A hormone is a chemical messenger conveyed by the Sang or the Sève which remotely acts of its production site by fixing on receiving S specific.

Operation

A hormone is a Molécule messenger produced by the Système endocrinien (a endocrine Gland, or a fabric endocrinien) in answer to a stimulation, and able to act with very low dose.

It is then diffused in the whole of the Organisme or outside this one. The animal hormones are secreted by Glande S specialized, and mainly diffused by the Sang or the Lymphe. But of the hormones can be excreted in the Excrément S and the Urine, via the Haleine or the body odors by the Transpiration. They are sometimes produced by external glands, which are used for example in the animal to mark the territory, predominance in the group or the provisions sexual.

At the plants, the hormones either are conveyed by the Sève, or transported actively by the cells, or they are diffused between the cells in the wall or towards outside, with possible emissions in the Atmosphère in gas form (ethylene for example) or in the Rhizosphère in the ground.

The transmitting body acts thus remotely on the target whole of the bodies of the organizations or organizations close to same the species, even of organizations Symbiote S whose receiving S are activated in contact with the specific hormones (durable Interactions).

Role

The hormones have a communication function which, in comparison with that of the Nervous system, can be described as slow, continuous and diffuse. The hormonal concentrations, studied in Endocrinology, thus contain information representative of various states. They thus control the activity of one or more Organe S or organizations of which they modify the behavior and the interactions.
Example: the hormone of the sleep according to its concentration is representative of the state of awakening. It acts on many bodies to allow or prevent the drowsiness of the individual.

The regulation of hormonal secretion is made via Rétrocontrôle, known as “positive” in the event of increase in secretion of the hormone, and “negative” if it induces a reduction in hormonal secretion. This regulation is also influenced by many hormonal cycles where systems cascades about it where the concentration in a first hormone orders the release of (or of) following or on the contrary the inhibition of their secretion.

Example: the GnRH control release of FSH and LH. (It thus acts on their own cycles of rétrocontontrôle to influence their concentrations). FSH and LH play an important role in the release of sex hormones in blood. It is according to this concentration in sex hormones that GnRH is released.

The hormones intervene in many processes, of which the reproduction, the cellular Différenciation, the Homéostasie, or regulation of the rate/rhythm chronobiologic…

The role of the sex hormones external still is very discussed at the Homme which has compared to the others Mammifère S a weak Odorat and a more complex Sexualité, but certain studies let think that there exists. The hairs of the armpits and the pubic zone, the scrotum and of périnée could thus play a hormonal part of “diffusion” , for example of Androstadienone (derivative of testosterone present in sweat and other male secretions, which influences the mood of the women and affects the secretion of the hormone lutéinisante stimulating the Ovulation). It was shown that extracts of female sweat placed on the upper lip, under the nostrils of other women could modify their rates of hormones and synchronize their menstrual cycles with the cycle of the woman having provided the sample of sweat. One as showed as of the extracts of male sweat, deposited on the upper lip of a woman raises the cortisol rate of this woman in the 15 minutes which follow, with persistent effects one hour (one is unaware of still if it is the cortisol rate affects the mood of the women or the reverse).

Various types of hormones

At the vertebrate ones, one distinguishes the following chemical classes:
  1. the hormones derived from amines, which make up of only one amino-acid (the Tyrosine or the Tryptophane) but in a derived form. Examples: the Catecholamine S and the Thyroxine.
  2. the peptide hormones; who are chains of amino-acids, therefore Protéine S, called Peptide S for shortest. Examples of hormones containing oligopeptides: TRH and the Vasopressine. Examples of hormones of the proteins type: the Insulin and the Growth hormone.
  3. the hormones steroids, which are Stéroïde S derived from the Cholestérol. The independent sources are the cortico-suprarenal and the Gonade S. Exemples of hormones steroids: Estrogen S, the Testosterone and the Cortisol. The hormones of the sterol type the such calcitriol are a homologous system.
  4. the hormones containing Lipid S and of Phospholipide S are derived from lipids like the Linoleic acid and from phospholipides like the arachidonic Acide. The Eïcosanoïde S form the principal class, among which the most studied are the Prostaglandine S.

Vegetable

See also: vegetable Hormone

The vegetable hormones (more rigorously called Phytohormone S or growth factors) have often like function to ensure the growth plant or its Morphogénèse. It is the case in particular of the Auxine which contributes to the formation of the Organe S of the plant (the roots for example) and to its growth but also intervenes in the phenomena of Tropisme.

They are distinguished from the animal hormones in several points:

  • Their secretion is not ensured by specific bodies of the plant (just there exist privileged zones of synthesis);
  • Their effect varies according to their concentration (ex: with weak concentration 10-10 g/mL, the Auxine has a positive discrete effect on the growth racinaire. With stronger concentrations, 10-8 g/mL, it inhibits the elongation and induces the Rhizogenèse);
  • They seldom only act: their effects very often result from a coordinated action several hormones (ex: stimulation of the cellular Division thanks to the combined action of the Auxine and the Cytokinine S).

Others

On the same mode of chemical action:
  • In the case of diffusions limited to a restricted zone, one speaks about hormone Paracrine or substance paracrine. There exists also a particular case where the substance acts on the producing cell, one speaks then about hormone autocrine.
  • the hormones released by neurons are called Neurohormone S (not to be confused with the neurotransmitter S). They are secreted same manner as the Neurotransmetteur S whose mode of action is identical, but in blood and not in the Synapse. It happens besides that the same molecule is called neuro-transmitter or hormone according to its use or the context in which she is studied.

See too

Related articles

External bonds

  • the discovery of a new hormonal messenger controlling the transmission of the pain: a video of the Educational channel at the Request of partnership with the Institute Pasteur
  • Hormones; I That-know n°63:

Simple: Hormone

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