Homeostasis (Edexcel GCSE Biology): Revision Notes

Homeostasis

Conditions in your body need to be kept steady so cells need the right conditions to function properly (enzyme action) Your body needs both internal & external changes whilst balancing inputs with outputs for example:

• Osmoregulation
• Thermoregulation
• Blood glucose regulation

Thermoregulation – The Effect on Enzyme Activity

• Thermoregulation is the process of controlling body temperature to ensure that it remains at an optimal level, typically around 37°C in humans.

• Enzymes, which are proteins that catalyse biochemical reactions in the body, function best at this temperature.

• If body temperature rises too high (above 40°C), enzymes begin to denature, meaning their shape changes and they can no longer catalyse reactions efficiently. This leads to the breakdown of important processes like respiration.

• If body temperature falls too low, enzyme activity slows down, reducing the rate of vital reactions, which can result in less energy being produced for the body to function. Thermoregulatory Mechanisms:

• Sweating: When the body overheats, sweat is produced. Its evaporation cools the body.

• Shivering: When cold, muscles contract rapidly to generate heat.

• Vasodilation: In hot conditions, blood vessels widen to increase heat loss.

• Vasoconstriction: In cold conditions, blood vessels narrow to reduce heat loss.

Thermoregulation and the Role of the Skin

The Role of the Dermis:

The dermis is the inner layer of the skin, located beneath the epidermis. It contains several structures that help with thermoregulation:

• Sweat glands: When the body overheats, the sweat glands produce sweat, which is released onto the surface of the skin. As sweat evaporates, it removes heat from the body, cooling it down.
• Blood vessels: The blood vessels in the dermis can undergo vasodilation or vasoconstriction:
• Vasodilation: When the body is too hot, the blood vessels widen, allowing more blood to flow near the surface of the skin. This increases heat loss.
• Vasoconstriction: When the body is too cold, the blood vessels narrow, reducing blood flow near the skin surface, which decreases heat loss and conserves heat.
• Nerve endings: The dermis contains nerve receptors that detect temperature changes and send signals to the brain.

The Role of the Epidermis:

• The epidermis is the outer layer of the skin that acts as a barrier to the environment. It also plays a minor role in thermoregulation:
  • It prevents excessive water loss, helping maintain the body's hydration levels, which is important for temperature regulation.
  • Hairs on the surface of the epidermis can trap air close to the skin, acting as insulation when the body is cold. Erector muscles in the dermis contract to make the hairs stand up (goosebumps), trapping more air and helping to retain heat.

The Role of the Hypothalamus:

• The hypothalamus is a part of the brain that acts as the body's thermoregulatory centre. It monitors the body's internal temperature and receives signals from temperature receptors in the skin.
  • When the hypothalamus detects that the body is too hot or too cold, it sends nerve signals to the skin and other parts of the body to trigger responses that help regulate temperature.
  • If the body is too hot, the hypothalamus triggers sweating and vasodilation. If the body is too cold, it triggers shivering, vasoconstriction, and the contraction of erector muscles to raise body hairs.

Summary:

Thermoregulation involves the coordinated actions of the dermis, epidermis, and hypothalamus to maintain a stable internal body temperature.

• The dermis controls sweating and blood flow to regulate heat loss.
• The epidermis provides insulation and prevents water loss.
• The hypothalamus acts as the control centre, detecting temperature changes and sending signals to maintain balance.

Osmoregulation – The Effect on Animal Cells

• Osmoregulation is the control of water levels and mineral ions (salts) in the blood to maintain the correct balance for cells to function properly.

• It is vital to keep water concentration the same inside and outside cells. If this balance is not maintained, water may move in or out of cells by osmosis, which can damage them. Effects on Animal Cells:

• If the concentration of water outside the cells is too high, water will move into the cells by osmosis, causing them to swell and possibly burst.

• If the concentration of water outside the cells is too low, water will move out of the cells, causing them to shrink and become dehydrated. Both of these scenarios can prevent the cells from functioning properly. Osmoregulatory Mechanisms:

• Kidneys: The kidneys play a crucial role in osmoregulation by filtering the blood and adjusting the amount of water and mineral ions reabsorbed. Excess water and ions are excreted in urine.

• ADH (Antidiuretic Hormone): This hormone controls the reabsorption of water in the kidneys, helping regulate water levels in the blood.

Summary:

• Homeostasis ensures that internal conditions remain stable for optimal enzyme activity and cell function.
• Thermoregulation maintains body temperature for enzyme efficiency, while osmoregulation controls water balance to prevent damage to cells. Both processes are crucial for the proper functioning of the body's systems.