Salt and Metabolism

 Just how salt became so crucial to our metabolism is a mystery; one

 appealing theory traces our dependence on it to the chemist ry of the late

 Cambrian seas. It was there, a half  billion years ago, that tiny  metazoan

 organisms first evolved systems for sequestering and circulating fluids.

 The water of the early oceans might thus have become the chemical prototype

 for the fluids of all animal life - the medium in which cellular operations

 could continue no matter how the external environment changed. This

 speculation is based on the fact that, even today, the blood serums of

 radically divergent species are remarkably similar. Lizards, platypuses,

 sheep, and humans could hardly be more different in anatomy or eating

 habits, yet the salt content in the fluid surrounding their blood cells is

 virtually identical. As early marine specics made their way to fresh water

 and eventually to  dry land, sodium remained a key ingredient  of their

interior,  if not their exterior,

 milieu. The most successful mammalian species would have been those that

 developed efficient hormonal  systems  for  maintaining  the  needed 

 sodium  concentrations.  The  human  body,  for example, uses the hormones

 renin, angiotensin, and aldosterone to retain or release tissue fluids and 

 blood plasma.  The result, under favorable conditions, is a  dynamic

 equilibrium in which neither fluid volume nor sodium concentration

 fluctuates too dramatically. But  if the  body is deprived of salt, the

 effects soon become dangerous, despite compensatory mechanisms.    

鹽與新陳代謝

 鹽為何成為人類新陳代謝的關鍵是一個謎；一個富有吸引力的理論認為我們對鹽的依 賴可從寒武紀海洋的化學變化中得到線索。

 五億年前，就是在那里，微小的后生動物首先 進化成與外隔絕的循環液體系統。  因此，早期海洋里的水可能是所有動物體內液體的化學

 原型--一個無論外界環境如何改變，其細胞活動仍將繼續的環境。  這個設想是建立這一事 實基礎上：  即使是在今天，物種迥異的眾多動物血清非常相似。

 蜥蜴、鴨嘴獸、綿羊和人 類，在解剖學和飲食習慣上完全不同，但細胞周圍的液體中的鹽含量卻基本上是相等的。 在

 海洋生物向淡水區域并最終向陸地移動的過程中，鹽始終是它們生存環境--如果不是外部環 境，其碼也是內部環境中的關鍵成份。

 最高級的哺乳類動物為保持所需的鹽濃度而進化出 了高效的內分泌系統。 例如，人體為了保留或釋放組織液體和血漿而使用高血壓蛋白原酶、

 血管緊張素、醛固酮等激素。  這樣在有利的環境下，液體與其中鹽濃度之間形成的動態平 衡，兩者均不致出現大起大落。

但如果身體里喪失了的鹽分，盡管有各種的補償機制，后 果將馬上極其危險。

譯路通武漢翻譯公司整理

2012.7.11