blood (made by the liver) in which the other parts are suspended. It’s made up of about 92% water and normally appears yellowish – though it can sometimes be milky after a meal high in fat. The remaining 8% of plasma is comprised of dissolved proteins, salts, glucose and other chemicals necessary to the body. Plasma also carries hormones and electrolytes throughout the body, making up the largest portion of the blood.

  • Platelets

The last part of the blood, platelets, are also made by white bone marrow and are responsible for clotting wounds. Humans have between 150,000 to 400,000platelets in each microliter of blood. These spiky-looking cells usually only last about ten days before they become too old and worn (and are destroyed by the lymphatic system).

As you can see, blood is more complicated than we tend to think.

Studies show that 1 in 7 people who go to the hospital will need blood. That may not seem like a huge amount, but when you consider that only 38% of the U.S. population are actually able to donate, and less than 10% of these eligible individuals actually do donate, the need becomes more apparent.

If we could all take the time once a year to donate blood, this simple deed would have a huge impact on the blood shortages hospitals face every day. Donating blood only takes about an hour, but it could have a lasting impact on the life of another.