The electron microscopy of the developing human renal glomerulus

• 1.1. Electron microscopic observations of developing human renal glomeruli are presented.
• 2.2. The Malpighian corpuscle develops as a mass of epithelial cells in continuity with the convoluted tubule. It is surrounded by a sparse, incomplete layer of basement membrane material.
• 3.3. Capsular space develops by cleft formation when the primitive glomerular tuft appears, leaving a single layer of Bowman's capsule on one side.
• 4.4. The cells that develop into visceral epithelial cells rapidly differentiate in appearance from the parietal cells by developing a more dense protoplasm and cytoplasmic foot processes. Foot processes are present only where the cells are apposed to the developing glomerular tuft.
• 5.5. The developing capillary tuft originates as broad sheets and cords of endothelial-like cells, and appears to be shaped by penetration of the visceral epithelial cells. There is no sign of invagination of a hollow vesicle in any preparation.
• 6.6. The glomerular basement membrane is a product of endothelial and visceral epithelial cells, and appears to receive a contribution in the form of double membranes from each.
• 7.7. Fully matured red blood cells are observed frequently, before capillary lumens are present. This is taken to indicate in situ development of red blood cells in the glomerulus. It is suggested that the capillary lumen develops about these red cells by retraction and shrinking back of endothelial cytoplasm.