Spleen Development

The spleen on the left side of the abdomen. It has been found to undergo four clear stages of development, with two of the main stages involved with the development of blood cells when the fetus is first growing, and later with the development of the body's immune system.

Red Blood Cell Formation

• The spleen first helps with both red and white blood cell formation from the 11th to 14th weeks of gestation.

Spleenic Tissue Formation

• The spleen starts to develop veins and spleenic tissue commonly referred to as lobules, usually in the 15th to 17th weeks of gestation. It no longer creates red blood cells, but stores them.

White Blood Cell Formation

• White blood cells become prevalent in the spleen from the 18th to the 20th week. Their appearance is the start of the immune system function of the spleen.

Immune System Formation

• B cells as well as T cells are present, which are key components of the immune system in the body starting from the 21st to 23rd weeks.

Other Key Developments in the Spleen

• The spleen cells become more obviously differentiated from the surrounding organs in the abdominal cavity, most particularly separating from the pancreas and the stomach as the spleenic cells, commonly referred to as lobules, mature. As the time for birth nears, the spleen's lobules smooth out and more B and T cells develop.