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Physiology

Oil painting depicting Claude Bernard, the father of modern physiology, with his pupils

Physiology (/ˌfɪziˈɒlədʒi/; from Ancient Greekφύσις (physis), meaning 'nature, origin', and -λογία (-logia), meaning 'study of'^[1]) is the scientific study of the functions and mechanisms which work within a living system.^[2][3]

As a sub-discipline of biology, the focus of physiology is in how organisms, organ systems, organs, cells, and biomoleculescarry out the chemical and physical functions that exist in a living system.^[4]

Central to an understanding of physiological functioning is the investigation of the fundamental biophysical and biochemical phenomena, the coordinated homeostaticcontrol mechanisms, and the continuous communication between cells.^[5]

The physiologic state is the condition occurring from normal body function, while the pathological state is centered on the abnormalities that occur in animal diseases, including humans.^[6]

According to the type of investigated organisms, the field can be divided into, animal physiology (including that of humans), plant physiology, cellular physiology and microbial physiology.^[4]

The Nobel Prize in Physiology or Medicine is awarded to those who make significant achievements in this discipline by the Royal Swedish Academy of Sciences.

Foundations of physiologyEdit

This section does not cite any sources. Learn more

AnimalsEdit

Main article: Zoology § Physiology

HumansEdit

Main article: Human body § Physiology

Human physiology seeks to understand the mechanisms that work to keep the human 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.^{[citation needed]}

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.^[7] Change in behavior as a result of these substances is often used to assess the health of individuals.^[8][9]

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.^[10]

PlantsEdit

Main article: Plant physiology

Plant physiology is a subdiscipline of botanyconcerned 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.

CellsEdit

Main article: Cell physiology

Although there are differences between animal, plant, and microbial cells, the basic physiological functions of cells can be divided into the processes of cell division, cell signaling, cell growth, and cell metabolism.

MicroorganismsEdit

Main article: Microorganism

Microorganisms can be found almost everywhere on Earth. Types of microorganisms include archaea, bacteria, eukaryotes, protists, fungi, and micro-plants. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel, enzymesand other bioactive compounds. They are essential tools in biology as model organismsand have been put to use in biological warfareand bioterrorism. They are a vital component of fertile soils. In the human bodymicroorganisms make up the human microbiota including the essential gut flora. They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation, transformation and transduction, even between widely divergent species.

VirusesEdit

Main article: Virus

HistoryEdit

The classical eraEdit

The study of human physiology as a medical field originates in classical Greece, at the time of Hippocrates (late 5th century BC).^[11]Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time in China,^[12] India^[13] 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.^[14] 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.^[15] 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.^[15] Galen was also the founder of experimental physiology.^[16] And for the next 1,400 years, Galenic physiology was a powerful and influential tool in medicine.^[15]

Early modern periodEdit

Jean Fernel (1497–1558), a French physician, introduced the term "physiology".^[17] 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.^[18] Santorio Santorio in 1610s was the first to use a device to measure the pulse rate (the pulsilogium), and a thermoscope to measure temperature.^[19]

In 1791 Luigi Galvani described the role of electricity in nerves of dissected frogs. In 1811, Julien Jean César Legallois studied respiration in animal dissection and lesions and found the center of respiration in the medulla oblongata. In the same year, Charles Bell finished work on what would later become known as the Bell-Magendie law, which compared functional differences between dorsal and ventral roots of the spinal cord. In 1824, François Magendie described the sensory roots and produced the first evidence of the cerebellum’s role in equilibration to complete the Bell-Magendie law.

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).^[20]

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 death rate from surgery by a substantial amount.^[6][21]

The Physiological Society was founded in London in 1876 as a dining club.^[22] 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."^[23]

In 1891, Ivan Pavlov performed research on "conditional responses" that involved dogs' saliva production in response to a bell and visual stimuli.^[21]

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. 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),^[24][25]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."^[26] 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 as Michael Foster, Max Verworn, and Alfred Binet, based on Haeckel's ideas, elaborated what came to be called "general physiology", a unified science of life based on the cell actions,^[20] later renamed in the 20th century as cell biology.^[27]

Late modern periodEdit

In the 20th century, biologists became interested in how organisms other than human beings function, eventually spawning the fields of comparative physiology and ecophysiology.^[28] Major figures in these fields include Knut Schmidt-Nielsen and George Bartholomew. Most recently, evolutionary physiology has become a distinct subdiscipline.^[29]

In 1920, August Krogh won the Nobel Prize for discovering how, in capillaries, blood flow is regulated.^[21]

In 1954, Andrew Huxley and Hugh Huxley, alongside their research team, discovered the sliding filaments in skeletal muscle, known today as the sliding filament theory.^[21]

Recently, there have been intense debates about the vitality of physiology as a discipline (Is it dead or alive?).^[30][31] If physiology is perhaps less visible nowadays than during the golden age of the 19th century,^[32] it is in large part because the field has given birth to some of the most active domains of today's biological sciences, such as neuroscience, endocrinology, and immunology.^[33]Furthermore, physiology is still often seen as an integrative discipline, which can put together into a coherent framework data coming from various different domains.^[34][35][31]

Notable physiologistsEdit

Main article: List of physiologists

Women in physiologyEdit

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.^[36] In 1902, the American Physiological Society elected Ida Hyde as the first female member of the society.^[37] Hyde, a representative of the American Association of University Womenand a global advocate for gender equality in education,^[38] attempted to promote gender equality in every aspect of science and medicine.

