[A quantitative ultrastructural analysis of fenestrations and basal laminae of the blood capillaries in the knee joint synovial membrane (author's transl)].

Studies were carried out on the materials comprising the knee joint synovial membrane, kidney and lung from 13 young dogs and the knee joint synovial membrane obtained surgically from a 16-year old boy. The number of endothelial fenestrations of the blood capillary in the synovial membrane was 330 per 100 mu2 of the fenestrated vascular bed in 3--4 day-old dogs, 938 in 1 month-old dogs, 570 in 2 month-old dogs and 530 in the boy. The conspicuous peak in the development of vascular endothelial fenestrations seen in the synovial membrane of the dogs at 1 month of postnatal age appears to reflect a rapid increase in the mechanical load for the knee joint about 1 month after birth. A similar peak was absent for the blood capillaries in the renal glomeruli where the endothelial fenestrations continued to increase for the first 2 months of the postnatal period in dogs. The basal laminae of blood capillaries in the synovial membrane were often observed to be multi-layered, and this was remarkable especially in the human material. However, the thickness of the laminae of blood capillaries in the synovial membrane, as well as in the renal glomeruli and the lungs, showed a gradual increase with advance of the postnatal age of puppies up to 2 months.