physiology

1. The biological study of the functions of living organisms and their parts.
2. All the functions of a living organism or any of its parts.

For more information on physiology, visit Britannica.com.

Physiology is defined by dictionaries as ‘the science of the normal functions and phenomena of living things’. The physiology of animals emerged in Europe out of the Renaissance nterest in the experimental method, as exemplified by the work of William Harvey (doctor to Charles I). Harvey's book of 1628 on the Motion of the Heart, ‘Exercitationes Anatomicae de Motu Cordis’, brilliantly analyses structural and functional observations (quantitative as well as qualitative), which remorselessly led him, and similarly lead the present day reader, to the conclusion that the blood circulates, in man as well as in other animals. This volume remains central to our current understanding of the word ‘physiology’ because of its emphasis on experiment, data analysis, and hypothesis testing. Harvey's work also exemplifies the natural symbiois between physiology (‘function’) and anatomy (‘structure’), a science from which physiology was to emerge as a separate discipline in the second half of the nineteenth century. Harvey's book also connects physiology to medicine. Understanding of every disease follows from combining knowledge of the relevant normal physiology to the way in which it is perturbed in the particular disorder (‘pathophysiology’).

Historically, the subsequent meaning of ‘physiology’ is well illustrated by the way in which the word is used in the two following quotations. The first is from 1704 (J. Harris, Lexicon Technica): ‘Physiology, is by some also accounted a Part of Physick’ (i.e. Medicine), ‘that teaches the Constitution of the Body so far as it is sound, or in its Natural State; and endeavours to find Reasons for its Functions and Operations, by the Help of Anatomy and Natural Philosophy’. The second (a definition of Charles Darwin's colleague T. H. Huxley), 150 years later, is virtually identical to current usage: ‘whereas that part of biological science which deals with form and structure is called Morphology; that which concerns itself with function is Physiology’.

It was the experimental work of Claude Bernard in France in the mid nineteenth century that led to the profound insight that homeostasis is central ot the success and survival of any organism. This implies that physiological systems must necessarily function in such a way as to regulate their internal environment, by means of what we now call ‘feedback’. A homeostatic mechanism requires, at a minimum, a set of sensors to measure the relevant variable (e.g. body temperature), feeding back ‘error signals’ to an integrator (the brain), which controls an effector mechanism to adjust that variable (sweating, shivering, etc.). Such a negative feedback control system will act to return the variable towards the non-perturbed state. Such ideas of control and order are central to understanding and defining the discipline of physiology, whether it be in microorganisms, plants or animals.

The significance of physiology as the key science underpinning health and disease (human and veterinary) accounts for the nomenclature adoped in 1900 by the Nobel Foundation. To recognize key developments in this field, the relevant Nobel Prize is still awarded in ‘Physiology or Medicine’, although many Nobel prize-winners in this category (working in such fields as immunology, molecular biology and bioengineering) would not readily have identified themselves as physiologists. But many would have done so. For example: in cardiovascular physiology, Krogh (for his studies of capillary function), Einthoven (who described the electrocardiogram) and Forssman (who developed cardiac catheterization) ; in neurophysiology, Sherrington (who conceived the idea of synapses), Adrian (responsible for our original understanding of coding of information by patterns of nerve impulses), and Hubel and Weisel (who worked out how the visual areas of the cerebral cortex analyse specific features of the image) ; in endocrinology, Banting (insulin) and Guillemin and Schally (identification of the hypothalamic peptides that control the pituitary gland).

The interface between physiology and chemistry led directly to the emergence, in the first half of the twentieth century, of the major new discipline of biochemistry. Hence, such Nobel laureates in ‘Physiology or Medicine’ as Warburg (respiratory enzymes), Krebs (metabolic integration), Brown and Goldstein (cholesterol) and Sutherland (cyclic AMP) would probably not have thought of their scientific research as being part of ‘physiology’.

