What Is the Spleen?

The spleen is an organ containing blood vessels and lymph nodes. It serves important immune functions.

The spleen is an organ located in the upper left part of the abdomen, behind the stomach and under the diaphragm. It is a soft, purple, vascular organ, shaped like a small smooth rounded catcher's mitt with notches on the upper front edge. The spleen contains blood vessels that carry and circulate bodily fluids and it works with the blood and lymph systems.

The size and weight of the spleen can vary. The average healthy adult's spleen measures about five inches long, three inches wide, and one and a half inches thick, and a healthy spleen weighs about six ounces. The spleen can become enlarged due to infections, cancers, liver disease, parasites, and other conditions, and can grow in weight to about four pounds.

The spleen has several functions: 

• Filtering the blood
  • This is the main function of the spleen 
  • Healthy blood cells pass through the spleen and circulate throughout the bloodstream
  • Red blood cells that are old, malformed, or damaged can't pass through and are broken down in the spleen by macrophages, which are large white blood cells that destroy unhealthy red blood cells
• Conserving iron
  • The spleen also saves useful components from the old cells, such as iron
  • The iron eventually returns to the bone marrow, where the protein hemoglobin is made
  • Hemoglobin transports oxygen from the lungs to the rest of the body
• Storing blood
  • The spleen can hold up to one cup of reserve blood
  • If the body experiences trauma and extra blood is needed, the spleen can release this reserve back into the body
• Part of the immune system
  • Along with lymph nodes, the spleen creates lymphocytes, a type of white blood cell that produces antibodies to help weaken or kill invaders, such as viruses and bacteria

The spleen is a useful organ, but it is not vital. A person may need a spleen removed if it becomes injured or cancerous. If this occurs, other parts of the body, including the lymph nodes and liver, can take over many of the spleen's functions. However, people without spleens are more vulnerable to infections.