Resumen
¿Delgado u obeso? La masa de tejido adiposo (TA) es función de la interacción de factores genéticos y ambientales. Señales visuales, olfatorias, metabólicas, se integran en el Sistema Nervioso Central (SNC) para mantener la homeostasis energética y conservar la masa del tejido adiposo en un punto de ajuste (set-point). Al disminuir el tejido adiposo, disminuyen la leptina e insulina circulantes lo cual es percibido en el núcleo arcuado hipotalámico. Este punto de control, suprime la vía anorexigénica (vía a-MSH) y estimula la orexigénica (vía NPY/ AGRP). A su vez, la ghrelin (gastrointestinal) estimula la vía NPY/ AGRP lo que promueve la ingesta. Se favorece el anabolismo y se inhibe el gasto energético, restaurándose el tejido adiposo a su set-point. Las señales aferentes integradas en el núcleo arcuado proyectan a corteza, sistema límbico e hipófisis definiendo la conducta alimentaria y la respuesta endocrina. Este sistema de control esta preservado en la obesidad a un set-point elevado.

Palabras clave: set-point, leptina, núcleo arcuado, obesidad, delgadez.

Between thinness and fatness

Abstract
Thin vs Fat? The adipose tissue (AT) mass is a function of genetics and environmental factors. Visual, olfactory, metabolic signals become integrated by the Central Nervous System (CNS) to keep energy homeostasis and AT mass at a set-point. Reduction in AT decrease circulating leptin and insulin which is sensed in the Arcuate Nucleus (AN) of the hypothalamus causing suppression of anorexigenic signals (through ?-MSH) and stimulation of orexigenic signals (through NPY/AGRP). Additional activation of NPY/AGRP neurons by ghrelin (gastrointestinal) promotes feeding. The net balance favors anabolism and a decrease in energy expenditure that ultimately aims to restore AT set-point. Afferent signals integrated in the AN projects to cortex, limbic system and pituitary, defining food seeking behavior and endocrine responses. Evolution had generated multiplicity of factors governing energy balance to ensure sufficient caloric intake, this is preserved in obesity at a higher set-point, making difficult to generate an effective anti-obese therapy.

Keywords: set-point, leptin, arcuate nucleus, obesity, thinnes.