Another science that grew out of physiology concerns nutrition; yet another is pharmacology, whose foundations arose from the experiemental studies of physiologists such as Loewi (the discoverer of the transmitter substance acetylcholine) and Dale (chemical transmission between nerve cells). Despite the natural and deepening methodological and cultural divergence, over time, of both biochemistry and pharmacology from physiology, they all share the goal of explaining the functions of the body. Moreover, now that the concepts of genetics and the power of molecular biology pervade the whole of biology, the communality of physiology, pharmacology and biochemistry has re-emerged. This is well illustrated by the recent discovery of Furchgott (another Nobel prize winner) and others, that nitric oxide, a tiny gaseous molecule, can convey information between cells simply by diffusing through their membranes.

Harder to define, yet critical to the discipline of physiology, is the term ‘general physiology’. This subject emerged originally from the convergence of nineteenth-century physical chemistry with experimental biology. It was founded on quantitative studies of plant and animal cells. Because of its reductionist goal, general physiology was an obvious forerunner of what is now described as cell and molecular physiology. However, more than this, it attempted to use the theoretical insights gained from the ‘hard sciences’ (physics and chemistry) to provide a rational basis for analyzing living matter, and was thus eager to embrace and test theory quantitatively. An outstanding example of the success of this approach is the experimental analysis of the resting potential and the action potential (nerve impulse) by Hodgkin and colleagues in the late 1940s. Indeed, successful analysis of ‘bioelectricity’ is one of the factors that led to the foundation by physiologists of yet another off-shoot — biophysics. Although there are still (notably in North America) a number of distinguished university departments of Biophysics, growth of this subject as an independent discipline has been hampered somewhat by its failure to meld its ‘physiological’ roots with its links to biological physics (especially X-ray crystallography). However, the work of Nobel laureates Neher and Sakmann provides a spectacular example of how electrophysiological analysis can give biophysical insight not available through other means. These scientists, through clever technical developments, were able to design experiments that allowed structural, and hence functional, changes in single protein molecules (membrane ion channels) to be followed in real time by recording the flow of ionic current through them. By tightly sealing a fine, fluid-filled capillary tube to an extremely small part of a cell membrane, and linking it to a sophisticated amplifier (‘patch clamping’), they were able to measure the current through individual channels, flicking quickly from closed to open states. This physiological insight has very recently been matched by structural studies by MacKinnon and colleagues on membrane channels at atomic resolution.

Physiology has a complex, deep relationship with the approach of reductive science. This is in part because ‘function’, particularly ‘interesting’ or unexpected function, emerges from interactions that can be found only in relatively complex systems; hence physiologists are unlikely (unless they are working on essentially trivial problems) to find that molecular structures in isolation give more than partial insight into the problem under attack. ‘Explanations’ of physiological questions seem more likely to arise from combining such reductionist approaches with, on the one hand, thermodynamics and, on the other, control systems theory. Life depends on ‘non-equilibrium’ properties — i.e. on complex interactions that require the constant expenditure of energy to maintain them. And networks of information and control (the nervous system, hormones etc.) are central to the development, function, and probably the evolution of complex biological systems.

Seen in this way, the information encoded in the genes provides a very challenging experimental opportunity for physiologists. To have read the sequence of DNA is only a small step on the route to understanding how and to what extent our genes build and control our bodies, and cause disease. Genes do just one thing: they translate their information into proteins. To understand how the products of genes work individually and together to create the magnificent complexity of a whole organism is part of the exciting challenge that faces the revitalized science of physiology in the twenty-first century. Indeed, the prospects for physiology are wider still: it will ultimately need to link such understanding ‘upwards’ to such disciplines as experimental psychology, ecology and human biology.

— Richard Boyd

Bibliography

• Hodgkin, A. L. (1977). The pursuit of nature. Cambridge University Press, Cambridge.
• Boyd, C. A. R. and Noble, D. (1993). The logic of life: the challenge of integrative physiology. Oxford University Press, Oxford

See also Bernard, Claude; biochemistry; biotechnology; Harvey, William; molecular biology; pharmacology.

