What about diabetes makes one excessively thirsty?
The condition you are referring to is Diabetes Mellitis, which is essentially an inability of the body to adequately regulate blood sugar levels, and deliver glucose to the cells. Prior to the advent of blood sugar testing, diabetes mellitis was (and still is) detected by measuring the sugar content in urine (mellitis is latin for “sweet”).
When blood sugar levels rise too high, it is usually because there is insuffucient insulin available to facillitate transport of the glucose molecules across the cell membrane, hence it stays in extracellular fluid and reurns back to the blood stream.
Fom here it is transported to the kidneys. When gluciose reaches a threshhold limit, it will spill over into urine. However this proces is one of several stages within the kidneys, where some eliminated substances can actually be reclaimed prior to urination (water for example).
When glucose spills over into the filtrate, it substantually raises the osmotic pressure within the nephphron (the kidney’s basic mechanism of filtration), because of the enormous difference in concentraion either side of the membrane. Water is drawn across into the glucose rich filtrate as the two side try to achieve equilibrium. This additional water and the glucose are eliminated in urine.
This explains why undiagnosed diabetics notice an increase in urination frequency and an increase in thirst. It also explains why people with elevated blodd sugar levels become dehydrated.
As a diabetic, let me just say that when your blood sugar is really high, the thirst is unbearable - I would almost drink battery acid, urine, or even Diet Pepsi at that point. One of the few times I look towards my insulin shot almost like a “fix”.
Just to rephrase DVous Means answer:
As the blood sugar level rises, it can reach a point where the kidneys cannot hold it in the blood any longer. The sugar then goes out in the urine. But you can’t pee out pure sugar - the sugar pulls water out with it (The sugar is like a sponge). So, you lose water. Lots. And you get thirsty.
But in addition:
A second mechanism has to do with the fact that as the sugar level rises in the blood, the blood becomes more concentrated i.e. there is now relatively less water in it. This concentration of the blood makes you feel thirsty.
A third mechanism, one that can operate chronically, is that diabetics frequently get fungus in the mouth. This can dry it out. Thirst results.
Just a tweak: Many cases of type 2 (adult-onset) diabetes results not only from a lack of insulin, but from the body’s inability to use the insulin already there. Many people with type 2 diabetes are treated not with external insulin but with drugs that help the body use the insulin already being produced. Some are not treated with drugs at all; losing weight and exercising can restore the body’s ability to use its insulin and correctly metabolize its glucose.
In addition to Diabetes Mellitis there is also Diabetes Insipidus. Diabetes Insipidus gets its name from the sufferer’s insipid thirst. As far as I know it is a lot rarer and not really related to Diabetes Mellitis in any way except for some similar symptoms. Diabetes Insipidus is caused by a deficiency of antidiuretic hormone (ADH). This causes water to run through the body… well, like water.
Actually, I thought it got its name from the fact that the urine of those with the disease is flavorless (insipid), as contrasted with patients who have diabetes mellitus whose urine is sweet (mellitus = sweet like honey). I was a very brave or very mad man who first tasted the difference.
You don’t need to taste it, you can smell it. Just as you can smell it on their breath, you can smell it in the urine.
Thanks for the correction Biblio. It would be nice if I knew the meaning of the words I used in my posts. My bad.
I was trying to recall something that a teacher told me over 10 years ago. I should have checked my facts.
Karl Gauss mentions 3 mechanisms for increased thirst. Clearly excessive urination is the chief mechanism. In addition to the hyperosmolality*-stimulated thirst, and fungal infections, there is another mechanism, which is probably more likely & more serious than the fungal infection.
*Osmolality = total concentration of all dissolved substances.
*Hyperosmolality = too high total concentration.
The fourth mechanism applies to those individuals with type 1 diabetes mellitus, with an absolute insulin deficiency. When their insulin levels fall too low, not only do their sugar levels go way up, but they also develop a condition called keto-acidosis. Here, the cells are starved for glucose due to the lack of insulin, and use other metabolic processes to generate ATP. Byproducts of these metabolic pathways include ketones (acetone, and acetoacetone), and organic acids (B-hydroxybutyric acid). As the pH of the blood falls, the person hyperventilates to get rid of CO2 and bring the pH closer to the normal of 7.40. Hyperventilation can result in the loss of large amounts of fluid (think panting dogs here), thus worsening the already hyperosmolar state. Ketones and acids add to the overall osmolality, so that a diabetic in ketoacidosis might have a serum osmolality of 320 or higher, with the normal range being 275-290. This extremely high osmolality stimulates extreme thirst, until the osmolality becomes so high that brain functions start shutting down, and the person becomes comatose.
Prior to the introduction of chemical tests for sugars in the '60s and superfast instruments in the '70s, lab techs DID taste the urine to diagnose diabetes mellitus.
Those must have been really well-paid lab techs. I can’t imagine applicants were stampeding to win a position that involved regularly tasting other people’s piss. The very thought makes me shiver…
Moving past simple disgust, though, isn’t that dangerous? I think I’ve heard varying opinions on the, ah, cleanliness of human urine.
Interestingly enough, opinions on just this question of mine are flying back and forth in this thread.