Homeostasis

Rise In Body Temperature

• Thermoreceptors in the skin/hypothalamus detect temperature is too high.
• Hypothalamus sends impulses along motor neurones to effectors.
• Which bring about:- vasdilation where arterioles near the surface of the skin dilate so more blood flows through the capillaries. Heat is lost from the skin by radiation.

- Sweating; water in the sweat evaporates from the surface of the skin taking heat from the body with it.

- Hairs lie flat; less air is trapped so the skin is less insulated and heat can be lost more easily.

- No adrenaline or throxine released.

- No shivering.

• More heat's lost and less is produced so it goes back to normal body temperature.

Fall In Body Temperature

• Thermoreceptors detect temperature is too low.
  
• Hypothalamus sends signals to effectors which brings about:

- Vasoconstriction; arterioles near the surface of the skin constrict so less blood flows through the capillaries thus reducing heat loss.

- Less sweating.

- Hair stands up to trap air to prevent heat loss.

- Shivering; muscles contract in spasms so more heat is produced from increased respiration.

- Adrenaline and throxine released.

• More heat is produced and conserved by the body and it goes back to normal body temperature.

Rise In Blood Glucose Concentration

• Beta cells in the pancreas detect blood glucose concentration is too high and so secrete insulin while alpha cells stop secreting glucagon.
• Insulin binds to specific receptors on the cell membranes of liver and muscle cells.
• This increases the permeability of cell membranes to glucose so they take up more glucose.
• It also activates glycogenesis where glucose is converted to glycogen.
• It increases the rate of respiration of glucose.
• As a result less glucose is in the blood which brings it back down to normal blood glucose concentration.

Fall In Blood Glucose Concentration

• Alpha cells in the pancreas detects blood glucose concentration is too low and so secrete glucagon while beta cells stop secreting insulin.
  
• Glucagon binds to specific receptors on the cell membranes of liver cells.
• It activates glycogenolysis where glycogen is broken down into glucose.
• It activates gluconeogenesis where glucose is formed from fatty acids and amino acids.
• It also decreases the rate of respiration of glucose in cells.
• Cells release glucose into the blood as a result and brings the blood glucose concentration back to normal levels.

Adrenaline Increases Blood Glucose Concentration

• Its secreted from the adrenal glands when there's a low concentration of glucose in the blood.
  
• Activates the secretion of glucagon and inhibits isulin secretion.
• Adrenaline and glucagon bind to their specific receptors in the cell membrane of liver cells and activate the enzyme adenylate cyclase.
• Activated adenylate cyclase converts ATP into a second messenger called cyclic AMP ( cAMP).
• cAMP activates a cascade that breaks down glycogen into glucose via glycogenolysis.
• Glycogenesis is inhibited.