Study of tissue and organism behavior. The physiologic process is a dynamic state of tissue as compared with the static state of descriptive morphology (anatomy). Physiology is differentiated from descriptive morphology by the following qualifying properties: rate, direction, and magnitude. Physiologic processes are thus morphologic alterations in the three dimensions of space associated with a temporary (time) sequence. Physiologic processes relate to a wide spectrum of life activities on three levels: biochemical and biophysical activity of a subcellular nature, the activity of cells and tissues aggregated into organ systems, and multiorgan system activity as expressed in human behavior.

In humans, the study of the functioning of normal, healthy people and their body structures. Compare pathology.

Physiology can be traced back to Greek natural philosophy, yet in our age it has emerged as a sophisticated experimental science with numerous subspecialties. After distinction from its origins in the older discipline of anatomy, physiology encompassed study of physical and chemical functions in the tissues and organs of all living matter. Dynamic boundaries of the field are evident in that neuroscience, pharmacology, biophysics, endocrinology, and other scientific and medical specialties have roots in physiology. Given that plant physiology came to be defined as a specialization of botany, however, "physiology" today connotes the study of life-sustaining body functions and structures of animals, especially humans.

Development of Physiology in the United States

Scientific physiology in the United States developed slowly at first. Medical schools in the late eighteenth and early nineteenth centuries taught classes in physiology—then called the "institutes of medicine"—with no laboratory work being done. The earliest physiology professorship was founded in 1789 at the College of Philadelphia. Robley Dunglison, once a physician to Thomas Jefferson and one of a few full-time medical teachers at the time, wrote the subject's first comprehensive American textbook, Human Physiology,in 1832. William Beaumont (1785–1853) published a classic work on digestive function in 1833, given his opportunity to observe the subject in nineteen-year-old Alexis St. Martin, whose abdomen was blown open in a shotgun accident.

Prior to the Civil War (1861–1865), American physiologists were amateurs who tended to earn their livelihood through medical practice or teaching. Significant change in that state of affairs resulted from work by two pioneers of American physiology, John C. Dalton Jr. (1825–1889) and S. Weir Mitchell (1825–1914). As did many of their medical colleagues, Dalton and Mitchell traveled to Europe for postgraduate work, particularly in Paris, where they studied with physiologist Claude Bernard, famous for his carbohydrate metabolism research. Returning to the United States around 1851, Dalton eschewed a promising medical career, accepted a New York medical college professor's chair, and there became Amerrica's first professional physiologist. Like his French mentor, Dalton was a strong proponent of experimental physiology and favored vivisection in his teaching, a practice that later placed him in controversy with early animal rights activists. Mitchell returned from Paris at the same time, settling in Philadelphia, where he failed in two significant efforts to secure a physiology professorship, due in part, as he saw it, to his expressed enthusiasm for the sort of experimental approach to the science he had learned in Europe. After serving as a surgeon in the Civil War, Mitchell's career turned toward excellent work in the study and treatment of neurological disorders, but he retained his devotion to physiology and eventually helped to found the science's first professional society.

Dalton and Mitchell's love for experimental physiology found fruition and institutional support in Henry P. Bowditch (1840–1911) and H. Newell Martin (1848–1896). Bowditch had studied in the prominent German school of physiology under Carl Ludwig, a master laboratory technician. As he returned to the United States in 1871, a reform movement in higher education fortunately called for more emphasis on experimentation, and Bowditch established America's first full-fledged physiology lab as a professor at the Harvard Medical School. Martin, a postgrad student in the prestigious British physiology school, was recruited by newly formed and well-endowed Johns Hopkins University, where he accepted a biology professorship and established a state-of-the-art physiology laboratory in 1876. In turn, Martin developed a mammalian heart preparation that led to important cardiac physiology discoveries. Fellowships allowed Martin to attract a bright cohort of students at Johns Hopkins, and, along with Bowditch and his students at Harvard, they founded physiology as an experimental research-based science in the United States.

