Outline the structure (20% of marks) and function (80% of marks) of the hypothalamus
Most candidates understood the endocrine functions of the hypothalamus, and to some degree its interactions with the pituitary. Fewer candidates mentioned the importance of the hypothalamus as an integrator for the autonomic nervous system, or its roles in arousal/emotions. Many candidates had only a vague idea of the structure of the hypothalamus, while the best candidates were able to relate function to structure quite accurately.
One could counter by saying that most successful ICU consultants also have "only a vague idea of the structure of the hypothalamus" and are still somehow able to function, casting a shadow over the usefulness of this assessment item. Still, here we are trying to create a model answer for this SAQ. Thus:
- Structure of the hypothalamus
- Small (4cm3) diencephalon 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)
- These hormones are released into a portal system which connects the hypothalamus and pituitary
- Hypothalamic-pituitary portal circulation:
- Feeding artery: superior hypophyseal artery
- Primary capillary bed: hypothalamic capillaries and posterior pituitary capillaries
- Portal vessel: the long portal vessels and short portal vessels
- Secondary capillary bed: capillaries of the anterior pituitary
- Draining vein: hypophyseal veins, which variably drain into the cavernous sinuses
Page, R. B. "The pituitary portal system." Morphology of Hypothalamus and its Connections. Springer, Berlin, Heidelberg, 1986. 1-47.
Lechan, Ronald M., and Roberto Toni. "Functional anatomy of the hypothalamus and pituitary." Endotext [Internet] (2016).
Pop, Miana Gabriela, Carmen Crivii, and Iulian Opincariu. "Anatomy and function of the hypothalamus." Hypothalamus in health and diseases. IntechOpen, 2018.