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# Lec 1- Human Physiology ## Introduction Physiology is the scientific study of functions and mechanisms in a living system. It is a sub-discipline of biology focusing on how organisms, organ systems, individual organs, cells, and biomolecules carry out chemical and physical functions in a living...

# Lec 1- Human Physiology ## Introduction Physiology is the scientific study of functions and mechanisms in a living system. It is a sub-discipline of biology focusing on how organisms, organ systems, individual organs, cells, and biomolecules carry out chemical and physical functions in a living system. The field can be divided into medical physiology, animal physiology, plant physiology, cell physiology, and comparative physiology. Human physiology studies how the human body's systems and functions work together to maintain a stable internal environment (homeostasis). This includes the nervous, endocrine, cardiovascular, respiratory, digestive, and urinary systems, as well as cellular and exercise physiology. Medical physiology describes the chemistry and physics behind basic body functions, from how molecules behave in cells to how systems of organs work together. This helps understand healthy function and what goes wrong when the body is sick. ## Cell Physiology A cell consists of three parts: the cell membrane, the nucleus, and the cytoplasm which lies between them. The cytoplasm contains thousands of small but distinct structures called organelles and intricate arrangements of fine fibers. ## Structure of the Cell Membrane Every cell in the body is enclosed by a cell membrane (plasma membrane). The membrane separates the material outside the cell (extracellular) from the material inside the cell (intracellular). It maintains the: 1. integrity of the cell 2. controls passage of materials into and out of the cell. The cell membrane consists of: * **A- a lipid bilayer:** This is composed of two layers of phospholipids with cholesterol molecules interspersed between them. This structure maintains appropriate membrane fluidity at various temperatures. * **B- membrane proteins:** The membrane contains various proteins including: * **integral proteins:** These span the membrane and act as membrane transporters.