7: Hormones

• Primary endocrine gland organs have the major job of secreting hormones, while secondary endocrine organs have a different primary role.
• Some of the common stimuli causing hormone secretion include:

  • Release of NT from an autonomic neuron (like ACh from parasympathetic or NE from sympathetic)
  • Circulating hormone like CRH (corticotropin releasing hormone) from the hypothalamus
  • A change in concentration of a nutrient (like glucose) or an ion (like K+)
• The main type of catecholamine is epinephrine. This is a lipid insoluble hormone, so it binds to receptors located extracellularly to produce an effect that can occur in minutes.
• Lipid insoluble hormones travel free in the blood because they are hydrophilic; therefore, concentrations can rise quickly but hormone is also degraded quickly.
• Peptide and small protein hormone types are a type of lipid insoluble hormone. A couple examples of this type are insulin and CCK.
• Lipid soluble hormones mostly bind to intracellular receptors, which often leads to the direct alteration of gene transcription for the generation of new proteins in the cell.
• Lipid soluble hormones travel through the blood bound to a carrier protein, which protects the hormones from degradation.

  Because of the solubility this affords, the hormone cannot be stored in advance (in vesicles) and must be produced as needed; thus, these hormones act slowly (hours to days) but can also have a longer-lasting effect.
• Types of lipid soluble hormones include steroids, which typically come from the gonads (androgens, estrogens, and progesterones) or the adrenal gland (cortisol and more androgens), and thyroid hormones.
• The same hormone can have different responses by interacting with different receptors.

  For example, epinephrine can bind to either alpha or beta adrenergic receptors on smooth muscle. Alpha receptor binding would cause contraction of the muscle while beta receptor binding would cause relaxation.
• The main example of hormones controlling the release of other hormones is neurons from the hypothalamus releasing hormones into blood vessels towards the anterior pituitary gland, which then alter hormone release by endocrine cells into blood circulation.
• Hypothalamic-pituitary-adrenal axis: CRH > ACTH > cortisol
• Some of the functions of cortisol include:

  • Blood pressure regulation via smooth muscle responses to norepi and epi
  • Maintenance of metabolic enzymes (fat & glucose)
  • Anti-inflammatory functioning
  • Proper differentiation and development of brain, adrenal medulla, intestine, and lungs
  • During "stress": helps mobilize energy, increase blood pressure, inhibit inflammation, and inhibit non-essential functions