The medullary thick limb: Function and modulation of the single-effect multiplier

This article will focus particularly on the transport functions of the medullary segment. The specific issues discussed will include the mechanism of NaCl absorption by the mTALH, the enhancement of this salt absorptive process by antiduiretic hormone (ADH), at least in certain mammalian species, and the major factors that appear to regulate or modulate both ADH-dependent and -independent NaCl transport processes. Sufficient information is currently available which indicates that these modulating factors provide feedback loops which sense interstitial osmolality and serve as a means of controlling the magnitude of interstitial hypertonicity, and hence concentrating power.