A researcher plots vitreous potassium against time since death in a large autopsy series. The relationship is linear for the first day or so, but at longer intervals the curve flattens and underestimation of the true interval becomes common. What is the PRIMARY reason for this loss of linearity?
- A Continuing bacterial diffusion of potassium into the vitreous from the gut
- B Progressive evaporation of water concentrating the remaining solutes
- C Exhaustion of the intracellular potassium reserve once retinal cell lysis is complete, allowing equilibration with surrounding tissues ✓
- D Ongoing secretion of fresh potassium by the ciliary epithelium after death
Correct answer: C. Exhaustion of the intracellular potassium reserve once retinal cell lysis is complete, allowing equilibration with surrounding tissues
Explanation
The postmortem rise in vitreous potassium depends on leakage from a finite intracellular pool in retinal and adjacent ocular cells down a gradient maintained by living membranes. Once these cells are fully lysed and their potassium released, the concentration approaches equilibrium with the surrounding humours and tissues, so the slope falls and the curve flattens. Bacteria do not pump potassium into the eye, evaporation would raise rather than flatten values, and secretory activity ceases at death.
Reference: Knight's Forensic Pathology, 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.