Hormones and Metabolism HL

• Endocrine system


  Ductless glands that release chemicals into the blood to regulate body functions
• Hormone

  Chemical messenger that is transported indiscriminately via the bloodstream to act on distant target cells
• Target receptor

  Specific to hormones and will only activate cells or tissues that possess the appropriate target receptor
• Endocrine system


  Slower to initiate, but has a more prolonged response when compared to the nervous system
• Endocrine glands


  Glands that secrete their product (hormones) directly into the bloodstream, rather than through a duct
• Major endocrine glands

  • Pancreas
  • Adrenal gland
  • Thyroid gland
  • Pineal gland
  • Gonads (ovaries and testes)
• Neuroendocrine glands


  Glands that function to link the nervous and endocrine systems
• The hypothalamus and pituitary gland are neuroendocrine glands
• Some organs may also secrete hormones despite not being endocrine glands (e.g. adipose tissue secretes leptin)
• Steroid hormones

  Lipophilic (fat-loving) hormones that can freely diffuse across the plasma membrane of a cell
• Steroid hormones action

  1. Bind to receptors in either the cytoplasm or nucleus of the target cell, to form an active receptor-hormone complex

  2. Activated complex moves into the nucleus and binds directly to DNA, acting as a transcription factor for gene expression
• Steroid hormones

  • Estrogen
  • Progesterone
  • Testosterone
• Peptide hormones


  Hydrophylic and lipophobic (fat-hating) hormones that cannot freely cross the plasma membrane
• Peptide hormones action

  1. Bind to receptors on the surface of the cell, which are typically coupled to internally anchored proteins (e.g. G proteins)

  2. Receptor complex activates a series of intracellular molecules called second messengers, which initiate cell activity
• Signal transduction

  The external signal (hormone) is transduced via internal intermediaries
• The use of second messengers enables the amplification of the initial signal (as more molecules are activated)
• Peptide hormones

  • Insulin
  • Glucagon
  • Leptin
  • ADH
  • Oxytocin
• Hypothalamus


  The section of the brain that links the nervous and endocrine systems in order to maintain homeostasis
• Hypothalamus

  1. Receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses

  2. Secretes neurochemicals (releasing factors) into a portal system targeting the anterior lobe of the pituitary gland

  3. Secretes hormones directly into the blood via neurosecretory cells extending into the posterior pituitary lobe
• Pituitary Gland


  Lies adjacent to the hypothalamus and is in direct contact due to a portal blood system
• Pituitary Gland


  Receives instructions from the hypothalamus and consists of two lobes (anterior and posterior lobe)
• Anterior Lobe


  Also called the adenohypophysis ('adeno' = relating to glands)
• Anterior Lobe

  1. Hypothalamus produces releasing factors, released into portal vessels by neurosecretory cells

  2. Releasing factors cause endocrine cells in the anterior pituitary to release specific hormones into the bloodstream
• Releasing factor

  • GnRH triggers the release of LH and FSH from the anterior pituitary
• Posterior Lobe


  Also called the neurohypophysis ('neuro' = relating to nerves)
• Posterior Lobe

  1. Releases hormones produced by the hypothalamus itself via neurosecretory cells

  2. Neurosecretory cells extend into the posterior lobe from the hypothalamus and release hormones into the blood
• Pituitary Gland

  Often referred to as the 'master gland', as it controls the secretion of other endocrine glands
• Functions controlled by pituitary hormones

  • Metabolism (e.g. TSH activates thyroxin)
  • Adult Development (e.g. LH / FSH trigger puberty)
  • Reproduction (e.g. LH / FSH control menstruation)
  • Growth (e.g. growth hormone promotes growth)
  • Equilibrium / Homeostasis (e.g. ADH and water balance)
• Pituitary hormones target endocrine glands in other organs (e.g. gonads, pancreas, thyroid, mammary gland)
• Pituitary hormones control vital body processes including Metabolism, Adult Development, Reproduction, Growth, and Equilibrium / Homeostasis
• Mnemonic: MARGE
• Growth hormone (somatotropin)


  An anabolic peptide hormone that stimulates growth
• Anabolic


  Promotes growth and regeneration
• Growth hormone reduces the formation of adipose cells
• Growth hormone acts indirectly via insulin growth factor (IGF) to increase muscle mass and bone size
• Growth hormone is used by some athletes as a performance enhancer
• The use of human growth hormone is banned in sports
• Proven cases of doping with human growth hormone are strictly punished
• Traditional urine testing could not detect doping with human growth hormone
• Recent blood tests can identify between natural and artificial variants of growth hormone