 Dear students, in this module we shall discuss the spectrum of study of physiology. We define physiology as the study of functions of cells, tissues, organs and organ systems of organisms. Our ultimate goal of the study of animal physiology is to understand the mechanisms that operate in animals at all levels in physical and chemical terms. Dear students, the laws of physics and chemistry, which you have read in the last classes in the study of physics and chemistry, have many of the laws that apply to physiological mechanisms and processes. We will take a few examples from which we will look at the applications of physiological processes. First of all, you are familiar with Ohm's law. In physiology, this law is applicable to blood flow and pressure. It is also applicable to ionic currents and capacitance of the membrane. Then the Boy's law and very familiar ideal gas law, these two laws are applicable to gas exchange mechanisms in animals, that is respiration. Then law of gravity is applicable to blood flow. In addition, kinetic and potential energy concepts, which you have achieved through physics, they are applicable to muscle contraction in animals. They are also applicable to chest movements that occur during inhalation and exhalation. Similarly, the concepts of drag, inertia, momentum and velocity are applicable to locomotion in animals. Dear students, physiology is an interesting field and curiosity underlies the studies of physiology. The desire to know, that is, the justice or juxtajoo, is created because of interest. There are many things in physiology that enrich our interest. We will take a few examples of classical curious questions of physiology. The classical example is that when a hummingbird is hovering, its heart beats 20 times per second. How is it possible? Then insects can see in the ultraviolet spectrum, while we cannot. How? One more question, kangaroo rats are a small mammal like rats. They live in deserts and live without drinking water. How? So, these are some of the questions that provoke curiosity. Dear students, the animal physiology is the basis of human physiology also because human sophisticies has a linked evolutionary history with all animals. That is why when we study comparative animal physiology, we come to understand many mechanisms that are operating in our own bodies. That is why the physiology, animal physiology lays the foundation of human physiology. And the human physiology lays the foundation of medical science. Actually, there is a lot of knowledge that we know about human physiology, about human tissues, about human organs and it is based on the experiments that were carried on animals. Dear students, the human physiology has laid the foundation of human physiology. Modern medical science, that is the basis of scientific medical practice. Understanding the physiological basis of disease helps in developing the effective and sound treatments for human diseases. In the modern times, physiology has contributed through the development of special model organisms for specific human diseases. As a disease, it is difficult to experiment and collect data on humans. Physiological principles are used to carry animal models and experiments are carried on them. For example, diabetic mice are the disease of sugar. Congenitally, fat rats are the prey of fat. Similarly, zebrafish models with heart defects. These models allow wide range of experimentation that provide insight into the physiological basis of disease.