Neuroendocrinology

• What is neuroendocrinology?

  The study of how the nervous system and endocrine system interact to regulate physiological processes. It focuses on how the brain controls hormonal activity in the body through neuroendocrine cells.
• What are neuroendocrine cells and what is their function?

  Are specialised neurons that receive neural signals and respond by releasing hormones into the bloodstream, thus linking the nervous system to the endocrine system.
• What is neuroendocrine signalling?

  A form of cell-to-cell communication where neurons release hormones (instead of neurotransmitters) into the blood to affect distant target organs.
• Where are neuroendocrine cells mainly located in the human body?

  Primarily in the hypothalamus, especially in the paraventricular and supraoptic nuclei. These cells project to the posterior and anterior pituitary glands.
• How does the hypothalamus control the posterior pituitary (neurohypophysis)?

  Magnocellular neuroendocrine cells in the hypothalamus directly release hormones (e.g., oxytocin and vasopressin) into the bloodstream via axon terminals in the posterior pituitary.
• How does the hypothalamus control the anterior pituitary (adenohypophysis)?

  Parvocellular neuroendocrine cells release releasing or inhibiting hormones into the hypophyseal portal system, which regulates hormone secretion from anterior pituitary cells.
• What is the hypophyseal portal system?

  A network of blood vessels that connects the hypothalamus to the anterior pituitary, allowing neurohormones to travel directly and rapidly to the pituitary.
• What is an example of a neuroendocrine feedback loop?

  The hypothalamic-pituitary-adrenal (HPA) axis:

  1. CRH from the hypothalamus stimulates ACTH release from the anterior pituitary.
  2. ACTH stimulates cortisol release from the adrenal cortex.
  3. Cortisol exerts negative feedback on the hypothalamus and pituitary.
• What are the key characteristics of neuroendocrine signalling compared to synaptic signalling

  • Slower onset but longer-lasting effects
  • Acts over longer distances via bloodstream
  • Uses hormones instead of neurotransmitters
  • Targets multiple tissues or organs
• What types of hormones are typically released in neuroendocrine signalling?

  Peptide hormones (e.g., oxytocin, vasopressin, CRH, TRH) and, indirectly, steroid hormones via downstream endocrine glands (e.g., cortisol, testosterone).
• Why is neuroendocrine signalling important for homeostasis?

  It allows the brain to coordinate complex physiological processes (e.g., stress, metabolism, growth, reproduction) by integrating neural and hormonal inputs.
•  What is the anatomical location of the hypothalamus?

  Located below the thalamus and above the brainstem; it forms the floor and part of the walls of the third ventricle in the diencephalon.
• Which part of the brain connects the nervous system to the endocrine system?

  The hypothalamus connects the nervous system to the endocrine system via the pituitary gland.
• What is the role of the hypothalamus in neuroendocrine regulation?

  The hypothalamus integrates neural signals and regulates endocrine functions by producing releasing and inhibiting hormones that control pituitary hormone secretion.
• What are the two major portions of the pituitary gland?

  The anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).
• How is the anterior pituitary connected to the hypothalamus?

  Through the hypophyseal portal system, a network of blood vessels that transports hypothalamic releasing/inhibiting hormones directly to the anterior pituitary.
• How is the posterior pituitary connected to the hypothalamus?

  Through the hypothalamo-hypophyseal tract, a bundle of axons from magnocellular neurons in the hypothalamus that extend into the posterior pituitary.
• Which hypothalamic nuclei produce hormones secreted by the posterior pituitary?

  The paraventricular nucleus (PVN) and supraoptic nucleus (SON) produce oxytocin and vasopressin (ADH), respectively.
• What hormones are secreted by the posterior pituitary, and what are their functions?

  Oxytocin – stimulates uterine contractions and milk ejection;ADH (vasopressin) – promotes water reabsorption in the kidneys and vasoconstriction.
• What type of cells are found in the anterior pituitary and what do they secrete?

  • Somatotrophs – GH
  • Lactotrophs – Prolactin
  • Thyrotrophs – TSH
  • Gonadotrophs – LH and FSH
  • Corticotrophs – ACTH
• Name the key hypothalamic releasing hormones and the pituitary hormones they regulate.

  • TRH → stimulates TSH
  • CRH → stimulates ACTH
  • GnRH → stimulates LH & FSH
  • GHRH → stimulates GH
  • Somatostatin → inhibits GH
  • Dopamine → inhibits prolactin
• What structural feature protects the pituitary gland?

