The kidneys are two bean-shaped organs in the renal system. They help the body pass waste as urine. They also help filter blood before sending it back to the heart.
The kidneys perform many crucial functions, including:
maintaining overall fluid balance
regulating and filtering minerals from blood
filtering waste materials from food, medications, and toxic substances
creating hormones that help produce red blood cells, promote bone health, and regulate blood pressure
Nephrons
Nephrons are the most important part of each kidney. They take in blood, metabolize nutrients, and help pass out waste products from filtered blood. Each kidney has about 1 million nephrons. Each has its own internal set of structures.
Renal corpuscle
After blood enters a nephron, it goes into the renal corpuscle, also called a Malpighian body. The renal corpuscle contains two additional structures:
The glomerulus. This is a cluster of capillaries that absorb protein from blood traveling through the renal corpuscle.
The Bowman capsule. The remaining fluid, called capsular urine, passes through the Bowman capsule into the renal tubules.
Renal tubules
The renal tubules are a series of tubes that begin after the Bowman capsule and end at collecting ducts.
Each tubule has several parts:
Proximal convoluted tubule. This section absorbs water, sodium, and glucose back into the blood.
Loop of Henle. This section further absorbs potassium, chloride, and sodium into the blood.
Distal convoluted tubule. This section absorbs more sodium into the blood and takes in potassium and acid.
By the time fluid reaches the end of the tubule, it’s diluted and filled with urea. Urea is byproduct of protein metabolism that’s released in urine.