Blood vascular bed and pericapillary space in rat parathyroid glands.

The blood vascular bed and pericapillary space of the rat parathyroid gland were studied by scanning electron microscopy of vascular casts, freeze-cracked tissue blocks, and NaOH-treated tissue specimens. The findings were supplemented by transmission light and electron microscopy of sectioned tissue samples. The rat parathyroid gland contained a rich network of freely anastomosing capillaries. These capillaries were surrounded by marked pericapillary spaces that were demarcated by basal lamina of both capillaries and parenchymal cells. The pericapillary spaces contained many collagen fibrils and frequently issued some projections running deep into the sheets of parathyroid cells. The latter projections may be useful to supply the parenchymal cells located far from the capillaries. The collagen fibrils may regulate the flow of tissue fluid in the pericapillary space and convey parathyroid hormone, which is released at the apicolateral domain, into the capillaries.