Physiology ( /ˌfɪziˈɒlədʒi/; from Ancient Greek φύσις (physis) 'nature, origin', and -λογία (-logia) 'study of' ^[1]) is the scientific study of functions and mechanisms in a living system. ^{[2] [3]} As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical and physical functions in a living system. ^[4] According to the classes of organisms, the field can be divided into medical physiology, animal physiology, plant physiology, cell physiology, and comparative physiology. ^[4]

Central to physiological functioning are biophysical and biochemical processes, homeostatic control mechanisms, and communication between cells. ^[5] Physiological state is the condition of normal function, while pathological state refers to abnormal conditions, including human diseases.

The Nobel Prize in Physiology or Medicine is awarded by the Royal Swedish Academy of Sciences for exceptional scientific achievements in physiology related to the field of medicine.

History

Ancient Egypt

The use of practical medicine traces its roots back to archaic times where papyri about injuries started to be written. One of them was the Edwin Smith Papyrus, which may be dated as early as c 3000 BCE to c 2500 BCE. Attributed to Imhotep, a physician and an administrator in the construction of pyramids who tended the workers’ injuries and wrote his knowledge on human physiology on the papyrus. ^[6] Is a 15 feet long paper with writing on both sides consisting of 22 columns or nearly 500 lines of text. The text contains 48 illustrative cases dealing with various traumatic and accidental injuries to the head, face, neck, arms, chest, shoulder, and spinal column, in that order. Each case is arranged in a logical, quite modern fashion including a descriptive heading, results of examination, diagnosis, and treatment. ^{[7] [6]}

Classical Era

Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time in China, ^[8] India ^[9]and elsewhere. Hippocrates incorporated his belief system called the theory of humours, which consisted of four basic substance: earth, water, air and fire. Each substance is known for having a corresponding humour: black bile, phlegm, blood and yellow bile, respectively. Hippocrates also noted some emotional connections to the four humours, which Claudius Galenus would later expand on. The critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece.Like Hippocrates, Aristotle took to the humoral theory of disease, which also consisted of four primary qualities in life: hot, cold, wet and dry. ^[10] Claudius Galenus (c. 130–200 AD), known as Galen of Pergamum, 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. ^[11] 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 humours, 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. ^[11] Galen was also the founder of experimental physiology. ^[12] And for the next 1,400 years, Galenic physiology was a powerful and influential tool in medicine. ^[11]

Early modern era

Jean Fernel (1497–1558), a French physician, introduced the term "physiology". ^[13] Galen, Ibn al-Nafis, Michael Servetus, Realdo Colombo, Amato Lusitano and William Harvey, are credited as making important discoveries in the circulation of the blood. ^[14]

In 1610 Santorio Santorio was the first to use a device to measure the pulse rate (the pulsilogium), and a thermoscope to measure temperature. ^[15]

In 1628 William Harvey discovered blood constantly being pumped through a single system of arteries and veins around the body.

The discovery of the function of the heart and the circulation of blood was a huge discovery that opened many doors. Not only did it initiate the field of physiology, but it also introduced the principle of experimentation in medicine. Its discovery was attributed to various physicians, such as Galen, Michael Servetus, Realdo Columbo, and William Harvey ^[16]

Late moderrn era

In the 19th century, physiological knowledge began to accumulate at a rapid rate, in particular with the 1838 appearance of the Cell theory of Matthias Schleiden and Theodor Schwann. ^[17] It 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), ^{[18] [19]} which would later be taken up and championed as " homeostasis" by American physiologist Walter 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." ^[20]

In the 1820s, the French physiologist Henri 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 of Adam 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 or systems (called by him as appareils). ^[21]

1847,  Carl Ludwig(1816 – 1895) invented the kymograph, which could record simultaneously variables such as blood pressure, pulse rate and respiratory rate. ^[22]

In 1851, Claude Bernard (1813-1878)." The father of modern physiology" described the role of the pancreas in digestion, the glycogenic function of the liver, and the regulation of the blood supply by the vasomotor nerves. Also introduced the concept of the milieu intérieur ( homeostasis) to describe the principle of dynamic internal physiological equilibrium to sustain the organism in an external environment typified by variability. ^[23]

In 1852- Carl Ludwig published the first volume of his book of physiology where he challenged traditional scientific theories, suggested new concepts, and proposed what he believed were the best experimental approaches for expanding man's knowledge of living organisms. Also described his formulation of physiology as a science-based on the principles of physics and chemistry. ^[22]

In 1858, Joseph Lister studied the cause of blood coagulation and inflammation that resulted after previous injuries and surgical wounds. He later discovered and implemented antiseptics in the operating room, and as a result, decreased the death rate from surgery by a substantial amount. ^[24]

In 1865 Ernst Heinrich Weber alongside his brother Wilhelm Weber demonstrated the importance of capillary resistance and blood volume on circulatory dynamics and the distribution of the blood in the vascular system. ^[22]

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. ^[27]

With the beginning of the twentieth century physiology became a mature science where it began to divade in diifferent related disciplines like: comparative physiology and ecophysiology, biochemistry, biophysics, and molecular biology ^[28]

