The hypothalamus is at the base of the brain, just below the thalamus on the midline: a small almond-sized region forming the lowest part of the diencephalon, with the pituitary gland hanging from its underside. [1][2]
The 3D brain needs JavaScript. The text below still says where the hypothalamus is and what it does.
Slice
Opens cut by a side (sagittal) slice through the hypothalamus. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Below the thalamus, forming the basal (bottom) part of the diencephalon; it is part of the limbic system. [1]
OpenStax places it below and slightly in front of the thalamus, as the other major region of the diencephalon. [3]
On the midline: it lines the lower front part of the side walls of the third ventricle, below the groove (hypothalamic sulcus) that separates it from the thalamus. [4]
The pituitary gland protrudes from its underside, seated in the sella turcica, a hollow in the sphenoid bone of the skull base. [2]
What it does
Links the nervous system to the endocrine (hormone) system through the pituitary gland. [1]
Makes releasing hormones that stimulate or inhibit the pituitary’s own hormones; they reach the anterior pituitary through a small set of blood vessels, the hypophyseal portal system. [1]
Neurons in its paraventricular and supraoptic nuclei produce oxytocin and vasopressin, which are released from the posterior pituitary. [1][2]
Controls body temperature, hunger, thirst, fatigue, sleep and circadian rhythms, as well as aspects of parenting and attachment behaviour. [1]
Described by OpenStax as the executive region in charge of the autonomic nervous system and the endocrine system, largely regulating homeostasis (keeping the body’s internal conditions steady). [3]
Connections
Pituitary gland: just behind the optic chiasm the floor of the third ventricle extends down into a funnel, the infundibulum, bordered by the tuber cinereum and ending in the posterior lobe of the pituitary. [4]
Hippocampus: fibres of the fornix run through the hypothalamus to its mammillary bodies, which then project to the anterior thalamus. [5]
Amygdala: the stria terminalis carries fibres from the amygdala to the hypothalamus (including its ventromedial nucleus), and the amygdala’s cortical and medial nuclei connect with it. [6][7]
Inside it
Front to back it has four regions (preoptic, supraoptic, tuberal and mammillary); from the midline outwards, three zones (periventricular, intermediate and lateral). [1]
Other names
From Greek hupo, “under”, and thalamos, “chamber”: the part under the thalamus. Plural: hypothalami. [1]
On this model the hypothalamus measures about 18 mm front to back, 20 mm top to bottom and 17 mm side to side (the box it fits in, not its volume). [8]
Centre of the hypothalamus compared with the centre of the left thalamus: 22 mm further forward, 12 mm lower, 13 mm closer to the midline; 28 mm apart in a straight line. [8]
Centre of the hypothalamus compared with the centre of the pituitary gland: 5 mm further back, 13 mm higher; 14 mm apart in a straight line. [8]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.