14.5 Temperature Control

2026 Syllabus Objectives

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

  1. Identify, on a diagram of the skin: hairs, hair erector muscles, sweat glands, receptors, sensory neurones, blood vessels, and fatty tissue
  2. Describe the role of insulation in maintaining a constant internal body temperature in mammals
  3. Describe the roles of the hypothalamus and temperature receptors in the skin in maintaining a constant internal body temperature in mammals
  4. Explain how each of the following processes contributes to the maintenance of constant internal body temperature in mammals:
    • (a) Sweating
    • (b) Shivering
    • (c) Contraction of hair erector muscles
    • (d) Vasodilation and vasoconstriction of arterioles supplying skin surface capillaries

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Why Does Body Temperature Need to Stay Constant?

Mammals (including humans) are warm-blooded, which means the body works hard to keep its internal temperature constant at around 37°C, no matter how hot or cold the environment is.

This is important because enzymes (the proteins that control chemical reactions in the body) only work properly at the right temperature. If the body gets too hot or too cold, enzymes stop working efficiently, and the body's chemical reactions slow down or fail. This can be life-threatening.

The process of keeping a stable internal environment — including temperature — is called homeostasis (pronounced "home-ee-oh-stay-sis"). Think of it as the body's self-regulating system.

Objective 1 — Structure of the Skin

The skin is the body's largest organ and plays a key role in temperature control. It has several important structures that you need to be able to identify on a diagram.

Diagram Description: Layers and Structures of the Skin

The skin has two main layers:

  • Epidermis — the outer layer, which forms a tough protective surface
  • Dermis — the thicker layer underneath, where most of the temperature-control structures are found
  • Below the dermis is a layer of fatty tissue (also called subcutaneous fat)

Structures to Identify:

1. Hairs

  • Thin, thread-like structures that grow out of the skin through small openings called hair follicles
  • Hairs stick up above the surface of the skin
  • In animals with thick fur, hairs play a major role in insulation (keeping warmth in)

2. Hair Erector Muscles

  • Small muscles attached to each hair follicle
  • When they contract (tighten), they pull the hair upright, making it stand on end
  • This is sometimes called getting "goosebumps" in humans

3. Sweat Glands

  • Coiled, tube-like glands found in the dermis
  • They produce sweat, a watery liquid that travels up a tube (called the sweat duct) to the surface of the skin through a tiny pore (opening)
  • Sweating is a cooling mechanism

4. Receptors

  • Specialised cells in the skin that detect changes in temperature
  • They are called temperature receptors (or thermoreceptors)
  • Some detect heat; others detect cold
  • They send signals (nerve impulses) to the brain when the temperature changes

5. Sensory Neurones

  • Neurones are nerve cells. Sensory neurones are the type that carry information from the receptors to the brain
  • Think of them as the body's telephone wires — they transmit the temperature "message" to the brain

6. Blood Vessels

  • The dermis contains a network of small blood vessels, including arterioles (tiny arteries) and capillaries (very small, thin-walled blood vessels)
  • These blood vessels can widen or narrow to control how much heat is lost through the skin

7. Fatty Tissue (Subcutaneous Fat)

  • A layer of fat found just below the dermis
  • Acts as an insulator — it traps heat and stops it from escaping too quickly from the body
  • Also provides a store of energy and acts as a cushion against physical knocks

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