| Abstract: | An electron microscopic study of the functional mesonephros in the 8-day chick embryo revealed the following features of the nephron: Proximal tubule cells. Nuclei are spherical and basally oriented. Mitochondri are round or elongate with clear-cut cristae. Intramitochondrial granules occur sporadically. The Golgi complex, lying adjacent to the nucleus in apical cytoplasm, consists of flattened lamellae and associated secretion droplets. The cytoplasm is filled with ribosomes which occasionally are spiral in arrangement. Characteristic microvilli project from the apical end of cells. Basal regions of the cells are bounded by a homogeneous basement membrane. Adjacent epithelial cells are separated at their base by wide intercellular spaces. Interdigitating processes between cells are common in this area. At their apices, cells are joined by junctional complexes. Distal tubule cells. Nuclei are round and centrally located. Microvilli are sparse and usually absent. When present, they are short and blunt. Cells are closely allied at their base and joined tightly at their apices. Interdigitating processes are not as prevalent as in proximal tubules. Infoldings of the plasma membrane are prominent and compartmentalize mitochondria. Glomerulus. Endothelial cells are elongate, bordering the capillary lumen, and their membranes contain definite slit-pores. Epithelial pedicels extend from the cell body, intergiditate with each other and rest on the capillary basement membrane. The latter consists of three layers resembling those in adults. The similarity in the fine structural characteristics between chick mesonephros and adult metanepros corroborates the holonephric theory of vertebrate kidney evolution. |
