Urea Cycle (Ornithine Cycle) Process

What is the role of the urea cycle in the body?

What is the normal value of blood urea?

What is the rate-limiting enzyme of the urea cycle?

What is the result of negative nitrogen balance?

What is the function of allopurinol in the context of gout?

What is the site of urea synthesis?

What is the result of diseases that affect liver mitochondria?

What is the normal value of serum uric acid?

What is the primary function of the urea cycle in many animals?

What is the toxic range of ammonia in the plasma?

What is the primary route by which ammonia travels to the liver?

What is the purpose of excreting NH4+ in the kidneys?

What is the normal percentage of urea in urine?

What is the result of elevated uric acid concentration in kidney diseases and leukemia?

What is measured in the blood to assess kidney function?

What is the consequence of congestive heart failure on kidney function?

The urea cycle, also known as the ornithine cycle, is a biochemical reaction that produces urea from ammonia in many animals.
The liver converts nitrogen from amino acids into urea, and the carbon skeletons are converted into glucose (in fasting state) or fatty acid (in fed state).

Ammonia is toxic, with normal levels ranging from 15-40 μM and a maximum of 70 μM.
Hyperammonemia (> 500 μM) is related to inborn errors of metabolism and liver failure.

The urea cycle's primary function is to rid the body of toxic ammonia, allowing amino acids to be used as an energy source.
The liver is the major site of urea synthesis, with the small intestine also involved.

Blood urea nitrogen (BUN) is measured in the blood, and elevated levels may indicate kidney failure or urinary tract obstruction.
Normal blood urea levels range from 3.3-7.5 mmol/L.

The normal nitrogen balance is a state where the amount of nitrogen ingested is balanced by the amount excreted, resulting in no net change in body nitrogen.
Negative nitrogen balance occurs when more nitrogen is excreted than ingested, often due to starvation, disease, or injury.

Uric acid is synthesized from adenine and guanine in nucleotides, not from ammonia.
Elevated levels of uric acid may occur in kidney diseases and leukemia, and can cause gout.