Urinary System
Questions Received:
Responses:
19th December 1997
This is something of a speculative answer until I can find a better explanation - perhaps the heightened activity of the bladder is due to the increased amounts of adrenaline and noradrenaline circulating in the bloodstream in response to the cold? These hormones are released from the adrenal medulla as part of a generalised stress response and promote energy mobilisation and the generation of additional heat: adrenaline and noradrenaline stimulate the liver to release glucose into the blood and cause a general rise in the basal metabolic rate. We usually assume that during an arousal response of this sort the activity of the urinary system will diminish - there is renal vasoconstriction and generally less urine is produced when we are under stress, so therefore it seems unlikely that the increased urge to urinate is due to increased output by the kidneys. As the wall of the urinary bladder is largely composed of smooth muscle (the detrusor muscle), it is possible that muscle tone in the bladder wall increases in response to the circulating catechol amine hormones so that pressure in the partially-filled bladder rises more than usual. (We need to know which hormone receptors are carried by these muscle fibres.) Such a pressure increase might cause the nervous system to come to the erroneous conclusion that the bladder is much fuller than it actually is, and give a feeling of urgency. Or could it be that extra cup of hot tea before going out?
Does a strong ammonia smell from the urine indicate a serious problem?
3rd February 1999
The pH of the body fluids has to be carefully regulated in the range 7.35 to 7.45, since deviations outside this range affects normal functioning of cells and body systems. One of the ways the kidneys have of excreting excess acid in the body fluids is to excrete ammonia (or rather, the ammonium ion: NH4+) in the urine. Exposed to air, the ammonium ions in urine change back to ammonia and produce the distinctive smell. The source of the excess acid could be from the diet, for example - acidic foods such as citrus fruits, vinegar and so on, or as a result of heavy exercise. This may be enough to produce transient rises in ammonium content of the urine.
Another component of urine which can result in the release of ammonia is urea, particularly if the urine is left standing for a while. Urea is produced during protein metabolism. The building blocks of proteins are amino acids, and these contain carbon, hydrogen, oxygen and nitrogen. When proteins are broken down by cells throughout the body by a process called deamination, ammonia is formed as a waste product and released into the blood. The liver converts this ammonia to urea which is then excreted by the kidneys. The amount excreted will therefore depend on the amount of protein consumed and the rate of protein breakdown in the tissues. On standing a specimen of urine will be exposed to oxygen in the atmosphere. The presence of oxygen converts the urea in the specimen back into ammonia. Hence, a specimen of urine can give off an ammoniacal smell if allowed to stand for any length of time.
If the ammonia smell becomes noticeable over longer periods, and particularly if it is accompanied by illness, then it is important to seek a medical opinion. An infection of the urinary tract can produce urine with a strong ammoniacal smell as many of the pathogens (commonly gram-negative bacilli found in the gastrointestinal tract) are urea-splitting organisms. A vaccine against persistent bladder and urinary tract infections is due to go on trial at the end of this year (Coghlan, 1999). The vaccine targets Escherichia coli, the bacterium responsible for 85 per cent of all urinary tract and bladder infections. Other clinical problems such as diarrhoea and respiratory problems can also increase the smell of ammonia. A metabolic disturbance such as diabetic ketoacidosis will lead to an increase production of ammonia as protein is utilised for heat and energy (gluconeogenesis).
References
Coghlan, A. (1999) Blessed relief - a simple jab could save women from an irritating problem. New Scientist, 2173, 7 (Feb 13).
Edwards, C.R.W., Bouchier, I.A.D., Haslett, C., and Chilers, E.R. (Editors) (1996) Davidson's Principles and Practice of Medicine. Edinburgh: Churchill Livingstone (p 589 ).
Why is there a tendency for my urine to smell of asparagus shortly after I eat the vegetable? Do I have a malabsorption syndrome?
27th April 1999
The smell is due to the presence of several sulphur-containing chemicals that are excreted into the urine by some people after eating asparagus: methanethiol, dimethyl sulphide, dimethyl disulphide, bis-(methylthio)methane, dimethyl sulphoxide and dimethyl sulphone (Waring, Mitchell, and Fenwick, 1987; Mitchell, 1989; Richer et al, 1989). These chemicals are thought to be produced by the breakdown of S-methylmethionine and asparagusic acid that are present in the asparagus. It appears that are you digesting, absorbing and metabolising the asparagus effectively, so this would not seem to be evidence of a malabsorption syndrome.
