Final answer:
Urea is a metabolic waste produced by liver cells during protein catabolism and is excreted by the kidneys. The urea cycle converts nitrogen waste into urea for elimination, and the urinary system also includes the ureters and urethra for transporting and expelling urine from the body.
Step-by-step explanation:
Blood transports urea, a metabolic waste produced primarily by liver cells, to the kidneys for elimination. Urea is a key nitrogen-containing waste product formed during protein catabolism; when proteins and certain vegetables are digested, urea is generated as a by-product. The urea cycle is a biological process that converts nitrogen waste into urea, which the kidneys then filter from the blood. The kidneys are part of the urinary system and play a crucial role in excretion of waste products, including not just urea but also uric acid and excess water and electrolytes. Urine is formed in the kidneys and consists of these dissolved waste products, which the body subsequently eliminates.
Patients with kidney impairments sometimes rely on dialysis machines to remove urea and other wastes from their blood. The urinary system's components include the ureters, which transport urine from the kidneys to the bladder, and the urethra, which carries urine out of the body. Thus, the primary function of the urinary system is to maintain the body's internal environment by selectively removing waste and regulating water and electrolyte balance.