One of the spleen’s important functions is to filter (clean) the blood. It removes old red blood cells & breaks down their constituent parts for recycling (iron/haemoglobin). The spleen also removes abnormal cells & particles from the blood. The spleen contains a reservoir of blood & can release it like a “transfusion” if necessary, for example in the event of hemorrhagic shock (profuse bleeding). The spleen holds reserves of red blood cells, lymphocytes & can hold platelets in emergency situations.
You may have noticed that you dog can suddenly wake up & run instantly because their spleen is able to release it’s blood reserve into their vascular system very quickly. Injury to the spleen will obviously cause massive blood loss.
The spleen is classed as a hematopoeitic organ, capable of producing blood cells (as it does in fetal stages & early life). Although in normal dogs most blood cells are produced by the bone marrow, certain cells are still produced by the spleen. Under certain circumstances such as bone marrow failure, the spleen can produce more blood cells if needed (see extramedullary hematopoeisis) to maintain an adequate supply in the body.
The spleen contains red pulp & white pulp, which are separated by the marginal zone. It removes antibody coated bacteria & antibody coated blood cells, playing a significant part in immune system function. The spleen is full of long, convoluted blood vessels which twist & turn. The blood slowly works it’s way through them.
In the red pulp area of the spleen, areas of red blood cells that are infected with parasites have been marked by the immune system are bitten (called pitting) by the spleen to stop the spread of the infection & often the red blood cells are completely destroyed by the spleen. Sometimes so many red cells are damaged or destroyed that the animal becomes anemic. Rarely in cases of AIHA the pitting (biting off lumps) action of the spleen can continue even with drug treatment & splenectomy may be considered.
The white pulp acts as part of the lymphatic system & lymphocytes circulate through it as well as through the lymphatic system. The splenic white pulp plays an important part in the immune system’s attack against viruses, bacteria & other foreign invaders of the body.
Although, the spleen can be removed, this leaves the dog at far greater risk from infection & you will need to follow strict activity guidelines (see splenectomy).
Diseases of the spleen include:
1. Enlargement caused by certain auto-immune disorders, inflammatory bowel disease, some anemias, polycythemia (overproduction of red cells), bacterial infections, canine hepatitis & some drugs. Sometimes enlargement of the spleen is a symptom of another disease or illness, rather than a problem with the spleen itself.
2. Benign tumors.
3. Malignant tumors such as hemangiosarcoma – common in middle aged & elderly dogs, particularly large breeds. Other malignant tumors including lymphosarcoma, mast cell tumors, multiple myeloma.
4. Hematoma (a collection of blood outside the blood vessels), blood clots from injury to the abdomen, bleeding tumours, bleeding disorders.
5. Splenic torsion (twisting of a blood vessel) causing enlargement/congestion of the spleen. Sometimes stomach (gastric) torsion & dilation occur at the same time. Large breeds of dogs with deep chests are particularly prone to these problems.