GLOSSARY

Physiology explains how living systems work and how they adjust to changing demands. During running, the working muscles, heart, lungs and blood vessels must operate together to support oxygen delivery and carbon dioxide removal.

• Cell: Ion movement across a membrane changes the excitability of nerves and muscles.
• Organ: Cardiac output is heart rate multiplied by stroke volume.
• Whole body: Ventilation and blood-flow distribution adjust together during exercise.

An acute rise in heart rate differs from an adaptation that develops over repeated training sessions. At 120 beats per minute and 100 mL per beat, output is 12 L/min; at 150 and 80 mL, it is also 12 L/min. A faster pulse does not by itself establish a greater output.

Further reading: OpenStax — Overview of Anatomy and Physiology · OpenStax — Cardiac Physiology

Human physiology examines how the human body functions from the level of cells to the coordination of organs. Anatomy identifies the location of heart valves; physiology explains how pressure differences open and close them and direct blood flow.

Standing shifts blood distribution under gravity. Pressure sensors and autonomic responses help maintain perfusion, and contracting leg muscles can assist venous return. The time since standing and the measurement position therefore matter when comparing pulse or blood pressure between people.

Further reading: OpenStax — Overview of Anatomy and Physiology · OpenStax — Homeostatic Regulation of the Vascular System

Exercise physiology studies responses during activity, recovery afterward and adaptations to repeated training. The choice of measurement depends on exercise mode, intensity, duration and environmental conditions.

Comparing responses at a matched workload and in similar conditions helps distinguish training effects from differences in heat, pacing or equipment.

Further reading: OpenStax — Exercise and Muscle Performance · OpenStax — Cardiac Physiology

Applied physiology uses a physiological mechanism to answer a practical question. A cyclist may fatigue sooner at the usual power in a warm room. Heat dissipation, changes in circulation and fluid loss are possible contributors, so record the environment and the response together.

At a constant power, track heart rate and perceived exertion over time. Repeat under comparable starting conditions before attributing the difference to fitness.

Decision example: If both markers rise faster in heat, account for the environment when setting effort or comparing sessions.

Further reading: OpenStax — Exercise and Muscle Performance · OpenStax — Homeostatic Regulation of the Vascular System

Integrative physiology examines how mechanisms at several levels combine to produce a whole-body response. Oxygen use during uphill running depends on a connected pathway.

1. Ventilation renews alveolar gas, permitting oxygen and carbon dioxide exchange.
2. Cardiac pumping supplies blood flow, and vessels distribute that flow among tissues.
3. Active muscle extracts oxygen while neural and chemical signals help regulate the cardiorespiratory response.

Whole-body oxygen uptake measures the outcome of the pathway. Additional measurements are needed to separate the contributions of blood flow and tissue oxygen extraction.

Further reading: OpenStax — Cardiac Physiology · OpenStax — The Process of Breathing

Systems physiology studies a body system through the organization and regulation of its components. The circulatory system includes a pump, conducting vessels, exchange surfaces and a path for venous return.

Further reading: OpenStax — Overview of Anatomy and Physiology · OpenStax — Body Fluids and Fluid Compartments

A physiological function is the contribution of a cell, tissue, organ or system to what the body does. The diaphragm contributes to ventilation: its contraction increases thoracic volume and helps produce inward airflow.

A function should be interpreted in context. Quiet breathing and strenuous exercise make different demands on the respiratory muscles. Describing the diaphragm’s contribution to ventilation states its function; tracing the volume and pressure changes explains its mechanism.

Further reading: OpenStax — Overview of Anatomy and Physiology · OpenStax — The Process of Breathing

A physiological mechanism connects the events that produce a response. Quiet inspiration illustrates how a muscle action leads to airflow.

1. Diaphragm contraction expands the thorax.
2. Lung expansion briefly lowers alveolar pressure below atmospheric pressure.
3. Air flows inward along the pressure gradient and stops when the pressures equalize at the end of inspiration.

A temporal association alone is weaker evidence than a prediction tested by controlling or measuring an intermediate step.

Further reading: OpenStax — The Process of Breathing

Physiological regulation changes system activity to control a process or variable as conditions shift. Feedback responds to a detected change; feedforward control can begin before the full disturbance develops.

As muscular work increases heat production, sweating and changes in skin blood flow can increase heat loss. Humidity limits evaporative cooling even when sweating is substantial.

To identify the loop, ask what is sensed, which effector responds and which variable its response changes.

Further reading: OpenStax — Homeostasis · Modell et al. — A physiologist’s view of homeostasis

A structure–function relationship links physical organization to a biological capability. Thin barriers can support exchange, whereas a force-transmitting tissue needs a different architecture.

A structure provides a capability. The actual rate of exchange also depends on operating conditions such as blood flow.

Further reading: OpenStax — Overview of Anatomy and Physiology · OpenStax — Body Fluids and Fluid Compartments