The region known as the macula densa is part of

The region known as the macula densa is part of excretory system.

More precisely, macula densa is a structure located in the kidney, in the wall of the distal tubule. The macula densa is composed of tightly packed specialized cells on the place where the distal tubule touches the glomerulus.

The role of this structure is to detect changes in concentration of sodium chloride and to send a signal to the afferent arterioles (to change blood pressure) or to the juxtaglomerular cells (renin release).

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.

maybe because its impossible for balloons to lift a whole entire house.