Human physiology

Academic and non-academic biologists study human physiology to understand the workings of the human body and its component parts, at many levels and modes of scientific investigation and at many levels in the heirarchy of the human body’s complex and changing organization.

By workings, physiologists refer to the underlying mechanisms that operate to manifest themselves in observable properties, functions and behaviors of the body and its components (e.g., sweating, digestion, muscle contraction, vision, cell division). They emphasize sequences of cause-effect interactions. By one or more levels of scientific investigation physiologists refer to such levels as the fundamental chemical level, intracellular molecular networks, cellular activity, organ activity, inter-organ interactions, and whole-body behavior — always in relation to a level's environment. Instrumental modes of observation and analysis abound. At any level of the body's organization — molecular interactions and network functioning, cellular behavior, organ physiology, for example — elucidating the operative underlying mechanisms require, integrating principles and information from other disciplines, including chemistry, physics, mathematics, computer modeling, cybernetics, anatomy, nutritional science, systems biology, evolutionary biology, and many others.

A human physiologist might ask, for example:

• How does the body respond to large or small decreases or increases in ambient temperature;
  • which of its component parts participate in the response;
  • in what way do they participate;
  • what accounts for the mechanisms that operate in each individual component response;
  • how does the overall response become integrated;
  • How important is the response to the person's health;
  • how efficient and how effective is the response.

The description of the human body’s complicated coordinated response to an unusually hot or cold day, and many other perturbations from outside or inside the body, do not admit of simplistic accounts — i.e., accounts sufficient to fully explain the response, predict its properties, or control it.

Whereas physiologists aim to learn the workings of the body in its state of health — i.e., to learn normal physiological function — they often gain insights into normal physiological function by studying the physiological effects of disease states, i.e., by studying pathophysiology. Injury to known segments of the brain, for example, might reveal its normal physiological function, or normal neurophysiological function, more specifically.

Because physiological functions emerge through interactions of structures, submicroscopic to macroscopic, human structure and anatomy integrate as an essential part of human physiology. In physiology, function links inseparably to structure, and in human physiology, unique human functionality links inesparably to unique human structure. For example, speech, the parent of language, requires uniquely human aspects of vocal and auditory anatomy, and uniquely human aspects of brain structure.

This article will describe the major subsystems that comprise the components of the living human system and attempt to show how those subsystems interact in a coordinated way that contributes to the emergence, development, and maintenance of the self-organizing, automous human living system.