问题 问答题

动脉血压降低时交感神经是如何进行调节的

答案

参考答案:

解析:交感神经的升压作用大致可通过以下四条途径得以实施:
(1)对心排出量的影响:当动脉血压下降时,压力感受器兴奋性降低。向心血管中枢发出的神经冲动减少,心交感中枢和缩血管中枢活动增强,同时使心迷走中枢活动减弱,从而使之心肌收缩力增强、心率加快、心内传导加速。总的效应是使心排出量增多,如其他因素不变则血压升高。
(2)对全身阻力血管的影响:血压下降时,由压力感受器兴奋性降低,传入到心血管中枢的神经冲动减少,使缩血管中枢兴奋性活动增强,通过交感缩血管神经的传出冲动,使阻力血管收缩,外周阻力增加,反射性引起血压升高。
(3)对肾上腺素和去甲肾上腺素分泌的影响:当血压降低之后,反射性引起全身性的交感神经系统的兴奋,其中支配到肾上腺髓质的交感神经兴奋可使其肾上腺素和去甲肾上腺素的分泌增多,从而使心脏活动加强,心排出量增加;外周阻力增强,导致血压升高。
(4)对于血管紧张素分泌的影响:由于血压降低,肾入球小动脉压力下降,以及交感神经的兴奋,使肾素的分泌增多,从而激活血浆中的血管紧张素原,使其血管紧张素转为血管紧张素1(AI),后者在转换酶的作用下转变为血管紧张素11(All)。All一方面直接使小动脉收缩增加外周阻力,升高血压;另一方面可以使容量血管收缩,回心血量增多,间接升高血压。All还可以促进肾上腺皮质的醛固酮分泌,促进Na+、H2O等重吸收,进而增加血容量提高血压。

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     One day I visited an art museum while waiting for my husband to finish a business meeting. I was
expecting a quiet  1  of the splendid artwork.
     A young   2  viewing the paintings ahead of me   3    nonstop between themselves. I watched them a
moment and decided the lady was doing all the talking. I admired the mans  4   for putting up with her    5    stream of words.   6    by their noise, I moved on.
     I met them several times as I moved   7   the various rooms of art. Each time I heard her continuous
flow of words, I moved away  8  .
     I was standing at the counter of the museum gift shop making a   9    when the couple approached
the  10  . Before they left, the man   11    into his pocket and pulled out a white object. He 12   it into a
long stick and then  13   his way into the coatroom to get his wifes jacket.
    "Hes a  14    man," the clerk at the counter said. "Most of us would give up if we were blinded at such
a young age. During his recovery, he made a promise his life wouldnt change. So, as before, he and his
wife come in   15    there is a new art show."
     "But what does he get out of the art?" I asked. "He cant see."
     "Cant see! Youre  16  . He sees a lot. More than you and I do," the clerk said. "His wife   17   each
painting so he can see it in his head."
     I learned something about patience,   18    and love that day. I saw the patience of a young wife
describing paintings to a person without   19    and the courage of a husband who would not   20  
blindness to change his life. And I saw the love shared by two people as I watched this couple walk
away, their arms intertwined (交缠).
( )1.  A. touch
( )2. A. lady  
( )3. A. chatted
( )4. A. attempt
( )5. A. vivid
( )6. A. Adopted
( )7. A. through
( )8. A. anxiously
( )9. A. comment
( )10. A. entrance
( )11. A. plugged
( )12. A. made
( )13. A. led
( )14. A. brave
( )15. A. wherever
( )16. A. wrong
( )17. A. describes
( )18. A. kindness
( )19. A. support
( )20. A. get
B. view  
B. man  
B. argued  
B. independence
B. constant
B. Adapted
B. to    
B. urgently
B. decision
B. exit  
B. held  
B. lengthened
B. found  
B. rough  
B. whatever
B. silly
B. draws  
B. pride
B. sight
B. hope  
C. wander
C. couple
C. screamed
C. wisdom
C. casual
C. Conducted
C. towards
C. quickly
C. purchase
C. front
C. reached
C. brought
C. forced
C. smart
C. whichever
C. equal
C. shows  
C. enthusiasm
C. expectation
C. allow
D. stare        
D. clerk        
D. yelled        
D. patience      
D. vague        
D. Disturbed    
D. from        
D. sensibly      
D. profit        
D. queue        
D. bent          
D. broadened    
D. tapped        
D. generous      
D. whenever      
D. unique        
D. decorates    
D. courage      
D. confidence    
D. cause