Structure of the Kidney

Bowman's capsule is a thin-walled, cup-shaped structure in the nephron that surrounds the glomerulus and collects the filtrate from the blood.

The glomerulus is a knot-like network of blood capillaries located inside the Bowman's capsule, where blood filtration occurs.

The Malpighian capsule is the combined structure of the Bowman's capsule and glomerulus, forming the filtration unit of the nephron.

• Nephrons are the structural and functional units of the kidney, each consisting of a glomerulus and a renal tubule, and measuring about 4–6 cm in length.
• The Malpighian corpuscle (glomerulus + Bowman’s capsule) is the site of ultrafiltration, where blood enters through the afferent arteriole and leaves via the efferent arteriole.
• The proximal convoluted tubule (PCT), lined with cuboidal cells and microvilli, is the main site of selective reabsorption of water, ions, and nutrients.
• The loop of Henle extends into the medulla and helps in concentration of urine; its descending limb is permeable to water, while the ascending limb is impermeable to water but allows movement of electrolytes.
• The distal convoluted tubule (DCT) carries out tubular secretion and regulation of ions, and opens into the collecting duct, which reabsorbs water and transports urine to the renal pelvis.
• Nephrons are of two types: cortical nephrons with short loops of Henle and juxtamedullary nephrons with long loops that play a key role in urine concentration.
• The kidneys receive rich blood supply and filter large volumes of blood daily, with most filtrate reabsorbed and about 1–1.5 litres of urine excreted per day.