Bowditch and Martin mentored a generation of physiologists who were eager, willing, and able to further the science, despite few gainful employment opportunities. They established new labs at the University of Michigan, Yale University, and Columbia University. Their professionalization of physiology coincided with medical education reforms calling for increased emphasis on experimental science and research. Thus the new physiology gained more than a foothold in medical schools; it became the preeminent discipline, leading to America's international prominence in biomedical science that has continued into the twenty-first century. In 1887, Bowditch and Martin heralded their scientific establishment to the world by founding the American Physiological Society (APS). Another original APS member, Johns Hopkins–educated William Howell, published his landmark American Textbook of Physiology in 1896. That was followed by initial circulation of the APS's prestigious American Journal of Physiology (AJP) in 1898.

Despite animal physiology's enhanced position, however, experimental biologists were not willing to concede the field. Replete with antagonism toward their counterparts in the 1880s, the biologists proposed a broader notion of physiology, combining the study of plants, zoology, microorganisms, and embryology toward a unified theory of life. These general physiologists, as they came to be known, found a leader in Charles Otis Whitman, who established a school for the broader science at the University of Chicago. The general physiology movement lost momentum around 1893, however, lacking broad institutional support and firm disciplinary structure. Although the Chicago school remained a haven for general physiologists, the medically oriented stream of animal physiology maintained power enough to define the term.

American Physiology in the Twentieth Century

Burgeoning into the twentieth century as well, American physiology achieved international ascendance during World War I (1914–1918). Progress in German and English labs was profoundly stifled by the war, while American physiologists continued their work in relative isolation. Even as new research continued, practical physiology was applied to submarine and aviation adaptation, troop nutrition, poison gas effects, munitions factory worker fatigue, wound shock, and other areas. Physiology continued to stimulate the medical field. Harvey W. Cushing, for example, a former student of Bowditch who also worked in the Johns Hopkins physiology lab, pioneered the practice of brain surgery. By all indications, including publications in the AJP and American research citations in international journals, American physiology was excellent.

Four physiologists stood out during the early to mid-twentieth century. Foremost among them was Walter B. Cannon (1871–1945), another former student of and eventual successor to Bowditch at Harvard. Among his achievements, Cannon used the new X-ray technology to advance understanding of digestive processes; he explained adrenal gland functions in response to emotional stress; and his classic work, The Wisdom of the Body, introduced a profound physiological principle, homeostasis. Not to forget the influence of his Textbook, William Howell (1860–1945) at Johns Hopkins did important heart research, described the pituitary gland, made momentous blood coagulation discoveries, and presided over the International Physiological Congress, which met in the United States in 1929. A. J. Carlson (1875–1956) at the University of Chicago was prolific in cardiac and gastric physiology research. Joseph Erlanger at Washington University in St. Louis, along with Herbert Gasser, won the 1944 Nobel Prize for research in nerve action, which incorporated valve amplification and introduced cathode ray tube technology, thus heralding the electronic age of physiological research.

A disciplinary orientation had developed in twentieth-century American physiology, emphasizing the study of intrinsic and extrinsic function, integration, and regulation of body systems over their structures. A talented national field of scientists operating in well-funded programs thus undertook the study of metabolism, reproduction, muscular contractility, cardiopulmonary transport, regulation (for example, homeostasis), and how information is passed through the nervous system. This trend toward functional specialization, facilitated by advances in microscopy, imaging, and other technology, allowed physiological analysis to intensify from the level of entire bodies to specific organs, down to cells, and eventually to molecules. After many practical applications during World War II (1939–1945), American physiology expertise continued to gain during the Cold War, finding novel uses in the space program and especially in medical surgery. Latter twentieth century Americans enjoyed increased and enhanced life spans, if also rising health care costs. The heart and other vital organs, for example, could now be restored and even replaced; sexual function was demythologized; mental illness was treated with new drugs and lesser side effects; and nutritional information lowered cholesterol counts—all advances stemming from physiology research. Now given a vast array of subdisciplines, the specialization trend has separated the close association of physiology with medicine, although benefits to well-being are still claimed as justification for experimental research funding.