In 1910 August Krogh, – won the Nobel Prize for discovering how blood flow is regulated in capillaries. ^[29]

Andrew Huxley and Alan Hodgkin – discovered the ionic mechanism by which nerve impulses are transmitted.They made advances in the study of muscles with the discovery of sliding filaments in skeletal muscles. Their work won them a share of the 1963 Nobel Prize in Physiology or Medicine ^[30]

Foundations of Physiology

Anatomy

Anatomy is the field in the biological sciences concerned with the identification and description of the body structures of living things. Gross anatomy involves the study of major body structures by dissection and observation and in its narrowest sense is concerned only with the human body.   ^[31]

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Human physiology

Human physiology is the science of the mechanical, physical, and biochemical function of humans, and serves as the foundation of modern medicine. As a discipline, it connects science, medicine, and health, and creates a framework for understanding how the human body adapts to stresses, physical activity, and disease. ^[32]Human physiology seeks to understand the mechanisms that work to keep the human body alive and functioning,through scientific enquiry into the nature of mechanical, physical, and biochemical functions of humans, their organs, and the cells of which they are composed. ^[33] 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. ^[34]

Much of the foundation of knowledge in human physiology was provided by animal experimentation. Due to the frequent connection between form and function, physiology and anatomy are intrinsically linked and are studied in tandem as part of a medical curriculum. ^[35]

Animals

Plants

Plant physiology is a subdiscipline of botany concerned with the functioning of plants. Closely related fields include plant morphology, plant ecology, phytochemistry, cell biology, genetics, biophysics, and molecular biology. Fundamental processes of plant physiology include photosynthesis, respiration, plant nutrition, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, seed germination, dormancy, and stomata function and transpiration. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology. ^[36]

Cells

Comparative physiology

Involving evolutionary physiology and environmental physiology, comparative physiology considers the diversity of functional characteristics across organisms. ^[37]

Women in Physiology

Initially, women were largely excluded from official involvement in any physiological society. The American Physiological Society, for example, was founded in 1887 and included only men in its ranks. In 1902, the American Physiological Society elected Ida Hyde as the first female member of the society. Hyde, a representative of the American Association of University Women and a global advocate for gender equality in education, attempted to promote gender equality in every aspect of science and medicine.

Soon thereafter, in 1913, J.S. Haldane proposed that women be allowed to formally join The Physiological Society, which had been founded in 1876.

Prominent women physiologists include:

• Bodil Schmidt-Nielsen, the first woman president of the American Physiological Society in 1975. ^[38]
• Gertrude B. Elion- Alongside Sir James W. Black and George H. Hitchings won the Nobel Prize in Physiology or Medicine in 1988 for developing a systematic method for producing drugs based on knowledge of biochemistry and diseases. One of the first drugs produced by the pair was for leukemia and other drugs they created have been used to fight malaria , infections, and gout, as well as help with organ transplantations. ^[39]
• Gerty Theresa Cori,- Won the Nobel Prize in Physiology or Medicine alongside Carl Cori, they described what is known as the Cori cycle; an important part of metabolism. Lactic acid forms when we use our muscles , which are then converted into glycogen in the liver. ^[40]
• Linda B. Buck, ^[41] along with Richard Axel, received the Nobel Prize in Physiology or Medicine in 2004 for their discovery of odorant receptors and the complex organization of the olfactory system.
• Françoise Barré-Sinoussi, ^[42] along with Luc Montagnier, received the Nobel Prize in Physiology or Medicine in 2008 for their work on the identification of the Human Immunodeficiency Virus (HIV), the cause of Acquired Immunodeficiency Syndrome (AIDS).
• Elizabeth Blackburn, ^[43] along with Carol W. Greider ^[44] and Jack W. Szostak, was awarded the 2009 Nobel Prize for Physiology or Medicine for the discovery of the genetic composition and function of telomeres and the enzyme called telomerase.
• Patricia S. Cowings- psychophysiologist, and was the first African American woman scientist to be trained as an astronaut by NASA. Well known for her studies in the physiology of astronauts in outer space, as well as helping find cures for astronaut's motion sickness ^[45]
• Barbara McClintock - was rewarded the 1983 Nobel Prize in Physiology or Medicine for the discovery of genetic transposition. McClintock is the only female recipient who has won an unshared Nobel Prize. ^[46]

Subdisciplines

There are many ways to categorize the subdisciplines of physiology: ^[47]

• based on the taxa studied: human physiology, animal physiology, plant physiology, microbial physiology, viral physiology
• based on the level of organization: cell physiology, molecular physiology, systems physiology, organismal physiology, ecological physiology, integrative physiology
• based on the process that causes physiological variation: developmental physiology, environmental physiology, evolutionary physiology
• based on the ultimate goals of the research: applied physiology (e.g., medical physiology), non-applied (e.g., comparative physiology)

Physiological societies

Transnational physiological societies include:

• American Physiological Society
• International Union of Physiological Sciences
• The Physiological Society

National physiological societies include:

• Brazilian Society of Physiology

See also

References