Human physiology is the science of the mechanical, physical, and biochemical functions of humans in good health, their organs, and the cells of which they are composed. The principal level of focus of physiology is at the level of organs and systems. Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology, and animal experimentation has provided much of the foundation of physiological knowledge. Anatomy and physiology are closely related fields of study: anatomy, the study of form, and physiology, the study of function, are intrinsically tied and are studied in tandem as part of a medical curriculum.
The biological basis of the study of physiology, integration refers to the overlap of many functions of the systems of the human body, as well as its accompanied form. It is achieved through communication which occurs in a variety of ways, both electrically as well as chemically.
In terms of the human body, the endocrine and nervous systems play major roles in the reception and transmission of signals which integrate function. Homeostasis is the process by which the body maintains a stable internal environment, or one of “similar condition” as described by Walter Bradford Cannon. In Cannon’s Postulate, the body's ability to regulate pH, temperature, fluid volume, pressure, and osmolarity are recognized through highly evolved feedback systems, which act to finely tune many different chemical and electrical responses.
The concentration of ions in relations to one another (e.g. Na+, K+, H+) determine the body's pH, which is closely regulated by the respiratory and urinary systems.
Temperature in the body is determined by both the external environment of the organism as well as the amount of heat produced by anabolic reactions within the body regulated by respiratory and cardiovascular systems
Fluid volume and pressure, and osmolarity are regulated by the urinary, cardiovascular, and respiratory systems.
Physiology is the study of these systems' integrated functions and the processes by which they maintain the milieu interieur, or internal environment.
Systems
Traditionally, the academic discipline of physiology views the body as a collection of interacting systems, each with its own combination of functions and purposes.
The circulatory system consists of the heart and blood vessels (arteries, veins, capillaries). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer oxygen, fuel, nutrients, waste products, immune cells, and signalling molecules (i.e., hormones) from one part of the body to another. The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and back, as well as the spleen and bone marrow.
The integumentary system consists of the covering of the body (the skin), including hair and nails as well as other functionally important structures such as the sweat glands and sebaceous glands. The skin provides containment, structure, and protection for other organs, but it also serves as a major sensory interface with the outside world.
The urinary system consists of the kidneys, ureters, bladder, and urethra. It removes water from the blood to produce urine, which carries a variety of waste molecules and excess ions and water out of the body.
The reproductive system consists of the gonads and the internal and external sex organs. The reproductive system produces gametes in each sex, a mechanism for their combination, and a nurturing environment for the first 9 months of development of the offspring.
The endocrine system consists of the principal endocrine glands: the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads, but nearly all organs and tissues produce specific endocrine hormones as well. The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function.
The traditional divisions by system are somewhat arbitrary. Many body parts participate in more than one system, and systems might be organized by function, by embryological origin, or other categorizations. In particular, is the "neuroendocrine system", the complex interactions of the neurological and endocrinological systems which together regulate physiology. Furthermore, many aspects of physiology are not as easily included in the traditional organ system categories.
The study of how physiology is altered in disease is pathophysiology.
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