noun
definition
A water-soluble organic compound, CO(NH2)2, formed by the metabolism of proteins and excreted in the urine.
definition
Any N-substituted derivative of urea, with the general formula (R1R2N)CO(NR3R4).
Examples of urea in a Sentence
Dry chlorine gas passed into melted urea decomposes it with formation of cyanuric acid and ammonium chloride, nitrogen and ammonia being simultaneously liberated.
Alkaline hypobromites or hypochlorites or nitrous acid decompose urea into carbon dioxide and nitrogen.
Parabanic acid (oxalyl urea), C0[NH C0] 21 is formed by oxidizing uric acid; or by condensing oxalic acid and urea in the presence of phosphorus oxychloride.
On oxidation with potassium permanganate it is converted into acetyl urea, together with other products.
On the latter they act as diuretics, but less powerfully than potassium, increasing the flow of water and the output of urea and rendering the urine less acid.
Urea may be recognized by its crystalline oxalate and nitrate, which are produced on adding oxalic and nitric acids to concentrated solutions of the base; by the white precipitate formed on adding mercuric nitrate to the neutral aqueous solutions of urea; and by the so-called "biuret" reaction.
For example, aa-dimethyl urea is sweet, aß-dimethyl urea is tasteless; p-phenetol carbamide or dulcin, NH 2 CO NH C 6 H 4.0C 2 H 51 is sweet, while the di-p-phenetol carbamide, CO(NH C 6 H 4.0C 2 H 5) 21 is tasteless.
The derivatives of urea containing acid radicles are known as ureides.
Those derived from monobasic acids, obtained by the action of acid chlorides or anhydrides on urea, decompose on heating and do not form salts.
Allophanic acid, NH 2 C0 NH CO 2 H, is not known in the free state, as when liberated from its salts, it is decomposed into urea and carbon dioxide.
They show all the reactions of esters, being readily hydrolysed by caustic alkalis, and reacting with ammonia to produce carhamic esters and urea.
Several methods are employed for the quantitative estimation of urea.
Bromural or a-bromisovaleryl urea, NH 2 C0 NH C0 CHBr CH(CH 3) 2, has been introduced as an hypnotic; its action is mild, and interfered with by the presence of pain, cough or delirium.
Veronal (q.v.) is diethyl malonyl urea.
Baryta water hydrolyses it to carbon dioxide, ammonia and urea.
Baryta water hydrolyses it to urea.
In health most of the nitrogenous waste in the body is eliminated as urea, but in gout uric acid is either formed in too great quantity or too little is eliminated, so that it tends to be deposited as urate of soda in the joints and other tissues.
In 1862 Pasteur placed it beyond reasonable doubt that the ammoniacal fermentation of urea is due to the action of a minute Schizomycete; in 1864 this was confirmed by van Tieghem, and in 1874 by Cohn, who named the organism Micrococcus ureae.
In effect the urea first becomes carbonate of ammonia by a simple hydrolysis brought about by bacteria, more and more definitely known since Pasteur, van Tieghem and Cohn first described them.
The excreta of urea alone thus afford to the soil enormous stores of nitrogen combined in a form which can be rendered available by bacteria, and there are in addition the supplies brought down in rain from the atmosphere, and those due to other living debris.
As regards the ammonium carbonate accumulating in the soil from the conversion of urea and other sources, we know from Winogradsky's researches that it undergoes oxidation in two stages owing to the activity of the so-called " nitrifying " bacteria (an unfortunate term inasmuch as " nitrification " refers merely to a particular phase of the cycle of changes undergone by nitrogen).
It has been suggested that urea is formed by polymerization of ammonium carbonate, and formic aldehyde is synthesized from CO 2 and 011 2.
The combined nitrogen of dead organisms, broken down to ammonia by putrefactive bacteria, the ammonia of urea and the results of the fixation of free nitrogen, together with traces of nitrogen salts due to meteoric activity, are thus seen to undergo various vicissitudes in the soil, rivers and surface of the globe generally.
The amount of urea, creatin, creatinin, sulphates and phosphates in the urine is diminished, clearly showing that quinine exerts an inhibitory influence over the metabolic processes of the body.
Kinetic methods which measure the clearances (removal) of urea and creatinine are now the gold standard for the assessment of dialysis adequacy.
Usually the pH is made more alkaline by hydrolysis of urea (NH 2 CONH 2) in boiling aqueous solution.
The liver converts this ammonia to urea which is then excreted by the kidneys.
Stool antigen tests do not require a separate appointment at the practice and are cheaper than carbon urea breath testing.
Urea is used as a top dressing in Portugal, mainly calcareous soils.
In 1870 urea was produced by heating ammonium carbamate in a sealed vessel.
Serum urea and electrolytes and creatinine to assess renal function (but a normal serum creatinine does not rule out obstruction ).
Urease breaks down urea to form ammonia and free hydrogen ions which raise the pH of the urine making it alkaline.
Urea is a relatively inert substance compared with ammonia.
Urea is the main form in which nitrogen is excreted in mammals UV radiation invisible rays that are part of the electromagnetic spectrum.
This minimizes the loss of urea from the renal medulla, and allows the concentration of urea in urine.
They also assist saprophytes by excreting useful minerals such as urea, and by aerating the soil.
In addition, the cleavage of arginine by nitric oxide synthetase generates citrulline, which is a urea cycle intermediate.
Urography Care should be exercised in patients with moderate to severe impairment of renal function (as reflected by a raised blood urea ).
The cream is an intense formula containing urea, which is the body's natural moisturizer.
The same applies for thermal insulation materials which use urea and formaldehyde.
Modern stain removers use artificially produced urea to achieve the same result.
However, the kidneys are continuously removing urea from the blood and producing urine as a result.
The greater the protein breakdown, the more urea is created and therefore more water is required for dilution.
Certain metabolic products (e.g. urea) in excess can cause tissue damage.
Excess non-protein nitrogen in the form of dietary urea reduced embryo quality.
These changes result in an increase of about 50% in creatinine clearance, and a fall in serum urea, creatinine and urate.
The dialysis disequilibrium syndrome is associated with rapid initial reduction in plasma urea levels at the commencement of dialysis.
The test is based on the capacity of H. pylori to secrete the enzyme urease, which hydrolyses urea to ammonia and carbon dioxide.
On heating with water it undergoes hydrolysis into urea and allanturic acid C 3 H 4 O 3 N 2.
It is reduced by sodium amalgam to glycouril C 4 H 6 N 4 O 2, whilst with hydriodic acid it yields urea and hydantoin C 3 H 4 N 2 O 2.