The differentiation of white pulp and red pulp in the spleen of human fetuses (72-145 mm crown-rump lenght).

Abstract

AbstractThe development of the white and red pulp in spleen from thirteen human fetuses measuring from 72 mm to 145 mm in crown‐rump length (CRL) was studied using the electron microscope. This period follows the development of the primary vascular reticulum (Weiss, '73).The white pulp appears first as a periarterial sheath with variable numbers of large and medium‐sized lymphocytes, monocytes, macrophages, and some granulocytes and erythrocytes. It is always rich in macrophages. At 90 to 100 mm CRL, reticular cells closely associated with collagen and having a distinctive dark hyaloplasm appeared first in the endothelium and close about blood vessels and then out in the pulp. In the white pulp they became circumferentially arranged about the central artery while in the red pulp they formed a branching reticulum. Small lymphocytes were present in increasing number in the periarterial lymphatic sheath after the development of the circumferential reticulum. The venous sinuses developed and the marginal zone stood out as an erythrocyte‐rich and macrophage‐rich shell of reticulum surrounding the periarterial sheath.