Miller S C
J Cell Biol. 1977 Oct;75(1):104-18. doi: 10.1083/jcb.75.1.104.
The medullary bone serves as a source of labile calcium mobilized during calcification of the egg shell in birds. Quantitative histological methods demonstrate that the numbers of medullary bone osteoclasts and nuclei per osteoclast remain unchanged during the egg cycle in the Japanese quail (Coturnix). Therefore, cyclic changes in bone resorption cannot be explained by modulations of osteoclasts from and into other bone cells, a mechanism previously suggested for certain species of birds. Rather, dramatic changes in osteoclast cell-surface features occur during the egg cycle, which might account for cyclic variations in resorptive activity. During egg shell calcification, osteoclasts with ruffled borders are closely apposed to bone surfaces; the cytoplasm is rich in vacuoles that contain mineral crystals and seem to derive from the ruffled border. At the completion of egg shell calcification, the ruffled borders and vacuoles move away from the bone surface, although the osteoclast remains attached to the bone along the filamentous or "clear" zone. Associated with the disappearance of the ruffled borders is the appearance of extensive interdigitated cell processes along the peripheral surface of the osteoclast away from the bone. These unusual structures, which may serve as a reservoir of membrane, largely disappear when ruffled borders and associated structures reappear. Therefore, in these hens, the osteoclasts modulate their cell surface rather than their population during the egg cycle.
骨髓骨是鸟类蛋壳钙化过程中可动员的不稳定钙的来源。定量组织学方法表明，在日本鹌鹑（Coturnix）的产蛋周期中，骨髓骨破骨细胞的数量以及每个破骨细胞的细胞核数量保持不变。因此，骨吸收的周期性变化无法用破骨细胞与其他骨细胞之间的相互转化来解释，而此前曾有观点认为某些鸟类存在这种机制。相反，在产蛋周期中破骨细胞的细胞表面特征会发生显著变化，这可能是吸收活性周期性变化的原因。在蛋壳钙化过程中，具有褶皱边缘的破骨细胞紧密贴附于骨表面；细胞质中富含含有矿物晶体的液泡，这些液泡似乎源自褶皱边缘。在蛋壳钙化完成时，褶皱边缘和液泡会从骨表面移开，尽管破骨细胞仍通过丝状或“透明”区域附着于骨上。随着褶皱边缘的消失，在远离骨的破骨细胞外周表面会出现广泛的指状细胞突起。这些不寻常的结构可能作为膜的储存库，当褶皱边缘及相关结构再次出现时，它们大多会消失。因此，在这些母鸡中，破骨细胞在产蛋周期中调节的是其细胞表面而非数量。
