Urine is the fluid which is secreted or separated by the kidneys from the blood, and it is the principal means of removing the worn-out tissues, especially the nitrogenous and saline matters, from the system. It is a very complex fluid, and its composition varies considerably in different classes of animals—among the mammalia mainly in accordance with the nature of the food. The study of its modifications in disease forms a most important branch of medical work.
Healthy human urine, when freshly discharged, is a clear fluid of a bright amber colour, a bitter, saltish taste, and a peculiar aromatic odour. Its normal reaction is acid, and its specific gravity ranges from 1.015 to 1.025. A healthy adult man passes on an average about 50 fluid ounces (2½ pints) of urine in twenty-four hours; but the amount is subject to very great variation, being diminished during sweating or thirst, and increased under the influence of cold, by copious draughts of fluid, and by large quantities of salt or sugar, as well as many drugs. The solid constituents of the daily urine weigh a little more than two ounces, of which about half is urea. The other substances present are, in the order of quantity, common salt (sodic chloride), phosphates, sulphates, uric and hippuric acids, with others of less importance (mucus, colouring matters, &c.). The amount of solids, and the amount of urea excreted per day, are less subject to variation in health than the whole amount of urine; careful observations of the daily excretion of urea are of special importance in the investigation of disease.
Urea (chemical formula, ) is the form in which the great bulk of the nitrogenous waste of the human body is removed. It is formed in the tissues during the disintegration of proteid material, and carried by the blood to the kidneys, which separate it and pass it off in the urine. It is very readily soluble in water; it gives rise to carbonic acid and ammonia during ordinary decomposition. It is of great interest chemically, being the first animal product which has been produced by synthesis from inorganic bodies without the intervention of animals.
Uric acid, , is present in small amount in the blood and in normal urine, chiefly in combination with alkaline bases. It is very much less soluble in water than urea; its presence in excess in the blood is the chief feature of the gouty state. In birds and reptiles, however, the nitrogenous waste is excreted chiefly in this form.
Hippuric acid, , is usually present in still smaller quantity in human urine; but in considerable amount in the urine of herbivora.
Of abnormal constituents dissolved in urine the most frequent is albumen (see KIDNEYS, DISEASES OF). It causes no change in the appearance of the urine; but is visible as a white precipitate, insoluble in dilute acids, on boiling, or on the addition to the urine of certain reagents (e.g. strong nitric acid, solution of picric acid). Sugar is excreted in considerable quantity in Diabetes (q.v.) Mellitus. Bile is present in cases of jaundice, giving the urine a deep yellow, brown, or almost black colour. Blood-pigment may be present without blood-corpuscles, but more commonly as a result of the escape of blood from the vessels in some part of the urinary tract. It may give the urine either a bright red or a 'smoky' tint.
Urinary Deposits.—When normal urine is allowed to stand in a clear glass vessel for some hours, a faint cloudy deposit appears at the lower part, consisting chiefly of mucus from the bladder. When the urine is much concentrated, as it often is in hot weather, a dense yellow or reddish deposit frequently appears as it cools, readily soluble on heating. This consists of urates, and is generally of no particular importance; but it may be an indication of digestive disturbance. When from administration of alkalies or otherwise the urine is alkaline, a white deposit of phosphates may be seen, readily dissolved by acids. If habitually present, it may arise from an unhealthy condition of the bladder. Small red 'cayenne-pepper' grains consist of uric acid, and indicate its presence in excess. Larger particles (gravel) are sometimes passed; if retained in the bladder they lead to the formation of a Calculus (q.v.). Casts of the kidney tubules in Bright's disease, pus from the kidney or bladder, and blood are distinct indications of disease in the urinary tract. They are best recognised under the microscope. Numerous other deposits are occasionally met with, but they are not of any general interest.
Incontinence of Urine, or Eneuresis, is a troublesome affection, far more common in childhood than in more advanced life, and in boys than in girls. The child may have no bad symptom of any kind that can be detected, but it is in the constant habit of discharging its urine in bed during sleep. The act may take place once or several times during the night, and sometimes there is an interval of a night, but seldom more. The child may often be broken off this unpleasant habit by proper domestic management, as withholding any excess of fluids before going to bed, and waking it, and making it discharge the contents of the bladder at the time when the elder members of the family retire to bed. Some hard substance—e.g. a cotton-reel in a towel—fixed over the spine, so as to prevent the little patient from lying on its back, sometimes has a good effect. When such means as these fail, recourse must be had to medical advice. Some slight abnormality in the urinary organs is frequently present, the correcting of which cures the complaint. Cold douches to the spine, combined with the internal use of chalybeates, are frequently serviceable. The most certain remedy, however, is extract of belladonna, given at first, according to the age of the patient, in doses varying from th to th of a grain, twice daily, and increased, if required, till it gives rise to marked constitutional disturbance. The various forms of mechanical pressure that have been suggested, with the view of preventing the passage of the urine, cannot be too strongly reprobated. The same remark applies to the too common practice of punishing the unfortunate child for a condition which is utterly beyond its control, and deserves pity rather than chastisement.
