Urea in the Blood and Urine, in Skin Creams and in Fertilizers
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. Urea is also known as carbamide and has very low toxicity.
Urea Production in the Body and the Urea Cycle
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 Make Urine and Get Rid of Urea
Urea Concentration 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 urea from the body, the amount of urea in the blood will increase.
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 but the same amount of urea, the concentration of the urea will be higher.
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 cause this effect 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. Gluten is a protein component of certain grains, including wheat. While most people eat gluten with no problem, some people are gluten intolerant.
Urea as a Skin Moisturizer
Benefits and precautions when using a urea skin cream, from the NHS (National Health Service)
Urea and Skin Health
Urea is added to some skin creams. 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.
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. Therefore 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 - a substance that retains moisture in the skin. At a concentration of 20% or higher urea is keratolytic.
Fertilizing Soil With Urine in Vermont
Recycling Urine for Sustainable Living
This National Geographic report discusses "peecycling" and its benefits.
Using a Urine Fertilizer
Would you use urine as a soil fertilizer?
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 all elements that plants need.
Practitioners of urine fertilization say that the urine must be diluted before use, since 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, urine can be a very helpful fertilizer.
Instead of diluting urine, some commercial fertlizer companies collect urine, 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. Urine 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.
© 2012 Linda Crampton