Hunger (motivational state)
Encyclopedia
Hunger is a sensation
experienced when one is required to eat
food
. In contrast Satiety is the absence of hunger; it is the sensation of feeling full. Appetite
is another sensation experienced with eating, however, it differs from hunger; it is the desire to eat food without a physiological need. The often unpleasant feeling of hunger originates from the hypothalamus
releasing hormones that target receptor
s in the liver
. Although a healthy, well-nourished individual can survive for weeks without food intake, the sensation of hunger typically manifests after only a few hours without eating and is generally considered to be unpleasant.
Hunger is also the most commonly used term to describe the social condition of people who suffer from a chronic lack of sufficient food and constantly or frequently experience the physical sensation of hunger. See Hunger (malnutrition).
, they are informally referred to as hunger pangs. Hunger pangs usually do not begin until 12 to 24 hours after the last ingestion of food. A single hunger contraction lasts about 30 seconds, and pangs continue for around 30–45 minutes, then hunger subsides for around 30–150 minutes. Individual contractions are separated at first, but are almost continuous after a certain amount of time. Emotion
al states (anger, joy etc.) may inhibit hunger contractions. Levels of hunger are increased by lower blood sugar
levels, and are higher in diabetics. They reach their greatest intensity in 3 to 4 days and may weaken in the succeeding days, although research suggests that hunger never disappears. Hunger contractions are most intense in young, healthy people who have high degrees of gastrointestinal tonus
. Periods between contractions increase with old age.
and ghrelin
hormone levels results in the motivation
of an organism to consume food. When an organism eats, adipocytes trigger the release of leptin into the body. Increasing levels of leptin result in a reduction of one's motivation to eat. After hours of non-consumption, leptin levels drop significantly. These low levels of leptin cause the release of a secondary hormone, ghrelin, which in turn reinitiates the feeling of hunger.
Some studies have suggested that an increased production of ghrelin may enhance appetite evoked by the sight of food, while an increase in stress may also influence the hormone's production. These findings may help to explain why hunger can prevail even in stressful situations.
in starved spiders, resulting in larger weight gain. This pattern is seen in many animals, including human
s while sleeping. It even occurs in rat
s with their cerebral cortex
or stomachs completely removed. Increased activity on hamster wheel
s occurred when rats were deprived not only of food, but also water or B vitamins
such as thiamine
. This response may increase the animal's chance of finding food, though it has also been speculated the reaction relieves pressure on the home population.
is an intense desire to consume a specific food, as opposed to general hunger. Similarly, thirst
is the craving for fluids. Withdrawal craving
is a "hunger" for administering addictive drugs.
Sensation
Sensation is the fiction-writing mode for portraying a character's perception of the senses. According to Ron Rozelle, “. . .the success of your story or novel will depend on many things, but the most crucial is your ability to bring your reader into it. And that reader will be most completely...
experienced when one is required to eat
Eating
Eating is the ingestion of food to provide for all organisms their nutritional needs, particularly for energy and growth. Animals and other heterotrophs must eat in order to survive: carnivores eat other animals, herbivores eat plants, omnivores consume a mixture of both plant and animal matter,...
food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
. In contrast Satiety is the absence of hunger; it is the sensation of feeling full. Appetite
Appetite
The appetite is the desire to eat food, felt as hunger. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is...
is another sensation experienced with eating, however, it differs from hunger; it is the desire to eat food without a physiological need. The often unpleasant feeling of hunger originates from the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
releasing hormones that target receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s in the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. Although a healthy, well-nourished individual can survive for weeks without food intake, the sensation of hunger typically manifests after only a few hours without eating and is generally considered to be unpleasant.
Hunger is also the most commonly used term to describe the social condition of people who suffer from a chronic lack of sufficient food and constantly or frequently experience the physical sensation of hunger. See Hunger (malnutrition).
Hunger pangs
When hunger contractions start to occur in the stomachStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, they are informally referred to as hunger pangs. Hunger pangs usually do not begin until 12 to 24 hours after the last ingestion of food. A single hunger contraction lasts about 30 seconds, and pangs continue for around 30–45 minutes, then hunger subsides for around 30–150 minutes. Individual contractions are separated at first, but are almost continuous after a certain amount of time. Emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
al states (anger, joy etc.) may inhibit hunger contractions. Levels of hunger are increased by lower blood sugar
Blood sugar
The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...
levels, and are higher in diabetics. They reach their greatest intensity in 3 to 4 days and may weaken in the succeeding days, although research suggests that hunger never disappears. Hunger contractions are most intense in young, healthy people who have high degrees of gastrointestinal tonus
Tonus
Tonus is the Latin equivalent of the English word tone. It is especially used to refer to:* Muscle tone, the continuous and passive partial contraction of the muscles* Arterial tone, the continuous and passive partial contraction of the arterioles...
