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And it's taken as a long time to realize how important that can be but when that happens then the whole system plays itself out, just as I showed you a moment ago
人們花了很久才意識到這非常重要，這之后，整個系統就能運作了，如我剛才講的那樣
So whether you get it from 1,25D coming in from the outside 1,25D, or 25D you make it inside the cell, the same thing happens
不管是從外界來還是25D在細胞內生成，后面都一樣
but we now understand that this is the way the tissues are designed to work
現在我們知道這是組織工作的方式
It's the 25D present in the serum which gets into the tissues and then is converted to 1,25D
血清內有25D進入組織然后轉化為1,25D
And the reason for that if you stop to think about it is that 25D is present in the serum and that's thousand fold greater concentration than is 1,25D
你們可以想想原因，25D存在于血清中濃度是1,25D的一千倍
So there's three orders of magnitude more molecules of 25D present in the tissues than there is 1,25D and that becomes important
組織中25D的分子數大出三個數量級，這非常重要
because each tissue can make the amount of 1,25D it needs independent of what the other tissues have or need
這讓每個組織都能制造足夠的1,25D而不用管其它組織的情況
It can do it when it needs it and is not dependent upon a "one-size fits all" circulating through the body stream basing all the tissues at the same time
需要就能制造，不需要所有組織都依賴于一刀切的系統循環
It wouldn't want to activate all of those systems at the same time. That wouldn't make any sense
不需要同時激活所有這些系統，這沒有任何必要
I mean, if you're the good lord in designing the system you would do it this way rather than working through a circulating 1,25D level
我是說，如果你是造物主，你也會這樣設計，你也不會通過1,25D循環來進行
The only tissue that really respond importantly to circulating 1,25D is intestine mucosa and that's in the control of calcium absorption
唯一依賴1,25D循環的組織是腸粘膜控制鈣吸收
