The main differences between hormone and neurotransmitter

Our body needs hormones and neurotransmitters to function properly.

Neurotransmitters allow communication between neurons and other cells, crossing the synaptic gap and through nerve impulses. Hormones, for their part, are secreted by the endocrine glands, intervening in the regulation of a multitude of basic bodily functions.

Although they share structural and functional characteristics, there are also aspects that differentiate them. In this article we explain what they are, how they work and what they are. the main characteristics of hormones and neurotransmitters, as well as the most important differences between them.

• Related article: "Types of neurotransmitters: functions and classification

Hormones: definition, characteristics and classification

Hormones are chemical substances that act as messengers and activate different processes for our body to function properly. Produced in endocrine or secretory glands (such as the hypothalamus, pituitary or thyroid, for example) and are released into the extracellular space, diffusing through the blood vessels into the blood.

The main characteristics of these chemical messengers is that they are involved in metabolism and other functions (immune system, sexual reproduction, etc.); they act in tissues of the organism that can be at long distances from the point of origin from where 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 classified, chemically, into three large groups.: peptide hormones, composed of amino acids, polypeptides or oligopeptides, such as insulin or vasopressin; hormones derived from amino acids, which use them to synthesize, such as adrenaline; and lipid hormones, from the group of eicosanoids or steroids, such as cortisol and testosterone.

Hormones can produce stimulatory effects, promoting activity in a tissue (eg. eg prolactin); inhibitory effects, decreasing activity (eg. eg somatostatin, which inhibits the release of growth hormone); antagonistic effects, when two hormones have opposite effects on each other (eg. eg insulin and glucagon); and synergistic effects, when two hormones together produce a stronger effect than they do alone (eg. eg growth hormone and thyroid hormones).

• You may be interested in: "Types of hormones and their functions in the human body"

Neurotransmitters: definition, classification and characteristics

neurotransmitters are chemicals that our body uses to send information from one neuron to another, through the synaptic gap that mediates between them. These signals travel to and from the central nervous system, with the aim of coordinating our organism, regulating muscle activity, body secretions and the activity of different organs.

The chemical messengers that act as neurotransmitters share some basic characteristics: they are stored in synaptic vesicles, they are released when they are introduced calcium ions (Ca2+) in the axon terminal in response to the action potential and produce their effect by binding to receptors on the cell membrane post-synaptic.

The main function of neurotransmitters is to inhibit or stimulate the activity of post-synaptic cells, depending on the type of receptor on which they exert their effect, triggering changes in the permeability of the neuronal membrane and its enzymatic activity, mediated by other neuromodulators (such as cAMP and cGMP).

There are different types of neurotransmitters that can be classified as follows:

• amines: neurotransmitters that derive from different amino acids. In this group we can include dopamine or serotonin.
• Amino acidsThey are the precursor substances of amines (eg. 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 (eg. eg enkephalins and endorphins), responsible for modulating pain, among other functions.
• gases: the most representative, nitric oxide, which produces vasodilator effects.
• esters: in this group, the most representative neurotransmitter, acetylcholine, which is involved in regulating sleep or muscle activity, among many other functions.

Differences Between Hormones and Neurotransmitters

Hormones and neurotransmitters share a basic characteristic and that is that both act as chemical messengers, taking part in the regulation of different bodily functions. However, there are important differences between a hormone and a neurotransmitter. Next, we will 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 contrary, neurotransmitters are released into the synaptic gap that exists between neurons. This leads us to point out another basic difference, and that is that the effect produced by hormones is, in general, much longer than that of neurotransmitters.

Another characteristic that differentiates these two types of chemical messengers is that the neurotransmitter, when released, only communicates with the nearest neuron, across the synaptic gap; however, hormones communicate with other cells that may be a great distance away as they travel through the bloodstream. The difference would also be that neurotransmitters act specifically on the nervous system, while hormones could do so anywhere in the body.

Sometimes the distinction between hormone and neurotransmitter is not entirely clear. Some neurotransmitters also act as hormones, such as catecholamines (adrenaline, norepinephrine, and dopamine). These can be produced by the adrenal glands and released into the bloodstream, exerting a hormonal effect; and at the same time, they are released in the nerve endings, acting as neurotransmitters. In these cases, they are also called neurohormones.

According to the French doctor, Roger Guillemin, a neurotransmitter would be nothing more than a paracrine secretion hormone (a type of communication cell by chemical secretion), although due to their specific characteristics, it is usually considered that they are another type of messenger different from 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, either 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 thus remain open to interpretation.

Bibliographic references:

• Cuenca, E. m. (2006). Fundamentals of physiology. Editorial Paraninfo.
• Gomez, M. (2012). Psychobiology. CEDE Preparation Manual PIR.12. CEDE: Madrid.
• Guyton-Hall (2001). Treatise on Medical Physiology. 10th ed., McGraw-Hill-Interamericana.