Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology

()Map REABSORPTION AND SECRETION ALONG THE NEPHRON (Map)

Distal Tubule

Exchange in the Principal Cells of the Distal Tubule

• Important site of regulation of ions and water
• Less emphasis on bulk transport compared with proximal tubule
• More emphasis on fine management
• It is able to do this as it has high resistance epithelia. Allowing it to maintain substantial gradients across it
• Very important for the homeostasis of:
  • Sodium
  • Potassium
  • Acid Base

• There are two cell types present each with different functions. They are similar to the cells of the collecting ducts
  • Principal cells
    • Absorb sodium
    • Excrete potassium and hydrogen
    • Site of action of Aldosterone
  • Intercalated cells
    • ATP driven proton secretion

Juxtaglomerular Apparatus

Histology section showing the juxtaglomerular apparatus (© RVC 2008)

• The terminal portion of the straight distal tubule contacts the afferent and efferent vessels supplying its own glomerulus
• These vessels are said to embrace the distal tubule
• Here a special apparatus called the Juxtaglomerular Apparatus has 3 different structures:
  • The tubular epithelial cells of the distal tubule which are in contact with the arterioles supplying the glomerulus of that nephron are called the macula densa. They play a vital role in the regulation of the GFR.
  • The Juxtaglomerular Cells are smooth muscle cells which adjoin the macula densa in the capillary wall.
  • The Extraglomerular Mesangium has an unclear function

Developmental

Develops from metanephric tubule