PP 2 Endocrinology 1

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PP 2Endocrinology 1

• Chapter 10 pg 179-198
• ANS 3043
• University of Florida
• Dr. Michael J. Fields

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Types of Hormone Action

• Endocrine Hormones are secreted and transmitted
  through the bloodstream to act on target cells
• Paracrine Hormones are secreted by one cell that
  travel through the interstitial fluid to evoke a
  response in an adjacent cell

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Types of Hormone Action

• Autocrine Hormones cause a response in the cells
  that synthesize them or in neighboring cells of
  the same type
• Neuroendocrine Hormones are secreted in respones
  to a neural input
• -Example Suckling Stimulus

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Types of Hormone Secretion

• Suckling is neural stimlus
• Signal travels to hypothalamus stimulating
  oxytocin production
• Hypothalamus signals the Posterior Pituitary
  through the Median Eminence

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Types of Hormone Action

• Oxytocin is released into circulation by the
  Posterior Pituitary
• Oxytocin stimulates Myoepitheilial cells that
  stimulate milk letdown

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Function of the Endocrine System

• The endocrine system maintains
• Homeorhesis chronic regulation of the stability
  of the body
• Homeostasis acute regulation of the stability of
  the body

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Hormone Receptors

• Allow for tissue specificity by only allowing
  hormones to bind to those tissues that express
  their corresponding receptors
• Usually a protein
• Binding promotes a biological response

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Hormone-Receptor Complex Characteristics

• Hormone only binds to its specific receptor
• -like a lock and key
• Hormone-Receptor binding modifies the activity of
  the target cell or tissue
• - Stimulates intercellular messengers
• (calcium, magnesium) or regulatory
  proteins
• Can exhibit different affinities in different
  tissues

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Hormone-Receptor Complex Characteristics

• Receptor Affinity The strength of the bond
  between a hormone and its receptor (tightness of
  fit)
• - regulates how long hormone will continue to
• elicit biological response

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Hormone Receptor Locations

• Cell membrane typically binds protein hormones
• Nuclear membrane typically binds steroid and
  thyroid hormones
• Cytosol possibly binds steroid and protein
  hormones
• - Some cytosolic-binding hormones are
  transcription
• factors bind to
  receptor in cytosol and
• travel to the nucleus to modify
  DNA production

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Controlling Biological Response

• Increased receptor number usually causes a more
  dramatic biological response
• Large concentrations of hormones can cause
  down-regulation of receptor and extinction of
  biological response
• - Down-regulation moment of receptors from the
  cell
• membrane to the intercellular compartment
• (internalization) to prevent further
  hormone binding
• and biological response
• Receptors return to cell surface when hormone
  concentrations return to normal levels

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Concept of Receptor Up and Down Regulation
CL progesterone secretion over 8-10 days
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Mechanisms of Hormone Action

• Peptide and Protein Hormones Activation of
  second messenger system

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Second Messenger Systems
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Mechanisms of Hormone Action

• Steroids
• Free Hormone enters cells by diffusion and
  binds to receptor
• Hormone/Receptor Complex binds DNA in nucleus and
  controls the transcription of RNA
• Bound Hormone bound to globulin protein that
  does not enter cell
• Bound protein increases half life of hormone in
  circulation

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Transcription Factors