Anatomy of the Nephron in the Kidney

The Nephron: Functional Unit of the Kidney

• Composed of blood vessels and tubules that collect filtrate, ultimately turning it into urine
• Each nephron receives one afferent arteriole, which divides into the glomerulus and reunites to form an efferent arteriole

Glomerular Corpuscle

• Renal Corpuscle Filters blood plasma, consists of two structures:
  • Glomerular capillaries: Glomerulus
  • Glomerular capsule (Bowman’s capsule)
• Glomerular capsule has two layers:
  • Visceral layer with podocytes in inner wall of capsule that wrap pedicels around single layer of endothelial cells
  • Parietal layer forms outer wall of capsule

Filtration Membrane

• Formed by endothelial cells of glomerular capillaries and podocytes
• Consists of three selective barriers:
  • Glomelular endothelial cells with fenestrations (pores)
  • Basement membrane between endothelium and podocytes
  • Pedicels of podocytes creating filtration slits
• Allows filtration of water and small solutes, preventing larger ones

Renal Tubule

• Filtered fluid passes through the renal tubule, consisting of:
  • Proximal convoluted tubule (PCT)
  • Loop of Henle
  • Distal convoluted tubular (DCT)
• Distal convoluted tubules of many nephrons empty into a single collecting duct

Loop of Henle

• First part (descending limb) dips into renal medulla, then returns to renal cortex as ascending limb
• Descending limb is composed of simple squamous epithelium
• Ascending limb may be composed of simple squamous epithelium or simple cuboidal to low columnar cells

Nephron Classification

• Cortical Nephrons (80-85%):
  • Located in the outer part of the cortex
  • Short loop of Henle
  • Have peritubular capillaries that arise from efferent arterioles
• Juxtamedullary Nephrons (15-20%):
  • Lie deep in cortex closer to medulla
  • Have long loops of Henle that extend into the deepest region of the medulla
  • Receive blood supply from vasa recta, which arise from perturbed capillaries before becoming peritubular venules

Juxtaglomerular Apparatus (JGA)

• Final part of the ascending limb of the loop of Henle makes contact with afferent arteriole serving the renal corpuscle
• Columnar tubule cells in this region are crowded, known as macula densa
• Wall of the afferent arteriole contains juxtaglomerular (JG) cells, which help regulate blood pressure in the kidneys