An artificial kidney is a machine that performs the function of failed natural kidneys through the process of dialysis, used for patients suffering from chronic or acute renal (kidney) failure.

The essential job of a kidney is to purify the blood by removing nitrogenous waste products such as urea, uric acid and creatinine, which accumulate continuously from the breakdown of proteins during metabolism and would be toxic if allowed to build up.

In haemodialysis, the patient's blood is pumped through a dialyser that contains a semi-permeable membrane bathed in a specially prepared dialysing fluid; the dissolved waste molecules diffuse across the membrane from the blood, where their concentration is high, into the fluid, where it is low.

Useful substances such as glucose, essential salts and blood proteins are retained because the dialysing fluid is balanced to prevent their loss, and the cleaned blood is then returned to the patient's body.

Examining the wrong options: the machine does not manufacture and store urine the way a living kidney and bladder do; it removes wastes directly from blood. Its aim is not to filter out useful glucose, which the body needs and which dialysis is designed to conserve. And it is certainly not meant to increase blood pressure; if anything, fluid removal during dialysis helps control hypertension.

Hence, the primary function of an artificial kidney is To remove nitrogenous waste products from the blood.