Hormone

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Hormone signaling
Hormonal signaling across this hierarchy involves the following:

1. Biosynthesis of a particular hormone in a particular tissue
2. Storage and secretion of the hormone
3. Transport of the hormone to the target cell(s)
4. Recognition of the hormone by an associated cell membrane or intracellular receptor protein.
5. Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop.
6. Degradation of the hormone.

As can be inferred from the hierarchical diagram, hormone biosynthetic cells are typically of a specialized cell type, residing within a particular endocrine gland (e.g., the thyroid gland, the ovaries, or the testes). Hormones may exit their cell of origin via exocytosis or another means of membrane transport. However, the hierarchical model is an oversimplification of the hormonal signaling process. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal. Because of this, hormonal signaling is elaborate and hard to dissect.
Publicat de health victorro la 08:12 0 comentarii
Etichete: Hormone, signaling
Physiology of hormones
Most cells are capable of producing one or more molecules, which act as signaling molecules to other cells, altering their growth, function, or metabolism. The classical hormones produced by cells in the endocrine glands mentioned so far in this article are cellular products, specialized to serve as regulators at the overall organism level. However they may also exert their effects solely within the tissue in which they are produced and originally released.

The rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors which influence the metabolism and excretion of hormones. Thus, higher hormone concentration alone can not trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone.

Hormone secretion can be stimulated and inhibited by:

* Other hormones (stimulating- or releasing-hormones)
* Plasma concentrations of ions or nutrients, as well as binding globulins
* Neurons and mental activity
* Environmental changes, e.g., of light or temperature

One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands. For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones.

A recently-identified class of hormones is that of the "hunger hormones" - ghrelin, orexin and PYY 3-36 - and "satiety hormones" - e.g., leptin, obestatin, nesfatin-1.

In order to release active hormones quickly into the circulation, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre- or prohormones. These can then be quickly converted into their active hormone form in response to a particular stimulus.
Publicat de health victorro la 08:11 0 comentarii
Etichete: hormones, Physiology
Hormone effects
Hormone effects vary widely, but can include:

* stimulation or inhibition of growth,
* In puberty hormones can affect mood and mind
* induction or suppression of apoptosis (programmed cell death)
* activation or inhibition of the immune system
* regulating metabolism
* preparation for a new activity (e.g., fighting, fleeing, mating)
* preparation for a new phase of life (e.g., puberty, caring for offspring, menopause)
* controlling the reproductive cycle

In many cases, one hormone may regulate the production and release of other hormones

Many of the responses to hormone signals can be described as serving to regulate metabolic activity of an organ or tissue.
Publicat de health victorro la 08:10 0 comentarii
Etichete: effects, Hormone
Chemical classes of hormones
Vertebrate hormones fall into three chemical classes:

* Amine-derived hormones are derivatives of the amino acids tyrosine and tryptophan. Examples are catecholamines and thyroxine.
* Peptide hormones consist of chains of amino acids. Examples of small peptide hormones are TRH and vasopressin. Peptides composed of scores or hundreds of amino acids are referred to as proteins. Examples of protein hormones include insulin and growth hormone. More complex protein hormones bear carbohydrate side chains and are called glycoprotein hormones. Luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone are glycoprotein hormones.
* Lipid and phospholipid-derived hormones derive from lipids such as linoleic acid and arachidonic acid and phospholipids. The main classes are the steroid hormones that derive from cholesterol and the eicosanoids. Examples of steroid hormones are testosterone and cortisol. Sterol hormones such as calcitriol are a homologous system. The adrenal cortex and the gonads are primary sources of steroid hormones. Examples of eicosanoids are the widely studied prostaglandins.
Publicat de health victorro la 08:09 0 comentarii
Etichete: classes, hormones
Pharmacology
Many hormones and their analogues are used as medication. The most commonly prescribed hormones are estrogens and progestagens (as methods of hormonal contraception and as HRT), thyroxine (as levothyroxine, for hypothyroidism) and steroids (for autoimmune diseases and several respiratory disorders). Insulin is used by many diabetics. Local preparations for use in otolaryngology often contain pharmacologic equivalents of adrenaline, while steroid and vitamin D creams are used extensively in dermatological practice.

A "pharmacologic dose" of a hormone is a medical usage referring to an amount of a hormone far greater than naturally occurs in a healthy body. The effects of pharmacologic doses of hormones may be dif

• Added on: Mar 13th, 2009
• Country: Romania
• Language: English

• Author: rorac2009
• Listed in: Health Medicine
• Tags: hormone signaling physiology of hormones