Medical Nocturia, frequent need to urinate, causes

The elderly may retain fluid during the day which is mobilised by lying down.

Too many cups of tea or coffee before bed.

Renal or prostate disease or bladder outlet obstruction can also cause nocturia in which case your probably trying to urinate all day long.

 

I'm not nearly qualified to give you a definite answer, but my guess is, that it doesn't have to do with the time of day at all, but rather with your sleep patterns. The part of the nervous system which deals with stuff you can't control, like bowel movements, and urineproductioncontrol, pupil-dilation, heart-rate and so on, is called the autonomic nervous system. When you sleep, or relax, it enhances functions such as digestion. When your frightened, (let's say you're robbed) your heart-rate goes up, trachea is dilated, pupils dilate, but your digestion and urine-produciton goes down (to name a few functions).

Seems the nocturia is simply your body producing a lot of urine when you sleep, which usually is at night.

 

If you pay attention to your own patterns of urination, you'll notice that you urinate several times during the day...certainly more frequently than every 8 hours, usually more like every 2 hours or so. At night, you're not getting up every two hours to urinate, so you can sleep through an 8 hour night. If you drink a lot before going to sleep, you may have to get up once in the middle of the night to urinate, but that should be about it. Nocturia would be needing to get up several times during the night due to the urge to urinate, which is going to disrupt ones sleep, which is what makes it a problem.

Our bodies have circadian rhythms, synchronized by melatonin release (melatonin is released at night and lower when we're exposed to light), of all sorts of functions, as greghouse indicated, such as heart rate, digestive functions, sleep patterns, and yes, even kidney function. It does have to do with time of day more than sleep patterns (though normally, they're all synchronized to happen together). Disruptions of these rhythms, either due to disease or something as simple as lack of sleep (i.e., first day on the night shift), can desynchronize some or all of them. (Again, you may have noticed this if you've ever pulled an all-nighter or otherwise had sleep disrupted...excessively hungry the next day outside of your usual meal times, perhaps a more frequent urge to urinate, even your heart rate might feel a bit odd.)

 

Circadian rythms are proven to be endogenous, merely affected by melatonin release. Experiments in the 19th century proved that primates, locked in a room with non-variable light strength, kept circadian rythms.

 

Hmmm, I do get up several times a night to urinate. But I don't have any sleeping problems. I drink a lot in the hours before I go to bed...

 

Actually, the definition of a circadian rhythm requires it to be endogenous, it is not something "proven" but required. "Merely affected" is rather downplaying the role of melatonin for entraining the rhythms, although in the absence of photoperiodic cues, melatonin also has endogenous patterns of release. Not quite sure what point you were trying to make though.

 

Aren't there examples of plants/animals whos circadian cycle is not stimulated but dictated by external stimuli?

 

Circadian rythm = any rythmic behaviour with periodic time of 24 hours

 

No, that's a diurnal rhythm, which can be endogenous or driven by external cues. A circadian rhythm is endogenous, by definition. I know, the general biology textbooks never make this distinction between definitions of diurnal and circadian rhythms clear and leave a lot of students confused on this point, so that's probably where your confusion is coming from too.

 

In that case, thanx