The Hypothalamus Flashcards
The hypothalamus is made up of distinct nuclei (collections of cell bodies) that include the
supraoptic, paraventricular (PVN), suprachiasmatic, ventromedial, dorsomedial, and arcuate nuclei.
It secretes neurohormones from neurons that control
the synthesis and secretion of the anterior pituitary hormones.
The nomenclature of these neurohormones describes their actions and can be subdivided into
‘releasing’ and ‘inhibiting’ hormones
The axons of these neurons all converge in the median eminence to deposit their endocrine products into the capillary plexus that empties into the portal blood vessels of the
anterior pituitary permitting hypothalamic neurohormone delivery in a rapid concentrated fashion to the anterior pituitary.
The neurohormone gonadotropin-releasing hormone (GnRH) stimulates the
anterior pituitary to release FSH and LH and is thus involved in folliculogenesis.
The preoptic area (POA) of the hypothalamus contains many GnRH neurons that
project (along with the GnRH neurons in the ARC) to the median eminence.
GnRH secretion is influenced by the neuropeptide
kisspeptin.
The kisspeptin system is critical for maturation and function of the reproductive axis including
the onset of puberty.
Kisspeptin neurons (whose cell bodies reside in the ARC and rostral hypothalamus) interact with
GnRH neurons influencing GnRH secretion by several different mechanisms.
There is evidence that hypothalamic kisspeptin also mediates
sex-steroid feedback and metabolic input on the reproductive axis.
Other active factors exert important actions at the level of the anterior pituitary. Thus the specific protein hormone-secreting endocrine cells of the anterior pituitary must process signals not only from the hypothalamic hormone(s)but also
additional centrally derived factors that are secreted into the hypophyseal portal blood.
