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Flashcards in Hormones & Receptors Deck (18)
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Steroid hormone structure characteristics

  • Lipophilic ==> permeate cell membranes
  • hydrophobic ==> carried by carrier proteins in the blood stream
    • Steroid bound by carrier = inactive
    • only a small fraction (1-5%) exists in the free form (active form)
  • Steroid hormones can linger in the blood for a long time and they have a long half life. 
  • e.g. estradiol



Peptide hormone structure characteristics

  • relatively polar ==> can not permeate cell membranes
  • hydrophillic ==> not carried by carrier proteins
  • Peptide hormones have a short half-life because they move through the blood in their free form; they are easily degraded by proteases.
  • e.g. GnRH



Unique characteristics of GH, prolactin, and insulin-like growth factor (IGF-1)

Growth hormone (GH), prolactin (PRL), and insulin-like growth factor (IGF-1)behave differently because they are not transported in the blood as free hormones.


Thyroid hormone structure characteristics

  • derived from tyrosine
  • iodine-dependent
  • e.g. T4


Location and types of peptide hormone receptors

  • Peptide and protein hormones can not move through cell membranes so their receptors are located on the plasma membrane of target cells.  
  • Receptors types include:
    • G-protein coupled receptors
    • Cytokine receptor family (with JAK/STAT signaling pathways)
    • Epidermal growth factor receptor (EGFR) family with inherent tyrosine kinase  activity 


Peptide hormones ==> g-protein coupled receptors

  • Epinephrine and Norepinephrine
  • glucagon
  • Somatostatin (SST)
  • DA
  • etc (most hypothalamic hormones)


Peptide hormones ==> cytokine receptor family

  • prolactin
  • GH


Peptide hormones ==> epidermal growth factor receptor family w/tyrosine kinase activity

  • insulin
  • IGF-1 (insulin-like growth factor)


Location/types of steroid and thyroid hormones

  • Steroid/thyroid hormones can permeate cell membranes and their receptors are in the cytosol or nucleus.
  • Receptor-hormone complexes bind to specific hormone responsive elements (HRE) on DNA which activate transcription of specific genes.



Mechanism of signaling of G-Protein Coupled Receptors

  • Gs → ↑ Adenylyl cyclase → ↑ cAMP →  ↑ PKA → Glucagon, hypothalamic
  • Gi → ↓(inhibits) Adenylyl cyclase → ↓ cAMP → inhibits PKA →  ↑ K+ → Somatostatin, dopamine
  • Gq → ↑ Phosolipase C →  PIP2 → IP3 → ↑ Ca2+ from ER → DAG → ↑ PKC


G-protein coupled mnemonics


Gs → Sam’s Assless Chaps At cAMP Provide Kind Accolades

Gq → Quinn plays craps, poops in casinos, drinks percolating Korean coffee


EGFR family receptor mechanism of signaling

  • receptor itself has tyrosine kinase activity
  • receptor then targets downstream effectors
  • Example is insulin/insulin receptor activity


Cytokine receptor mechanism of signaling

  • membrane receptors that activate intracellular tyrosine kinase called Janus Kinase
  • Janus Kinase phosphorylates the receptor and the downstream kinase, which activates signal transduction and activators of transcription (STATs).  
  • This pathway is called JAK/STAT.
  • Growth hormone and prolactin act this way.


MOA of steroid vs. thyroid hormones

  • Steroid hormones bind to intracellular (cytosol/nuclear) receptor ==> receptor hormone complex ==> binding @ hormone responsive element on genomic DNA ==> transcription of specific genes
  • Thyroid hormones T4 and T3 act through a similar mechanism as steroid hormones.
  • TRH and TSH, however, are peptides and act through GPCR’s.


Main targets of regulation of hormone synthesis/release

  • @ receptors
  • via feedback loops
  • @ mechanism/type of release of hormones


Characteristics of regulation of hormone release

  • Pulsatile → in matter of minutes pulse may happen and then no release at all
  • Circadian → levels vary throughout day


Characteristics of feeback loops regulating hormones

  • Type 1 → Hormone is the regulated variable. Example is cortisol.
  • Type 2 → Plasma concentration of a metabolite or mineral acts as the regulated variable. Example is glucose levels in blood are regulated by insulin and counterregulatory hormones


Characteristics of regulation of hormones @ receptors

  • Chronic increased levels of a hormone causes the receptors to become internalized
  • Spare receptors; 90% of receptors on cell surface are inactivated, but the cellular signalling is unchanged for the active receptors.