Soon thereafter, in 1913, J.S. Haldaneproposed that women be allowed to formally join The Physiological Society, which had been founded in 1876.^[39] On 3 July 1915, six women were officially admitted: Florence Buchanan, Winifred Cullis, Ruth C. Skelton, Sarah C. M. Sowton, Constance Leetham Terry, and Enid M. Tribe.^[40] The centenary of the election of women was celebrated in 2015 with the publication of the book "Women Physiologists: Centenary Celebrations And Beyond For The Physiological Society." (ISBN 978-0-9933410-0-7)

Prominent women physiologists include:

• Gerty Cori,^[41] along with husband Carl Cori, received the Nobel Prize in Physiology or Medicine in 1947 for their discovery of the phosphate-containing form of glucoseknown as glycogen, as well as its function within eukaryotic metabolic mechanisms for energy production. Moreover, they discovered the Cori cycle, also known as the Lactic acid cycle,^[42] which describes how muscle tissue converts glycogen into lactic acid via lactic acid fermentation.
• Barbara McClintock was rewarded the 1983 Nobel Prize in Physiology or Medicine for the discovery of genetic transpositionMcClintock is the only female recipient who has won an unshared Nobel Prize.^[43]
• Gertrude Elion,^[44] along with George Hitchings and Sir James Black, received the Nobel Prize for Physiology or Medicine in 1988 for their development of drugs employed in the treatment of several major diseases, such as leukemia, some autoimmune disorders, gout, malaria, and viral herpes.
• Linda B. Buck,^[45] 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,^[46] 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,^[47] along with Carol W. Greider^[48] 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.

SubdisciplinesEdit

There are many ways to categorize the subdiscplines of physiology:^[49]

• 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, systemsphysiology, organismal physiology, ecological physiology, integrative physiology
• based on the process that causes physiological variation: developmentalphysiology, 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 societiesEdit

Main article: International Union of Physiological Sciences

See alsoEdit

• Outline of physiology
• Biochemistry
• Biophysics
• Cytoarchitecture
• Defense physiology
• Ecophysiology
• Exercise physiology
• Fish physiology
• Insect physiology
• Human body
• Molecular biology
• Metabolome
• Neurophysiology
• Pharmacology
• Physiome
• Physiology is the study of normal function within living creatures. It is a sub-section of biology, covering a range of topics that include organs, anatomy, cells, biological compounds, and how they all interact to make life possible.

From ancient theories to molecular laboratory techniques, physiological research has shaped our understanding of the components of our body, how they communicate, and how they keep us alive.

Merrian-Webster defines physiology as:

"[A] branch of biology that deals with the functions and activities of life or of living matter (such as organs, tissues, or cells) and of the physical and chemical phenomena involved."

Fast facts on physiology

Here are some key points about physiology. More detail and supporting information is in the main article.

    Physiology can be considered a study of the functions and processes that create life.

    The study of physiology can be traced back to at least 420 BC.

    The study of physiology is split into many disciplines covering topics as different as exercise, evolution, and defense.

What is physiology?

[Musculature of the face]

Physiology covers a multitude of disciplines within human biology and beyond.

The study of physiology is, in a sense, the study of life. It asks questions about the internal workings of organisms and how they interact with the world around them.

Physiology tests how organs and systems within the body work, how they communicate, and how they combine their efforts to make conditions favorable for survival.

Human physiology, specifically, is often separated into subcategories; these topics cover a vast amount of information. 

 Researchers in the field can focus on anything from microscopic organelles in cell physiology up to more wide-ranging topics, such as ecophysiology, which looks at whole organisms and how they adapt to environments.

The most relevant arm of physiological research to Medical News Today is applied human physiology; this field investigates biological systems at the level of the cell, organ, system, anatomy, organism, and everywhere in between.

In this article, we will visit some of the subsections of physiology, developing a brief overview of this huge subject. Firstly, we will run through a short history of physiology.

History

[Bust of Hippocrates]

Hippocrates is considered by many to be the "father of medicine."

The study of physiology traces its roots back to ancient India and Egypt.

As a medical discipline, it goes back at least as far as the time of Hippocrates, the famous "father of medicine" - around 420 BC.

