Hormones are molecules of different nature that are produced in the secretory or endocrine glands . Working together with the nervous system, they are responsible for making us act, feel and think as we do.
The different types of hormones are either released into the blood vessels or the interstitial space where they circulate on their own (bioavailable), or they are associated with certain proteins until they reach the target organs or tissues (or target) where they act. Hormones are part of the group of chemical messengers, which also includes neurotransmitters such as dopamine, serotonin or GABA.
The most important functions of hormones
The functions of hormones are varied, but whether a hormone comes from a plant, invertebrate or vertebrate animal, it is responsible for regulating several important functions. Now… why are hormones so important?
One of the functions they perform is to ensure proper growth. In humans, the pituitary gland is responsible for secreting growth hormones during childhood and adolescence. In invertebrate animals, such as insects, growth hormone is involved in the moulting or renewal of the integuments (body coverings), i.e. the shedding of the outer layer. In the case of plants, several hormones are responsible for the proper growth of roots, leaves and flowers.
In addition to this very important function, the functions of hormones include :
- Dynamic action on various organs
- Activate or inhibit enzymes
- Appropriate development
- Sexual characteristics
- Energy use and storage
- Blood levels of fluids, salt and sugar
Coordinating with the brain
Another fact that we must take into account is that some biological processes are less costly if, instead of creating a constant electrical firing stream by the neurons to activate certain regions of the body, we simply emit types of hormones and let them be carried by the blood until they reach their destination. In this way we achieve an effect that lasts for several minutes while our nervous system can take care of other things.
In that sense, the hormones work by coordinating with the brain to activate and deactivate parts of the body to ensure that we adapt to the circumstances in real time. However, the effects of the release of these hormones take a little longer to be noticed than those caused by the neurons.
Classification of hormones: what types of hormones are there
However, there are different classifications of hormones .
What are these classifications and according to what criteria are they established? We explain them below.
1. By proximity of your site of synthesis to your site of action
Depending on whether they have an effect on the same cells that synthesized it or on adjacent cells, the hormones can be
- Autocrine Hormones : Autocrine hormones act on the same cells that synthesized them.
- Paracrine Hormones : Are those hormones that act close to where they were synthesized, that is, the effect of the hormone is produced by a cell neighboring the emitting cell.
2. According to its chemical composition
According to their chemical composition, there are four types of hormones
- Peptide Hormones : These hormones are composed of chains of amino acids, polypeptides or oligopeptides. The vast majority of these types of hormones do not manage to cross the plasma membrane of the target cells, which causes the receptors of this class of hormones to be located on the cell surface. Among the peptide hormones, we find: insulin, growth hormones or vasopressin.
- Amino acid derivatives : These hormones emanate from different amino acids, such as tryptophan or tyrosine. For example, adrenaline.
- Lipid Hormones : This type of hormones are eicosanoids or steroids. Unlike the previous ones, they do manage to cross the plasma membranes. Prostaglandins, cortisol and testosterone are some examples.
3. According to their nature
Depending on this class of substances produced by the body through its nature, there are the following types of hormones:
- Steroid Hormones : These hormones come from cholesterol and are produced mainly in the ovaries and testicles, as well as in the placenta and adrenal cortex. Some examples are: androgens and testosterone, which are produced in the testes; and progesterone and estrogen, which are produced in the ovaries.
- Protein Hormones : Are hormones formed by chains of amino acids and peptides.
- Phenolic derivatives : Despite being of a protein nature they have a low molecular weight. One example is adrenaline, which intervenes in situations where a large part of the body’s energy reserves must be invested in moving the muscles quickly.
4. According to its solubility in the aqueous medium
There are two types of hormones according to their solubility in the aqueous medium:
- Hydrophilic (water-soluble) hormones : These hormones are soluble in the aqueous medium. Since the target tissue has a membrane with lipid characteristics, hydrophilic hormones cannot cross the membrane. Thus, this type of hormones bind to receptors on the outside of the tissue. For example: insulin, adrenaline or glucagon.
- Lipophilic (lipophilic) hormones : These hormones are not soluble in water, but are soluble in lipids. Unlike the previous ones, they can cross the membrane. Therefore, the receptors of this type of hormones can bind to intracellular receptors to carry out their action. Examples: thyroid hormone or steroid hormones.
Endocrine Gland Types
Hormones are produced in the endocrine glands throughout the body. In many ways, our nervous system needs the collaboration of other parts of the body to make the processes that take place within the body coordinated and to maintain a certain balance.
To achieve this level of coordination, our brain regulates the release of various types of hormones responsible for performing different functions. In addition, these types of substances vary according to the type of gland that secretes them, and their location.
The main endocrine glands are:
- The pituitary gland : It is considered the most important gland of the endocrine system, because it produces hormones that regulate the functioning of other endocrine glands. It can be influenced by factors such as emotions and seasonal changes.
- The hypothalamus: This endocrine gland controls the functioning of the pituitary gland, secreting chemicals that can stimulate or inhibit hormone secretions from the pituitary.
- thymus : secretes a hormone called thymosin, which stimulates the growth of immune cells
- The pineal gland : Produces melatonin, a hormone that plays an important role in adjusting sleep and wake cycles.
- The testicles : These produce hormones called estrogens, the most important of which is testosterone, which tells males that it is time to initiate the body changes associated with puberty, for example, the change in voice and the growth of beard and pubic hair.
- The ovaries : secrete estrogen and progesterone. Estrogen signals girls to initiate the body changes associated with puberty.
- The thyroid : This endocrine gland produces thyroxine and triiodothyronine, hormones that control the speed at which cells burn fuel from food to produce energy.
- The adrenal glands : These glands have two parts. One produces hormones called corticosteroids, which are related to the balance between mineral salts and water, the response to stress, metabolism, the immune system and sexual development and function. The other part produces catecholamines, for example, adrenaline
- The parathyroid : From here parathyroid, a hormone related to blood calcium concentration, is released.
- The pancreas : Secrets insulin and glucagon, allowing it to maintain a stable concentration of glucose in the blood and to supply the body with enough fuel to produce the energy it needs.
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