Basic Principles of Physiology and Body Temperature

Basic principles of physiology

Formal: the study of the functions of living organisms; Operational: how cells interact with their environment to obtain substances to sustain life.

Compartmentalization

Separation of substances into different compartments (intracellular fluid vs extracellular fluid), enabling regulated transport and homeostasis.

Intracellular fluid (ICF)

Fluid inside cells; a major component of body water.

Extracellular fluid (ECF)

Fluid outside cells, including plasma and interstitial fluid.

Interstitial fluid (ISF)

ECF that bathes cells and is not inside the circulatory system.

Plasma

The liquid portion of blood that carries cells, nutrients, and wastes.

Homeostasis

Maintenance of internal conditions within narrow limits despite external changes.

Negative feedback

Effector actions oppose the stimulus to restore a set point and maintain stability.

Sensor

Device that measures a physiological variable (e.g., temperature) in the internal environment.

Integrator

Component that compares sensor input to the set point and determines the response.

Effector

Output mechanism that changes the internal environment to move toward the set point.

Positive feedback

Feedback where the effector amplifies the initial stimulus, often driving processes away from homeostasis.

Asymmetry in ion distribution

Uneven distribution of ions across compartments due to the organism’s exchange systems.

Exchange system

Mechanisms by which organisms interact with the environment by exchanging substances (respiratory, digestive, urinary, circulatory).

Levels of biological organization

From cellular to system level: cellular, tissue, organ, system.

Cellular level

Includes epithelial, connective tissue, nerve, and muscle cells.

Tissue level

Tissues are groups of similar cells functioning together.

Organ level

Organs are organized groups of tissues performing specific functions (e.g., heart, brain, stomach).

System level

Multiple organs organized to carry out major physiological functions (e.g., cardiovascular system).

Size principle

Relationship of surface area to volume; larger bodies store more heat and have less surface-area-to-volume for heat exchange, aiding thermoregulation in cold environments.

Heat transfer transport equation (driving force vs ease of movement)

Driving force = temperature gradient; ease of movement = thermal conductivity; together govern heat transfer.

Conduction

Heat transfer through direct contact between substances.

Convection

Heat transfer via movement of a fluid (air or water) around a surface.

Evaporation

Heat loss through phase change of a liquid to vapor (e.g., sweating, evaporation).

Radiation

Heat transfer through electromagnetic waves from warmer to cooler bodies.

Aerobic metabolism

Metabolism that uses oxygen; more energy-efficient but requires oxygen delivery.

Anaerobic metabolism

Metabolism that does not require oxygen; faster but yields less energy and can produce lactate.

Cellular respiration

Process of producing ATP by degrading glucose in the presence of oxygen (glycolysis, Krebs cycle, electron transport chain).

ATP

Adenosine triphosphate; primary energy currency of the cell.

Metabolic rate

The rate at which energy is used by an organism per unit time, often assessed by oxygen consumption.

Basal metabolic rate (BMR)

Energy expenditure at rest for essential physiological processes.

Exchange systems

Physiological processes that exchange substances between external and internal environments (respiratory, digestive, urinary, circulatory).

Heat in/out and body temperature

Heat input from the environment and metabolism; heat loss to the environment; net balance determines body temperature.