Because physiology focuses on the functions and mechanisms of living organisms at all levels, from the molecular and cellular level to the level of whole organisms and populations, its foundations span a range of key disciplines:
Anatomy is the study of the structure and organization of living organisms, from the microscopic level of cells and tissues to the macroscopic level of organs and systems. Anatomical knowledge is important in physiology because the structure and function of an organism are often dictated by one another.
Biochemistry is the study of the chemical processes and substances that occur within living organisms. Knowledge of biochemistry provides the foundation for understanding cellular and molecular processes that are essential to the functioning of organisms.
Biophysics is the study of the physical properties of living organisms and their interactions with their environment. It helps to explain how organisms sense and respond to different stimuli, such as light, sound, and temperature, and how they maintain homeostasis, or a stable internal environment.
Genetics is the study of heredity and the variation of traits within and between populations. It provides insights into the genetic basis of physiological processes and the ways in which genes interact with the environment to influence an organism's phenotype.
Evolutionary biology is the study of the processes that have led to the diversity of life on Earth. It helps to explain the origin and adaptive significance of physiological processes and the ways in which organisms have evolved to cope with their environment.
Human physiology is the study of how the human body's systems and functions work together to maintain a stable internal environment. It includes the study of the nervous, endocrine, cardiovascular, respiratory, digestive, and urinary systems, as well as cellular and exercise physiology. Understanding human physiology is essential for diagnosing and treating health conditions and promoting overall wellbeing.
It seeks to understand the mechanisms that work to keep thehuman body alive and functioning,[4] through scientific enquiry into the nature of mechanical, physical, and biochemical functions of humans, 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 within systems. The endocrine and nervous systems play major roles in the reception and transmission of signals that integrate function in animals.Homeostasis is a major aspect with regard to such interactions within plants as well as animals. 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 that occurs in a variety of ways, both electrical and chemical.[8]
Changes in physiology can impact the mental functions of individuals. Examples of this would be the effects of certain medications or toxic levels of substances.[9] Change inbehavior as a result of these substances is often used to assess the health of individuals.[10][11]
Much of the foundation of knowledge in human physiology was provided byanimal experimentation. Due to the frequent connection between form and function, physiology andanatomy are intrinsically linked and are studied in tandem as part of a medical curriculum.[12]
The study of human physiology as a medical field originates inclassical Greece, at the time ofHippocrates (late 5th century BC).[14] Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time inChina,[15] India[16] and elsewhere. Hippocrates incorporated the theory ofhumorism, which consisted of four basic substances: earth, water, air and fire. Each substance is known for having a corresponding humor: black bile, phlegm, blood, and yellow bile, respectively. Hippocrates also noted some emotional connections to the four humors, on whichGalen would later expand. The critical thinking ofAristotle and his emphasis on the relationship between structure and function marked the beginning of physiology inAncient Greece. LikeHippocrates, Aristotle took to the humoral theory of disease, which also consisted of four primary qualities in life: hot, cold, wet and dry.[17] Galen (c. 130–200 AD) was the first to use experiments to probe the functions of the body. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, including the entire body.[18] His modification of this theory better equipped doctors to make more precise diagnoses. Galen also played off of Hippocrates' idea that emotions were also tied to the humors, and added the notion of temperaments: sanguine corresponds with blood; phlegmatic is tied to phlegm; yellow bile is connected to choleric; and black bile corresponds with melancholy. Galen also saw the human body consisting of three connected systems: the brain and nerves, which are responsible for thoughts and sensations; the heart and arteries, which give life; and the liver and veins, which can be attributed to nutrition and growth.[18] Galen was also the founder of experimental physiology.[19] And for the next 1,400 years, Galenic physiology was a powerful and influential tool inmedicine.[18]
In 1791Luigi Galvani described the role of electricity in the nerves of dissected frogs. In 1811,César Julien Jean Legallois studied respiration in animal dissection and lesions and found the center of respiration in themedulla oblongata. In the same year,Charles Bell finished work on what would later become known as theBell–Magendie law, which compared functional differences between dorsal and ventral roots of thespinal cord. In 1824,François Magendie described the sensory roots and produced the first evidence of the cerebellum's role inequilibration to complete the Bell–Magendie law.
