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July 1983

Hematopoiesis in the Human Spleen

Author Affiliations

Department of Hematology Walter Reed Army Institute of Research Walter Reed Army Medical Center Washington, DC 20012

Arch Intern Med. 1983;143(7):1321-1322. doi:10.1001/archinte.1983.00350070037004

For a few months in utero the normal human spleen is hematopoietic. By the close of the fifth fetal month, the function has moved permanently into the marrow. Except for some lymphocytes and plasma cells, which continue to be contributed from the white pulp of the spleen and other lymph tissues, the production of blood cells—monocytes, granulocytes, erythrocytes, and megakaryocytes—remains entirely in the marrow. The basis of this obligatory behavior probably resides in the quality of the marrow's unique sinusoidal microcirculation, which provides an essential environment.1

In adult small mammals, the spleen remains a normal hematopoietic organ. In the mouse, for example, all available space in the marrow cavities contains what we would call, in the human condition, hypercellular marrow; there is no fat. In these tiny animals, the proportion of marrow cavity to solid bone is small and the life span of blood cells is relatively short (requiring

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