14.4 Homeostasis

2026 📋 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Describe homeostasis as the maintenance of a constant internal environment
  2. Explain the concept of control by negative feedback with reference to a set point

📖 Main Content

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Objective 1: What is Homeostasis?

The Basic Idea

Your body is constantly being challenged by changes — the temperature outside drops, you eat a large meal, you run a race. Despite all of these changes happening around you and inside you, your body works very hard to keep its internal conditions (the conditions inside your body) stable and steady.

This process of keeping the internal environment constant is called homeostasis.

Homeostasis = the maintenance (keeping) of a constant internal environment inside the body.

Think of it this way: your body cells need the right conditions to work properly. If those conditions change too much, cells — and the whole body — can stop working correctly. Homeostasis is your body's way of protecting those conditions.

Why Does the Internal Environment Need to Stay Constant?

Every cell in your body carries out chemical reactions to keep you alive. These reactions are controlled by special proteins called enzymes (biological catalysts — substances that speed up chemical reactions in the body). Enzymes are very sensitive. If conditions change even slightly, they may stop working properly.

The internal conditions that must be kept constant include things like:

  • Body temperature — must stay close to 37°C for enzymes to work properly
  • Blood glucose concentration — the amount of sugar dissolved in the blood must stay within a safe range so cells always have enough energy
  • Water content of the blood — cells must not gain or lose too much water, or they will be damaged

If any of these drift too far from the correct level, the body detects the change and takes action to bring it back to normal. That corrective action is homeostasis.

A Simple Analogy

Imagine your home has a central heating system. The heating is set to keep the room at 20°C. If it gets too cold, the heater turns on. If it gets too warm, the heater turns off. The room temperature is being kept constant, even though the weather outside keeps changing.

Your body works in exactly the same way — but instead of a thermostat and heater, it uses nerves, hormones, and organs.

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