Why Does The Spleen Get No Respect?

by Jennifer Coates, DVM

The spleen just doesn’t get any respect.  From the point of view of a veterinarian, this occurs for two reasons:
  1. We can completely remove it and our patients typically do just fine, and
  2. When we do have to deal with the spleen, it’s generally because it is causing big problems for our patients (e.g., it contains a cancerous tumor that is bleeding). 
This begs the question, why have a spleen in the first place?

Image: Lowchens Australia
The spleen is part of the immune system.  

In fact, it is the largest lymphoid organ in the body (according to Duke’s Physiology of Domestic Animals), which mean that in some ways you can think of it as a giant lymph node.

The spleen makes several different kinds of white blood cells, including lymphocytes and monocytes, which help fight infection.

The spleen also plays an important role in the manufacture and storage of red blood cells – the cells that contain hemoglobin and carry oxygen around the body.

When the body needs a sudden influx of oxygen, the spleen can contract and send out more blood and therefore more oxygen carrying capacity into the bloodstream.  This might happen when a dog is exercising or bleeding, for example.

The spleen also stores iron, which is a necessity when more hemoglobin needs to be produced.

In an adult animal, most red blood cells are made by the bone marrow, but the spleen is an important source of red blood cell production for the developing fetus.  Interestingly, this function can be ramped up again in an adult animal when necessary.

The spleen is also a filtering organ.  

Cells in the spleen remove old or damaged red and white blood cells from circulation and also engulf and destroy bacteria, viruses, and other microscopic foreign objects.  The organ uses some of the breakdown products of red blood cell destruction to make bile pigments (e.g., bilirubin), which are necessary for digestion.

So if the spleen does all of these wonderful things, how is it that a surgeon can completely remove one with little risk to the patient? 

The answer:  all of the spleen’s functions are redundant.  Other lymphoid tissues can take over some of its immune functions, the bone marrow makes red and white blood cells, and the liver can ramp up its ability to filter the blood when the spleen is missing.

This is not to say that a splenectomized animal is completely “normal,” however.

For example, dogs without spleens are much more likely to contract hemobartenollosis (a disease caused by infection of red blood cells with Mycoplasma haemocanis microorganisms that are transmitted by ticks) than are those with an intact immune system.

So, give your dog’s spleen the respect it deserves, but be thankful that if it starts causing trouble, your veterinarian can give it the old heave-ho if necessary.

Editor's note: What I am wondering, is there more to the spleen than we believe to be? Holistic medicine seems to pay much more attention to it.

Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian

Dr. Coates has recently joined the PetMD team and she is now writing for the Fully Vetted column; great blog, do check it out.

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.

Articles by Dr. Coates:
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The Other Side Of The Coin: The Cost Of Defensive Medicine
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Common Misdiagnoses (Part 1)
Common Misdiagnoses (Part 2)
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