肾单位又称肾元（英语：Nephron），是肾制造尿液的基本功能单位，人体的肾脏中，约含100万个肾元，每一个肾元是由肾小体和肾小管所组成，肾小体包含肾丝球（glomerulus）和鲍氏囊（Bowman's capsule）。肾元的主要功作是利用超滤作用，调节血液中的水份和溶解物质，重新吸收有用的物质，并将剩余的部分以尿液的形式分泌出去。肾元的功能除了将身体的废物排出，还可以调节血量和血压，控制电解质和代谢，并调节血液的酸碱值。它对生命的维持具有重要性。肾元会受到抗利尿激素、醛固酮（aldosterone）和副甲状腺素（parathyroid hormone）等荷尔蒙的影响，

The nephron (from Greek νεφρός - nephros, meaning "kidney") is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. A nephron eliminates wastes from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. In humans, a normal kidney contains 800,000 to 1.5 million nephrons.