the hypothalamus

• the hypothalamus controls/modifies the function of endocrine and exocrine glands

  • pancreas, adrenal, pineal, salivary glands are all directly innervated and regulated by the nervous system
• the hypothalamus is responsible for coordinating, directly or indirectly, almost every basic function of the body

  • destruction of the hypothalamus is not compatible with life
• endocrine functions of the hypothalamus (physiological coordination)

  • by the release from neurons in various hypothalamic nuclei of specific releasing hormones
  • control thyroid, adrenal gland and gonads
  • regulat GH and PRL secretion
  • regulate oxytocin (uterine contractions, lactation) and vasopressin (water balance) release from the posterior pituitary
• non-endocrine functions of the hypothalamus (homeostatic/external -> internal coordination):

  • regulate body temperature
  • regulate food intake
• who talks to the hypothalamus?

  • almost everyone
  • brainstem
  • fornix
  • stria terminalis
• fornix


  white matter tract from the hippocampus (terminates in the medial mammillary nucleus of the mammillary bodies)
• stria terminalis


  white matter tract from the amygdala (indirect)
• where does the hypothalamus connect?

  pretty much with any part of the nervous system, directly or indirectly

  • bidirectional pathways
  • fornix
  • stria terminalis
• papez (medial limbic) circuit


  emotional expression
• medial forebrain bundle

  • involved in the integration of reward and pleasure
  • also bidirectional
• rostral caudal axis of nuclei in the hypothalamus

  • preoptic area
  • anterior hypothalamus
  • middle hypothalamus
  • posterior hypothalamus
• preoptic area

  medial preoptic nucleus
• anterior hypothalamus


  suprachiasmatic nucleus (SCN); paraventricular nucleus (PVN); periventricular nucleus and supraoptic nuclei (SON)
• middle hypothalamus

  arcuate nucleus; ventromedial nucleus and median eminence
• posterior hypothalamus

  arcuate nucleus, tuberomammillary nucleus
• molecules in blood

  • minerals, nutrients
  • generally about homeostasis
  • these signals tend to bypass the hypothalamus, at least in part
  • ex: low blood calcium -> parathyroid gland -> release parathyroid hormone -> increase blood calcium by taking calcium from bone store (but hypothalamus finds out via gastric and parathyroid aspect of vagus)
  • ex: high blood glucose -> pancreas -> insulin release
  • hypothalamus -> ? -> blood glucose changes -> pancreas -> insulin changes
• external and internal stimuli

  • lots of signals from outside or inside the body
  • the environment causes changes in production of releasing hormones
  • helps body adapt to the change in the environment
  • lots of these stimuli are filtered by the nervous system

  1. molecules in the blood
  2. other hormones
  3. nervous system signals
• other hormones

  • hormonal feedback induces tropic hormones
  • stimulate the secretion of other hormones
  • ex: GHRH from hypothalamus -> anterior pituitary -> GH -> hypothalamus -> somatostatin release
  • ex: TSH from anterior pituitary -> thyroid -> T3 and T4 -> hypothalamus -> decrease TRH
• nervous system signals

  • input from other cells in the nervous system
  • ex: amygdala tells hypothalamus and then...
  • sympathetic preganglionic neurons -> adrenal glands -> adrenaline
  • ex: sympathetic -> pancreatic beta cells -> inhibit insulin
  • parasympathetic -> pancreatic beta cells -> stimulate insulin
• tropic


  causing or driving

  • ex: ACTH -> acts on the adrenals to cause cortisol secretion
• trophic 


  supporting, growth factor

  • ex: ACTH -> survival of adrenal cells that produce cortisol
• releasing hormones

  • function to control the secretions of the pituitary hormones
  • primarily anterior pituitary hormones
  • positive or negative regulation
  • meaning - can stimulate or inhibit the release of another hormone
  • released into the closed portal system
• closed portal system

  • median eminence: part of the hypothalamus from which releasing hormones are released
  • median eminence is continuous with the posterior pituitary by way of the infundibular stalk (hollow)
  • median eminence is not continuous with the anterior pituitary
  • hormones have to be released into the primary plexus
• median eminence


  part of the hypothalamus from which releasing hormones are released
• three zones of the median eminence:

  1. ependymal zone
  2. internal zone (zona interna)
  3. external zone (zona externa)
• ependymal zone: forms floor of the 3rd ventricle

  • tight junctions
  • tanycytes: special cells with bleb-like protrusions and microvilli that extend into the CSF (ventricle) and processes extending into the ME
  • one of the functions of the ependymal zone is to create a barrier to the brain, preventing substances released into the periportal capillary spaces from entering the CSF
• the internal zone (zona interna)

  • axons of magnocellular neurons
  • SON and PVN axons -> posterior pituitary
• the external zone (zona externa)

  • blood vessel zone
• The hypothalamic-hypophyseal vascular (portal) system is a closed system.
• Circumventricular organs lack a normal blood brain barrier.
• The median eminence is a circumventricular organ characterized by fenestrated capillaries and a rich portal plexus.
• The purpose of the hypothalamic-hypophyseal vascular (portal) system is to allow hormones out and let other substances in the blood make contact with the central nervous system without getting loose in the brain.
• A number of different arteries, arising from the internal carotid artery, supply blood to the brain.
• The superior hypophyseal artery arises from the internal carotid artery and ends in the primary portal plexus.
• When these arteries enter the median eminence, they branch to give fenestrated capillaries.
• These capillaries are the primary portal plexus in the upper median eminence.
• portal systym

  primary plexus: first stop for releasing hormones

  • no blood brain barrier between capillaries and pericapillary space
  • releasing hormones picked up from pericapillary space

  second plexus

  • fenestrations let releasing hormones get into the extracellular space around the anterior pituitary
• what is the advantage of a closed portal system?

  economy of the system

  • closed systems imply that there is no dilution of the neurohormone released from the hypothalamus
  • small amounts of neurohormone can bind cells which contain cognate receptors in the pituitary and have a large effect
  • small amounts of hormone need to be synthesized in hypothalamic neurons
• the advantage of the closed portal system can be seen when the mPOA is electrically stimulated and GnRH is released. there is only a small change in stored GnRH content in the hypothalamus but a massive LH and FSH release
• classification of releasing hormones (RH)

  2 different ways downstream hormones can be controlled by releasing hormones:

  1. a single releasing hormone positively regulates anterior pituitary secretion
  2. TRH, GnRH, CRH
  3. a pair of releasing hormones modulates anterior pituitary secretion
  4. GHRH, GIH (regulates GH)
  5. PRF, PIF (regulates PRL)