Our bodies need hormones and neurotransmitters to function.
Neurotransmitters enable communication between neurons and other cells, crossing the synaptic space and via nerve impulses. Hormones, in turn, are secreted by the endocrine glands, involved in the regulation of many basic bodily functions.
Although they share structural and functional characteristics, there are also aspects that differentiate them. In this article we tell you what they are, how they act and what they are the main characteristics of hormones and neurotransmitters, as well as the most important differences between them.
Hormones: definition, characteristics and classification
Hormones are chemicals that act as messengers and activate different processes for our bodies to function properly. They occur in the endocrine or secretory glands (Like the hypothalamus, pituitary or thyroid, for example) and are released into the extracellular space, spreading through blood vessels into the blood.
The main characteristics of these chemical messengers are that they are involved in metabolism and other functions (immune system, sexual reproduction, etc.); they act on the tissues of the body which may be far from the point of origin from which the hormone is released; the effect they cause depends on the amount of hormones there is, being directly proportional to their concentration.
Almost all hormones can be chemically classified into three major groups: Peptide hormones, composed of amino acids, polypeptides or oligopeptides, such as insulin or vasopressin; hormones derived from amino acids, which are used to synthesize them, such as adrenaline; and lipid hormones, from the group of eicosanoids or steroids, such as cortisol and testosterone.
Hormones can produce stimulating effects, promoting activity in a tissue (eg prolactin); inhibitory effects, decreased activity (for example, somatostatin, which inhibits the release of growth hormone); antagonistic effects, when two hormones have opposite effects (for example, insulin and glucagon); and synergistic effects, when two hormones together produce a more powerful effect than separately (eg, growth hormone and thyroid hormones).
Neurotransmitters: definition, classification and characteristics
Neurotransmitters are chemicals our bodies use to send information from one neuron to another, By means of the synaptic space between them. These signals travel to and from the central nervous system, with the aim of coordinating our body, regulating muscle activity, body fluids and the activity of different organs.
Chemical messengers that act as neurotransmitters share some basic characteristics: they are stored in synaptic vesicles, they are released when calcium ions (Ca2 +) are introduced into the terminal axon in response to the action potential, and they produce their effect. – Synaptic cell membrane receptors.
The main function of neurotransmitters is to inhibit or stimulate the activity of postsynaptic cells, Depending on the type of receptor on which they exert their effect, triggering changes in neuronal membrane permeability and enzymatic activity, mediated by other neuromodulators (such as cAMP and cGMP).
There are different types of neurotransmitters which can be classified as follows:
- amines: Neurotransmitters derived from different amino acids. In this group we can include dopamine or serotonin.
- amino acids: These are the precursor substances of amines (eg glutamate or glycine).
- purines: Substances such as ATP or adenosine can also act as chemical messengers.
- peptides: Distributed throughout the brain, the best known are opioid peptides (for example, encephalins and endorphins), which are responsible, among other things, for the modulation of pain.
- Gases: The most representative nitric oxide, which produces vasodilator effects.
- esters: In this group, the most representative neurotransmitter, acetylcholine, which is involved in the regulation of sleep or muscle activity, among many other functions.
Differences between hormones and neurotransmitters
Hormones and neurotransmitters share a fundamental characteristic, namely that they both act as chemical messengers, intervening in the regulation of different bodily functions. however, there are important differences between a hormone and a neurotransmitter. Then we’ll see which ones.
One of the differences between hormones and neurotransmitters is that the former are released by the endocrine glands into the bloodstream; on the other hand, neurotransmitters are released into the synaptic space which is between neurons. This brings us to underline another fundamental difference, namely that the effect produced by hormones is generally much more prolonged than that of neurotransmitters.
Another characteristic that differentiates these two types of chemical messengers is that the neurotransmitter, when released, it only communicates with the closest neuron, Through the synaptic space; however, the hormones communicate with other cells which may be at a great distance as they move through the bloodstream. The difference would also be that neurotransmitters act specifically on the nervous system, whereas hormones could do so anywhere in the body.
Sometimes the distinction between hormone and neurotransmitter is not at all clear. Some neurotransmitters also act as hormones, just like catecholamines (adrenaline, norepinephrine, and dopamine). These can be produced by the adrenal glands and put into the bloodstream, exerting a hormonal effect; and at the same time, they are released at nerve endings, acting as neurotransmitters. In these cases, they are also called neurohormones.
According to French physician Roger Guillemin, a neurotransmitter is nothing more than a secreting paracrine hormone (a type of cellular communication by chemical secretion), although due to its specific characteristics, it is generally considered to be another type of messenger other than the hormone.
However, at present there are still authors who consider that a hormone is any substance that is released by a cell to act on another, Near or far, and regardless of its origin or location, as well as the route used for its transport (blood circulation, extracellular fluid or synaptic space). The definitions of hormone and neurotransmitter are therefore still subject to interpretation.
- Conca, EM (2006). Fundamentals of physiology. Editorial Paranimf.
- Gómez, M. (2012). Psychobiology. CEDE PIR preparation manual 12. CEDE: Madrid.
- Guyton-Hall (2001). Treatise on medical physiology, 10th ed., McGraw-Hill-Inter-American.