الكليتان

The kidneys are paired, bean-shaped organs of the urinary system responsible for filtering blood, maintaining fluid and electrolyte balance, and producing urine. Each kidney contains approximately one million nephrons as its functional filtering units.

The kidneys are located retroperitoneally on either side of the vertebral column at the T12–L3 level. The right kidney sits slightly lower than the left due to the presence of the liver above it.

The kidneys filter blood through nephrons to remove waste products and excess substances, which are excreted as urine. They also regulate blood pressure, fluid balance, electrolyte levels, and red blood cell production via erythropoietin.

The kidneys may be involved in conditions such as chronic kidney disease, nephrolithiasis (kidney stones), glomerulonephritis, and polycystic kidney disease. The renal hilum, which transmits the renal artery, vein, and ureter, is a common site of pathological obstruction.

Each kidney is a reddish-brown, bean-shaped organ roughly 10–12 cm in length with a concave medial border—the renal hilum. On cross-section or imaging, the outer cortex, inner medulla with renal pyramids, and central renal pelvis are distinguishable.