how is urine produced in the kidney?

The first step of urine formation is ultrafiltration. Blood passes through a network of capillaries in the kidney called the glomerulus. It is filtered into the Bowman’s capsule (the first part of the nephron) through a fine membrane which acts like a sieve. Blood cells and proteins are too big to pass through the membrane so they remain in the blood, but everything else – water, ions, waste produce (urea) and glucose passes into the nephron. The solution entering the nephron is called the ultrafiltrate.

The next step is selective reabsorption. It is important that waste products (urea) are excreted from the body in urine while substances your body needs – ions, water and glucose – remain in the blood so they can be used. To achieve this, most ions and all glucose is pumped back into the blood from the nephron. This mostly happens in the first part of the nephron, the proximal convoluted tubule. Everything that is not pumped back into the blood moves into the bladder down the ureters as urine and is excreted.