Question 16

Outline the role of the hypothalamus.

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College Answer

This question required candidates to integrate parts of the syllabus that are often not presented together in the reference texts. Many candidates provided only an incomplete list of the roles of the hypothalamus as their answer which did not score enough marks to pass. Additionally, presenting information succinctly and in a format that demonstrated an understanding of priority of function with respect to the CICM syllabus, was critical for time management and ensuring that more the important/major roles were presented in more detail. This question required candidates to cover roles including autonomic control, thermoregulation, hormonal regulation, body rhythms and regulation of drives with feedback control mechanisms where appropriate. Those who scored well demonstrated a comprehensive breadth of knowledge of these areas as well as giving the pertinent points around areas of positive and negative feedback and the sensor areas and effector responses required to answer an outline question.

Discussion

  • Structure of the hypothalamus
    • Small (4cm3) d​iencephalon structure which sits under the 3rd ventricle
    • Surrounded laterally by the basal ganglia, limited anteriorly by the lamina terminalis, and posteriorly  by the tegmentum and periaqueductal grey matter
    • Connected to the pituitary by the infundibulum inferiorly
    • Composed of interconnected nuclei with distinct regulatory functions
  • Functions of the hypothalamus
    • Thermoregulation (preoptic, anterior, posterior nuclei)
    • Homeostasis of body fluid tonicity (supraoptic nucleus)
    • Autonomic regulation (paraventricular nucleus)
    • Arousal and emotions (preoptic, anterior, dorsomedial and mamillary nuclei)
    • Regulation of satiety (lateral complex of nuclei)
    • Circadian rhythm (suprachiasmatic nucleus)
    • Control of pituitary endocrine function (arcuate nucleus)
  • Hypothalamic hormones:
    • Regulate endocrine function, using the pituitary as a "cascading amplifier"
      • Thyrotropin-releasing hormone (TRH)
      • Gonadotropin-releasing hormone (GnRH)
      • Growth hormone-releasing hormone (GHRH)
      • Corticotropin-releasing hormone (CRH)
      • Somatostatin
      • Dopamine
      • These hormones are released into a portal system which connects the hypothalamus and pituitary 
    • Synthesis and release of hormones directly:
      • Vasopressin
      • Oxytocin
      • These are produced in cell bodies of the supraoptic and paraventricular nuclei of the hypothalamus and then transported via their axons to the posterior pituitary whee they are released from nerve terminals.

References

Pop, Miana Gabriela, Carmen Crivii, and Iulian Opincariu. "Anatomy and function of the hypothalamus." Hypothalamus in health and diseases. IntechOpen, 2018.

Lang, J. "Surgical anatomy of the hypothalamus." Acta neurochirurgica 75.1 (1985): 5-22.

Spiegel, Ernst Adolf, et al. "THE CENTRAL MECHANISM OF THE EMOTIONS: (Experiences with Circumscribed Thalamic Lesions)." American journal of psychiatry 108.6 (1951): 426-432.

Kanda, Shinji. "Evolution of the regulatory mechanisms for the hypothalamic-pituitary-gonadal axis in vertebrates–hypothesis from a comparative view." General and comparative endocrinology 284 (2019): 113075.

Norris, D. O., et al. "The hypothalamus–pituitary system in non-mammalian vertebrates." Vertebrate endocrinology (2013): 151-205.

Lemaire, Laurence A., et al. "The hypothalamus predates the origin of vertebrates." Science Advances 7.18 (2021): eabf7452.

Hall, Reginald, and Antonio Gomez-Pan. "The hypothalamic regulatory hormones and their clinical applications." Advances in Clinical Chemistry 18 (1976): 173-212.