绿OG 374页 阅读

joanwong

绿OG P374 阅读（翻译加段落结构分析）

※  逻辑信号词用下划线和黑体标出

In terrestrial environments, gravity placesspecial demands on the cardiovascular systems of animals.  Gravitationalpressure can cause blood to pool in the lower regions of the body, making itdifficult to circulate blood to critical organs such as the brain. Terrestrial snakes, in particular, exhibit adaptations that aid in circulatingblood against the force of gravity.

翻译：在陆地环境中，重力对动物的心血管系统有特殊的要求。重力压会促使血液积聚在身体下部，这样就很难将血液循环到一些关键的组织，如大脑。特别的，陆地上的蛇（简称陆蛇）就展现出了他们血液循环过程中为了对抗重力而增加的特殊适应能力。

The problem confronting terrestrial snakes isbest illustrated by what happens to sea snakes when removed from theirsupportive medium.  Because the vertical pressure gradients withinthe blood vessels are counteracted by similar pressure gradients in thesurrounding water, the distribution of blood throughout the body of sea snakesremains about the same regardless of their orientation in space, provided theyremain in the ocean. When removed from the water and tilted at various angleswith the head up, however, blood pressure at their midpoint dropssignificantly, and at brain level falls to zero.  That many terrestrialsnakes in similar spatial orientations do not experience this kind ofcirculatory failure suggests that certainadaptations enable them to regulate blood pressure more effectively inthose orientations.

翻译：陆蛇面临的问题可以通过探讨海蛇离开其支撑介质时面临的问题得到很好的说明。因为血管中的垂直压力梯度和与之相似的水压梯度可以相互抵消，所以只要海蛇呆在水里，无论他们朝向任何方向，他们体内的血液分布总是均匀的。然而，一旦它们离开水面，他们身体中部的血压会大幅下降，大脑的血压则会降至零。陆蛇就不会面临这种血液难以循环的问题，这说明他们一定有某种适应机能来确保他们在朝向任何方向时都能有效地控制血压平衡。

One such adaptation is the closer proximity of the terrestrialsnake's heart to its head, which helps to ensure circulation to the brain,regardless of the snake's orientation in space.  The heart of sea snakescan be located near the middle of the body, a position that minimizes the workentailed in circulating blood to both extremities.  In arboreal snakes, however,which dwell in trees and often assume a vertical posture, the average distancefrom the heart to the head can be as little as 15 percent of overall bodylength.  Such a location requires that blood circulated to the tail of thesnake travel a greater distance back to the heart, a problem solved by another adaptation.  Whenclimbing, arboreal snakes often pause momentarily to wiggle their bodies,causing waves of muscle contraction that advance from the lower torso tohead.  By compressing the veins and forcing blood forward, thesecontractions apparently improve the flow of venous blood returning to the heart.

其中一项适应机能就是陆蛇的心脏离它们的头很近，这就确保了它们在朝向任何方向时大脑里都能保持血液循环。海蛇的心脏则可以位于他们的身体中部附近，这样可以减少身体两端血液循环所需的工作量。然而，对于那些住在树上并且市场保持垂直姿势的树蛇来说，他们的心脏和头部的距离仅仅只有他们整个身长的15%。 这就要求尾部的血液循环穿过很长的距离回到心脏，这个问题可以通过另外一种适应机制来得到解决。树蛇在攀爬的时候都会暂时地停下来摆动一下身体，引起从躯干底部到头部的一系列肌肉收缩。通过压迫血管并迫使血液向前流动，这样的收缩显著地增加了静脉血液的向心脏的回流。

看完每段之后一定要在心里回想一遍并记住这一段的主要内容

第一段:第一句交代大背景：重力对陆地生物的心血管系统有特殊的要求。之后解释(illustrate)为什么会这样，并说明陆蛇应对这种特殊要求有其自身的适应机能。

第二段：通过将海蛇和陆蛇进行对比来说明陆蛇为什么会有特殊的适应机能(point)。因为体内和体外的压力梯度可以抵消，所以海蛇在水里可以朝向任意方向游动，而一旦上岸就面临和陆蛇一样的问题——重力导致大脑供血不足。(Illustrate)

第三段：分述了上一段说的特殊适应机能，一共有两种，一种是心脏离头部很近，另一种是在停下来摆动身体，通过肌肉收缩迫使血液回流(point)。并通过描述树蛇的特点来阐述第二种适应机能(illustrate)

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感谢分享！