. Periods between contractions increase with old age.
Biological mechanisms
The fluctuation of leptinLeptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
and ghrelin
Ghrelin
Ghrelin is a 28 amino acid peptide and hormone that is produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone...
hormone levels results in the motivation
Motivation
Motivation is the driving force by which humans achieve their goals. Motivation is said to be intrinsic or extrinsic. The term is generally used for humans but it can also be used to describe the causes for animal behavior as well. This article refers to human motivation...
of an organism to consume food. When an organism eats, adipocytes trigger the release of leptin into the body. Increasing levels of leptin result in a reduction of one's motivation to eat. After hours of non-consumption, leptin levels drop significantly. These low levels of leptin cause the release of a secondary hormone, ghrelin, which in turn reinitiates the feeling of hunger.
Some studies have suggested that an increased production of ghrelin may enhance appetite evoked by the sight of food, while an increase in stress may also influence the hormone's production. These findings may help to explain why hunger can prevail even in stressful situations.
Behavioral response
Hunger appears to increase activity and movement in many animals - for example, an experiment on spiders showed increased activity and predationPredation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
in starved spiders, resulting in larger weight gain. This pattern is seen in many animals, including human
Human
Humans are the only living species in the Homo genus...
s while sleeping. It even occurs in rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s with their cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
or stomachs completely removed. Increased activity on hamster wheel
Hamster wheel
Most wheels are constructed of steel or plastic, both with advantages and problems. Solid plastic wheels are safer for some types of pets, such as hamsters and hedgehogs, because the space between rungs is solid and the animal's feet or legs cannot get stuck between rungs, an injury risk in steel...
s occurred when rats were deprived not only of food, but also water or B vitamins
B vitamins
B vitamins are a group of water-soluble vitamins that play important roles in cell metabolism. The B vitamins were once thought to be a single vitamin, referred to as vitamin B . Later research showed that they are chemically distinct vitamins that often coexist in the same foods...
such as thiamine
Thiamine
Thiamine or thiamin or vitamin B1 , named as the "thio-vitamine" is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects if not present in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are...
. This response may increase the animal's chance of finding food, though it has also been speculated the reaction relieves pressure on the home population.
Similar cravings
A food cravingFood craving
A food craving is an intense desire to consume a specific food, stronger than simply normal hunger. According to Marcia Levin Pelchat "It may be the way in which foods are consumed A food craving is an intense desire to consume a specific food, stronger than simply normal hunger. According to...
is an intense desire to consume a specific food, as opposed to general hunger. Similarly, thirst
Thirst
Thirst is the craving for fluids, resulting in the basic instinct of animals to drink. It is an essential mechanism involved in fluid balance. It arises from a lack of fluids and/or an increase in the concentration of certain osmolites, such as salt...
is the craving for fluids. Withdrawal craving
Craving (withdrawal)
When going through withdrawal, craving is a psychological urge to administer a discontinued medication or recreational drug.-Duration:The duration that cravings last after discontinuation varies substantially between different addictive drugs...
is a "hunger" for administering addictive drugs.
See also
- AnorecticAnorecticAn anorectic or anorexic , also known as anorexigenic or appetite suppressant, is a dietary supplement and/or drug which reduces appetite, food consumption, and as a result, causes weight loss to occur.-List of anorectics:Numerous pharmaceutical compounds are marketed as appetite suppressants.The...
- Eating disorderEating disorderEating disorders refer to a group of conditions defined by abnormal eating habits that may involve either insufficient or excessive food intake to the detriment of an individual's physical and mental health. Bulimia nervosa, anorexia nervosa, and binge eating disorder are the most common specific...
- FastingFastingFasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...
- HypoglycemiaHypoglycemiaHypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
- StarvationStarvationStarvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...
- Stomach growling
- GhrelinGhrelinGhrelin is a 28 amino acid peptide and hormone that is produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone...
- Specific appetiteSpecific appetiteSpecific appetite, also known as specific hunger is a drive to eat foods with specific flavors or other characteristics.Regulation of homeostasis is essential to the survival of animals...