   The pituitary gland sits in the sella turcica, a bony cavity of the sphenoid bone.
•  How does negative feedback regulate hypothalamic-pituitary hormone secretion?

  Target gland hormones (e.g., cortisol, thyroid hormones) inhibit further release of hypothalamic and pituitary hormones via long-loop negative feedback.
• What is the median eminence and what is its role?

  A part of the hypothalamus where neurosecretory neurons release regulatory hormones into the hypophyseal portal system, influencing the anterior pituitary.
• What is a neuroendocrine reflex?

  A physiological response in which a sensory stimulus leads to hormone release via a neural pathway, combining elements of the nervous and endocrine systems.
• What are the two main components of a neuroendocrine reflex arc?

  1. Afferent limb – sensory input transmitted via neurons
  2. Efferent limb – hormonal output through endocrine cells
•  Give a classic example of a neuroendocrine reflex involving oxytocin.

  The milk let-down reflex: stimulation of the nipple during suckling sends signals to the hypothalamus, triggering oxytocin release from the posterior pituitary, which causes milk ejection from the mammary glands.
•  Describe the neural pathway involved in the milk let-down reflex.

  1. Suckling stimulates mechanoreceptors in the nipple
  2. Afferent signals travel via the spinal cord to the hypothalamus
  3. Hypothalamic neurons stimulate the posterior pituitary
  4. Oxytocin is released into circulation
  5. Oxytocin causes myoepithelial contraction in mammary glands
• What hormone is involved in the milk let-down reflex, and from where is it released?

  Oxytocin, released from the posterior pituitary (neurohypophysis).
•  What is the role of oxytocin in childbirth as a neuroendocrine reflex?

  Stretching of the cervix during labour activates stretch receptors, sending signals to the hypothalamus. This leads to increased oxytocin secretion, which stimulates uterine contractions—a positive feedback loop.
•  How does the childbirth reflex demonstrate positive feedback?

  Uterine contractions cause more cervical stretching, which leads to more oxytocin release and stronger contractions until delivery occurs.
•  Give an example of a neuroendocrine reflex involving prolactin.

  Suckling stimulates afferent neurons that inhibit dopamine release from the hypothalamus. This reduces inhibition of prolactin secretion from the anterior pituitary, promoting milk production.
• Why is prolactin regulation considered a neuroendocrine reflex, even though it is controlled by inhibition?

  Because neural input (suckling) affects hypothalamic inhibition (via dopamine), leading to a hormonal output (prolactin), fulfilling the criteria for a neuroendocrine reflex.
• Compare the roles of oxytocin and prolactin in lactation.

  • Oxytocin: Milk ejection via contraction of myoepithelial cells
  • Prolactin: Milk production via stimulation of mammary alveoli
• What is the primary function of growth hormone (GH) in the body?

  GH stimulates growth of tissues (especially bone and muscle), increases protein synthesis, promotes lipolysis (fat breakdown), and raises blood glucose levels (anti-insulin effect).
• Where is growth hormone (GH) synthesised and secreted from?

  GH is synthesized and secreted by somatotrophs in the anterior pituitary gland (adenohypophysis).
• Which hypothalamic hormones regulate GH secretion, and how do they act?

  • GHRH (Growth Hormone-Releasing Hormone): Stimulates GH release from anterior pituitary.
  • Somatostatin (GHIH – Growth Hormone-Inhibiting Hormone): Inhibits GH release.
• What is the role of IGF-1 (Insulin-like Growth Factor 1) in GH action?

  GH stimulates the liver to produce IGF-1, which mediates many of GH’s growth-promoting effects (e.g. cell proliferation, cartilage growth, bone growth) and provides negative feedback to inhibit GH and GHRH release.
• How does GH influence metabolism?

  • Increases protein synthesis
  • Promotes fat breakdown (lipolysis)
  • Decreases glucose uptake in tissues (anti-insulin effect)
  • Increases gluconeogenesis in liver
• Describe the feedback loop that regulates GH secretion.

  1. Hypothalamus releases GHRH → stimulates GH release
  2. GH stimulates IGF-1 production in liver
  3. IGF-1 inhibits GH and GHRH release and stimulates somatostatin (GHIH) → suppresses GH secretionThis forms a negative feedback loop.