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Appetite
 
 
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The appetite is the desire to eat
Eating

In general terms, eating is the process of consuming food to provide for the nutritional needs of an animal, particularly their food energy requirements and to growth....
 food
Food

Food is any substance, usually composed of carbohydrates, fats, proteins and water, that can be Eating or Drinking by an animal or human for nutrition or pleasure....
, felt as hunger
Hunger

Hunger is a feeling experienced when one has a desire to eat. The often unpleasant feeling originates in the hypothalamus and is released through receptors in the liver....
. Appetite exists in all higher lifeforms, and serves to regulate adequate energy intake to maintain metabolic
Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
 needs. It is regulated by a close interplay between the digestive tract, adipose tissue
Adipose tissue

In histology, adipose tissue or fat is loose connective tissue composed of adipocytes. Adipose tissue is derived from lipoblasts. Its main role is to store energy in the form of fat, although it also cushions and Thermal insulation the body....
 and the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
. Decreased desire to eat is termed anorexia
Anorexia (symptom)

Anorexia is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition, or pose a significant risk....
, while polyphagia
Polyphagia

Polyphagia is a compound word which literally means "eating too much." It derives from the Greek words p??? which means "very much", and fa? which means "food"....
 (or "hyperphagia") is increased eating. Disregulation of appetite contributes to anorexia nervosa
Anorexia nervosa

Anorexia nervosa is a psychiatry illness that describes an eating disorder characterized by extreme low body weight and body image distortion with an obsessive fear of gaining weight....
, bulimia nervosa
Bulimia nervosa

Bulimia nervosa is an eating disorder characterized by recurrent binge eating, followed by compensatory behaviors. The most common form?practiced by more than 75% of people with bulimia nervosa?is defensive vomiting, sometimes called purging; fasting, the use of laxatives, enemas, diuretics, and over exercising are also common....
, cachexia
Cachexia

Cachexia is weight loss, muscle atrophy, fatigue, weakness and significant anorexia in someone who is not actively trying to lose weight. It can be a sign of various underlying disorders; when a patient presents with cachexia, a doctor will generally consider the possibility of cancer, metabolic acidosis , certain infectious diseases , and...
, overeating
Overeating

Overeating generally refers to the long-term consumption of excess food in relation to the energy that an organism expends , leading to weight gain and often obesity....
, and binge eating disorder
Binge eating disorder

Binge eating disorder , is a psychiatric disorder in which a subject shows the following symptoms:* Periodically does not exercise control over consumption of food...
.

regulation of appetite has been the subject of much research in the .






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The appetite is the desire to eat
Eating

In general terms, eating is the process of consuming food to provide for the nutritional needs of an animal, particularly their food energy requirements and to growth....
 food
Food

Food is any substance, usually composed of carbohydrates, fats, proteins and water, that can be Eating or Drinking by an animal or human for nutrition or pleasure....
, felt as hunger
Hunger

Hunger is a feeling experienced when one has a desire to eat. The often unpleasant feeling originates in the hypothalamus and is released through receptors in the liver....
. Appetite exists in all higher lifeforms, and serves to regulate adequate energy intake to maintain metabolic
Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
 needs. It is regulated by a close interplay between the digestive tract, adipose tissue
Adipose tissue

In histology, adipose tissue or fat is loose connective tissue composed of adipocytes. Adipose tissue is derived from lipoblasts. Its main role is to store energy in the form of fat, although it also cushions and Thermal insulation the body....
 and the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
. Decreased desire to eat is termed anorexia
Anorexia (symptom)

Anorexia is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition, or pose a significant risk....
, while polyphagia
Polyphagia

Polyphagia is a compound word which literally means "eating too much." It derives from the Greek words p??? which means "very much", and fa? which means "food"....
 (or "hyperphagia") is increased eating. Disregulation of appetite contributes to anorexia nervosa
Anorexia nervosa

Anorexia nervosa is a psychiatry illness that describes an eating disorder characterized by extreme low body weight and body image distortion with an obsessive fear of gaining weight....
, bulimia nervosa
Bulimia nervosa

Bulimia nervosa is an eating disorder characterized by recurrent binge eating, followed by compensatory behaviors. The most common form?practiced by more than 75% of people with bulimia nervosa?is defensive vomiting, sometimes called purging; fasting, the use of laxatives, enemas, diuretics, and over exercising are also common....
, cachexia
Cachexia

Cachexia is weight loss, muscle atrophy, fatigue, weakness and significant anorexia in someone who is not actively trying to lose weight. It can be a sign of various underlying disorders; when a patient presents with cachexia, a doctor will generally consider the possibility of cancer, metabolic acidosis , certain infectious diseases , and...
, overeating
Overeating

Overeating generally refers to the long-term consumption of excess food in relation to the energy that an organism expends , leading to weight gain and often obesity....
, and binge eating disorder
Binge eating disorder

Binge eating disorder , is a psychiatric disorder in which a subject shows the following symptoms:* Periodically does not exercise control over consumption of food...
.

