Nephron

A nephron is a structure inside the kidney that helps filter waste from the blood. Each kidney in the human body contains approximately one million nephrons. Each nephron is made up of three main parts—a renal corpuscle, a renal tubule, and a capillary network. These parts filter waste from the blood, reabsorb water into the blood, and help move the final waste product out of the kidneys, and contribute to regulating blood pressure and fluid balance. Nephrons are the main functional units of the kidneys and are vital to renal function.

Background

The kidneys are part of the urinary system in the human body. This system helps rid the body of liquid waste, and it helps the body maintain a balance of certain materials, including sodium and potassium, and plays a role in regulating blood pressure and producing hormones such as erythropoietin. Humans typically have two kidneys, and they are located below the ribs toward the middle of the back. The kidneys are purple-red and bean-shaped. One is on the right side of the body, and the other is on the left side of the body. Humans can live with only one kidney.

Kidneys act like filters for the blood. They remove waste and unwanted material from the body. When humans eat food, the digestive system breaks the food down into chemicals and compounds that the body can use for energy. As the food breaks down, some chemicals are leftover. One of these leftover chemicals is ammonia, which is poisonous to the body. The ammonia travels in the blood to the liver, where it is turned into urea, which is a less dangerous chemical. Urea, however, must also be removed from the body. The urea in the human bloodstream then travels to the kidneys.

The kidneys contain capillaries, arteries, and veins that transport blood. The kidneys' main job is to filter waste from the blood, and they can hold a great deal of blood. A person's entire blood volume passes through the kidneys many times each day. Blood first enters the kidney through the renal artery, which branches out into many arteries. The blood eventually flows into capillaries. The capillaries transport the blood to nephrons, which are the functional units of the kidneys. The nephrons filter the blood that passes through them via the capillaries. Most of the filtration that occurs in the nephrons happens through changes in pressure, while osmosis plays a key role in reabsorption. Transport proteins, which are proteins that move material within living things, help reabsorb useful substances and secrete certain wastes into parts of the nephron so that they can be transported out of the body. The kidneys contain two types of nephrons: cortical and juxtamedullary. About 85 percent of the nephrons in a kidney are cortical nephrons, and about 15 percent are juxtamedullary nephrons. The two types are in different locations and are different sizes, but they perform the same basic functions.

Overview

Each kidney is made up of three main parts: the renal cortex, the renal medulla, and the renal pelvis. The cortex and the medulla are mostly made up of nephrons and blood vessels. The renal pelvis is a collection area for urine. It is connected to the ureter, which is the tube that transports urine away from the kidney.

The blood enters the kidney through the renal artery, and the artery branches many times until it becomes smaller and smaller. Eventually, the arteries turn into millions of tiny capillaries, which transport blood to the nephrons. Each kidney contains about one million nephrons. These nephrons make the kidney look granular when dissected, but individual nephrons are not visible to the naked eye. The nephrons are made of different parts that help the kidney filter out waste and keep water and other materials that help the body function. The nephrons are located in the cortex and the medulla.

Each nephron has three parts—a renal corpuscle, a renal tubule, and a capillary network. The renal corpuscle is made up of the Bowman's capsule and the glomerulus. The Bowman's capsule is a rounded body that contains the glomerulus. Blood vessels called the afferent arterioles send blood into the Bowman's capsule through the capillary network. Inside the capsule, waste, water, and other materials filter out from the blood traveling through the glomerulus, which is a bundle of capillaries. The pressure of the blood in the glomerulus forces the water and solutes out of the capillaries and into the Bowman's capsule. The material that is filtered out from the blood travels to the renal tubule, and this material is called filtrate. The blood, which has been filtered by the glomerulus, exits the renal corpuscle through the efferent arterioles. It will eventually exit the kidney through the veins.

The renal tubule is a long, twisting piece of the nephron located in the cortex and the medulla. The first part of the tubule is called the proximal convoluted tubule (PCT). The filtrate moves from the renal corpuscle into the PCT. Although some of the material in the PCT needs to be removed from the body, other materials (such as water) are valuable and need to stay inside the body. The tubule helps reabsorb some of this useful material. The waste and other materials travel from the PCT to the loop of Henle, which is also called the nephron loop. This loop has a descending limb and an ascending limb. The loop is very important for reabsorbing water. It uses osmosis to reabsorb water back into the blood. The descending limb is water permeable, which means water can escape through this limb. Water escapes through the descending limb and is reabsorbed into the blood. The ascending limb is not water-permeable. However, ions escape through the ascending limb primarily through active transport rather than osmosis. During this process, about 80 percent of the filtrate is reabsorbed by the blood.

The filtrate then moves from the ascending limb of the loop of Henle to the distal convoluted tubule (DCT). Transport proteins secrete other waste materials to join the filtrate in the DCT. The DCT makes final adjustments to the concentration of solutes and materials in the waste. The DCT then empties into the collecting duct. The liquid waste in the ducts is urine. The collecting ducts descend into the medulla. There, these ducts merge to form larger ducts called the papillary ducts, which connect to the minor calyx and the major calyx in the renal pelvis. The ureter is a muscular tube that connects to the kidney at the renal pelvis and transports urine to the bladder. Urine travels from the bladder, through the urethra, and out of the body.

Bibliography

"Anatomy and Function of the Urinary System." University of Rochester Medical Center, www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P01468. Accessed 28 Mar. 2026.

Chung, Andrew. "Kidney Anatomy and Function." Health Pages, 27 June 2022, www.healthpages.org/anatomy-function/kidney. Accessed 28 Mar. 2026.

"41.2: The Kidneys and Osmoregulatory Organs." LibreTexts, bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_1e_(OpenStax)/7%3A_Animal_Structure_and_Function/41%3A_Osmotic_Regulation_and_Excretion/41.2%3A_The_Kidneys_and_Osmoregulatory_Organs. Accessed 28 Mar. 2026.

“In Brief: How Does the Liver Work?” National Library of Medicine, 28 Feb. 2023, www.ncbi.nlm.nih.gov/books/NBK279393/. Accessed 28 Mar. 2026.

Latif, Walead. "Glomerulus and Nephron." MedlinePlus, 2 Sept. 2025, medlineplus.gov/ency/imagepages/19932.htm. Accessed 28 Mar. 2026.

Madrazo-Ibarra, Antonio, and Pradeep Vaitla. "Histology, Nephron." National Library of Medicine, 17 Feb. 2023, www.ncbi.nlm.nih.gov/books/NBK554411/. Accessed 28 Mar. 2026.