In addition, the pyloric region of the stomach secretes gastrin, a hormone that increases the secretion of hydrochloric acid into the stomach. The placenta has been shown to secrete progesterone and chorionic gonadotropin. There is evidence that it even contains a substance similar to growth hormone. Insects have a unique hormonal system that includes ecdysone, a steroid that influences molting and metamorphosis, and juvenile hormone, needed for early development. Plants, too, have a hormonal system, which includes the auxins , the gibberellins, the cytokinins, and substances associated with the formation of flowers, tubers, bulbs, and buds.
Ethylene is said to function as a hormone in plants, acting to hasten the ripening of fruits.
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