Encyclopedia of Pathology
Definition The hypothalamus is a key brain site for integration of multiple biologic essential functions and consequently is connected to several sites of the brain through distinct afferent and efferent pathways carrying information to the forebrain and limbic system, the visual system, the thalamus, the brain stem, the spinal cord, and the pituitary gland. These biologic functions include: (1) maintenance of homeostasis including regulation of blood pressure, body temperature, fluid and
... olyte balance, body weight, and circadian rhythm via activation and inhibition of the parasympathetic and sympathetic division of the autonomic nervous system; (2) regulation of drive-related behavior and emotion in response to hunger, thirst, sex drive, rage, and cravings; (3) modulation of memory via the mammillary bodies and as part of the limbic system; and (4) control of the pituitary gland functions (Molina 2018). The hypothalamus participates in two main endocrine regulatory processes of the pituitary gland: (1) the production of the two posterior pituitary hormones, vasopressin and oxytocin, and (2) the production and secretion of releasing and inhibiting hormones that regulate the secretion of pituitary hormones by the anterior pituitary lobe. The interactions of the hypothalamus and the pituitary gland form a complex neurohormonal circuit essential for maintenance of a normal endocrine status. Macroscopy The hypothalamus is located inferiorly to the thalamus forming the lowest walls and floor of the third ventricle, and lies above the pituitary to which it is connected by the pituitary stalk. The hypothalamus has well-defined anatomical boundariesit is anteriorly bordered by the anterior commissure, optic chiasm, and lamina terminalis; posteriorly and superiorly by the midbrain tegmentum and mammillary bodies; dorsally by the hypothalamus sulcus; and laterally by the subthalamic nuclei (Kahle and Frotscher 2010). The entire structure weighs about 5 g and constitutes less than 1% of the brain volume. The anterior portion of the hypothalamus, also called the poorly myelinated hypothalamus, is the site of secretion of numerous neuropeptides by several ill-defined neuronal nuclei that are functionally related. Afferent and efferent connections bring these nuclei into contact with nearby as well as remote portions of the central nervous system.