Endocrine System

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Endocrine System
Function- to secrete hormones into the
bloodstream Hormones- chemical messengers in the
body
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Types of glands

• Endocrine glands- secrete a substance made in
  that cell (ductless glands)
• Exocrine glands (excretory system)-release
  substances through ducts (already covered)

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Glands

• Thyroid
• Parathyroid
• Adrenal
• Testes
• Ovary
• Pancreas
• Pituitary- controls other glands
• Hypothalamus (Master) gland- controls pituitary
  gland
• Thymus
• Pineal

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Prostaglandins Hormone action

• Prostaglandins- local hormones that cause
  contractions of smooth muscle
• Menstrual cramps are caused by prostaglandins
• Target cells- area of the body that has receptors
  to bind specific hormones
• Receptors- proteins on the surface of target cell
  that binds protein
• very specific!

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Negative Feedback

• This mechanism operates/self-regulates like a
  thermostat controlling heat in your house
• an increase in one substance inhibits the process
  that creates that substance (feedback inhibition)
• Ex. Insulin is released by the pancreas to
  increase glucose metabolism? Blood glucose
  decreases? Glucagon is then released by the
  pancreas to slow glucose metabolism? Blood
  glucose increases
• Hypoglycemia?!!!

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Another example

• When you feel cold
• Hypothalamus releases TRH (thyroid releasing
  hormone) which stimulates the pituitary gland?
  pituitary releases TSH (thyroid stimulating
  hormone) ? thyroid gland releases thyroxine?
  thyroxine causes metabolism to increase? you feel
  warm!
• Once you are warm, the increased level of
  thyroxine shuts off (inhibits) the release of TRH
  from the hypothalamus
• People with hyperthyroidism are usually very thin
  b/c they are releasing too much thyroxine

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