Infographic 9.2: Mechanisms in Hunger Regulation

The photograph of the two rats shows one normal sized rat and one abnormally large rat. Text under the photograph reads “The rat on the right weighs 988 grams— about as much as a pineapple. Researchers destroyed this animal’s ventromedial hypothalamus, which prevented the communication of satiety signals. This resulted in extreme overeating. The more typical rat on the left, which has no such damage to the hypothalamus, weighs about a third as much (King, 2006).” Underneath the photograph of the rat is the photograph of a brain scan, which has the hypothalamus highlighted on it. The hypothalamus is a round, marble-sized structure at the approximate vertical and horizontal center of the head. The photograph of a woman shows the woman eating an apple. An illustrated rendition of her intestines, fat deposits, and brain has been superimposed over the photograph and labeled. There are two different types of signals shown in the illustration - safety signals and hunger signals. There are two safety signals - Cholecystokinin (CKK), and Leptin. Text for CKK is attached to the intestines and reads “Hormone released from the Gastrointestinal tract that aids digestion.” Text for Leptin is attached to a fat deposit on the woman’s side, and reads “A protein hormone released by fat cells to communicate information about the body’s fat stores.” There are three Hunger signals: Orexins, ghrelin, and Insulin. Text for Orexins is attached to the hypothalamus, and reads “Hormones produced in the lateral hypothalamus. Stimulate increased eating.” Text for Ghrelin is attached to the stomach and reads “Hormone released by empty stomach. Levels rise when we are hungry.” Text for Insulin is attached to the pancreas and reads “Hormone produced by pancreas in response to food intake; controls levels of glucose in the bloodstream. A drop in glucose is a primary hunger signal for the body.” The illustrated cross-section of the brain shows a horizontal section, with the top of the brain above and the bottom of the brain below. In the center of the bottom of the brain section are two structures, the ventromedial hypothalamus and the lateral hypothalamus. The ventromedial hypothalamus is shown as a pair of small ovals, mirrored around the center of the brain. Attached text explains that the ventromedial hypothalamus “works to decrease appetite”. The Lateral hypothalamus is shown as a pair of ovals that are approximately twice as large as those in the ventromedial hypothalamus, and are also mirrored around the center, directly beside the outer edges of each of the smaller oval. Attached text explains that the lateral hypothalamus “works to increase appetite”. Text attached to the illustration reads “Different divisions of the hypothalamus perform distinct functions in relation to regulating hunger.”