• Homeostasis is the maintenance of a constant internal environment around the cells of the body.
• Homeostasis accurately means “staying the same”.
• The body temperature, the composition and pressure of body fluid is maintained and keep within a specific range.
• Factors regulated by homeostasis
* pH of internal environment
* Blood pressure
* The concentration of nutrients and waste products.
* Volume and pressure of extra cellular fluid
• Homeostasis takes place through negative feedback mechanism.
• The mechanism of this system acts as a corrective measure to restore any factors back to normal conditions.
• Negative feedback occurs when the response to a stimulus diminishes the original stimulus. Negative feedback is most common in biological systems.
* Blood glucose concentrations rise after a meal and insulin causes glucose to be removed from the bloodstream, which decreases blood glucose.

Main organs involved in Homeostasis

• Hypothalamus: monitors water, temperature and carbon dioxide content of blood
• Pituitary gland: secretes a number of hormones, a key one is ADH which is important in regulating the water content of the body.
• Liver: helps to control glucose content of the body by storing it as glycogen. It is also involved in temperature regulation, acting as the body’s furnace by increasing the rate of respiration when we are cold.
• Lungs: helps to getting rid of carbon dioxide from the body.
• Pancreas: maintaining a constant amount of glucose in the body through the actions of glucagon and insulin.
• Muscles: help to maintain a stable body temperature as muscular activity and shivering help to generate heat.
• Kidney: controlling the amount of water salt in the body.
• Skin: largest organ and has a central role in maintaining a constant temperature.

Skin Structure


  • Epidermis: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.
  • Dermis: The dermis, beneath the epidermis, contains tough connective tissue, hair follicles and sweat glands.
  • Hypodermis: The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.
  • Blood vessels: To help keep your body a constant temperature, blood vessels in the skin dilate in response to heat or constrict in response to cold.
  • Sebaceous glands: The sebaceous glands secrete sebum, an oily substance that helps keep skin from drying out. Most of the glands are located in the base of hair
  • Sweat glands: When your body gets hot or is under stress, these glands produce sweat, which evaporates to cool you. Sweat glands are located all over the body but are especially abundant in your palms, soles, forehead, and underarms.
  • Hair follicle: Every hair on your body grows from a live follicle with roots in the fatty layer called subcutaneous tissue.

Functions of the skin

  • Provides a protective barrier against mechanical, thermal and physical injury and hazardous substances.
  • Prevents loss of moisture.
  • Reduces harmful effects of UV radiation.
  • Acts as a sensory organ (touch, detects temperature).
  • Helps regulate temperature.
  • An immune organ to detect infections etc.
  • Production of vitamin D.

Controlling Temperature

Temperature control is important for the normal operation of enzymes and cells. The brain has a key role in coordinating this function. Near the bottom of the brain is a place called the hypothalamus, which monitors a number of key things in the body, include temperature. When the hypothalamus detects a change in the temperature of the blood it sends impulses down neurones to the skin.

The role of the skin in temperature regulation

  • When there is a change in the temperature, it will be detected by the temperature receptors in the skin and an impulses will be sent to the brain and along a motor neurone impulses would be send to different effectors which responses.
  • The skin keeps our water in, has a layer of fat to keep us warm and is tough enough to keep out microbes that might cause disease. It is also a great place for nerve receptors
  • In addition to all of this, the skin has some interesting mechanisms to help control temperature. It can alter blood flow, hair position and the amount of sweating.

It is important to keep our body temperature at about 37 °C. This is because it is the best temperature for enzymes to work. The blood temperature is monitored by the brain and if it varies from 37 °C, various changes are brought about.

If body temperature rises above 37 °C

  • Sweating– as water evaporates from our skin, it absorbs heat energy. This cools the skin and the body loses heat.
  • Vasodilation – blood capillaries near the skin surface get wider to allow more blood to flow near the surface. Because the blood is warmer than the air, it cools down and the body loses more heat.
  • If the blood temperaturegets too high it could lead to heat stroke and dehydration.

If body temperature falls below 37 °C

  • Shivering: rapid contraction and relaxation of body muscles. This increases the rate of respiration and more energy is released as heat
  • Vasoconstriction: blood capillaries near the skin surface get narrower and this process reduces blood flow to the surface. The blood is diverted to deeper within the body to conserve heat.