What is Hormones?
Answers: Hormone
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For other uses, see Hormone (disambiguation).
Epinephrine (adrenaline), a catecholamine-type hormone
Epinephrine (adrenaline), a catecholamine-type hormone
A hormone (from Greek ρμ - "impetus") is a chemical messenger that carries a signal from one cell to another. All multicellular organisms produce hormones; plant hormones are also called phytohormones. Hormones within animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone. The hormone binds to the receptor protein, resulting surrounded by the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses.
Endocrine hormone molecules are secreted (released) directly into the bloodstream, while exocrine hormones (or ectohormones) are secreted directly into a duct, and from the duct they any flow into the bloodstream or they flow from cell to cell by diffusion in a process known as paracrine signalling.
Contents
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* 1 Hierarchical temper of hormonal control
* 2 Hormone signaling
* 3 Interactions with receptors
* 4 Physiology of hormones
* 5 Hormone effects
* 6 Chemical classes of hormones
* 7 Pharmacology
* 8 Important human hormones
* 9 References
* 10 See also
* 11 External links
[edit] Hierarchical nature of hormonal control
Hormonal regulation of some physiological undertakings involves a hierarchy of cell types acting on each other any to stimulate or to modulate the release and action of a particular hormone. The secretion of hormones from successive level of endocrine cells is stimulated by chemical signals originating from cell higher up the hierarchical system. The master coordinator of hormonal activity contained by mammals is the hypothalamus, which acts on input that it receives from the medium nervous system.[1]
Other hormone secretion occurs contained by response to local conditions, such as the rate of secretion of parathyroid hormone by the parathyroid cells in response to fluctuations of ionized calcium level in extracellular fluid.
[edit] Hormone signaling
Hormonal signalling across this hierarchy involves the following:
1. Biosynthesis of a extraordinary 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 afterwards leads to a cellular response. The reaction of the target cell may then be recognized by the inspired hormone-producing cells, leading to a down-regulation contained by 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 in 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 funds 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 inwardly a number of different tissues, as is the case for insulin, which triggers a diverse compass of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal. Because of this, hormonal signaling is elaborate and intricate to dissect.
[edit] Interactions with receptors
Most hormones initiate a cellular response by initially combining with any a specific intracellular or cell membrane associated receptor protein. A cell may have several different receptors that recognize equal hormone and activate different signal transduction pathways, or alternatively different hormones and their receptors may invoke one and the same biochemical pathway.
For many hormones, including most protein hormones, the receptor is membrane associated and embedded contained by the plasma membrane at the surface of the cell. The interaction of hormone and receptor typically triggers a cascade of secondary effects in the cytoplasm of the cell, often involving phosphorylation or dephosphorylation of various other cytoplasmic proteins, change in ion channel permeability, or increased concentrations of intracellular molecules that may perform as secondary messengers (e.g. cyclic AMP). Some protein hormones also interact with intracellular receptors located contained by the cytoplasm or nucleus by an intracrine mechanism.
For hormones such as steroid or thyroid hormones, their receptors are located intracellularly within the cytoplasm of their target cell. In charge to bind their receptors these hormones must cross the cell membrane. The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, effectively amplifying or suppressing the commotion of certain genes, and affecting protein synthesis.[2] However, it has be shown that not all steroid receptors are located intracellularly, some are plasma membrane associated.[3]
An important consideration, dictating the height at which cellular signal transduction pathways are activated within response to a hormonal signal is the effective concentration of hormone-receptor complexes that are formed. Hormone-receptor complex concentrations are effectively determined by three factors:
1. The number of hormone molecules available for complex formation
2. The number of receptor molecules available for complex formation and
3. The binding affinity between hormone and receptor.
The number of hormone molecules available for complex formation is usually the switch factor in determining the level at which signal transduction pathway are activated. The number of hormone molecules available being determined by the concentration of circulating hormone, which is surrounded by turn influenced by the level and rate at which they are secreted by biosynthetic cells. The number of receptors at the cell surface of the delivery cell can also be varied as can the affinity between the hormone and its receptor.
[edit] Physiology of hormones
Most cells are skilled of producing one or more molecules, which act as signalling molecules to other cells, altering their growth, function, or metabolism. The classical hormones produced by cell in the endocrine glands mentioned so far in this article are cellular products, specialized to serve as regulators at the overall organism stratum. 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 commonly regulated by a homeostatic negative feedback control mechanism. Such a contraption depends on factors which influence the metabolism and excretion of hormones. Thus, higher hormome concentration alone can not trigger the cynical 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 buzz
* Environmental changes, e.g., of light or heat
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 instruct to release active hormones quickly into the circulation, hormone biosynthetic cell may produce and store biologically inactive hormones in the form of pre- or prohormones. These can afterwards be quickly converted into their active hormone form contained by response to a particular stimulus.
[edit] 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 investigational activity (e.g., fighting, fleeing, mating)
* preparation for a exotic phase of life (e.g., puberty, caring for spawn, 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.
[edit] Chemical classes of hormones
Vertebrate hormones jump down 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 call 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 most important classes are the steroid hormones.
I honestly think sometimes we forget that we run our bodies not the other way around. What I anticipate is if someone speaks to you in a way you do not close to, you still have the choice how you choose to respond to them. Hormones can make this choice harder so to be precise why children tend to react to everything emotionally but as we grow we learn to control ourselves better. its mc.donalldas
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