Hypothalamic Regulation of the Internal Environment

Abstract

Metabolism in the cells, tissues, and organ systems of the body requires a steady supply of oxygen and nutrients, waste removal, and the main- tenance of ionic, osmotic, and temperature conditions within a relatively narrow physiological range. The hypothalamus performs many ongoing computations that are essential to the maintenance (homeostasis) of these internal conditions. It regulates circulation, respiration, digestion, and excretion, as well as body temperature and the relative concentra- tions of extracellular fluid components. It also regulates primal appeti- tive behaviors, such as eating and drinking, that have direct bearing on the internal environment. During development, the hypothalamus influ- ences growth. Finally, the hypothalamus is essential to reproductive functions, such as gamete production, mating, parturition, and mother- ing, which perpetuate not the individual but the species. To accomplish these varied functions, the hypothalamus receives appropriate sensory input (visceral, somatic, olfactory, gustatory, visual) and expresses its output through both synoptic and hormonal routes. The synaptic routes lead, on the one hand, to the preganglionic efferent neurons of the lower visceromotor systems and, on the other, to parts of the brain that control skeletomotor behavior. The hormonal route is a direct regulation of the secretions of the pituitary gland. Most often, the hypothalamus exerts its influence over all three of these avenues simultaneously in a carefully choreographed output.