Endocrine

• Hormones


  Chemical substances secreted by cells into the extracellular fluids (blood)
• Hormones


  • Regulate the metabolic function of other cells
  • Under Negative Feedback Control
  • Are classified as either amino acid-based hormones or steroids
• Endocrine glands


  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pineal
  • Thymus
• The pancreas and gonads are both endocrine and exocrine organs
• Other tissues and organs that produce hormones


  • Placenta
  • Adipose Cells
  • Thymus
  • Cells in walls of Small Intestine
  • Stomach
  • Kidneys
  • Heart
• Amino acid-based hormones


  Water-soluble, work rapidly but have limited duration
• Steroid hormones


  Lipid soluble, work slowly but have long duration, require a plasma protein to be transported in bloodstream
• Eicosanoids


  Leukotrienes and prostaglandins, fatty-acid derivatives, not a true hormone, classified as a paracrine
• Paracrine


  Chemically acts on adjacent cells, not long distances
• Types of Amino Acid-Based Hormones

  • Amines
  • Thyroxine
  • Peptide
  • Protein hormones, including catecholamines
• Most hormones belong to the amino acid-based class
• Catecholamines


  Epinephrine, norepinephrine, adrenaline
• Steroid hormones


  Derived from cholesterol, lipid soluble, work slowly but have long duration, require a plasma protein to be transported in bloodstream
• Steroid hormones


  • Gonadal
  • Adrenocortical
• Hormone action mechanisms


  • Second messenger mechanism (used by amino acid-based hormones)
  • Direct gene activation (used by steroid and thyroxine hormones)
• Second messenger mechanism


  1. Hormone binds to receptor

  2. G protein activated

  3. Second messenger produced

  4. Biological effect achieved

  
• Second messenger mechanism examples


  • Epinephrine binds to heart receptors, increases Ca2+ permeability, increases heart rate/force
  • Glucagon binds to liver receptors, activates adenylate cyclase, generates cAMP, causes glycogenolysis
• Direct gene activation mechanism


  1. Hormone directly enters target cell

  2. Binds to/activates intracellular receptor

  3. Hormone-receptor complex travels to nucleus

  4. Binds DNA-associated receptor protein

  5. Prompts DNA transcription to produce mRNA

  6. mRNA translated into proteins that bring about cellular effect

  
• Target cell specificity


  • Target cells must have specific receptors to which the hormone binds
  • Target cell activation depends on blood hormone levels, relative number of receptors, and receptor affinity
• Up-regulation and down-regulation


  Up-regulation - target cells form more receptors in response to hormone

  Down-regulation - target cells lose receptors in response to hormone
• Stimuli for hormone release

  • Humoral (ion/nutrient levels in blood)
  • Neural (SNS stimulation)
  • Hormonal (tropic hormones stimulate release of other hormones)
• Pituitary gland is the "master gland" that secretes 9 major hormones
• Pituitary gland


  • Neurohypophysis (posterior lobe and infundibulum) receives, stores, and releases hormones made in the hypothalamus

  Adenohypophysis (anterior lobe) makes and secretes a number of hormones
• Stimulus: Action potentials in preganglionic sympathetic fibers to adrenal medulla


  Response: Adrenal medulla cells secrete epinephrine and norepinephrine
• Stimulus: Hormones from hypothalamus


  Response: Anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones
• Pituitary gland


  Two-lobed organ that secretes nine major hormones
• Neurohypophysis


  • Posterior lobe (neural tissue) and the infundibulum
  • Receives, stores, and releases hormones made in the hypothalamus
• Adenohypophysis


  • Anterior lobe, made up of glandular tissue
  • Makes and secretes a number of hormones
• Posterior Pituitary (Neurohypophysis)


  Has a neural connection with the hypothalamus (hypothalamohypophyseal tract)
• Nuclei of the hypothalamus

  Synthesize oxytocin and antidiuretic hormone (ADH)
• Oxytocin (OT)


  • Causes smooth muscle contraction in uterus and breasts (milk "let down")
  • Stimulated by suckling of baby or baby's cry
  • Under Positive Feedback
  • In Males: sperm release, sexual arousal, orgasm, and bonding with mother and child
• ADH (Anti-diuretic hormone or vasopressin)


  • Increases water reabsorption in kidneys, increased blood volume and BP, decreased urine output and blood osmolarity
  • Stimulated to be released by increased blood osmolarity and low BP
• Anterior Pituitary (Adenohypophysis)


  • The anterior lobe of the pituitary is an outpocketing of the oral mucosa (highly glandular)
  • There is no direct neural contact with the hypothalamus
  • There is a vascular connection, the hypothalamohypophyseal portal system
• Adenohypophyseal Hormones


  • Growth Hormone (GH)
  • Prolactin (PRL)
  • LH and FSH
  • TSH
  • ACTH
  • MSH
• Growth Hormone (GH)


  • Anabolic Hormone: stimulates most cells, but mostly targets bone and skeletal muscle
  • Promotes protein synthesis and encourages lipolysis and glycogenolysis for fuel ("glucose sparing")
  • Most effects are mediated indirectly by insulin-like growth factors ("somatomedins")
  • Peaks at Night
  • Triggered by Increased [aa], Decreased [glucose], and Increased Stress/Exercise
• Patho Check-in: Dwarfism, Gigantism, Acromegaly, and Pygmyism
• Growth Hormone–Releasing Hormone (GHRH)


  Produced in Hypothalamus, stimulates GH release
• Growth Hormone–Inhibiting Hormone (GHIH)


  Produced in Hypothalamus, inhibits GH release; aka "somatostatin"
• Thyroid Gland


  • Composed of follicular cells that produce the glycoprotein thyroglobulin T3/T4
  • Colloid (stored T3/T4) fills the lumen of the follicles
  • Parafollicular cells produce the hormone calcitonin
• Thyroid Hormone (TH)


  • Consists of two closely related iodine-containing compounds: T4 (thyroxine) and T3 (triiodothyronine)
  • 98% of Thyroid Hormones is T4, but most T4 is converted to T3 at target cells
  • Both bind to target receptors, but T3 is ten times more potent than T4
  • Secretion is highest at night