Hello everyone, my name is Lo Ka Kay, you can call me KK. I'm a council member of the Hong Kong Association of Sports Medicine and Sports Science, and the Certified Exercise Physiologist from the ACSM. Welcome to the lecture on human physiology, and today, we will talk about homeostasis. The content that we want to go through today, the learning objectives, are to explain the body's basic organization, from the macro to the micro points of view. Secondly, we want to define the body's fluid compartments and homeostasis. Thirdly, to explain the regulation of homeostasis of the body and how solutes such as sodium and glucose are transported with different cellular mechanisms. Lastly, to explain the relationship between transportation together with water and solute. In part one, we will talk about the levels of organization in the human body. Firstly, you can look at this graph of the human body. There are ten organ systems of the body. The organ system is a group of organs that function together, and they are going to perform very specific functions. For instance, the skin. The skin is the largest organ of your body. It has its specific functions. It is protective, so it forms a barrier to the outside world and keeps the inside materials organized. Inside our body, we have the gastrointestinal (GI) tract which allows food or nutrients to enter into the body, and then solid waste to be removed from the body. Thirdly the respiratory system allows the entry of oxygen and the expulsion of carbon dioxide (CO2). Cardiovascular system takes the nutrients that are entering the GI tract and delivers them to all of the cells. It takes the gases which are coming in from the lung, the respiratory system, and delivers to all tissues and organs of the body. We have to be able to remove materials from the body, and this is done by the renal system. Liquid waste is removed, excess ions are removed, excess water is removed from the urinary system, and the gastrointestinal tract removes solid waste products. There have four layers of the organization in our human body, from the micro points to a larger point of view. Every two to four organs form an organ system. For example, two kidneys, one ureter, the bladder, and the urethra interact in the urinary system. A more microlayer, tissues combine to form an organ. There are total four types of tissues called neural tissue, connective tissue, muscle tissue, and epithelial tissue. Cells and extracellular material and fluids combine to form tissues. The physiologist calls these two major fluid compartments. Cell is the basic structural and functional unit of living organisms. A cell is made up of an uncountable number of atoms, for say, atoms associate and form molecules that can then combine to form higher structures such as water, which is combined with hydrogen and oxygen to form the H2O. Why are the physiologists saying the Cell and the extracellular material and fluid as the major fluid compartments? The reason is the cells themselves require specific factors to be within a very tight range. These factors are the amount of oxygen, carbon dioxide and hydrogen ions which is presented to the cells. The cells require a very tightly regulated environment, while the extracellular material and fluids are the buffering zone for regulating our body. We will talk about the homeostasis in these two major fluid compartments of our body - cell and the extracellular material and fluids in the next lecture.
