When you get a cut or scrape and it starts to bleed, you probably just pop a band-aid on it and keep going with whatever you were doing. But did you ever stop to consider that red liquid oozing onto the little sterile pad? Blood is actually made up of a number of different types of cells with specific jobs. It also carries hormones to control bodily functions, glucose to give cells energy and infection-fighting antibodies.
You may know that blood is red because of the red blood cells in it which carry oxygen. RBCs contain a substance called hemoglobin, a complex iron-containing molecule that binds the oxygen and then releases it to the cells which need it. It also carries away the carbon dioxide. In the center of hemoglobin is an atom of iron, which is why iron is an important part of your diet. RBCs are made in the bone marrow and released into the bloodstream when they are mature. In their early growth phase, they contain a nucleus like many other cells, but in mammals, it is lost before they go into circulation. Birds and reptiles keep the nucleus in their RBCs.
Another other major family of cells in the blood are white blood cells. There are five types of WBCs — neutrophils, eosinophils, basophils, lymphocytes and monocytes. Their primary job is to fight various types of infections. In dogs, neutrophils are the most plentiful. In cats, lymphocytes sometimes predominate. Neutrophils will gravitate to areas of infection and ingest (or phagocytize) the invader and kill it. They also are destroyed in the process. When a wound is infected and you see pus, you are actually seeing the dead neutrophils that have gone to the site. A high neutrophil count can indicate an infection or inflammation. Sometimes viruses will decrease the neutrophil count, which helps them to multiply.
Eosinophils are often involved with allergic responses and parasite infections. If we see a pet with a high eosinophil count, we often will look for things like heartworm disease, intestinal parasites and allergies. Basophils are usually present in lower numbers and have a similar function to eosinophils. Monocytes also tend to be present in low numbers. They phagocytize old cells and other material and are often elevated in cases of chronic inflammation.
Lymphocytes are very important as they are responsible for producing antibodies. When they recognize a foreign organism entering the body, they will start to pump out the appropriate antibody. The key is that they have to have seen it before. This is also how vaccines work — by letting the lymphocytes recognize certain invaders so they can be ready to produce the antibodies if the pet is infected with the real thing.
The other major cell type in the blood are platelets. These help the blood clot by going to the site of the wound and sticking to it, acting like a band-aid. They go on to secrete chemicals that attract tissue-repairing cells to permanently fix the wound.
When a pet is sick, one of the tests we like to run is a CBC, which measures all of those cells and helps to give us a picture of what’s going on. If you have questions about the different kinds of bloodwork and other tests we run, don’t hesitate to ask.