WEIGHT CONTROL HORMONES
It is well settled now that there are a bunch of hormones influencing and regulating the human body weight.
Some of these hormones are centrally secreted in the brain centers, especially at the Hypothalamus (the part of the brain containing appetite and satiety centers). Others are secreted in the gastrointestinal tract, affecting the digestion, absorption and metabolism of food stuff. And it is quite astonishing to know that there is a major similarity between these two groups. A third group of hormones is secreted by the peripheral endocrinal glands and affecting the body weight. A last group is known as the prostaglandins is synthesized in the blood during body metabolism is also affecting body weight through various mechanisms.
The most important hormones will be mentioned sequentially:-
Serotonin
This hormone is a neurotransmitter synthesized in serotonergic neurons in the brain and in the gastrointestinal tract cells.
Serotonin is believed to play an important part of the biochemistry of depression, migraine, bipolar disorder and anxiety. It is also believed to be influential on sexuality and appetite.
The name "serotonin" is something of a misnomer and reflects the circumstances of the compound's discovery. It was initially identified as a vasoconstrictor substance in blood serum - hence serotonin, a serum agent affecting vascular tone.
Leptin
Leptin is a protein hormone that plays a key role in metabolism and regulation of adipose tissue.
Leptin was discovered in 1994 in mice by Jeffrey M. Friedman and team at the Rockefeller University. The Ob(Lep) gene is located on the 7th chromosome in humans. Leptin is produced by adipose (fat) tissue and interacts with brain receptors. These receptors are present in a number of hypothalamic nuclei, where it exerts its effects. A very small group of humans, mostly arising from inbred populations, are also mutant for the leptin gene. These people eat nearly constantly, and may be more than 100 pounds (45 kg) overweight by the age of 7.
Leptin is released by fat cells in amounts mirroring overall body fat stores. Thus, circulating leptin levels give the brain a reading of energy storage for the purposes of regulating appetite and metabolism. Leptin works by inhibiting the appetite center and increasing the activity of the satiety center.
Leptin as adiposity signal
To date, only leptin and insulin fulfill the criteria of an adiposity signal:
• It circulates at levels proportional to body fat.
• It enters the central nervous system (CNS) in proportion to its plasma concentration.
• Its receptors are found in brain neurons involved in regulating energy intake and expenditure.
Ghrelin
Ghrelin is a hormone that is produced by cells lining the stomach and stimulates the appetite. Ghrelin levels are increased prior to a meal and decreased after a meal. It is considered the counterpart of the hormone leptin, produced by adipose tissue, which induces satiation when present at higher levels.
Role in disease
Ghrelin levels in the plasma of obese individuals are lower than those in leaner individuals, and the level of ghrelin increases during the time of day from midnight to dawn in thinner people, suggesting a flaw in the circulatory system of obese individuals.
Those suffering from the eating disorder anorexia nervosa appear to have high plasma levels of ghrelin. Ghrelin levels are found to be increased in patients who have cancer-induced cachexia.
Relation to Obestatin
Obestatin is a hormone that was found in late 2005 to decrease appetite. Surprisingly, obestatin and ghrelin are encoded by the same gene; the gene's product breaks apart to yield the two peptide hormones. The purpose of this mechanism remains unknown.
Cholecystokinin
Cholecystokinin (CCK, previously pancreozymin) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. CCK is secreted by the duodenum, the first segment of the small intestine, and causes the release of digestive enzymes and bile from the pancreas and gall bladder, respectively. It also acts as a hunger suppressant. Recent evidence has suggested it plays a major role in inducing drug tolerance to opioids like morphine and heroin, and is partly responsible for the pain hypersensitivity often experienced during opioid withdrawal. So it mediates a number of physiological processes, including digestion and satiety. The effects of CCK vary between individuals.
Digestion
CCK is secreted by the duodenum when fat- or protein-rich chyme leaves the stomach and enters the duodenum. The hormone acts on the pancreas to stimulate the secretion of the enzymes lipase, amylase, trypsin, and chymotrypsin. Together these pancreatic enzymes catalyze the digestion of fat and protein.
CCK also stimulates both the contraction of the gall bladder, and the relaxation of the Sphincter of Oddi, which delivers, (not secretes) bile into the small intestine. Bile salts serve to emulsify fats, thereby increasing the effectiveness with which enzymes can digest them.
Thyroid hormone
The thyroid hormones, thyroxine (T4) and triiodothyronine (T3) are hormones produced by the thyroid gland. An important component in the synthesis is iodine.
The thyroxines act on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). The thyroid hormones are essential to proper development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds. Numerous physiological and pathological stimuli influence thyroid hormone synthesis.
Growth Hormone
Growth hormone, also known as somatotropin, is synthesized and secreted by the anterior pituitary. It is a major participant in control of several complex physiologic processes, including growth and metabolism. Growth hormone has important effects on protein, lipid and carbohydrate metabolism.
Epinephrine and Nore-epinephrine
Epinephrine or adrenaline is a hormone and a neurotransmitter produced by the suprarenal gland. A listing of some major effects mediated by epinephrine and norepinephrine are:
• Increased rate and force of contraction of the heart muscle: this is predominantly an effect of epinephrine acting through beta receptors.
• Constriction of blood vessels: norepinephrine, in particular, causes widespread vasoconstriction, resulting in increased resistance and hence arterial blood pressure.
• Dilation of bronchioles: assists in pulmonary ventilation.
• Stimulation of lipolysis in fat cells: this provides fatty acids for energy production in many tissues and aids in conservation of dwindling reserves of blood glucose.
• Increased metabolic rate: oxygen consumption and heat production increase throughout the body in response to epinephrine. Medullary hormones also promote breakdown of glycogen in skeletal muscle to provide glucose for energy production.
• Dilation of the pupils: particularly important in situations where you are surrounded by velociraptors under conditions of low ambient light.
• Inhibition of certain "non-essential" processes: an example is inhibition of gastrointestinal secretion and motor activity.
Common stimuli for secretion of adrenomedullary hormones include exercise, hypoglycemia, hemorrhage and emotional distress.
Prostaglandins
One of a number of hormone-like substances that participate in a wide range of body functions such as the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels, control of blood pressure, and modulation of inflammation. Prostaglandins are derived from an essential fatty acid called arachidonic acid. Prostaglandins are found in virtually all tissues and organs.
Prostaglandins have a wide variety of actions, including, but not limited to muscular constriction and mediate inflammation. Other effects include calcium movement, hormone regulation and cell growth control. Thromboxane is created in platelets and causes vascular constriction and platelet aggregation. Prostacyclin comes from cells in the blood vessel walls and is antagonistic to thromboxane.
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