In the 1820s, the French physiologistHenri Milne-Edwards introduced the notion of physiological division of labor, which allowed to "compare and study living things as if they were machines created by the industry of man." Inspired in the work ofAdam Smith, Milne-Edwards wrote that the "body of all living beings, whether animal or plant, resembles a factory ... where the organs, comparable to workers, work incessantly to produce the phenomena that constitute the life of the individual." In more differentiated organisms, the functional labor could be apportioned between different instruments orsystems (called by him asappareils).[23]
In 1858,Joseph Lister studied the cause of blood coagulation and inflammation that resulted after previous injuries and surgical wounds. He later discovered and implementedantiseptics in the operating room, and as a result, decreased the death rate from surgery by a substantial amount.[24]
The Physiological Society was founded in London in 1876 as a dining club.[25]The American Physiological Society (APS) is a nonprofit organization that was founded in 1887. The Society is, "devoted to fostering education, scientific research, and dissemination of information in the physiological sciences."[26]
In 1891,Ivan Pavlov performed research on "conditional responses" that involved dogs' saliva production in response to a bell and visual stimuli.[24]
In the 19th century, physiological knowledge began to accumulate at a rapid rate, in particular with the 1838 appearance of theCell theory ofMatthias Schleiden andTheodor Schwann.[27] It radically stated that organisms are made up of units called cells.Claude Bernard's (1813–1878) further discoveries ultimately led to his concept ofmilieu interieur (internal environment),[28][29] which would later be taken up and championed as "homeostasis" by American physiologistWalter B. Cannon in 1929. By homeostasis, Cannon meant "the maintenance of steady states in the body and the physiological processes through which they are regulated."[30] In other words, the body's ability to regulate its internal environment. William Beaumont was the first American to utilize the practical application of physiology.
Nineteenth-century physiologists such asMichael Foster,Max Verworn, andAlfred Binet, based onHaeckel's ideas, elaborated what came to be called "general physiology", a unified science of life based on the cell actions,[23] later renamed in the 20th century ascell biology.[31]
In 1920,August Krogh won the Nobel Prize for discovering how, in capillaries, blood flow is regulated.[24]
In 1954,Andrew Huxley and Hugh Huxley, alongside their research team, discovered the sliding filaments inskeletal muscle, known today as the sliding filament theory.[24]
Recently, there have been intense debates about the vitality of physiology as a discipline (Is it dead or alive?).[34][35] If physiology is perhaps less visible nowadays than during the golden age of the 19th century,[36] it is in large part because the field has given birth to some of the most active domains of today's biological sciences, such asneuroscience,endocrinology, andimmunology.[37] Furthermore, physiology is still often seen as an integrative discipline, which can put together into a coherent framework data coming from various different domains.[35][38][39]
Initially, women were largely excluded from official involvement in any physiological society. TheAmerican Physiological Society, for example, was founded in 1887 and included only men in its ranks.[40] In 1902, the American Physiological Society electedIda Hyde as the first female member of the society.[41] Hyde, a representative of theAmerican Association of University Women and a global advocate for gender equality in education,[42] attempted to promote gender equality in every aspect of science and medicine.
Gerty Cori,[46] along with her husbandCarl Cori, received the Nobel Prize in Physiology or Medicine in 1947 for their discovery of thephosphate-containing form ofglucose known asglycogen, as well as its function withineukaryoticmetabolic mechanisms for energy production. Moreover, they discovered theCori cycle, also known as the Lactic acid cycle,[47] which describes how muscle tissue converts glycogen into lactic acid vialactic acid fermentation.
Barbara McClintock was rewarded the 1983 Nobel Prize in Physiology or Medicine for the discovery ofgenetic transposition. McClintock is the only female recipient who has won an unshared Nobel Prize.[48]
^Widmaier, Eric P.; Raff, Hershel; Strang, Kevin T. (2016).Vander's Human Physiology Mechanisms of Body Function. New York, NY:McGraw-Hill Education. pp. 14–15.ISBN978-1-259-29409-9.
^Moyes, C.D., Schulte, P.M. Principles of Animal Physiology, second edition. Pearson/Benjamin Cummings. Boston, MA, 2008.
^Kremer, Richard L. (2009). "Physiology". In Bowler & Pickstone (ed.).The Cambridge History of the Modern Biological and Earth Science. Cambridge: Cambridge University Press. pp. 342–366.doi:10.1017/CHOL9780521572019.019.ISBN9781139056007.
^Neill, Jimmy D.; Benos, Dale J. (1993). "Relationship of Molecular Biology to Integrative Physiology".Physiology.8 (5):233–235.doi:10.1152/physiologyonline.1993.8.5.233.