Regulation

The regulation of appetite has been the subject of much research in the . Breakthroughs included the discovery, in 1994, of leptin
Leptin

Leptin is a 16 Atomic mass unit protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism....
, a hormone that appeared to provide negative feedback. Later studies showed that appetite regulation is an immensely complex process involving the gastrointestinal tract
Gastrointestinal tract

The digestive tract is the system of Organ s within multicellular animals that takes in food, digestion it to extract energy and nutrients, and expels the remaining waste....
, many hormone
Hormone

Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
s, and both the central
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
 and autonomic nervous system
Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
s.

Effector

The hypothalamus
Hypothalamus

The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
, a part of the brain, is the main regulatory organ for human appetite. The neuron
Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
s that regulate appetite appear to be mainly serotonergic
Serotonin

Serotonin is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract of animals including humans....
, although neuropeptide Y
Neuropeptide Y

Neuropeptide Y is a 36 amino acid peptide neurotransmitter found in the brain and autonomic nervous system.NPY has been associated with a number of physiologic processes in the brain, including the regulation of energy balance, memory and learning, and epilepsy....
 (NPY) and Agouti-related peptide
Agouti-related peptide

Agouti-related protein also called Agouti-related peptide is a neuropeptide produced in the brain by the AgRP/NPY neuron that increases appetite and decreases metabolism and energy expenditure....
 (AGRP) also play a vital role. Hypothalamocortical and hypothalamolimbic projections contribute to the awareness of hunger, and the somatic processes controlled by the hypothalamus include vagal
Vagus nerve

The vagus nerve is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem and extends, through the jugular foramen, down below the head , to the neck, chest and abdomen, where it contributes to the innervation of the viscera....
 tone (the activity of the parasympathetic
Parasympathetic nervous system

The parasympathetic nervous system is a division of the autonomic nervous system , along with the sympathetic nervous system and enteric nervous system ....
 autonomic nervous system
Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
), stimulation of the thyroid
Thyroid

The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to the thyroid cartilage and at approximately the same level as the cricoid cartilage....
 (thyroxine
Thyroxine

Thyroxine, or 3,5,3',5'-tetra?iodothyronine , a form of thyroid hormones is the major hormone secreted by the follicular cells of the thyroid gland....
 regulates the metabolic rate), the hypothalamic-pituitary-adrenal axis
Hypothalamic-pituitary-adrenal axis

The hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis , is a complex set of direct influences and feedback interactions among the hypothalamus , the pituitary gland , and the adrenal glands ....
 and a large number of other mechanisms.

Sensor

The hypothalamus senses external stimuli mainly through a number of hormones such as leptin
Leptin

Leptin is a 16 Atomic mass unit protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism....
, ghrelin
Ghrelin

Ghrelin is a hormone produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates appetite....
, PYY 3-36, orexin
Orexin

Orexins, also called hypocretins, are the common names given to a pair of highly excitatory neuropeptide hormones that were simultaneously discovered by two groups of researchers in rat brains....
 and cholecystokinin
Cholecystokinin

Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called pancreozymin, is synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum, the first segment of the small intestine, and ca...
; all modify the hypothalamic response. They are produced by the digestive tract and by adipose tissue
Adipose tissue

In histology, adipose tissue or fat is loose connective tissue composed of adipocytes. Adipose tissue is derived from lipoblasts. Its main role is to store energy in the form of fat, although it also cushions and Thermal insulation the body....
 (leptin). Systemic mediators, such as tumor necrosis factor-alpha (TNFa), interleukin
Interleukin

Interleukins are a group of cytokines that were first seen to be expressed by white blood cells as a means of communication . The name is something of a relic though ; it has since been found that interleukins are produced by a wide variety of body cells....
s 1 and 6 and corticotropin-releasing hormone
Corticotropin-releasing hormone

Corticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress ....
 (CRH) influence appetite negatively; this mechanism explains why ill people often eat less.

In addition, the biological clock
Biological clock

Biological clock may refer to:* Chronobiology, a field of science that examines periodic phenomena in living organisms and their adaptation to solar and lunar related rhythms....
 (which is regulated by the hypothalamus) modifies hunger. Processes from other cerebral loci, such as from the limbic system
Limbic system

The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, and limbic cortex, which support a variety of functions including emotion, behavior, long term memory, and olfactory....
 and the cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
, project on the hypothalamus and modify appetite. This explains why in clinical depression
Clinical depression

Major depressive disorder is a mental disorder characterized by a pervasive depression , low self-esteem, and anhedonia in normally enjoyable activities....
 and stress
Stress (medicine)

Stress is a biological term which refers to the consequences of the failure of a human or animal body to respond appropriately to emotional or body threats to the organism, whether actual or imagined....
, energy intake can change quite drastically.

