Hormone

A Hormone is a cell signaling molecule produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behavior.

AKA: Endocrine Messenger, Chemical Messenger, Hormonal Signal.
Context:
- It can typically be produced by Endocrine Glands through specialized secretory cells.
- It can typically travel through Bloodstream to reach target tissues.
- It can typically bind to Specific Receptors on or in target cells.
- It can typically regulate Physiological Processes including metabolism, growth, development, and reproduction.
- It can typically influence Behavior through neuroendocrine pathways.
- It can typically maintain Homeostasis through feedback mechanisms.
- It can typically act at Low Concentrations with high potency.
- It can typically have Tissue Specificity based on receptor distribution.
- It can typically undergo Metabolic Clearance through liver and kidney.
- It can typically exhibit Circadian Rhythms in secretion patterns.
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- It can often interact with Multiple Target Tissues producing pleiotropic effects.
- It can often be regulated by Hypothalamic-Pituitary Axises through feedback loops.
- It can often have Synergistic Effects with other hormones.
- It can often have Antagonistic Effects opposing other hormone actions.
- It can often be influenced by Environmental Factors including stress and nutrition.
- It can often show Age-Related Changes in production and sensitivity.
- It can often be affected by Pathological Conditions causing endocrine disorders.
- It can often be measured through Immunoassays for clinical diagnosis.
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- It can range from being a Protein/Peptide Hormone to being a Steroid Hormone to being an Amino Acid-Derived Hormone, depending on its chemical structure.
- It can range from being a Water-Soluble Hormone to being a Lipid-Soluble Hormone, depending on its solubility property.
- It can range from being a Fast-Acting Hormone to being a Slow-Acting Hormone, depending on its response time.
- It can range from being a Local Hormone to being a Systemic Hormone, depending on its action range.
- It can range from being a Stimulating Hormone to being an Inhibiting Hormone, depending on its regulatory effect.
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- It can utilize Endocrine Signaling for distant targets via circulation.
- It can employ Paracrine Signaling for nearby cells within local tissue.
- It can use Autocrine Signaling affecting the secreting cell itself.
- It can involve Intracrine Signaling acting within the producing cell.
- It can be stored in Secretory Granules or synthesized on demand.
- It can be transported by Carrier Proteins or circulate freely.
- It can be a Human Hormone, vertebrate hormone, invertebrate hormone, or plant hormone.
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Example(s):
- Peptide Hormones, such as:
  - Insulin, regulating glucose metabolism from pancreatic beta cells.
  - Growth Hormone, promoting somatic growth from anterior pituitary.
  - Glucagon-Like Peptide-1 (GLP-1), an incretin hormone from intestinal L-cells.
  - Oxytocin, involved in social bonding from posterior pituitary.
- Steroid Hormones, such as:
  - Sex Steroids, such as:
    - Estrogen, regulating female reproduction from ovaries.
    - Testosterone, controlling male characteristics from testes.
    - Progesterone, maintaining pregnancy from corpus luteum.
  - Corticosteroids, such as:
    - Cortisol, managing stress response from adrenal cortex.
    - Aldosterone, regulating sodium balance from zona glomerulosa.
  - Vitamin D, functioning as steroid hormone for calcium homeostasis.
- Amino Acid-Derived Hormones, such as:
  - Thyroid Hormones, such as:
    - Thyroxine (T4), regulating basal metabolism from thyroid gland.
    - Triiodothyronine (T3), the active thyroid hormone form.
  - Catecholamines, such as:
    - Epinephrine, mediating fight-or-flight response from adrenal medulla.
    - Norepinephrine, functioning as both hormone and neurotransmitter.
    - Dopamine, serving neuroendocrine functions from hypothalamus.
  - Melatonin, regulating circadian rhythms from pineal gland.
- Eicosanoid Hormones, such as:
  - Prostaglandins, mediating inflammation and pain response.
  - Thromboxanes, regulating platelet aggregation and vasoconstriction.
  - Leukotrienes, involved in immune response and allergic reactions.
- Gastrointestinal Hormones, such as:
  - Gastrin, stimulating gastric acid secretion.
  - Ghrelin, regulating appetite and energy balance.
  - Cholecystokinin, controlling digestion and satiety.
- Adipose-Derived Hormones, such as:
  - Leptin, signaling energy stores and satiety.
  - Adiponectin, regulating glucose metabolism and fatty acid oxidation.
  - Resistin, affecting insulin sensitivity and inflammation.
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Counter-Example(s):
- Neurotransmitter, which primarily acts across synaptic clefts rather than through circulation.
- Cytokine, which are immune signaling molecules with primarily local actions.
- Growth Factor, which typically promote cell proliferation through paracrine signaling.
- Enzyme, which catalyze biochemical reactions rather than serving as signaling molecules.
- Vitamin, which are essential nutrients rather than endogenous signaling molecules.
- Pheromone, which are external chemical signals between organisms rather than internal regulators.
See: Endocrine System, Cell Signaling, Receptor, Signal Transduction, Gland, Homeostasis, Feedback Mechanism, Neuroendocrine System, Hormone Receptor, Endocrine Disorder, Hormone Therapy, Circadian Rhythm, Metabolism, Growth and Development, Reproduction.

