Urea

Definition

Urea is a waste product that is formed in the liver as the end-product of protein metabolism. It is a small, water-soluble molecule that is filtered out of the blood by the kidneys and excreted in the urine, playing a crucial role in the urinary system's function of removing waste and maintaining fluid balance in the body.

5 Must Know Facts For Your Next Test

1. Urea is the primary nitrogenous waste product excreted by the kidneys, accounting for approximately 90% of the total nitrogen waste in urine.
2. The urea cycle, also known as the ornithine cycle, is the metabolic pathway that converts the toxic ammonia into the less toxic urea for excretion.
3. Urea plays a crucial role in maintaining the body's fluid balance by creating an osmotic gradient that helps regulate water reabsorption in the kidneys.
4. Elevated levels of urea in the blood, a condition known as uremia, can be an indicator of kidney dysfunction or dehydration.
5. Urea is also used in various medical and pharmaceutical applications, such as in the treatment of skin conditions and as a component in certain medications.

Review Questions

• Explain the role of urea in the urinary system and its importance in maintaining homeostasis.
  • Urea is a waste product that is filtered out of the bloodstream by the kidneys during the process of glomerular filtration. As the primary nitrogenous waste product, urea is excreted in the urine, which helps remove excess nitrogen and maintain the body's fluid balance. The urea cycle in the liver converts the toxic ammonia into urea, which is then transported to the kidneys for excretion. This process is crucial for maintaining homeostasis by regulating the concentration of waste products and water in the body.
• Describe the relationship between urea and the urea cycle, and explain how this metabolic pathway contributes to the formation and excretion of urea.
  • The urea cycle, also known as the ornithine cycle, is the metabolic pathway that converts the toxic byproduct ammonia into the less toxic urea for excretion. This cycle takes place primarily in the liver and involves a series of enzymatic reactions that ultimately produce urea. The urea is then transported in the bloodstream to the kidneys, where it is filtered out and excreted in the urine. The urea cycle is essential for maintaining the body's nitrogen balance and preventing the accumulation of ammonia, which can be harmful to the body. By converting ammonia into urea, the urea cycle plays a crucial role in the formation and excretion of this important waste product.
• Analyze the role of urea in regulating the body's fluid balance and explain how the osmotic properties of urea contribute to this process.
  • Urea plays a critical role in maintaining the body's fluid balance through its osmotic properties. As a small, water-soluble molecule, urea creates an osmotic gradient that helps regulate water reabsorption in the kidneys. The concentration of urea in the renal medulla, which is higher than in the bloodstream, draws water back into the bloodstream through the process of osmosis. This helps conserve water and maintain the appropriate fluid balance in the body. Additionally, the presence of urea in the renal medulla contributes to the formation of a concentrated urine, which is essential for the kidneys' ability to excrete waste products and excess water. By regulating fluid balance, the osmotic properties of urea contribute to the overall homeostatic function of the urinary system.

Related terms

Glomerular Filtration: The process by which the kidneys filter blood and remove waste products like urea from the bloodstream.

Urea Cycle: The metabolic pathway in the liver that converts the toxic byproduct ammonia into the less toxic urea for excretion.

Osmosis: The movement of water molecules across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration, which helps regulate the concentration of urea in the body.