Physiology (from the Greek φύσις, physis, “nature,” and λόγος, logos, “discourse,” hence “study of natural phenomena”) is the branch of biology that studies the functioning of living organisms by analyzing the chemical and physical principles of living things, whether single-celled or multi-celled, animal or plant.

A “physiological state” is the state in which the normal functions of an organism or system occur, while a pathological state is characterized by abnormalities that result in disease. Because of the breadth of the field, physiology is divided into animal physiology, plant physiology, cellular physiology, and microbial, bacterial, and viral physiology, among others. The Nobel Prize in Physiology or Medicine is awarded by the Royal Swedish Academy of Sciences to those who achieve significant results in this discipline.

Physiology is based strictly on the experimental method: only by removing, altering and otherwise manipulating a particular organ is it usually possible to understand its function. Since many basic processes (respiration, cell division, heredity, reproduction) are common to all or nearly all organisms, the results of the experiments can be extended to a wide range of living things. To explain many of the behaviors of organisms, physiology uses physical, chemical, and even mechanical models that are compatible with the anatomical structures of the organs in question, since the same laws that apply to these models can be applied to biological processes.

Given the articulation of studies, specializations have emerged within physiology, each dealing with a single organ or apparatus. Thus, neurophysiology studies the central and peripheral nervous system, cardiovascular physiology studies blood circulation and hemodynamics, nutritional physiology studies the mechanisms of digestion, work physiology studies the energy consumption of a working organism, and so on.

In sociology, that part of the discipline which, by analogy with human physiology, studies the functioning of and relations between the various “organs” of society. The term was codified by the Frenchman Ph. Buchez, who, while affirming the usefulness of the analogy between human and social physiology, pointed out their differences: while the human being does not change physically except over very long periods of time, society is subject to constant change. Despite this caution, much of nineteenth-century sociology, especially positivist sociology, made fruitful use of this analogy, embracing the distinction between “anatomical” (conditions of social existence) and “physiological” (social movements and processes) perspectives. In this sense, for example, A. Comte divided sociology into static and dynamic.


Physiology operates on several levels, dealing with both basic mechanisms at the molecular level and functions of cells and organs, as well as the integration of organ functions in complex organisms.

Depending on the specialized field, physiology draws on knowledge from numerous disciplines, in addition to the aforementioned chemistry and physics, some branches of biology such as: biochemistry, molecular biology, anatomy, cytology, and histology, and also forms the fundamental basis for numerous medical disciplines such as pathology, pharmacology, and toxicology.

There are several methods for classifying physiology:

  • By taxon:
    • Animal physiology: studies the phenomena and mechanisms associated with animal functions.
    • Plant physiology: studies the phenomena and mechanisms associated with plant functions.
    • Human physiology: studies the phenomena and mechanisms associated with the functions of humans
    • Microbial and viral physiology.
  • Based on the level of organization:
    • Cell physiology: studies the mechanisms associated with the functioning of cells and their interactions with the environment.
    • Molecular physiology: studies the phenomena and mechanisms associated with the functions of molecules
    • Neurophysiology: studies the functioning of the nervous system at both the cellular and systemic levels
    • Systemic physiology
    • Ecological physiology
    • Integrative physiology
    • Muscle physiology
  • Based on the processes that cause physiological changes:
    • Environmental physiology: studies the reactions and adaptation of the organism subjected to different environments (temperature, altitude, pollution, etc.).
    • Pathological physiology: studies changes in function following pathology.
    • Developmental physiology: studies the mechanisms and stages that lead an organism to reproductive maturity.
  • Depending on the ultimate goals of the research:
    • Applied physiology: studies the human ability to interact with the external environment.
    • Comparative physiology: studies the similarities and differences of different animal species.
    • Exercise physiology: studies the mechanisms involved in motor and sports activity and how to improve performance with training.
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