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Endocrine gland is a gland which secretes hormones directly into the blood

Exocrine gland is a gland that secretes molecules into a ducts which carries them to where they are used.

Target tissue are those that possess a specific receptor on the plasma membrane which is complementry in the shape to the hormone moelcule

Hormone chemical messengers which are releases by endocrine glands directly into the blood. carrying a signal from the endocrine gland to a specific tagret organ or tissue

First messenger is a hormone that acts as a message in the blood stream

Second messenger a chemical inside the cell which in released in response to a hormone binding to the cell surface membrane (e.g. cAMP)

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Hormone types and response

Hormones are secreted in response to :

  • change in conc. of a speciifc substance in the blood
  • chnage in conc. of another hormone in the blood
  • nervous stimulation

Hormones can be one of three groups:

  • amines and catecholamines e.g. adrenaline
  • peptides and proteins e.g. insulin and glucagon
  • steriods e.g. oestrogen and testosterone
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The action of adrenaline

  • Adrenaline is an amino acid derivitive
  • It must cause an effect inside the cell without entering the cell itself.
  • Recpeters on the cell surface membrane are complementry in shape to the shape of adrenaline. the receptors (alpha and beta adrenergic receptors) are assocaited with an enzyme(adrenyl cyclase) on the inner surface of the cell surafce membrane.
  • Adrenaline is the first messenger and binds to its receptor activating(usually through phophoprylation) the enzyme adenyl cyclase which converts ATP to cyclic AMP (cAMP is a second messeneger).
  • The cAMP can then cause an effect within the cell by activating enzyme action.
  • Phosphodiesterase breaks down the cAMP
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Insulin and Steroids ( probably don't need to know


  • Travels in the blood to the receptors
  • Binds with complementary receptors causing them to become an active tyrosine kinase which Puts phosphates onto proteins which then bring about changes in the cell.


  • Travels throught the blood with carrier proteins
  • Diffuses membrane as it is lipid soluble
  • Hormone binds to complementary intracellular  receptors.
  • Hormone then enters the nucleus
  • Hormone then binds to DNA and effects gene transcription. This can effect several genes.
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Adrenal glands

  • located just above the kidney

Adrenal medulla:

  • found in centre
  • rich supply of blood
  • when stimulated adrenaline and noradrenaline(effects are widespread and prepares the body for action)
  • adrenaline and noradrenaline are formed from the amino acid tyrosine and belong to the group catecholamines.

Adrenal cortex; uses cholestrol to produces certain types of steriod hormones:

  • mineralicorticoids-controls conc. of soidium and potassium ions in the blood. e.g. aldosterone
  • glucocorticoids - controls the metabolism of acrbohydrates and proteins in the liver and also in regulation of immune response. e..g cortisol
  • androgens-low conc-primarily involved in the developement of secndary sexual characterisitics  
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Adrenaline and Noradrenaline


  • relaxes smooth muscles in bronchioles-inhale more air
  • increased stroke volume - increased elivery and removal from cells
  • increased heart rate
  • causess vasoconstriction of blood vessels supply skin and gut.
  • vasdilation of blood vessels to brain and muscles.
  • converts glucogen to glucose-available for respiration 
  • dilates pupils-increases sensitivity
  • increased mental awareness
  • inhibits action of the gut
  • causes body hair to erect.
  • sensory threshold lowered- persepction of external stimuli is faster
  • mental awareness increased- dicisions made fastser.
  • hair riased- makes fluffy animals appear bigger.


  • casues vasoconstriction of blood vessels
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