Homeostasis

• Homeostasis is the maintenance of a constant internal environment.
  • An example is how the hormone insulin decreases blood glucose concentration when it gets too high.

Negative feedback control

• Homeostasis relies on a mechanism called negative feedback.
  • The set point is the normal, ideal level for a condition in the body (e.g. a core body temp. of 37°C or a specific blood glucose level).
  • How it works: If a factor deviates from the set point, the body detects this change and triggers a response that reverses the change to bring it right back to the set point.

Control of blood glucose concentration

High blood glucose levels

1. The pancreas detects the rise and secretes insulin into the blood.
2. Insulin travels to the liver.
3. The liver converts excess glucose into stored glycogen.
4. This causes the blood glucose concentration to decrease back to the set point.

Low blood glucose levels

1. The pancreas detects the drop and secretes glucagon into the blood.
2. Glucagon travels to the liver.
3. The liver breaks down stored glycogen into glucose.
4. The glucose is released into the blood, causing the blood glucose concentration to increase back to the set point.

Treatment of Type 1 diabetes

• Type 1 diabetes is a condition where the pancreas fails to secrete enough insulin, leading to dangerously high blood glucose levels. It is managed and treated using a combination of methods:
  • Insulin injections/insulin pump therapy: Regular doses of insulin are injected directtly into the subcutaneous fat layer to artificially lower blood glucose levels.
  • Blood glucose monitoring: Testing blood drop samples throughout the day to calculate exactly how much insulin is required.
  • Controlled diet: Carefully managing and balancing carbohydrate intake to prevent massive blood sugar spikes.

Skin

Diagram

Structures

• Hairs: Extend above the skin surface. Can be raised or lowered.
• Hair erector muscles: Tiny muscles attached to the base of each hair follicle.
• Sweat glands: Coiled tubes in the dermis that produce sweat.
• Receptors: Specialized nerve endings that detect temp. and pressure changes.
• Sensory neurones: Send electrical impulses from the skin receptors to the CNS.
• Blood vessels: Arterioles and capillaries that supply nutrients and play a massive role in temp. control.
• Fatty tissue (subcutaneous layer): Located beneath the dermis. Acts as a layer of insulation.

Maintaining a constant body temperature

• The hypothalamus detects changes in the temp. of the blood and sends electrical impulses along nerves to trigger a corrective response *(like shivering or sweating)

High body temperature

• Sweating: Sweat glands secrete sweat onto the skin surface. As the water in sweat evaporates, it absorbs and removes heat energy from the skin, cooling the body down.
• Vasodilation: Arterioles supplying the skin surface capillaries widen (dilate). This allows more blood to flow close to the skin surface, meaning more heat energy is lost to the environment via radiation.

Low body temperature

• Shivering: Muscles contract and relax rapidly. This muscle activity requires a high rate of respiration, which releases heat energy to warm the blood.
• Insulation:
  • The fatty tissue layer reduces heat loss from the core.
  • Hair erector muscles contract, pulling the hairs upright. This traps a layer of still, warm air next to the skin, acting as insulation. More effective in furry mammals than humans.
• Vasoconstriction: Arterioles supplying the skin surface capillaries narrow (constrict). This restricts blood flow to the skin surface, redirecting it to vital core organs and minimizing heat loss via radiation.