Hippocrates coined the theory of the four humors, stating that the body contains four distinct bodily fluids: black bile, phlegm, blood, and yellow bile. Any disturbance in their ratios, as the theory goes, causes ill health. 

laudius Galenus (c.130-200 AD), also known as Galen, modified Hippocrates' theory and was the first to use experimentation to derive information about the systems of the body. He is widely referred to as the founder of experimental physiology.

It was Jean Fernel (1497-1558), a French physician, who first introduced the term "physiology," from Ancient Greek, meaning "study of nature, origins."

Fernel was also the first to describe the spinal canal (the space in the spine where the spinal cord passes through). He has a crater on the moon named after him for his efforts - it is called Fernelius.

Another leap forward in physiological knowledge came with the publication of William Harvey's book titled An Anatomical Dissertation Upon the Movement of the Heart and Blood in Animals in 1628.

Harvey was the first to describe systemic circulation and blood's journey through the brain and body, propelled by the heart. 

 Perhaps surprisingly, much medical practice was based on the four humors until well into the 1800s (bloodletting, for instance). In 1838, a shift in thought occurred when the cell theory of Matthias Schleiden and Theodor Schwann arrived on the scene, theorizing that the body was made up of tiny individual cells.

From here on in, the field of physiology opened up, and progress was made quickly:

    Joseph Lister, 1858 - initially studied coagulation and inflammation following injury, he went on to discover and utilize lifesaving antiseptics.

    Ivan Pavlov, 1891 - conditioned physiological responses in dogs.

    August Krogh, 1910 - won the Nobel Prize for discovering how blood flow is regulated in capillaries.

    Andrew Huxley and Alan Hodgkin, 1952 - discovered the ionic mechanism by which nerve impulses are transmitted.

    Andrew Huxley and Hugh Huxley, 1954 - made advances in the study of muscles with the discovery of sliding filaments in skeletal muscle.

Biological systems

The major systems covered in the study of human physiology are as follows:

    Circulatory system - including the heart, the blood vessels, properties of the blood, and how circulation works in sickness and health.

    Digestive/excretory system - charting the movement of solids from the mouth to the anus; this includes study of the spleen, liver, and pancreas, the conversion of food into fuel and its final exit from the body.

    Endocrine system - the study of endocrine hormones that carry signals throughout the organism, helping it to respond in concert. The principal endocrine glands - the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads - are a major focus, but nearly all organs release endocrine hormones.

    Immune system - the body's natural defense system is comprised of white blood cells, the thymus, and lymph systems. A complex array of receptors and molecules combine to protect the host from attacks by pathogens. Molecules such as antibodies and cytokines feature heavily.

    Integumentary system - the skin, hair, nails, sweat glands, and sebaceous glands (secreting an oily or waxy substance).

    Musculoskeletal system - the skeleton and muscles, tendons, ligaments, and cartilage. Bone marrow - where red blood cells are made - and how bones store calcium and phosphate are included.

    Nervous system - the central nervous system (brain and spinal cord) and the peripheral nervous system. Study of the nervous system includes research into the senses, memory, emotion, movement, and thought.

    Renal/urinary system - including the kidneys, ureters, bladder, and urethra, this system removes water from the blood, produces urine, and carries away waste.

    Reproductive system - consisting of the gonads and the sex organs. Study of this system also includes investigating the way a fetus is created and nurtured for 9 months.

    Respiratory system - consisting of the nose, nasopharynx, trachea, and lungs. This system brings in oxygen and expels carbon dioxide and water.

Branches

[Musculature of man doing karate kick]

Defense physiology investigates nature's natural defensive reactions.

There are a great number of disciplines that use the word physiology in their title. Below are some examples:

    Cell physiology - studying the way cells work and interact; cell physiology mostly concentrates on membrane transport and neuron transmission.

    Systems physiology - this focuses on the computational and mathematical modeling of complex biological systems. It tries to describe the way individual cells or components of a system converge to respond as a whole. They often investigate metabolic networks and cell signaling.

    Evolutionary physiology - studying the way systems, or parts of systems, have adapted and changed over multiple generations. Research topics cover a lot of ground including the role of behavior in evolution, sexual selection, and physiological changes in relation to geographic variation.

    Defense physiology - changes that occur as a reaction to a potential threat, such as preparation for the fight-or-flight response.

    Exercise physiology - as the name suggests, this is the study of the physiology of physical exercise. This includes research into bioenergetics, biochemistry, cardiopulmonary function, biomechanics, hematology, skeletal muscle physiology, neuroendocrine function, and nervous system function.

The topics mentioned above are just a small selection of the available physiologies. The field of physiology is as essential as it is vast.

Physiology or anatomy?

Anatomy is closely related to physiology. Anatomy refers to the study of the structure of body parts, but physiology focuses on how these parts work and relate to each other. 

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