Physiology

Physiology (/?f?zi??l?d?i/; from Ancient Greek φ?σι? (phúsis)?'nature, origin', and -λογ?α (-logía)?'study of')[1] is the scientific study of functions and mechanisms in a living system.[2][3] As a subdiscipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out 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. In contrast, 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.

Foundations[edit]

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.

Subdisciplines[edit]

There are many ways to categorize the subdisciplines of physiology:[6]

• 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)

Subdisciplines by level of organisation[edit]

Cell physiology[edit]

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.[citation needed]

Subdisciplines by taxa[edit]

Plant physiology[edit]

Main article: Plant physiology

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.[7]

Animal physiology[edit]

Main article: Biology §?Animal form and function

Human physiology[edit]

Main article: Human body §?Physiology

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 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.[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 in behavior 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 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.[12]

Subdisciplines by research objective[edit]

Comparative physiology[edit]

Main article: Comparative physiology

Involving evolutionary physiology and environmental physiology, comparative physiology considers the diversity of functional characteristics across organisms.[13]

History[edit]

The classical era[edit]

The study of human physiology as a medical field originates in classical Greece, at the time of Hippocrates (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 in China,[15] India[16] and elsewhere. Hippocrates incorporated the theory of humorism, 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 which Galen would later expand. 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.[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 in medicine.[18]