【英语时差8,16】骨质疏松-上

（单词翻译）

Today’s word is: osteoporosis! Yep, osteoporosis. Now, you’ve heard this word before, and you know it has something to do with bones. But can you actually explain what it is? The answer is straight-forward. It comes down to the fact that we human beings need calcium¹ in our blood–it allows us to do all sorts of neat things, from contracting muscles to conducting nerve impulses. Where to get some calcium? Food is a good idea. But what if there isn’t always calcium-rich food to be had, as was probably the case for most of our long evolutionary² history? Best to store some for a rainy day. Store it where? The skeleton works! Then, when the blood runs low on calcium, a signaling device called the parathyroid gland³ can activate⁴ a process by which calcium is taken from the skeleton and put back into the blood.