Identification of ghrelin started with the discovery of growth hormone 
secretagogues, continued with the description of ghrelin receptors and ended 
with the elucidation of the chemical structure of ghrelin. However, several 
issues concerning the role of ghrelin in physiological and pathophysiological 
processes are still under investigation. Most of the ghrelin produced in the 
body is secreted in the stomach, but it is also expressed in the hypothalamus, 
pituitary, pancreas, intestine, kidney, heart and gonads. Ghrelin stimulates 
growth hormone secretion via growth hormone secretagogue receptors. Ghrelin 
secretion in the stomach depends on both acute and chronic changes in 
nutritional status and energy balance. Current data support the hypothesis that 
the stomach, in addition to its important role in digestion, not only influences 
pituitary hormone secretion but, via ghrelin production, it also sends 
orexigenic (appetite increasing) signals to hypothalamic nuclei involved in the 
regulation of energy homeostasis. In addition to these main effects, ghrelin 
influences insulin secretion and glucose metabolism and it may exert potentially 
important effects on cardiovascular and gastrointestinal functions. Because of 
its effects on a large number of physiological functions, ghrelin may be 
involved in the pathomechanism of several human disorders, including 
disturbances of appetite, energy homeostasis and glucose metabolism. Further 
research might lead to a better understanding of the pathophysiology of ghrelin 
and might provide more effective therapy for the above disorders.