简述钠泵的本质、作用和生理意义？
参考答案：
本质：钠泵每分解一分子ATP可将3个Na+移出胞外，同时将2个k+移入胞内。
作用：将细胞内多余的Na+移出膜外和将细胞外的K+移入膜内，形成和维持膜内高K+和膜外高Na+的不平衡离子分布。
生理意义：①钠泵活动造成的细胞内高K+为胞质内许多代谢反应所必需；
②维持胞内渗透压和细胞容积；
③建立Na+的跨膜浓度梯度，为继发性主动转运的物质提供势能储备；
④由钠泵活动的跨膜离子浓度梯度也是细胞发生电活动的前提条件；
⑤钠泵活动是生电性的，可直接影响膜电位，使膜内电位的负值增大。
A couple of years ago, I went to a lady’s house to buy some medicine. Upon entering the house, I 36 that there was a piano in the living room beside the wall.Being a piano music lover and player, I asked if the woman played. She said “Yes” and 37 that she had been taking lessons—at the age of 54! “I have been 38 for 8 years now.” I said, after hearing her words. “Then you must play a song for me before you leave,” she requested(请求). I thought she was kidding and I 39 smiled. When I had bought the medicine, she asked me to play some music. I thought for a moment and 40 to play David Lanz’s Return to the Heart, 41 she had so much passion(热情)for and interest in music, and it’s one of my favourite songs. I played the song to the best of my ability(能力), putting as much emotion into it as possible. She 42 it. As I was about to step out of the door, I heard a weak voice calling, “Young man!” I 43 , and saw an old lady taking one little step at a time with the help of another woman. “I wanted to come out to thank you for the 44 song that you played. I have been very sick, and it’s very hard for me to get out of bed, but I really wanted to thank you for the song. It made me feel good.” she said. With that, she turned around and walked slowly back to her room. I was deeply touched by her 45 and felt a deeper understanding for the song. It was 46 to its name, returning to one’s heart to 47 and joy.
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