鳃

Multi tool use
關於魚類的鰓,請見“
魚鰓”。
鳃是一种器官,很多水生动物依靠它将溶解在水中的氧气吸收到血液中。这种呼吸方式被称为鳃呼吸。最近的研究表明,鰓的進化起初並非為了呼吸,而是用來調節體液平衡,避免脱水。[1]
鳃被一层很薄的,具有通透性的膜所包绕。血液在内届的血管或者是腔隙里面流动,这样就可以尽可能的与外界的水接触到。鳃的位置不定:蠕虫和蟹的鳃在它们的肢体,贝壳动物的鳃则在它们的外套腔中,鱼的鳃在鳃裂。大部分动物的鳃是裸露的,但也有些鳃是被皮肤保护的,或者是为某些特别的结构保护(壳,外套,鳃盖)。为了增加与水的接触面积,鳃的形状有栉状,叶状,树状和丛状。鳃利用对流原则,即血液(血淋巴)流动的方向与水流动的方向相反,使得血液可以最大限度的补充氧气。在软体动物中(例如贻贝),鳃还有过滤食物颗粒的功能。
许多水生动物和一些在潮湿空气生活的陆生动物用鳃呼吸。如蜗牛(例外:肺螺亚纲),贝壳和其他软体动物,多种"蠕虫",蟹等,而鱼和两栖动物的幼虫(有些成虫还会)是鳃呼吸的代表。
而昆蟲大多是用氣管呼吸,只有少部分才用鳃呼吸(部分還會和器官相連),例如:蜻蜓, 蜉蝣和部分雙翅目的水生幼蟲。
大部分用鳃呼吸的动物会在水外的环境迅速窒息死亡,因为鳃叶极容易干燥,这也会因为水中的氧气耗尽而发生。
一些鱼类和蟹能通过特别的措施(如将水重新补充氧气),而能够较长时间脱水生活。
参考文献
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