References
Mitchell, S.C. (1989) Asparagus and malodorous urine. British Journal of Clinical Pharmacology, 27(5), 641-642 (May).
Richer, C., Decker, N., Belin, J., Imbs, J.L., Montastruc, J.L., and Giudicelli, J.F. (1989) Odorous urine in man after asparagus. British Journal of Clinical Pharmacology, 27(5), 640-641 (May).
Waring, R.H., Mitchell, S.C., and Fenwick, G.R. (1987) The chemical nature of the urinary odour produced by man after asparagus ingestion. Xenobiotica, 17(11), 1363-1371 (Nov).
Over the last several months I have noticed urine smells strong in the absence of any infection. It is also more intense yellow in color. No diet change, no medication change, etc have taken place. No other symptoms....
28th July 1999
Several factors can influence the composition of urine and cause changes in colour and odour. Dietary components and some medications can indeed cause discolouration of the urine, but in your case you feel that these are unlikely to be involved. Another possibility is that your body is having to conserve water because your fluid intake is somewhat less than optimum for your current levels of activity or the prevailing environmental conditions. In such a situation the kidneys produce urine that is more concentrated than usual and has a more yellowish colour and stronger smell. Another possibility is that more bilirubin (a yellowish bile pigment) is being excreted through your urine than normal. Bilirubin is produced when haemoglobin is broken down, as for example when aging red blood cells are removed from the circulation. The blood levels of bilirubin can rise if more than usual is being produced, as for example in haemolytic anaemia, or if the liver is unable to process it effectively. As you will be aware, one of the signs of liver disease is jaundice, in which the skin and whites of the eyes (sclerae) become more yellowish as bilirubin accumulates. In these situations, the amount of bilirubin in the urine will rise and give the urine a more yellowish colour. If you are at all concerned by the signs you describe it will be worthwhile to visit your doctor who will be able to find out the underlying cause.
The odor and color of my urine has changed drastically within the past 6 weeks. No diet changes. What is this caused by?
3rd January 2000
It will be worthwhile visiting your doctor to discuss these changes. Various factors can influence the composition of urine, including dehydration, the presence of bile pigments from the liver, metabolites from certain drugs, the presence of blood, or the presence of myoglobin. Tests are available to enable a diagnosis to be made and then an appropriate treatment started, if required.
I'm an engineer at a company which is producing catheters with pressure sensors for urology studies (worldwide distribution). For reliability testing it is very important for us to know what a "normal" ammonia level and what a "high" ammonia level is in the urine of Humans. I cannot find this information anywhere.
28th January 2000
Fresh normal urine does not contain ammonia (NH3) as such, but it does contain ammonium ions (NH4+). These are formed in the kidney when ammonia is produced by tubule cells from glutamine and passed into the tubular filtrate where it rapidly combines with hydrogen ions (H+). Most medical textbooks suggest that 30-50 mEq of ammonium ions are excreted in the urine over a 24 hour period. It is difficult to express this in a way that relates accurately to a single urine sample, since the composition of urine and the quantity being produced at different times of the day are subject to circadian rhythms and to environmental factors such as diet and levels of hydration and physical activity. If conditions within the body become more acidic over a period of a day or two, then the output of ammonium ions increases - this is one of the key methods the body has to get rid of unwanted hydrogen ions and restore homeostasis. Thus, the ammonium level can fluctuate for a number of reasons, not all of which are linked with clinical problems.
Ammonia is quite toxic to many cells in the body, especially brain cells. It is one of the main contributors to the comatose state that develops in severe liver disease. The normal value of ammonia in the blood is 80-110 m g/100 ml. Most of the ammonia produced in the body is the result of the breakdown of amino acids (both within the body tissues and the lumen of the digestive tract) and is processed by the liver into the less-toxic substance urea which is then excreted in the urine.
In some abnormal clinical states such as liver disease and diabetes mellitus the urine may contain uncombined ammonia. Ammonia is also released from urine that has been left exposed to the air for some time.