Chapter 13 : The Endocrine System
The endocrine system produces hormones
Endocrine glands = ductless organs that secrete into interstitial fluid, lymph and blood => INTERNALLY (not in ducts !)
Differences with nervous system as a communication tool :
Reach nearly every living cell as they circulate in the blood (exception : blood-brain barrier) => No need for direct
connections as nervous system
Each hormone acts only on its “target cells” (have the appropriate receptor)
Endocrine control slower : Nerve impuls can travel in fraction of sec. From secreting hormone to affect = at least
20 sec. => Highly effective for LT-controls (eg regulating blood pressure,etc.)
The endocrine and nervous often interact : eg release of some hormones depend on input from sensory neurons.
Hormones are classified as steroid or nonsteroid
Steriod hormones : related to cholesterol (a lipid) => Lipid soluble : Enters cell, bind to extracellular receptor =>
Activate genes that produce new proteins.
Nonsteroid hormones : related to proteins => Lipid unsoluble (cannot cross cell membrane) => Bind to receptors on
cells surface => initiates series of events but hormones never entered the cell.
STEROID HORMONES enter target cells
As cell membrane is composed of bilayer of phospholipids, SH can easily diffuse across => inside, SH bind to specific
hormone receptors => form “hormone-receptor” complex with NUCLEUS => Inside nucleus, hormone-receptor
complex attaches to DNA => activating specfic genes => causes formation of messenger RNA, which leaves nucleus
and directs synthesis of certain proteins => Proteins then carry out the cellular response to the hormone.
Slower than NSH because entire protein production process begins only after arrival of hormone in cell : mins- hours.
The endocrine system produces hormones
Endocrine glands = ductless organs that secrete into interstitial fluid, lymph and blood => INTERNALLY (not in ducts !)
Differences with nervous system as a communication tool :
Reach nearly every living cell as they circulate in the blood (exception : blood-brain barrier) => No need for direct
connections as nervous system
Each hormone acts only on its “target cells” (have the appropriate receptor)
Endocrine control slower : Nerve impuls can travel in fraction of sec. From secreting hormone to affect = at least
20 sec. => Highly effective for LT-controls (eg regulating blood pressure,etc.)
The endocrine and nervous often interact : eg release of some hormones depend on input from sensory neurons.
Hormones are classified as steroid or nonsteroid
Steriod hormones : related to cholesterol (a lipid) => Lipid soluble : Enters cell, bind to extracellular receptor =>
Activate genes that produce new proteins.
Nonsteroid hormones : related to proteins => Lipid unsoluble (cannot cross cell membrane) => Bind to receptors on
cells surface => initiates series of events but hormones never entered the cell.
STEROID HORMONES enter target cells
As cell membrane is composed of bilayer of phospholipids, SH can easily diffuse across => inside, SH bind to specific
hormone receptors => form “hormone-receptor” complex with NUCLEUS => Inside nucleus, hormone-receptor
complex attaches to DNA => activating specfic genes => causes formation of messenger RNA, which leaves nucleus
and directs synthesis of certain proteins => Proteins then carry out the cellular response to the hormone.
Slower than NSH because entire protein production process begins only after arrival of hormone in cell : mins- hours.
