Published on March 6, 2014
HUNGER Jonel Joshua Rosales
WHAT IS HUNGER? • It is a feeling of discomfort or weakness caused by lack of food, coupled with the desire to eat. • Having a strong desire or craving for.
How the digestive system influence food selection? • • • • • Digestion begins in the mouth. Swallowed food travels down the esophagus to the stomach. The stomach stores food for a time, and then a round sphincter muscle opens at the end of the stomach to release food to the small intestine. The small intestine has enzymes that digest proteins, fats, and carbohydrates. The large intestine absorbs water and minerals and lubricates the remaining materials to pass as feces.
Biological explanation for hunger • Hunger drive is triggered by the lowering of the sugar level of the blood, but our eating is controlled by the hypothalamus. • After the glucose supply has been replenished, ventromedial nucleus turns off the hunger drive. • If the body needs sugar, the person will be motivated to take plenty of sugar, which is called the innate wisdom of the body.
Enzymes and consumption of dairy products • Newborn mammals survive at first on mother’s milk. As they grow older, they stop nursing for several reasons: The milk dries up, the mother pushes them away, and they begin to try other foods. • LACTASE – an intestinal enzyme which is necessary for metabolizing lactose. • LACTOSE – a sugar in milk. • From then on, milk consumption causes stomach cramps and gas. • Many adults have enough lactase levels to consume milk and other dairy products throughout life. • Worldwide, however, most adults cannot comfortably tolerate large amounts of milk products.
Other influences on food selection • For a carnivore (meat eater), selecting a satisfactory diet is relatively simple. • herbivores (plant eaters) and omnivores (those that eat both meat and plants) must distinguish between edible and inedible substances and find enough vitamins and minerals • One way to do so is to learn from the experiences of others. • First, you would select sweet foods, avoid bitter ones, and eat salty or sour foods in moderation. Most sweets are nutritious, and bitter substances are harmful. • Second, you would prefer anything that tasted familiar. familiar foods are safe, and new foods may not be. • Third, you would learn the consequences of eating each food you try.
Other influences on food selection • This phenomenon is known as conditioned taste aversion. It is a strong phenomenon that occurs reliably after just a single pairing of food with illness, even if the illness came hours after the food.
• Factors controlling hunger include distension of the stomach and intestines, secretion of CCK by the duodenum, and the availability of glucose and other nutrients to the cells. • Appetite depends partly on the availability of glucose and other nutrients to the cells. The hormone insulin increases the entry of glucose to the cells, including cells that store nutrients for future use. Glucagon mobilizes stored fuel and converts it to glucose in the blood. Thus, the combined influence of insulin and glucagon determines how much glucose is available at any time.
BRAIN MECHANISMS • Hunger depends on the contents of your stomach and intestines, the availability of glucose to the cells, and your body’s fat supplies, as well as your health and body temperature. • many kinds of information impinge onto two kinds of cells in the arcuate nucleus of the hypothalamus, which is regarded as the “master area” for control of appetite. • Axons extend from the arcuate nucleus to other areas of the hypothalamus.
• Much of the output from the arcuate nucleus goes to the paraventricular nucleus of the hypothalamus. • It inhibits the lateral hypothalamus, an area important for eating. So the paraventricular nucleus is important for satiety. • Axons from the satiety-sensitive cells of the arcuate nucleus deliver an excitatory message to the paraventricular nucleus, which is a type of chemical called a melanocortin. • Melanocortin receptors in the paraventricular nucleus are important for limiting food intake, and deficiencies of this receptor lead to overeating.
Arcuate Nucleus & Paraventricular Hypothalamus • The arcuate nucleus of the hypothalamus has one set of neurons sensitive to hunger signals and a second set sensitive to satiety signals. • The hunger-sensitive cells receive input from the taste pathway. • Another input to the hunger-sensitive cells comes from axons releasing the neurotransmitter ghrelin. • The stomach releases ghrelin during a period of food deprivation, where it triggers stomach contractions. • It also acts on the hypothalamus to decrease appetite and acts on the hippocampus to enhance learning.
Lateral Hypothalamus • The lateral hypothalamus controls insulin secretion, alters taste responsiveness, and facilitates feeding in other ways. • The lateral hypothalamus contributes to feeding in several ways: • Axons from the lateral hypothalamus to the NTS (nucleus of the tractus solitarius), part of the taste pathway, alter the taste sensation and the salivation response to the tastes. • Axons from the lateral hypothalamus extend into several parts of the cerebral cortex, facilitating ingestion and swallowing and causing cortical cells to increase their response to the taste, smell, or sight of food
Lateral Hypothalamus • The lateral hypothalamus increases the pituitary gland’s secretion of hormones that increase insulin secretion. • The lateral hypothalamus sends axons to the spinal cord, controlling autonomic responses such as digestive secretions.
Somatosensory cortex (taste perception) Nucleus accumbens (control of ingestion and swallowing) Thalamus Prefrontal cortex Hypothalamus (food-seeking behaviors) Nucleus of the tractus solitarius (NTS)
ventromedial hypothalamus • Neuroscientists have known since the 1940s that a large lesion centered on the ventromedial hypothalamus (VMH) leads to overeating and weight gain. • damage limited to the ventromedial hypothalamus does not consistently increase eating or body weight. • To produce a large effect, the lesion must extend outside the ventromedial nucleus to invade nearby axons, especially the ventral noradrenergic bundle.
Multiple controls of hunger • Eating is controlled by many brain areas that monitor blood, glucose, stomach distension, duodenal contents, body weight, fat cells, hormones, and more. • However, the complexity of the system also provides a kind of security: If one part of the system makes a mistake, another part can counteract it. • Perhaps we should be even more impressed by how many people eat more or less appropriately. • The regulation of eating succeeds not in spite of its complexity but because of it.
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