Retention of Urine is the term employed in medicine to signify a want of power to discharge the urine from the bladder, and it must be carefully distinguished from a far more serious affection known as suppression of urine, in which also no urine is passed, because in this case there is none in the bladder. Retention may arise from Stricture (q.v.) in any of its forms; from some mechanical obstacle in the urethra, a tumour, calculus, clot of blood, &c.; from enlargement of the prostate gland; from want of power in the bladder; or by reflex nervous influence, either owing to some painful condition in the urinary or adjacent organs, or owing to a hysterical condition in the patient. The patient finds himself unable to pass his water, although he has a great desire and makes strong efforts to do so. The bladder soon becomes so distended that it can be felt as a tense round tumour above the pubes. If relief be not speedily afforded, the bladder may burst, and discharge its contents into the peritoneal cavity, in which case death rapidly ensues; or if the urethra be obstructed, it may give way behind the stricture, when the urine is extravasated into the cellular tissue of the adjacent parts—a condition which, if not promptly relieved by surgical interference, is likely to be followed by gangrene, typhoid symptoms, and death.
If the symptoms are not very severe, and there is no evidence of impassable obstruction, a hot bath, combined with the administration of steel-drops, in doses of ten minims, taken every ten minutes in thin gruel or in barley-water, will often give relief. Sometimes a full opiate administered by the mouth, or preferably as an enema, or the inhalation of a few whiffs of chloroform, will, by allaying spasm, give immediate relief. If these means fail, surgical assistance must be at once procured, and the bladder evacuated by a catheter—an operation often requiring very delicate manipulation. If this cannot be done, which rarely happens, except when the spasm is associated with old-standing disease of the urethra, the surgeon must either puncture the bladder through the rectum, or above the pubes, or make an incision into the urethra either at or behind the seat of the stricture. In cases of enlarged prostate permanent relief can sometimes be afforded by operation; but in most cases the patient is taught to use a catheter for himself, and thereby prevented from the danger of a recurrence of the retention.
Paralysis of the muscular coat of the bladder may arise from the debility of old age, from the depressed state of the nervous system in severe fevers, from injury or disease of the head or spine, and from various other causes. In a temporary form it is often a result of over-distention of the bladder from stricture or prostatic disease, and it sometimes occurs in the case of nervous sedentary persons, if they have allowed rather more than the usual time to elapse without evacuating the bladder. It should be generally known that retention of urine from paralysis, or even from incomplete obstruction, is sometimes accompanied by dribbling away of the water, so that the retention might at first sight be mistaken for incontinence of urine. On examination, however, it will be found that the bladder is abnormally distended, and cannot be evacuated by the act and will of the patient. In these cases the urine must for a time be regularly drawn away by the catheter. General tonics, such as the cold bath (or sometimes preferably the sitz-bath) and chalybeates, must be given to improve the general health; while medicines which are supposed to act locally on the muscular coat of the bladder or on the spinal cord must be simultaneously administered. A peculiar form of retention sometimes occurs in women of hysterical temperament, in which the will rather than the power is at fault.
Frequent and Painful Micturition may be a symptom of disease of the kidneys, the bladder, or some neighbouring organ, but is very often merely an indication of an abnormally concentrated, acid, and irritating condition of the urine, which causes excessive stimulation of the bladder and urethra. Persons suffering from this affection usually refrain from drinking fluid under the mistaken idea that a diminution in the quantity of urine to be passed will diminish their discomfort. The right course is exactly the opposite; for the more the urine is increased in quantity in such a case, the more its irritating constituents are diluted, and the less pain and annoyance it causes. Free drinking of diluents is often sufficient of itself to remedy the condition.
Strangury (Gr. strangē, 'that which oozes out,' oureō, 'I micturate') is a symptom of many diseases of the urinary organs (calculus, inflammation of the bladder, gonorrhœa, stricture, &c.). It shows itself in a frequent and irresistible desire to pass water, which is discharged in very small quantity, but causes scalding and cutting pains along the course of the urethra. The pain often extends to the bladder and even to the kidneys, and is sometimes so severe as to implicate the lower bowel (the rectum), and to produce the straining condition known as Tenesmus. It may also be caused by irritating substances in the urine, especially by cantharides or Spanish flies (whose irritant principle is liable to find its way into the renal secretion, whether the above-named drug is taken internally or merely applied to the skin as a blistering agent), and by oil of turpentine, when administered internally. Treatment must of course be directed if possible to the cause of the condition. But among measures generally beneficial may be mentioned a drachm of laudanum in a wine-glassful of starch mucilage thrown into the lower bowel, copious mild mucilaginous draughts (of barley-water, for example), the warm bath, and, if that cannot readily be obtained, hot local fomentations.