Kendalyn Gregar

Kendalyn Gregar

This week’s question was asked by: Kendalyn Gregar, fifth grader, LaGrange Elementary School.

Teacher: Chelsey Julio.

QUESTION: Why does blood turn blue?

ANSWER: My two brothers and I would argue about that when we were kids on the farm. Our general consensus was that blood was blue when it was in our body, but would turn red when it hits the air. Well, we were very wrong. It turns out the color of blood is determined by the amount of oxygen and carbon dioxide in the blood.

The primary function of blood is to carry oxygen and nutrients to our cells and to transport waste products away from cells. Blood is composed of plasma, which is mostly water, and three types of cells: red blood cells, white blood cells and platelets.

The most abundant cells are red blood cells that contain a protein called hemoglobin, which has iron atoms. It is the iron atoms that give blood its red color. We see this occurring in reddish rock formations that have a high iron content. Also, the reddish color of rust is due to iron. Think iron, think red color.

Oxygen in our lungs binds to the hemoglobin. So blood leaving the lungs in arteries, pumped by the heart, is high in oxygen content and bright red in color. The oxygen is delivered to tissues and organs and muscles, where it is used up.

The blood returning to the lungs in veins is depleted of oxygen, but instead has plenty of carbon dioxide. The returning blood, low on oxygen and high on carbon dioxide, yields a much darker red color. When we look at our veins, the color of the blood appears bluish because some of the dark red color is absorbed by the veins and skin. Mostly blue color is transmitted to our eyes. Contrary to popular belief, blood is never blue.

You can observe this phenomena by taking a small glass or plastic tube and filling it with water. Add a bit of red food dye to simulate red blood. Place the “blood filled” tube in a tray and slowly pour skim milk into the tray. The color of the “blood” will slowly change from a reddish to bluish tint as the milk covers the glass tube.

The use of the word “lifeblood” goes back as far as the year 1580. The meaning, of course, pertains to anything essential or vital to maintain life. Examples: Agriculture is the lifeblood of our country. Or spill one’s lifeblood in war.

The ratio of normal blood is 600 red blood cells for every white blood cell and 40 platelets. The red blood cells have an odd shape, described as a spiral biconcave disk with a flattened center. Both faces of the disk have a shallow bowl-like indentation. This shape produces extra surface area to allow more oxygen to be transported.

Red blood cells have no nucleus. The nucleus is extruded from the cell as it matures. A red blood cell can change shape, without breaking, as it squeezes single file through the capillaries.

There’s a lot to know about blood: classification into A, B, O groups, blood pressure, blood diseases, blood sugar, blood count, transfusions, genetic tests and cholesterol for starters.

Two vampires walked into a bar and called for the bartender.

“I’ll have a glass of blood,” said one.

“I’ll have a glass of plasma,” said the other.

“Okay,” replied the bartender, “That’ll be one blood and one blood lite.”

Send questions and comments to:

Larry Scheckel is a retired Tomah High School physics teacher.

If your question appears in this column, you will receive a free Value Meal from McDonald’s and a coupon from Pizza Hut.


Tomah Journal editor

Steve Rundio is editor of the Tomah Journal. Contact him at 608-374-7785.

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