Basal infoldings. Electron micrograph of the basal portion of a kidney tubule cell, showing the infolding of the plasma membrane. Note the aligned mitochondria. The infoldings of adjoining cells result in the interdigitations of cytoplasm between the two cells, x25,000.
nent in proximal and distal tubules of the kidney (Fig. 4.25) and in certain ducts of the salivary glands. Mitochondria are typically concentrated at this basal site to provide the energy requirements for active transport. The mitochondria are usually oriented vertically within the folds. The orientation of the mitochondria, combined with the basal membrane infoldings, results in a striated appearance along the basal aspect of the cell when observed in the light microscope. Because of this phenomenon, the salivary gland ducts that possess these cells are referred to as striated ducts.
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