Orexin A (hypocretin 1) and orexin B (hypocretin 2) are hypothalamic neuropeptides derived from one precursor molecule - preproorexin. They were discovered by two independent teams in 1998. Orexins are involved in regulation of food intake, energy homeostasis, sleep-wake cycle and neuroendocrine functions. There are two receptors for orexins - OXR1/Hcrtrl and OXR2/Hcrtr2. Cells producing these neuropeptides are localized in a small population within the lateral and perifornical hypothalamic area. Fibres of these cells are in many areas of the central nervous system and have mainly an excitatory effect. In animals orexins stimulate food intake. There are several mutations in the orexin system, that cause narcolepsy in mice, dogs and humans. Disorders of food intake are a very serious problem of childhood. Disturbances of the sleep-wake cycle often develop during adolescence and knowledge of involvement of neuropeptides in the pathogenesis of these processes may contribute to improvement of diagnostic and therapeutic procedures. Investigation of orexins in human can reveal the role of the orexin system in the pathogenesis of illnesses and can bring new knowledge in the field of paediatric nutrition, psychiatry and neurology.

        Key words: orexins, hypocretins, hypothalamus, obesity, anorexia nervosa, narcolepsy