Physiology

Study of the functions and mechanisms of living systems

Physiology is a fundamental scientific discipline that explores the functional mechanisms of living organisms, focusing on how organisms, organ systems, organs, cells, and biomolecules perform chemical and physical processes essential for life. The term originates from the Ancient Greek words:

• φύσις (physis) – meaning "nature" or "origin"
• -λογία (-logia) – meaning "study of"

Physiology is a multidisciplinary field, encompassing human physiology, plant physiology, cellular physiology, bacterial physiology, and viral physiology. It serves as the foundation for understanding biological processes and their interactions with the environment.

Human physiology research at the National Health and Environmental Effects Research Laboratory (NHEERL)

Historical Development

Physiology has a rich history that dates back to Ancient Greece and has evolved significantly over time.

Ancient Foundations

• Hippocrates (c. 420 BC) – Often regarded as the "father of medicine," he emphasized the role of natural causes in disease rather than supernatural forces.
• Aristotle (384–322 BC) – Proposed that the function of biological structures is linked to their form and purpose, laying the groundwork for physiology.
• Claudius Galenus (Galen) (c. 126–199 AD) – Conducted some of the first experimental physiological studies, focusing on the circulatory system, nervous system, and muscles.

Renaissance and Early Modern Physiology

• Jean Fernel (1497–1558) – Introduced the term "physiology" in 1525.
• William Harvey (1578–1657) – Discovered the circulatory system and the role of the heart as a pump.

19th Century: The Rise of Modern Physiology

• Matthias Schleiden & Theodor Schwann (1838) – Developed the Cell Theory, proposing that all organisms are composed of cells.
• Claude Bernard (1813–1878) – Introduced the concept of "milieu intérieur", the idea that living organisms maintain a stable internal environment.

20th Century and Beyond

• Walter Cannon (1871–1945) – Coined the term "homeostasis", describing how organisms regulate internal stability.
• Knut Schmidt-Nielsen & George Bartholomew – Pioneered research in comparative physiology and ecophysiology.
• Modern physiology – Expands into systems biology, integrative medicine, and molecular physiology, improving our understanding of health and disease.

Branches of Physiology

Physiology is categorized into several specialized fields, each focusing on different aspects of biological function.

1. Human Physiology

Human physiology studies the functions of the human body, emphasizing:

• Homeostasis – The regulation of internal conditions (e.g., body temperature, pH balance).
• Organ system functions – Including the cardiovascular, nervous, endocrine, digestive, and respiratory systems.
• Neurophysiology – How the brain and nervous system control bodily functions.
• Endocrinology – The role of hormones in regulating metabolism and growth.

2. Animal Physiology

Studies physiological processes in different animal species, including:

• Comparative physiology – Examining similarities and differences across species.
• Evolutionary physiology – Understanding how physiological traits evolve.

3. Plant Physiology

Examines how plants function, including:

• Photosynthesis – Conversion of light energy into chemical energy.
• Water and nutrient transport – Through xylem and phloem.
• Growth regulation – By plant hormones such as auxins and gibberellins.

4. Cellular and Molecular Physiology

Focuses on:

• Cell signaling and communication.
• Membrane transport mechanisms.
• Gene regulation in cellular functions.

5. Microbial and Viral Physiology

• Studies the metabolic processes and survival mechanisms of bacteria and viruses.
• Essential for understanding infectious diseases and developing antibiotics and vaccines.

Human Body Systems and Their Physiological Functions

The human body is composed of multiple interdependent organ systems, each responsible for vital functions.

Organ System	Primary Function
Nervous System	Controls bodily functions via electrical and chemical signals.
Cardiovascular System	Circulates blood, oxygen, and nutrients throughout the body.
Respiratory System	Facilitates oxygen intake and carbon dioxide removal.
Digestive System	Breaks down food and absorbs nutrients.
Endocrine System	Produces hormones to regulate metabolism, growth, and homeostasis.
Skeletal System	Provides structure, support, and protection for internal organs.
Muscular System	Enables movement and heat production.
Renal System (Urinary System)	Filters waste and maintains fluid balance.
Immune System	Defends against infections and foreign invaders.

Homeostasis and Regulation

Homeostasis is the self-regulating process by which organisms maintain a stable internal environment, despite external fluctuations.

Homeostatic Mechanisms

• Negative Feedback Loops – The most common homeostatic control mechanism (e.g., body temperature regulation).
• Positive Feedback Loops – Reinforce a physiological response (e.g., blood clotting, childbirth contractions).

Physiological Research and Applications

Physiological research is crucial for medical, environmental, and technological advancements. Areas of application include:

• Medicine – Understanding diseases and developing treatments.
• Sports Science – Studying muscle function, endurance, and recovery.
• Space Physiology – Investigating how the human body adapts to space environments.
• Artificial Organs & Biotechnology – Creating bioengineered tissues and prosthetics.

Nobel Prize in Physiology or Medicine

Since 1901, the Nobel Prize in Physiology or Medicine has recognized groundbreaking discoveries in physiology and medicine. It is awarded annually by the Royal Swedish Academy of Sciences for achievements in:

• Medical discoveries – e.g., antibiotics, vaccines, and gene-editing technologies.
• Breakthroughs in human physiology – e.g., understanding the nervous system, immune system, and molecular biology.

See Also

• Glossary of Anatomy and Physiology
• Human Physiology
• Homeostasis
• Neurophysiology
• Comparative Physiology
• Plant Physiology