Urea is a small organic molecule with the chemical formula CO(NH₂)₂. It is a colorless, odorless solid that dissolves readily in water. This compound is naturally produced in the bodies of mammals as a byproduct of protein metabolism. In the human body, urea serves as a primary way to excrete excess nitrogen. Beyond its biological role, synthetic urea is widely used across various industries.
How Urea is Made in the Body
The human body constantly breaks down proteins into amino acids, which contain nitrogen. When these amino acids are metabolized, they release ammonia, a substance that is highly toxic to cells, particularly those in the central nervous system. To prevent ammonia accumulation, the liver plays a central role in converting it into urea through a series of biochemical reactions known as the urea cycle.
This cycle is the primary mechanism for detoxifying ammonia in mammals. The urea cycle involves five enzymatic steps that occur partly in the mitochondria and partly in the cytoplasm of liver cells. During this process, two ammonia molecules and one carbon dioxide molecule are combined to form a urea molecule. This conversion is an energy-demanding process, requiring four ATP equivalents for each urea molecule produced. Once formed in the liver, urea is released into the bloodstream to be transported to the kidneys for excretion.
Urea’s Essential Function
Beyond waste excretion, urea also contributes to maintaining osmotic balance within the kidneys. As urea passes through the kidney tubules, some of it is reabsorbed into the medullary interstitium, creating a concentration gradient. This gradient helps the kidneys reabsorb water, thereby playing a role in fluid regulation and the production of concentrated urine. This mechanism is important for conserving water, especially for terrestrial animals.
Urea Levels and Health
Blood Urea Nitrogen (BUN) tests measure the amount of urea nitrogen in the blood, serving as an indicator of kidney and liver function. Elevated BUN levels can signal various health issues, with kidney dysfunction being a common cause. Conditions such as dehydration, urinary tract obstruction, congestive heart failure, or severe burns can also lead to increased BUN. A diet high in protein or certain medications, including some antibiotics, may also elevate BUN levels.
Conversely, abnormally low BUN levels are less common but can point to specific health concerns. These may include severe liver disease, as the liver produces urea, or malnutrition, particularly a severe lack of protein in the diet. Overhydration, or having too much fluid in the body, can also dilute the blood and result in lower BUN readings.
Urea’s Diverse Applications
Synthetic urea has found widespread use outside of biological systems due to its high nitrogen content and other chemical properties. Approximately 90% of globally produced urea is utilized in agriculture as a nitrogen-rich fertilizer. It provides a steady supply of nitrogen to plants, supporting their growth and development.
Urea is also incorporated into various cosmetic and skincare products, where it acts as a moisturizing and exfoliating agent. Its ability to hydrate the skin makes it a common ingredient in creams and lotions, particularly for dry or sensitive skin conditions. Additionally, urea serves as a raw material in the chemical industry for producing plastics, adhesives, and resins, such as urea-formaldehyde resins used in wood and furniture manufacturing.