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Some of our finest [ about ] Approved Articles (102) Developed Articles (over 900) "I was brought up to believe that the only thing worth doing was to add to the sum of accurate information in the world." —Margaret Mead Draft of the Week [ about ] There are tens of thousands of species, cultivars and varieties in the orchid family, the largest family of flowering plants. The word orchid may refer to any of the botanical family Orchidaceae, or, more often among lay persons, any of thousands of flowers called "orchids". Orchids have been cultivated for centuries. They include rare and recent discoveries such as the tiny Genoplesium plumosum, the large, showy orchids which are featured in bouquets and corsages, and 'food' orchids such as Vanilla. A few orchids have insignificant flowers but are grown for their foliage. Most orchids are epiphyte plants; they do not root in soil, and must gain all their water and nutrients from the air and rain. Orchids have evolved to make optimal use of these scarce resources. Some keep water in thickened, almost succulent stems, called pseudobulbs, others have highly porous roots covered by a spongy layer, that can absorb humidity from the air; other store water in thick leaves; and other terrestrial orchids in small root tubers. Some species go through long periods of rest when their metabolism is reduced, followed by a fast growth, blooming when resources are abundant. Many species lose their leaves to avoid dehydration during droughts, or while they are resting. [more...] New Draft of the Week [ about ] A major breakthrough in the study of appetite regulation came in 1994 when the molecular geneticist Jeffrey Friedman discovered the adiposity signal leptin. By studies of an inbred line of obese mice, the ob/ob mice which were thought to lack a satiety signal, Friedman and colleagues found that 'ob' codes for a gene that coded for a novel peptide hormone, which they called leptin, from the Greek ‘leptos’ meaning thin. Mice deficient in this gene are morbidly obese and this obesity can be reversed by giving the mice leptin. The leptin receptor was found in 1995 and is a member of the cytokine receptor family. Leptin is a signaling molecule secreted from adipocyte cells into the blood, and the plasma concentration of leptin is thus proportional to the total body fat mass. Leptin is transported into the brain from the blood, where it suppresses apetite by its effects on specific neurones in the brain that express leptin receptors; in particular on neurons of the arcuate nucleus and ventromedial nucleus of the hypothalamus. Leptin receptor mRNA is found primarily in the hypothalamic arcuate nucleus, ventromedial nuclei and dorsomedial hypothalamic nuclei, regions that are known to be involved in appetite control. [more...]