Biology- Chemical coordination and homeostsis

Chemical coordination and homeostsis

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  • Are either made from polypeptide or lipid.
  • Secreted by endocrine tissues/glands directly into the blood.
  • Transported in the blood until they reach specific target cell.
  • Target cells have specific receptor molecules on the plasma membrane/ inside the cell.
  • When they link to receptors they initiate reactions that activate enzymes inside the cell.
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Nervous control v hormonal control

  • Nervous control has a more localised effect as neurones link directly to their target organs/cells.
  • Hormonal control has a widespread effect, because hormones travel in the blood they effect any cell with an appropriate receptor.
  • Nervous control is very rapid because neurones transmit electrical impulses very quickly.
  • Hormonal control is slower as hormones are transported at the speed that blood flows.
  • The response of nervous control is short lived.
  • The effects of hormonal control are longer lasting because the hormones have to be removed from the blood by the liver or kidneys.
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  • Directional response towards or away from a stimulus (in plants).
  • e.g phototropism - response to light.
  • Caused by IAA which is a growth regulator.
  • IAA causes stem elongation.
  • IAA diffuses away from the light side of the plant and accumulates on the shady side.
  • This causes cell elongation on the shady side.
  • Therefore the stem grows more on the shady side, so the stem bends.
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  • Maintaining the internal environment within restricted limits.
  • Uses negative feedback.
  • There are three parts to the control system - A receptor (detects a stimulus), an integrator (determines and coordinates response) and an effector (carries out the response).
  • When conditions return to normal the receptors aren't stimulated so the control system is switched off.
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Control of core body temperature

  • Core temperature is monitered by receptors in the hypothalamus.
  • If temp falls - Impulses are sent to the heat gain centre in the hypothalamus
  • nerve impulses stimulate vasocontriction, raising body hair and shivering.
  • If temp rises - Impulses are sent to the heat loss centre in the hypothalamus.
  • nerve impulses stimulate vasodilation and sweating.
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Control of blood glucose concentration

When blood glucose conc increases:

  • Glucose is absorbed into beta cells (found in islets of langerhans) by facilitated diffusion.
  • Insulin is released from the beta cells.
  • This stimulates glucose uptake in muscle, liver and adipose tissue.
  • In the liver glucose is converted into glycogen (glycogensis)

When blood glucose conc falls:

  • Alpha cells (in IoL) secrete glucagon.
  • This affects the liver - activates enzymes that break glycogen down to glucose (glycogenolysis).
  • Glucose is made from non-carbs such as amino acids and lactate.
  • Glucose is added to the blood.  
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Endotherms/ ectotherms

  • Endotherms maintain  a constant body temperature.
  • There muscles and enzymes are always at a favourable temperature to operate efficently.
  • Endotherms need a lot of food (energy) to generate enough heat.
  • The body temp of ectotherms varies with external temperature.
  • Their muscles and enzymes may not work efficiently if too cold.
  • They use less energy for heat so do not need a lot of food.
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Adrenaline and the second messenger

Adrenaline also stimulates the breakdown of glycogen to glucose :

  • It combineswith a receptor on the cell surface membrane which activates an enzyme.
  • This converts ATP to cAMP.
  • cAMP activates the enzymes that breakdown glycogen to glucose.
  • This mechanism gives amplification as each molecule of hormone stimulates the production of many molecules of cAMP.
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  • Causes blood glucose levels to rise to very high levels.
  • Excess glucose is lost in the urine.

Type 1 :

  • Caused by the immune system destroying Beta cells.
  • This causes a lack of insulin.
  • Can be treated by insulin injections.

Type 2:

  • insulin is present but cells fail to respond to it.
  • Can be treated with diet - avoid sugary foods and eat starchy carbohydrates.
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