American physiology retains its world-class status achieved early in the twentieth century, evidenced by tens of Nobel Prizes in physiology and medicine awarded to U.S. citizens over the past thirty years. The work of Nobel winners Robert C. Gallo, Michael Bishop, and Harold E. Varmus, for example, led to the identification of retroviruses, which has proved invaluable in combating AIDS and even cancer. The simultaneous rise of sports and obesity in the United States has stimulated popular interest in exercise physiology. Aided by super computer technology and other American innovations, explosive recent discoveries in genetics, a field intimately related to physiology, promise monumental benefits, and moral controversies, to humankind. From its professional foundation in the latter nineteenth century to its status as a mature, expanding science in the new millennium, American study of animal body functions and structure (that is, physiology) promises further life-enhancing and perhaps even life-creating discoveries.

Bibliography

The American Physiological Society. Home page at http://www.the-aps.org/.

Fye, Bruce W. The Development of American Physiology: Scientific Medicine in the Nineteenth Century. Baltimore: Johns Hopkins University Press, 1987.

Geison, Gerald L. Physiology in the American Context, 1850–1940. Baltimore: Williams and Wilkins, 1987.

The study of the function of living things, including processes such as nutrition, movement, and reproduction. (Compare anatomy and morphology.)

A specialist in physiology.

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Physiology is the science of the functioning of living systems. It is a subcategory of biology. In physiology, the scientific method is applied to determine how organisms, organ systems, organs, cells and biomolecules carry out the chemical or physical function that they have in a living system. The word physiology is from Greek φύσις, physis, "nature, origin"; and -λογία, -logia, "study of".

Contents 1 History 2 See also 3 References 4 External links

History

Human physiology dates back to at least 420 B.C. and the time of Hippocrates,^[1] the father of medicine. The critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece, while Claudius Galenus (c. 126-199 A.D.), known as Galen, was the first to use experiments to probe the function of the body. Galen was the founder of experimental physiology.^[2] The ancient Indian books of Ayurveda, the Sushruta Samhita and Charaka Samhita, also had descriptions on human anatomy and physiology. The medical world moved on from Galvanism only with the appearance of Andreas Vesalius and William Harvey.^[3]

During the Middle Ages, the ancient Greek and Indian medical traditions were further developed by Muslim physicians, most notably Avicenna (980-1037), who introduced experimentation and quantification into the study of physiology in The Canon of Medicine. Many of the ancient physiological doctrines were eventually discredited by Ibn al-Nafis (1213-1288), who was the first physician to correctly describe the anatomy of the heart, the coronary circulation, the structure of the lungs, and the pulmonary circulation, for which he is considered the father of circulatory physiology.^[4] He was also the first to describe the relationship between the lungs and the aeration of the blood, the cause of pulsation,^[5] and an early concept of capillary circulation.^[6]

Following from the Middle Ages, the Renaissance brought an increase of physiological research in the Western world that triggered the modern study of anatomy and physiology. Andreas Vesalius was an author of one of the most influential books on human anatomy, De humani corporis fabrica.^[7] Vesalius is often referred to as the founder of modern human anatomy.^[8] Anatomist William Harvey described the circulatory system in the 17th century,^[9] demonstrating the fruitful combination of close observations and careful experiments to learn about the functions of the body, which was fundamental to the development of experimental physiology. Herman Boerhaave is sometimes referred to as a father of physiology due to his exemplary teaching in Leiden and textbook Institutiones medicae (1708).^{[citation needed]}

In the 18th century, important works in this field were by Pierre Cabanis, a french doctor and physiologist.^{[citation needed]}

