Skip to content

Homeostasis

Part of 4.5 Homeostasis and Response.

Homeostasis is the maintenance of a stable internal environment. The main idea is that cells and enzymes work best within narrow limits, so the body must detect change and respond automatically.

Learning Objectives

ID Official specification wording Main teaching sections
4.5.1-lo-1 4.5.1 Students should be able to explain that homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
4.5.1 Homeostasis maintains optimal conditions for enzyme action and all cell functions.
4.5.1 In the human body, these include control of:
4.5.1 • blood glucose concentration
4.5.1 • body temperature
4.5.1 • water levels.
4.5.1 These automatic control systems may involve nervous responses or chemical responses.
4.5.1 All control systems include:
4.5.1 • cells called receptors, which detect stimuli (changes in the environment)
4.5.1 • coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
4.5.1 • effectors, muscles or glands, which bring about responses which restore optimum levels.		 Control Systems

Control Systems

Homeostasis relies on automatic control systems that operate continuously. Each system has three components:

  1. Receptors — detect changes (stimuli) in the internal or external environment.
  2. Coordination centre — receives information from receptors, processes it, and sends instructions.
  3. Effectors — muscles or glands that carry out the response.

Homeostasis works by negative feedback: when a condition moves away from its set point, the response pushes it back towards normal.

  • Nervous responses are rapid and suited to immediate corrections.
  • Hormonal responses are slower, but their effects usually last longer.

Conditions Kept Within Narrow Limits

The specification names three main examples of internal conditions that must stay close to their set point:

  • Blood glucose concentration — cells need a steady supply of glucose for respiration.
  • Body temperature — enzymes only work properly in a narrow temperature range.
  • Water levels — cells must avoid gaining or losing too much water by osmosis.

These examples are developed in more detail on 4.5.2 The Human Nervous System and 4.5.3 Hormonal Coordination in Humans.

Common Confusions

  • Homeostasis does not mean perfectly constant conditions: small fluctuations happen, but negative feedback keeps them close to the set point.
  • Receptor vs effector: receptors detect the change; effectors bring about the response.
  • Nervous vs hormonal response: nervous responses are fast and short-lived, while hormonal responses are slower but longer-lasting.

Key Terms

  • Homeostasis: the maintenance of a stable internal environment.
  • Set point: the ideal value or narrow range around which a control system keeps a condition.
  • Stimulus: a change in the internal or external environment detected by receptors.
  • Receptor: a structure that detects a stimulus or change.
  • Coordination centre: a part of the body that receives and processes information from receptors.
  • Effector: a muscle or gland that brings about a response.
  • Negative feedback: a control mechanism where the response opposes the original change to return the system to the set point.

Connected Pages