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Urea in Blood, Urine, Skin Creams, and Fertilizer
An Important Compound
Urea is a small but important compound in the living world. It’s found naturally in our body and can also be made artificially. The liver produces urea as a waste substance when it breaks down amino acids. The urea then travels through the bloodstream to the kidneys, which excrete it in the urine. Doctors measure the concentration of urea in the blood to help them determine how well someone's kidneys are working.
Urea is added to skin creams to remove thickened or scaly areas and to moisturize the skin. It's also a useful soil fertilizer because it's a good source of nitrogen, an important nutrient for plants. Since human urine contains urea, some people fertilize soil with urine to improve plant growth.
In its solid form, urea exists as white or colorless crystals which have no odor and are highly soluble in water. The chemical is also known as carbamide and has very low toxicity.
Urea contains only four elements—carbon, nitrogen, hydrogen, and oxygen. The lines in the diagram above represent chemical bonds.
Urea Production in the Body
A protein is a chain of amino acids. These are separated from each other when the protein is digested. Excess amino acids are broken down in a process called deamination. In this process, the amino group of an amino acid (-NH2) is removed and converted to an ammonia molecule (NH3). Deamination takes place mainly in the liver.
Ammonia is very toxic to cells. Ammonia molecules react with carbon dioxide in the body to make urea, which is a much safer chemical. The conversion of ammonia to urea takes place in the liver in a process known as the urea cycle. Blood vessels transport the urea to the kidneys, which remove it from the blood and send it into the urine.
The Excretory System: How the Kidneys Get Rid of Urea
Concentration of Urea in the Blood
A BUN test (or Blood Urea Nitrogen test) detects the concentration of urea in the blood. If the kidneys aren’t doing their job of removing the chemical from the body, the amount of urea in the blood will increase. A BUN test can show how well the kidneys are functioning.
There are other possible reasons for an increase in the blood urea level besides kidney problems. Eating a lot of foods that are rich in protein will cause the liver to produce a large amount of urea. Dehydration will also increase the blood's urea concentration, since this depends on the amount of water in the blood. If there is less water than normal in the blood but the same amount of urea, the urea concentration will be higher than usual.
It’s also possible to have a lower than normal urea concentration in the blood. This can be caused by drinking too much water and diluting the blood, not eating much protein, or being unable to absorb enough amino acids through the wall of the small intestine due to a health problem.
One health problem that can produce a low urea concentration is celiac disease. Villi are tiny projections on the lining of the small intestine which absorb digested food. In celiac disease, the ingestion of gluten damages or destroys the villi. This greatly reduces the absorption of nutrients, including protein. Gluten is a protein complex found in certain grains, including wheat, rye, and barley. While most people eat gluten with no problem, some people are gluten intolerant.
Help for Skin Problems
In the body, urea is a waste substance that needs to removed. Outside the body, it's often a useful substance. For example, urea is added to some medicinal skin creams, where it has health benefits. Urea creams are useful in the treatment of conditions such as corns, calluses, eczema, psoriasis, and ichthyosis. Depending on its concentration, urea either removes thickened or scaly areas of skin or makes the skin soft and supple.
In eczema, the skin is inflamed, irritated, dry, and sometimes scaly. The disorder often involves flare-ups. In psoriasis, the skin has red patches that are itchy and scaly. The skin is generally thicker than in eczema. As in eczema, however, there are often flare-ups. In icthyosis, the skin is dry, thickened, scaly, and sometimes flaky. Anyone who suspects that they have one of these problems should visit a doctor for a diagnosis.
With respect to eczema, DermNet New Zealand (a website run by dermatologists) says that a urea cream is "very helpful for dryness but may sting active eczema". This quote might apply to psoriasis as well, so someone using the cream to help a skin problem should be cautious.
Urea creams have different effects depending on the concentration of the chemical. It's important that the right concentration is chosen for a skin problem. A doctor or pharmacist should be consulted for help.
A Keratolytic Substance and a Humectant
The tough outermost layer of the skin is called the stratum corneum. This layer is made of dead cells and contains a fibrous protein called keratin. When a cream containing a high concentration of urea is applied to a thickened area on the skin, the urea weakens the attachment between the cells of the stratum corneum and dissolves keratin, allowing the area to be shed. Under these conditions, urea is said to be a "keratolytic" substance—one that causes the stratum corneum to soften and peel. The removal of the thickened skin surface is called debridement.
Urea is also hygroscopic, which means that it absorbs water from the air. Skin creams containing low concentrations of urea act as emollients. The softened skin can absorb substances better, which helps medications such as corticosteroids enter the skin. At concentrations of 2% to under 20%, urea is used as a humectant, which is a substance that retains moisture in the skin. At a concentration of 20% or higher, urea is keratolytic.
Fertilizing Soil With Urine in Vermont
Urea in Fertilizers
Urea contains forty-six percent nitrogen by weight and is an excellent fertilizer. It’s cheaper and safer to transport and store than other nitrogen-containing products.
Bacteria in soil produce an enzyme called urease. This enzyme causes urea that is added to the soil to react with water. The reaction produces ammonia and carbon dioxide. The ammonia then reacts with water to make ammonium ions, which are absorbed by plant roots.
Urine contains urea, so it could be used as a natural fertilizer. In fact, some scientists in Finland have found that urine is a very good fertilizer for soil in which beets and other vegetables are planted. In a controlled experiment they found that the beets grown in urine-fertilized soil grew significantly bigger than the beets grown in soil treated with a mineral fertilizer while still looking attractive and tasting good.
Unlike feces, which may contain dangerous bacteria, urine is virtually sterile (unless someone has an infection of the urinary tract). It's rich in nitrogen, potassium, and phosphorus, which are elements that plants need.
Recycling Urine for Fertilizing Soil
Practitioners of urine fertilization say that the liquid must be diluted before use. The chemicals in undiluted urine are far too concentrated for the health of most plants. Anywhere from a 1:3 to a 1:10 mixture of urine and water is suggested. In addition, the urine should be applied to the soil and not placed directly on plants. If these precautions are followed, the liquid can be a very helpful fertilizer.
Instead of diluting urine, some commercial fertlizer companies collect the liquid, sterilize it, and then extract useful components from it. Urine is reportedly a good compost activator as well as a good fertilizer.
Although it may found strange and even repulsive, I think that the idea of recycling urine is an excellent one. The liquid contains important chemicals. It seems a shame to waste them. One of these beneficial chemicals is urea. Although it's a relatively simple molecule, urea is a very useful substance.
Using a Urine Fertilizer
Would you use urine as a soil fertilizer?
The Royal Society of Chemistry has a page about urea production in humans.
The Mayo Clinic website has facts about the BUN test.
DermNet New Zealand has a page about eczema treatment that mentions urea. Eczema is sometimes known as atopic dermatitis.
A National Geographic report discusses "peecycling" and its benefits.
The Scientific American website has information about urine-fertilized soil.
© 2012 Linda Crampton