ENTROPY GENERATION ANALYSIS IN THE EVOLUTION OF MAMMALIAN NEPHRONS

• Grant number: 23/00951-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): October 01, 2023
• Effective date (End): September 30, 2024
• Field of knowledge: Biological Sciences - Physiology - Compared Physiology
• Principal Investigator: José Guilherme de Souza Chaui Mattos Berlinck
• Grantee: Pedro Goes Nogueira de Sá
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The kidneys of terrestrial vertebrates face a paradoxical situation due to their evolutionary origin. The protovertebrates that invaded fresh rainwater had their body fluids hypertonic/hyperosmotic in relation to the new environment. As a result, the excretory system, which previously dealt with small flows of water, now has to be able to remove large amounts of free water from the body. Later, with the invasion of the terrestrial environment, the problem is reversed, since, now, free water is seldom available in large quantities. In this way, the reabsorption of the ultrafiltrate becomes paramount and the amount of urine formed becomes a small fraction of the total renal flow. A consequence of this filtration/reabsorption process is the formation of a futile cycle with an associated entropy generation. In this way, a model to approach how this system behaves from a thermodynamic point of view and why such a significant amount of fluid goes through a futile cycle is important both from the point of view of extant mammals and the evolutionary processes that preceded them. Based on fundamental principles of classical thermodynamics, out-of-equilibrium systems, physiology and control engineering, the model proposed here aims to calculate the entropy generation of the various steps of urine formation and relate them to the total entropy generated by maintaining renal blood flow. In the model, we propose a power index via the 2nd Law of Thermodynamics that represents the contribution of the various components associated with the system for the generation of total entropy. This efficacy index thus indicates the process in which the greatest entropic cost in urine formation is located.