Anemia in Animals, Part 1—Anatomy of the Red Blood Cell (RBC) • Long Beach Post

By Carl Palazzolo, DVM, Long Beach Animal Hospital 

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This is the first of a six-part series by Dr. Palazzolo that details anemia in pets.

 red blood cells

Photo by V. Yakobchuk.

Almost everyone has heard of anemia, but few people really understand what it is. When one of our doctors tells a client that their dog or cat has anemia, they invariably want to know what vitamin to give to correct it.

It’s much more complicated than that, as you will learn from this multipart series of articles on anemia. The information has been simplified for general understanding; without this background, the following articles in the series, which cover the actual diseases that cause anemia and how they’re treated, may be difficult to understand.

Red blood cells (RBCs) are made by the bones’ marrow when stimulated by the hormone erythropoietin. This hormone comes from the kidneys.

RBCs live for 120 days, after which time they are removed by the body in a complicated process involving organs like the liver, which recycles the iron in the RBCs. All of the organs involved with this are called the hematopoietic system.

When RBCs are first made, they have a nucleus (birds and reptiles have a nucleus) that disappears when the red blood cell matures seven to 10 days later. No nucleus present means that they cannot divide like other cells, but it does mean that they can be compressed, which becomes important when we talk about their physiology in the next article.

The outer layer of the red blood cells is made of proteins and lipids that allow oxygen and carbon dioxide to flow into and out of the RBC. This inflow and outflow occurs in the lungs and also at the level of each individual cell—a liver cell, for example.


A teaspoon, which is 5 ml, contains up to 10 million red blood cells. Think of how many red blood cells there are in this 20 ml transfusion bag! Photo courtesy of LBAH.

It is the hemoglobin in the RBCs that attracts oxygen to the RBCS. Iron is at the center of the hemoglobin molecule, and is the element that binds to oxygen. This is why we sometimes give iron to anemic animals.

RBCs’ red color is from the iron in their hemoglobin binding with oxygen. How red they appear depends on how much oxygen is attached to the hemoglobin. This is called oxygen saturation. This change in red color is utilized when we use an instrument called a pulse oximeter to measure oxygen saturation. This is an important instrument for us veterinarians in anesthesia and also when we are treating certain diseases.


The pulse oximeter allows us to determine the oxygen saturation percentage of the hemoglobin molecule in a red blood cell. This is vital information for us in a pet that is having a breathing problem, a pet that is anemic, and a pet under anesthesia. This picture is from our anesthetic monitor, showing an oxygen saturation of the hemoglobin molecule at 96%. This is where we want it to be. Photo courtesy of LBAH.

Normal blood is never blue. It looks blue when you look at veins through your skin because the skin changes the optical properties of the light passing through the skin. Cut yourself, and you will see that the blood that flows out is red, and now you know why.

Next week, we will have fun with red-blood-cell physiology!

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