Glucosuria begins to appear in a healthy person at plasma glucose concentrations around 180 mg/dL, even though the theoretical tubular transport maximum for glucose is about 375 mg/min. What explains this discrepancy?
- A Splay phenomenon due to nephron-to-nephron variation in transport capacity ✓
- B Glucose is secreted by the distal tubule at high plasma levels
- C Glomerular filtration rate falls sharply at high glucose levels
- D SGLT2 saturates earlier than SGLT1 in every nephron simultaneously
Correct answer: A. Splay phenomenon due to nephron-to-nephron variation in transport capacity
Explanation
The splay phenomenon arises because individual nephrons differ in their filtration rates and their GLUT/SGLT transport capacity, so some nephrons reach saturation and spill glucose well before the average transport maximum is attained. This widens the transition zone between threshold and Tm. Secretion of glucose does not occur, and GFR remains stable at these plasma levels.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.