The urea cycle converts excess ammonia into urea in the mitochondria of liver cells. The urea forms, then enters the blood stream, is filtered by the kidneys and is ultimately excreted in the urine. The urea cycle consists of 4 reactions. The first reaction occurs in the matrix of the mitochondria.

Where does urea synthesis take place?

The liver is the only site where urea is synthesized and ultimately excreted by the kidneys.

Why does urea cycle occur only in liver?

The urea cycle is partly cytoplasmic and partly mitochondrial. Only the liver possesses all the enzymes required to synthesize urea from ammonia, and this pathway is strictly located in periportal hepatocytes.