In the 19th century, physiological knowledge began to accumulate at a rapid rate, most notably^{[peacock term]} in 1838 with the Cell theory of Matthias Schleiden and Theodor Schwann, which radically stated that organisms are made up of units called cells. Claude Bernard's (1813-1878) further discoveries ultimately led to his concept of milieu interieur (internal environment), which would later be taken up and championed as "homeostasis" by American physiologist Walter Cannon (1871-1945).^{[clarification needed]}

In the 20th century, biologists also became interested in how organisms other than human beings function, eventually spawning the fields of comparative physiology and ecophysiology.^[10] Major figures in these fields include Knut Schmidt-Nielsen and George Bartholomew. Most recently, evolutionary physiology has become a distinct subdiscipline^[11].

See also

• Comparative physiology
• Defense Physiology
• Ecophysiology
• Evolutionary physiology
• Physiome
• The Physiological Society
• Somatopsychic

References

1. ^ Physiology - History of physiology, Branches of physiology
2. ^ Thoracic Surgery Clinics: Historical Perspectives of Thoracic Anatomy, Stanley C. Fell and F. Griffith Pearson
3. ^ Galen
4. ^ Chairman's Reflections (2004), "Traditional Medicine Among Gulf Arabs, Part II: Blood-letting", Heart Views 5 (2), p. 74-85 [80].
5. ^ Nahyan A. G. Fancy (2006), "Pulmonary Transit and Bodily Resurrection: The Interaction of Medicine, Philosophy and Religion in the Works of Ibn al-Nafīs (died 1288)", pp. 224-229, Electronic Theses and Dissertations, University of Notre Dame.[1]
6. ^ Paul Ghalioungui, Ibn an-Nafis, Cairo, 1966, pp. 109-129, and "The West denies Ibn Al Nafis's contribution to the discovery of the circulation" for the Symposium on Ibn al-Nafis, Second International Conference on Islamic Medicine: Islamic Medical Organization, Kuwait, 1982.
7. ^ Page through a virtual copy of Vesalius's De Humanis Corporis Fabrica
8. ^ Andreas Vesalius (1514-1567)
9. ^ Zimmer, Carl. 2004. Soul Made Flesh: The Discovery of the Brain - and How It Changed the World. New York: Free Press.
10. ^ Feder, M. E., A. F. Bennett, W. W. Burggren, and R. B. Huey, eds. 1987. New directions in ecological physiology. Cambridge Univ. Press, New York.
11. ^ http://www.biology.ucr.edu/people/faculty/Garland/GarlCa94.pdf Garland, T., Jr., and P. A. Carter. 1994. Evolutionary physiology. Annual Review of Physiology 56:579-621.

External links

Look up physiology in Wiktionary, the free dictionary.

• The Physiological Society
• Molecular & Integrative Physiology
• Developmental physiology
• The American Physiological Society
• physiologyINFO.org, a public information website sponsored by The American Physiological Society
• The Biophysical Society
• Physiwiki

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Dansk (Danish)
n. - fysiologi

Nederlands (Dutch)
fysiologie

Français (French)
n. - physiologie

Deutsch (German)
n. - Physiologie

Ελληνική (Greek)
n. - (βιολ.) φυσιολογία

Italiano (Italian)
fisiologia

Português (Portuguese)
n. - fisiologia (f)

Русский (Russian)
физиология

Español (Spanish)
n. - fisiología

Svenska (Swedish)
n. - fysiologi

中文（简体）(Chinese (Simplified))
生理学

中文（繁體）(Chinese (Traditional))
n. - 生理學

한국어 (Korean)
n. - 생리학, 생리, 생리 기능

日本語 (Japanese)
n. - 生理学, 生理

العربيه (Arabic)
‏(الاسم) فيسيولوجيا : علم وظائف الأعضاء‏

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n. - ‮חקר פעולות הגוף, פיסיולוגיה‬

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