Homeostasis
Homeostasis is the tendency of biological systems to maintain relatively stable internal conditions despite changes in the external environment, achieved through a series of regulatory feedback mechanisms. It operates primarily through negative feedback loops in which deviations from a set point trigger corrective responses to restore equilibrium. Maintaining homeostasis is essential for survival, as critical variables such as body temperature (37°C in humans), blood glucose (70–100 mg/dL), and blood pH (7.35–7.45) must be kept within narrow physiological ranges.
Key Homeostatic Variables in the Human Body
| Variable | Normal Range | Regulatory Organ | Mechanism |
|---|---|---|---|
| Core body temperature | 36.5–37.5°C | Hypothalamus | Sweating, shivering, vasodilation |
| Blood glucose | 70–100 mg/dL (fasting) | Pancreas | Insulin and glucagon secretion |
| Blood pH | 7.35–7.45 | Lungs and kidneys | CO2 excretion, bicarbonate buffering |
| Blood osmolarity | 275–295 mOsm/kg | Kidneys | ADH secretion, urine concentration |
| Blood pressure | 90–120 / 60–80 mmHg | Heart and kidneys | Baroreceptors, RAAS system |
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Related Terms
Nervous System
The nervous system is the organ system that coordinates voluntary and involuntary actions and transmits signals between different parts of the body using a network of neurons. In vertebrates it is divided into the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), comprising all neural tissue outside the CNS. The nervous system integrates sensory information, processes it, and generates appropriate motor or physiological responses, making it central to behavior, cognition, and homeostasis.
Action Potential
An action potential is a rapid, transient, self-propagating electrical signal in a neuron or muscle cell generated by the sequential opening and closing of voltage-gated ion channels, causing a characteristic depolarization followed by repolarization of the cell membrane. The membrane potential briefly shifts from approximately −70 mV (resting) to +40 mV (peak) before returning to resting levels, following an all-or-none principle in which the stimulus must reach a threshold of around −55 mV to trigger the full response. Action potentials propagate along axons without signal loss and serve as the primary mode of long-distance communication in the nervous system.
Neuron
A neuron is the fundamental structural and functional unit of the nervous system, specialized for receiving, processing, and transmitting electrochemical signals. Each neuron consists of a cell body (soma), dendrites that receive incoming signals, and an axon that transmits signals away to other neurons, muscles, or glands. The human brain contains approximately 86 billion neurons, and the precise connectivity and signaling between them underlies all cognitive processes, sensory perception, and motor control.
From Greek "homoios" (similar, alike) and "stasis" (standing still, stability). The term was coined by American physiologist Walter Bradford Cannon in his 1926 paper, building on Claude Bernard's earlier concept of "milieu intérieur" (internal environment).