What are hormones, their types and mechanisms

Hormones are substances produced and secreted in small amounts and that through the blood carries a signal to the remotely located target cell. There are some substances that exert their endocrine-type effect but are not performed through blood circulation.


Hormones perform different types of actions:

  • Telecrino-feromonal, is a part of the organism that releases a chemical and that exerts the effect on another individual of the same or other species, exerts effects on tissues of other individuals.
  • Juxtacrine. The substance produced is not even segregated. It occurs on the surface of the cell and recognized by adjacent cells producing an effect on these adjacent cells. A typical example of this would be the whole process of immune maturation. For example, the immune system, presentation of peptides through the histocompatibility molecule of class I and II.
  • Autocrine. A cell secretes a hormone and also has mechanisms of response against that hormone. He regulates himself. The circulatory system is not required. The segregated hormone influences the secreting cell.
  • Paracrino. The action is exercised at a very short distance. It influences the level of operation of a neighboring cell. It does not require the circulatory system.
  • Endocrine. A cell secretes a substance into the bloodstream that distributes it throughout the body to a distant target cell. It can affect all cells in the body but this doesn’t always happen. That’s why we’re talking about target tissues that have receptors specific to that substance.


It was given by Guillemin and is

Any substance released by one cell acted on another, both close and distant and regardless of its uniqueness, ubiquity of origin, the way used for transport is blood circulation, interstitial compartment or axonic flow or any other

It is a very extreme definition and includes almost any type of substance with biological activity.


Hay dos grandes grupos:

There are two large groups:

  1. Soluble. Like steroids, thyroid, vitamin A and D derivatives (colecalciferol and retinol).
  2. Soluble. They are classified into:
    1. Proteins of lipophysary and pancreatic origin.
    2. Derivatives of amino acids, such as catecholamines and catecole derivatives, serotonin (classic neurotransmitters).

Other ratings:

  1. Prostaglandins. They occur in every cell in the body.
  2. Atypical neurotransmitters (CO, NO2).
  3. Growth factors. Most of the protein origin.

Difference between fat-soluble and water-soluble hormones

Fat-soluble and water-soluble hormones have a number of differences such as:

  • Synthesis. Fat-soluble hormones come from cholesterol minus thyroid or lipid dietary precursors (Vitamin A and D). Water-soluble hormones are produced by protein synthesis.
  • Storage. Fat-solubles cannot be stored because the vesicles have lipid-formed membranes. Water-solubles are stored in vesicles.
  • Form of secretion. Fat-solubles their secretion is immediate because they cannot be stored are regulated through synthesis and water-soluble ones being almost always stored in vesicles their secretion is regulated.
  • Transport. Fat-solubles cannot travel in biological liquids per se, so they can perform their function are coupled to other substances called transporting proteins (Bps). In water-soluble proteins the situation is more varied, some circulate freely in plasma and others associated with transporting proteins.
  • Its mechanism of action is through specific receptor molecules. They’re always proteins. Fat-soluble hormones locate their receptors within cells, intracellular and may be located in the cytoplasm or nucleus. Water-soluble substances do not pass through the plasma membrane. The receptors are located on the surface of the membrane and act by means of second messengers.
  • Elimination. The removal of fat-soluble substances is done by metabolic pathways or through urine. In water-soluble hormones the most important process of hormone elimination is internalization after binding to receptors, internalization.


For it to be called hormone it has to bind to a target cell protein, receptors that are usually hormone-specific. All hormone receptors have high affinity (recognize low concentrations of a substance) and low capacity. There are two types of hormonal receptors: membrane and intracellular (cytoplasm or nuclear). The affinity constant has a degree of 10-10-10-12  M-1/l. and low capacity, i.e. a cell has such a receptor endowment that with a small amount of hormone these receptors are saturated.

Places of hormonal action and that have low affinity and high capacity. In some processes these low affinity and high capacity binding sites interfere with hormonal modulation processes. The effective hormonal concentration is low from 10-12-10-6  M, very important effects are obtained.

General characteristics of receivers

  • It is sufficient with 10% activation to produce the maximum biological effect, produce full effect (maximum effect or saturation).. In many cases the increase in the number of activated receptors does not produce greater biological effect.
  • Recruitment, recruitment of receptors, increasing number of receptors are being activated, receptor activation increases and the biological effect increases.
  • Receiver-mediated internalization. Receptors tend to accumulate in certain areas of the membrane that will result in gallbladders. Endocytic vesicles are generated with receptors and hormones linked to them. During this process a large number of molecules are used to clearly identify the message. The cells end up losing all receptors on the surface, they stop responding to hormonal action, down-regulation. It justifies with only 10% of the receptor population a complete biological effect is achieved, low number of receptors after overstimulation. This explains the phenomenon of throbbing secretion, giving the cell time to resent the receptors.
  • Down regulation. After overstimulation (prolonged stimulation), the number of receptors drops so that cells without receptors end up not responding to hormonal action. Thus the cell responds in pulses so that the biological effect ends until the number of receptors is recovered.
  • Up regulation. Increase in the number of receivers. It was replaced by primacy. It occurs in cells that are initially under-stimulated by a hormone. In these cells receptors are lost and the cell must be stimulated for a while. For example, when a hormonal stimulus is lacking, target tissues stop responding to that hormone. Until the response amount is reset, a time passes.
  • They are concentrated in areas near vessels, nerves (membrane).
  • Three functional domains in all membrane or intracellular receptors.

Types of fundamental receivers. Receptors for water-soluble hormones are located on the membrane surface of target cells and receptors for fat-soluble hormones are in the cytoplasm or nucleus. All receptors are glycoproteins and recognize spatial structures.

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