Role in disease

A limited or excessive appetite is not necessarily pathological. Abnormal appetite could be defined as eating habits causing malnutrition
Malnutrition

Malnutrition is a general term for a medical condition caused by an improper or inadequate diet and nutrition.According to the World Health Organization, hunger and malnutrition are the single gravest threats to the world's public health and malnutrition is by far the biggest contributor to child mortality, present in half of all cases....
 on the one side or obesity
Obesity

Obesity is a condition in which excess body fat has accumulated to an extent that health may be negatively affected. It is commonly defined as a body mass index of 30 kg/m2 or higher....
 and its related problems on the other.

Both genetic and environmental factors may regulate appetite, and abnormalities in either may lead to abnormal appetite. Poor appetite (anorexia
Anorexia (symptom)

Anorexia is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition, or pose a significant risk....
) may have numerous causes, but may be a result of physical (infectious, autoimmune or malignant disease) or psychological (stress, mental disorders) factors. Likewise, hyperphagia (excessive eating) may be a result of hormonal imbalances, mental disorders (e.g. depression
Clinical depression

Major depressive disorder is a mental disorder characterized by a pervasive depression , low self-esteem, and anhedonia in normally enjoyable activities....
) and others.

Dysregulation of appetite lies at the root of anorexia nervosa
Anorexia nervosa

Anorexia nervosa is a psychiatry illness that describes an eating disorder characterized by extreme low body weight and body image distortion with an obsessive fear of gaining weight....
, bulimia nervosa
Bulimia nervosa

Bulimia nervosa is an eating disorder characterized by recurrent binge eating, followed by compensatory behaviors. The most common form?practiced by more than 75% of people with bulimia nervosa?is defensive vomiting, sometimes called purging; fasting, the use of laxatives, enemas, diuretics, and over exercising are also common....
 and binge eating disorder
Binge eating disorder

Binge eating disorder , is a psychiatric disorder in which a subject shows the following symptoms:* Periodically does not exercise control over consumption of food...
. In addition, decreased response to satiety may promote development of obesity
Obesity

Obesity is a condition in which excess body fat has accumulated to an extent that health may be negatively affected. It is commonly defined as a body mass index of 30 kg/m2 or higher....
.

Various hereditary forms of obesity have been traced to defects in hypothalamic signalling (such as the leptin receptor and the MC-4
Melanocyte-stimulating hormone

The melanocyte-stimulating hormones are a class of peptide hormones that in nature are produced by cells in the intermediate lobe of the pituitary gland....
 receptor), or are still awaiting characterisation (Prader-Willi syndrome
Prader-Willi syndrome

Prader-Willi syndrome is a very rare genetic disorder, in which seven genes on chromosome 15 are missing or unexpressed on the paternal chromosome....
).

Pharmacology

Mechanisms controlling appetite are a potential target for weight loss drugs. Early anorectic
Anorectic

Anorexics, anorexigenics or appetite suppressants are substances that reduce the appetite and cause a person to eat less....
s were fenfluramine
Fenfluramine

Fenfluramine is a drug that was part of the Fen-Phen anti-obesity medication . Also known as Pondimin, fenfluramine was introduced on the U.S....
 and phentermine
Phentermine

Phentermine, a contraction for "phenyl-Butyl#Nomenclatureamine", is an appetite suppressant of the amphetamine and phenethylamine class.It is approved as an appetite suppressant to help reduce weight in obese patients when used short-term and combined with exercise, diet, and behavioral modification....
. A more recent addition is sibutramine
Sibutramine

Sibutramine , usually as sibutramine hydrochloride monohydrate, is an orally administered agent for the treatment of obesity, as an appetite suppressant....
 which increases serotonin
Serotonin

Serotonin is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract of animals including humans....
 and noradrenaline levels in the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
. In addition, recent reports on recombinant
Recombinant

Recombinant may refer to :* Recombinant DNA - a form of artificial DNA* , offers healthcare providers and academic medical centers proven, leading-edge data warehousing and clinical intelligence solutions to deliver higher quality outcomes, accelerate personalized medicine, and lower costs....
 PYY 3-36 suggest that this agent may contribute to weight loss
Weight loss

Weight loss, in the context of medicine or health or physical fitness, is a reduction of the total body weight, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue....
 by suppressing appetite.

Given the epidemic proportions of obesity
Obesity

Obesity is a condition in which excess body fat has accumulated to an extent that health may be negatively affected. It is commonly defined as a body mass index of 30 kg/m2 or higher....
 in the Western world, developments in this area are expected to snowball in the near future, as dieting alone is ineffective in most obese adults.