Table 1. Rate-Limiting Steps (Membrane Entry, Flip–Flop, or Membrane Exit) for Membrane Permeation Depending on the Steroid Structure and the Type of Membrane.

	cell	planar membrane	LUV (radius 0.2 μm)
long-tailed	exit	exit	exit
0–1 OH groups	entry	entry	exit
2–3 OH groups	flip–flop	flip–flop	flip–flop