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Control Of Body Temperature

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.
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Control Of 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.
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Control Of Blood Glucose Concentration

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.
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Control Of 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.
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Control Of Blood Glucose Concentration

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.
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