Kidney and Its Internal Structure

The kidney is composed of an enormous number of minute tubules called uriniferous tubules or nephrons or renal tubules or just kidney tubules. These are the structural and functional units of the kidney. 

The apex of each pyramid in the medulla of the kidney that projects into the pelvis is called the papilla.

• Humans have two bean-shaped kidneys located on either side of the vertebral column (from the 12th thoracic to the 3rd lumbar vertebra).
• Kidneys help in maintaining homeostasis by regulating water balance (osmoregulation) and pH of body fluids.
• They also secrete erythropoietin, a hormone important for red blood cell production.
• Each kidney has an outer cortex and an inner medulla; the medulla contains conical structures called renal pyramids.
• Cortex extends into medulla, forming renal columns (columns of Bertini), and pyramids open into minor calyces through renal papilla.
• Kidneys are protected by renal capsule, adipose capsule (fat layer), and renal fascia, and contain nephrons, which are functional units for urine formation.