References

2017

(Wikipedia, 2017) ⇒ https://en.wikipedia.org/wiki/hormone Retrieved:2017-5-26.
- A hormone is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour. Hormones have diverse chemical structures, mainly of 3 classes: eicosanoids, steroids, and amino acid/protein derivatives (amines, peptides, and proteins). The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).
  Hormones are used to communicate between organs and tissues for physiological regulation and behavioral activities, such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress, growth and development, movement, reproduction, and mood. Hormones affect distant cells by binding to specific receptor proteins in the target cell resulting in a change in cell function. When a hormone binds to the receptor, it results in the activation of a signal transduction pathway. This may lead to cell type-specific responses that include rapid non-genomic effects or slower genomic responseswhere the hormones acting through their receptors activate gene transcription resulting in increased expression of target proteins. Amino acid–based hormones (amines and peptide or protein hormones) are water-soluble and act on the surface of target cells via second messengers; steroid hormones, being lipid-soluble, move through the plasma membranes of target cells (both cytoplasmic and nuclear) to act within their nuclei.
  Hormone secretion may occur in many tissues. Endocrine glands are the cardinal example, but specialized cells in various other organs also secrete hormones. Hormone secretion occurs in response to specific biochemical signals from a wide range of regulatory systems. For instance, serum calcium concentration affects parathyroid hormone synthesis; blood sugar (serum glucose concentration) affects insulin synthesis; and because the outputs of the stomach and exocrine pancreas (the amounts of gastric juice and pancreatic juice) become the input of the small intestine, the small intestine secretes hormones to stimulate or inhibit the stomach and pancreas based on how busy it is. Regulation of hormone synthesis of gonadal hormones, adrenocortical hormones, and thyroid hormones is often dependent on complex sets of direct influence and feedback interactions involving the hypothalamic-pituitary-adrenal (HPA), -gonadal (HPG), and -thyroid (HPT) axes.
  Upon secretion, certain hormones, including protein hormones and catecholamines, are water-soluble and are thus readily transported through the circulatory system. Other hormones, including steroid and thyroid hormones, are lipid-soluble; to allow for their widespread distribution, these hormones must bond to carrier plasma glycoproteins (e.g., thyroxine-binding globulin (TBG)) to form ligand-protein complexes. Some hormones are completely activewhen released into the bloodstream (as is the case for insulin and growth hormones), while others are prohormones that must be activated in specific cells through a series of activation steps that are commonly highly regulated. The endocrine system secretes hormones directly into the bloodstream typically into fenestrated capillaries, whereas the exocrine system secretes its hormones indirectly using ducts. Hormones with paracrine function diffuse through the interstitial spaces to nearby target tissue.