Define acceptable operating conditions.
Many physiological variables are regulated within ranges rather than fixed values.
Side 139
Human Physiology
The human body as a coordinated control system: organs and tissues maintain viable internal conditions through transport, signaling, feedback and adaptation.
sensor→signal→organ response→feedback→homeostasis
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Regulation stabilizes key internal conditions despite changing demands.
Homeostasis is dynamic control, not constancy: regulated variables fluctuate around ranges through feedback.
Detect deviation or relevant change.
Receptors convert chemical, mechanical or thermal conditions into signals.
Integrate information and choose a response.
Neural and endocrine systems coordinate distributed control.
Change the regulated system.
Muscle, glands, vessels and organs alter function to close or reshape the feedback loop.
Cardiovascular and respiratory systems move gases, nutrients and heat.
Flow depends on pressure gradients, resistance, exchange surfaces and demand.
Move air between atmosphere and lungs.
Breathing changes gas availability at the exchange surface.
Exchange gases across thin membranes.
Partial-pressure gradients drive oxygen and carbon-dioxide movement.
Pump blood through systemic and pulmonary circuits.
Cardiac output and vascular resistance determine flow distribution.
Match oxygen transport to tissue demand.
Hemoglobin, perfusion and local metabolism jointly determine delivery.
Kidneys and endocrine systems regulate composition over longer timescales.
Water, electrolytes, glucose and acid-base balance depend on coordinated filtration, reabsorption and hormonal control.
Separate plasma components at the kidney.
Filtration rate responds to pressure and vascular regulation.
Recover water and useful solutes.
Segment-specific transport allows selective control of body composition.
Coordinate distant organs through circulating signals.
Hormonal systems trade speed for persistence and systemic reach.
Regulate hydrogen ion and bicarbonate.
Lungs and kidneys cooperate across different timescales to stabilize pH.
Physiological systems interact rather than operate in isolation.
Exercise, stress, temperature and illness reveal the coupling among control systems.
Coordinate increased metabolic demand.
Heart rate, ventilation, blood flow and fuel mobilization change together.
Balance heat production and loss.
Blood flow, sweating, behavior and metabolism jointly regulate temperature.
Mobilize resources under challenge.
Autonomic and endocrine pathways alter cardiovascular, metabolic and immune states.
Repeated demand changes system capacity.
Training, acclimatization and chronic exposure can shift structural and regulatory responses.
Physiology is organized around regulated variables. Understanding the body means tracing what is sensed, which controller responds, which organs change state and how feedback restores or shifts the operating range.