The hypothalamus (from Greek ὑπό, under and θάλαμος, room, chamber) is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis).The hypothalamus is located below the thalamus, just above the brainstem and is part of the limbic system.In the terminology of neuroanatomy, it forms the ventral part of the diencephalon.All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond.he hypothalamus is located below the thalamus, just above the brainstem and is part of the limbic system. In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond.