Hormones

Hormones are molecules produced by specific glands of the endocrine system. They are secreted directly into the bloodstream, allowing them to travel through the body and act on target organs and tissues. Unlike neurotransmitters, which act at specific synapses in the nervous system, hormones have broader and longer-lasting effects.

The word hormone comes from the Greek ‘hormao’, which means ‘to excite’ or ‘to stimulate’. This reflects its essential function in the regulation and coordination of the biological functions of the organism.

Classification of hormones

Hormones can be classified in various ways, depending on their chemical structure, function or origin. The most common classifications are described below:

1. According to its chemical structure

• Steroid hormones: Derived from cholesterol, these hormones are lipophilic and can easily cross cell membranes. They include sex hormones such as estrogen and testosterone, as well as adrenal hormones such as cortisol.

• Peptide hormones: Composed of chains of amino acids, these hormones are hydrophilic and cannot cross cell membranes. They are produced in the pituitary and pancreatic glands, and include hormones such as insulin and growth hormone.

• Hormones derived from amino acids: These hormones are products of the modification of specific amino acids. Examples are adrenaline (derived from tyrosine) and melatonin (derived from tryptophan).

2. According to its function

• Trophic hormones: These hormones stimulate other endocrine glands to release hormones. For example, adrenocorticotropic hormone (ACTH) stimulates the adrenal glands to release cortisol.

• Nontrophic hormones: These hormones have direct effects on target tissues. For example, insulin regulates the uptake of glucose into the body’s cells.

Main endocrine glands and their hormones

The endocrine system is made up of several glands that produce and secrete hormones. Some of the main endocrine glands and their hormones are:

1. Pituitary gland

Known as the “master gland,” the pituitary gland regulates many hormonal functions in the body. It is located at the base of the brain and secretes several hormones, including:

• Growth hormone (GH): stimulates cell growth and regeneration.

• Prolactin (PRL): regulates milk production in lactating women.

• Thyroid stimulating hormone (TSH): stimulates the thyroid to produce thyroid hormones.

• Gonadotropic hormones (LH and FSH): regulate the function of the ovaries and testicles.

2. Thyroid

Located in the neck, the thyroid gland produces hormones that regulate metabolism. The main hormones are:

• Thyroxine (T4) and triiodothyronine (T3): regulate metabolic rate and energy production.

• Calcitonin: regulates calcium levels in the blood.

3. Pancreas

The pancreas has a dual function, acting as both an endocrine and exocrine gland. Produces hormones such as:

• Insulin: facilitates the uptake of glucose by cells, reducing blood sugar levels.

• Glucagon– Increases blood sugar levels by stimulating the release of glucose stored in the liver.

4. Adrenal glands

Located above the kidneys, these glands produce hormones involved in the stress response. Among them are:

• Cortisol: regulates metabolism and stress response.

• Adrenaline (epinephrine)– Increases heart rate and blood pressure during stressful situations.

5. Gonads

The gonads are the reproductive organs that produce sex hormones:

• Testicles: produce testosterone, responsible for male characteristics and sperm production.

• Ovaries: produce estrogen and progesterone, which regulate the menstrual cycle and pregnancy.

Mechanisms of hormonal action

Hormones exert their effect on the body through specific receptors located on cell membranes or inside cells. The type of receptor determines how the cell will respond to the hormone:

1. Membrane receptors: Peptide hormones and some hormones derived from amino acids bind to receptors on the cell surface. This activates a series of cascade reactions within the cell, known as signal transduction, that produce cellular effects.

2. Intracellular receptors: Steroid hormones cross the cell membrane and bind to receptors within the cytoplasm or nucleus. This binding activates or deactivates specific genes, which alters protein production and therefore affects cellular function.

Hormonal regulation

The regulation of hormone production and release is a complex process that is carried out through different mechanisms, including:

• Negative feedback: This is the most common mechanism of hormonal regulation. When levels of a hormone reach a specific threshold, signals are sent to the body to reduce its production. For example, when cortisol levels are high, the hypothalamus and pituitary gland reduce the release of hormones that stimulate cortisol production.

• Positive feedback: In some cases, hormone production is stimulated rather than inhibited. An example is increased oxytocin production during childbirth, which causes stronger uterine contractions and, in turn, more oxytocin release.

• External stimulation: Hormone production can also be stimulated by external factors, such as stress or changes in diet. For example, blood glucose stimulates the release of insulin.

Impact of hormones on health

Hormones have a significant impact on physical and mental health. Some of the most important effects are explored here:

1. Regulation of metabolism. Hormones such as insulin, leptin and ghrelin play a crucial role in metabolism and body weight regulation. Insulin helps control blood glucose levels, while leptin and ghrelin regulate hunger and satiety. An imbalance in these hormones can contribute to problems such as obesity and type 2 diabetes.

2. Reproductive health. Sex hormones, such as estrogen and testosterone, are essential for reproductive health. A hormonal imbalance can lead to menstrual disorders, infertility and other reproductive problems. Hormonal therapies are often used to treat these disorders.

3. Mood and mental health. Hormones also affect mood and emotional well-being. For example, serotonin and dopamine, which are neurotransmitters, are influenced by hormones. Changes in hormone levels, such as those that occur during the menstrual cycle or menopause, can contribute to mood disorders, such as depression and anxiety.

4. Growth and development. Growth hormones are crucial for growth and development during childhood and adolescence. A deficiency or excess of growth hormone can cause growth disorders, such as dwarfism or gigantism.

Hormonal alterations

Disturbances in the production or action of hormones can lead to various medical conditions. Some of the most common hormonal conditions include:

1. Diabetes. Type 1 diabetes occurs when the pancreas does not produce insulin, while type 2 diabetes develops when the body becomes resistant to insulin. Both conditions affect the body’s ability to regulate blood sugar, which can lead to long-term complications.

2. Polycystic ovary syndrome (PCOS). PCOS is a hormonal disorder that affects women of reproductive age. It is characterized by hormonal imbalances that can cause menstrual irregularities, excess body hair, and fertility problems.

3. Hypothyroidism and hyperthyroidism. These conditions are related to the abnormal production of thyroid hormones. Hypothyroidism occurs when the thyroid does not produce enough hormones, leading to a slow metabolism. In contrast, hyperthyroidism occurs when there is excessive production of thyroid hormones, which speeds up the metabolism.

4. Cushing’s disease. This condition is caused by excessive levels of cortisol in the body, often due to a tumor in the pituitary gland. It can cause weight gain, muscle weakness, and skin changes.

Hormones and aging

As we age, hormone levels naturally change. For example, women experience a decrease in estrogen levels during menopause, which can lead to symptoms such as hot flashes, mood swings, and loss of bone density. In men, testosterone levels tend to decline with age, which can affect libido and muscle mass.

These hormonal changes are a normal part of aging, but they can also increase the risk of certain diseases. For this reason, some choose hormone replacement therapy (HRT) to mitigate the symptoms associated with declining hormones.

Hormonal therapies

Hormone therapy is used to treat various conditions related to hormonal imbalances. There are different types of therapies, including:

• Hormone replacement therapy for menopause: used to relieve symptoms associated with menopause, such as hot flashes and vaginal dryness.

• Hormonal therapy for thyroid disorders: Synthetic thyroid hormones are used to treat hypothyroidism.

• Hormonal contraceptives: Hormonal birth control methods, such as pills, patches, or intrauterine devices (IUDs), help regulate the menstrual cycle and prevent pregnancy.

• Testosterone therapy: used in men with low testosterone levels to improve libido, muscle mass and bone health.

It is important that hormone therapy be administered under the supervision of a doctor, since improper use can have adverse health effects.

In conclusion, hormones are essential messengers that regulate almost all aspects of our biology. Its role in growth, metabolism, reproductive health and emotional well-being is essential for the proper functioning of the body. Knowing how hormones work and how they influence our health can help people make informed decisions about their well-being. As research advances, our understanding of the hormonal system deepens, promising new opportunities for treating hormonal disorders and improving quality of life.