Lecture 27 - Neuro-Endocrine Connection

• Hypothalamus


  Connected to the posterior pituitary by neurons with axons extending to the gland, allowing for direct release of hormones
• Hypothalamus


  Releases hormones into a blood portal system to regulate the release of anterior pituitary hormones
• Posterior pituitary hormones


  • Made in hypothalamic neuron cell bodies
  • Travel down the axon to be stored in the axon terminals until required
  • Released into the main bloodstream when an action potential depolarises the axon terminal
• Posterior pituitary hormones


  • Oxytocin
  • Anti-Diuretic Hormone (ADH)
• Oxytocin


  • Water-soluble
  • Stimulates milk release during breastfeeding
  • Stimulates the contraction of uterine muscles during childbirth
• Anti-Diuretic Hormone (ADH)


  • Water-soluble
  • Stimulates the kidney to reabsorb water when a person is dehydrated
  • One of the hormones secreted during exercise and stress response
• Anterior pituitary


  • Connected to the hypothalamus by a portal bloodstream
  • Hypothalamic neurons secrete 'releasing' or 'inhibiting' hormones that travel via the blood portal system and bind to membrane receptors on anterior pituitary cells, causing them to release an anterior pituitary hormone
• Anterior pituitary hormones


  • Growth Hormone (GH)
  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotropin Hormone (ACTH)
• Growth Hormone (GH)


  • Water-soluble
  • Stimulates the liver, skeletal muscle and adipose (fat) for fuel mobilisation
  • Stimulates the liver to release IGF-1 for growth
• Thyroid Stimulating Hormone (TSH)


  • Water-soluble
  • Stimulates the thyroid gland to release thyroid hormones to increase basal metabolic rate
• Adrenocorticotropin Hormone (ACTH)


  • Water-soluble
  • Stimulates the adrenal gland (cortex) to release cortisol in a daily pattern and during the stress response
• General pattern of hormone release from the hypothalamus

  1. Stimulus triggers the hypothalamus to release a releasing or inhibiting hormone

  2. This hormone travels to the anterior pituitary gland which secretes a pituitary hormone

  3. The pituitary hormone targets an endocrine organ which releases a third hormone

  4. This third hormone negatively feedbacks to reduce the release of anterior pituitary and hypothalamic hormones
• Hypothalamic-Pituitary-Thyroid Axis


  1. Stimulus (exercise, cold stress) triggers the hypothalamus to secrete thyrotropin-releasing hormone (TRH)

  2. TRH moves through a blood portal connection to the anterior pituitary gland which triggers the release of thyroid stimulating hormone (TSH)

  3. TSH moves to the thyroid gland which secretes thyroid hormones T3 and T4

  4. Thyroid hormones negatively feedback to reduce the release of TSH and TRH
• Thyroid gland


  • Wraps around the trachea, just below the 'Adam's Apple'
  • Secretes thyroid hormones (T3 & T4) and calcitonin
• Thyroid hormones (T3 & T4)

  • Made by cells lining the thyroid follicles
  • Increase metabolic activity, growth, and alertness
• Synthesis, storage, and structure of thyroid hormones

  1. Iodine enters thyroid follicle cells and reacts with tyrosine in thyroglobulin to form T3 and T4

  2. Thyroid hormones detach from iodised thyroglobulin as needed

  3. Thyroid hormones travel in blood bound to a carrier protein
• Target cell activation by thyroid hormones

  • Thyroid hormones detach from carrier protein and enter target cell
  • Bind to receptor in nucleus
  • Activate transcription of mRNA and synthesis of proteins
  • Lead to increased basal metabolic rate
• Basal Metabolic Rate (BMR)


  • The energy the body requires for its most basic functions to sustain life
  • Influenced by sex, age, body type, food intake, activity level, and environmental temperature
• Effects of thyroid hormones on BMR

  Increase thermogenesis, oxygen consumption, ATP production and use, and fat and protein breakdown
• Growth Hormone (GH)


  • Plasma concentration fluctuates over a day, highest during sleep
  • Concentration is higher in children than adults, highest during puberty and declines with age
• Direct effects of GH

  • Inhibit muscular uptake of glucose, stimulate protein synthesis in muscle
  • Stimulate glucose synthesis in liver
  • Increase fat breakdown in adipose tissue
• Indirect effects of GH

  Stimulate release of IGF-1 from liver, promoting growth of muscles, bones, and other tissues
• Hypothalamic-Pituitary-Liver Axis


  1. Stimulus (exercise, sleep) triggers hypothalamus to secrete growth hormone releasing hormone and inhibiting hormone

  2. These act on anterior pituitary to secrete GH

  3. GH triggers liver, muscle, and fat to undergo fuel mobilisation and liver to secrete IGF-1

  4. IGF-1 acts in negative feedback to inhibit release of GH-releasing hormone and GH, and increase release of GH-inhibiting hormone