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This question is a result of my personal experience... But I guess that is common for many of us.

My school timing is 8:00 am to 1:30 pm (usually). During normal school days I typically urinate one time - at most. Last month when we were having our practical exams. There was a fair amount pressure to score high marks and on top of that we did not have any experience with such exams.

On the day of the exam; I was a little nervous about it. The duration of the exam was 3 hours (from 9:00 am to noon) on this day I urinated 4 times.

Several of my friends also experienced the same thing.

I was nervous also because for two days before the exam I was afraid that I hadn't even touched any book. I was thinking that there was no way I could cover the whole book and so I didn't even touch them.

Now that I have final exams in about two weeks, I was revising my syllabus but for the last 4 days I'm not touching the books. Whenever I start solving problems from any chapter then I have to look back for the formulas. Questions in which reasoning is asked, I love to do that. I'm not very good at memorizing things and so when I compare myself to my classmates then I feel like I don't know anything and so I give up. I have never tried to memorize anything, but I understand the reasoning and the concepts.

Kindly give me the answer of the question.

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It's all about chemical reactions in your body triggered by your brain.

Lot's of researches and documents confirmed this is what happens when you face a stressful situation.

Stress -> hypothalamus -> sympathetic nerves -> Epinephrine (Adrenaline) -> more urine flow

Domino neural connectivity (Thinking) => Domino Chemistry (Body reaction = stress and anxiety)

Situations like thinking about exam and how hard it would be or how it could change opportunities and feelings in your life you are triggering a chain of neural and chemical responses.

If your thoughts (Activated neurons) end with unsolved vital problem, it activates parts of your brain that is related to anxiety and stress and these neurons activate hypothalamus. Hypothalamus turns sympathetic nerves on. The sympathetic nerves release adrenaline (epinephrine). And adrenaline cause more urine flow.

This example shows two more kinds of polyuria

If you are interested in how increasing level of adrenaline results in more urine flow read this and this and this.

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  • $\begingroup$ Your last two links both state that an increase in adrenaline causes renal flow rate to decrease. So how does an increasing level of adrenaline result in more urine flow? $\endgroup$ – lightweaver Sep 29 '15 at 13:51
  • $\begingroup$ Copy and paste exact part to approve your claim. You are wrong about decreasing of the urine flow by the higher blood pressure. It's almost 50 years that scientists confirmed adrenaline has direct effect on urine flow as I explained from sources. For more info read these two like below. ajplegacy.physiology.org/content/192/1/131 AND forums.studentdoctor.net/threads/… The higher your blood pressure gets, the more urine flow $\endgroup$ – Eftekhari Sep 30 '15 at 20:03
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    $\begingroup$ I can see easily that increased blood pressure increases renal flow. But is there not a second effect that decreases renal flow? Your newest link in your answer mentions "by acting directly on the kidney to decrease the output” and your first link mentions "Postganglionic neurotransmitter of the sympathetic nervous system norepinephrine causes particularly in the afferent arteriole vasoconstriction, thereby reducing the renal blood flow (and thus the GFR).” Also, my textbook (Campbell Biology) states that the sympathetic nervous system inhibits urination. $\endgroup$ – lightweaver Oct 1 '15 at 9:34
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I found an interesting article that dealt with anxiety and micturition. There are no proven or accepted view on this. There are a few theories as to how this happens.

I am quoting it:

There are several beliefs for what causes frequent urination from anxiety, and the likelihood is that all of these factors play a role:

Muscle Tension – This is one of the most likely causes of frequent urination. When you have anxiety, your muscles get very tense. This tension puts pressure on your bladder, which in turn makes you feel like you need to urinate more than you would otherwise.

Evolutionary Adaptation – Another theory is that there is an evolutionary reason that frequent urination would be advantageous. Remember, anxiety is the misfiring of your healthy fight/flight system. In times of fear, urination may keep the body lighter by losing extra weight, making it easier to flee.

Light Overload – It's also possible that, because anxiety is a misfiring of the fight/flight system, your body may simply be lightly overloaded. The fear is not intense enough to cause immediate urination, but it may make it harder for you to feel like you can hold it back. Also, those with anxiety are more prone to focusing on different sensations unintentionally. There are often times when you may feel the need to urinate slightly but your body has no problem ignoring the feeling and holding it back. With anxiety, it's possible that your brain is focused on the sensation, potentially causing you to feel like you need to urinate more than you do.

Finally, anxiety can also change your body chemistry, altering your digestion and changing the way you process nutrients. That may cause more water to pass through your body.

Source:http://www.calmclinic.com/anxiety/signs/urination-problems

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