The kidneys are intricate organs with millions of working units known as nephrons. Each nephron features two major structures: the renal corpuscle, which facilitates blood plasma filtration, and the renal tubule, which handles the glomerular filtrate. Blood supply is directly linked to the nephrons. The renal corpuscle consists of the glomerulus, a capillary network, and the Bowman's capsule, a double-walled epithelial structure that encases the glomerulus. The filtering of blood plasma happens within the Bowman's capsule, where the processed liquid transfers into the renal tubule.

The renal tubule is subdivided into three primary segments: the proximal convoluted tubule (PCT), the loop of Henle (nephron loop), and the distal convoluted tubule (DCT). The PCT is nearer to the Bowman's capsule, while the DCT is further distanced. The renal corpuscles and the convoluted tubules are found in the renal cortex, whereas the nephron loop dips into the renal medulla, performs a U-turn, and returns to the renal cortex. The distal convoluted tubules from various nephrons empty into a collecting duct, which merges with other collecting ducts to form major papillary ducts that drain into the minor calyces. These ducts travel from the renal cortex, through the renal medulla, and into the minor calyces.

The loop of Henle acts as a connection between the PCT and DCT. The loop of Henle starts where the PCT ends and dips into the renal medulla, forming the descending limb. After a sharp turn, it ascends back to the renal cortex, forming the ascending limb, which ends at the DCT.

Around 80–85% of nephrons are cortical nephrons, found in the outer part of the renal cortex. They have short loops of Henle that mainly reside in the cortex and slightly enter the outer region of the renal medulla. Their short nephron loops receive blood from the peritubular capillaries, which stem from efferent arterioles. The remaining 15–20% are juxtamedullary nephrons, situated close to the medulla in the deeper parts of the cortex. They have long nephron loops that reach far into the medulla and receive blood from both the peritubular capillaries and the vasa recta, which also stem from efferent arterioles. Their ascending limb consists of a thin and a thick segment. The thin ascending limb's lumen is the same as that of other parts of the renal tubule; only the epithelial layer is slimmer. The presence of nephrons with long nephron loops is critical for the kidney's ability to eradicate urine of varied concentrations.

There are several diseases associated with nephrons. Chronic Kidney Disease (CKD) is a prevalent condition that signifies a gradual loss of kidney function over time. Acute Kidney Injury (AKI), on the other hand, is characterized by a sudden drop in kidney function, often triggered by an injury or infection. Glomerulonephritis refers to inflammation of the glomeruli, while nephrotic syndrome is a disorder where the kidneys excrete too much protein into the urine. Polycystic Kidney Disease (PKD) is a genetic disorder causing numerous cysts to grow within the kidneys, affecting their function over time. Finally, kidney stones, although not directly a nephron disease, can obstruct the flow of filtrate through the nephrons, causing severe discomfort and potential complications.