The original definition of a hormone by Starling in 1905 was: "a hormone is a substance produced by glands of internal secretion, which serve to transmit signals through the blood to target organs ".
Today, new definitions also do not cover the entire meaning of hormones as specific carriers of information. A major problem is the lack of distinction between hormones and other signaling molecules such as cytokines, growth factors or autacoid compounds.
However, it seems that a precise definition is not even possible, because some cytokines and growth factors act like hormones under certain conditions!
In this article we will focus on the recognized hormones that are essential chemical messengers and govern the complex functioning of the human body.
Emitted by endocrine glands, these substances play a central role in the regulation and coordination of physiological functions. To explore in depth the effects of hormones on the body, we examine and explain the different hormonal categories and their specific impact.
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Sex hormones: pillar of reproduction
Sex hormones, including estrogen, progesterone in women , and testosterone in men, are crucial for the development of secondary sexual characteristics .
Secondary sexual characteristics are distinct physical traits that develop during puberty that differentiate male and female individuals of a species. These characteristics are not directly linked to reproduction, unlike primary sexual characteristics such as genitalia , but they play an essential role in signaling sexual maturity.
Secondary sexual characteristics emerge under the influence of sex hormones , primarily estrogen and progesterone in women, and testosterone in men.
In women:
- Breast development: Under the influence of estrogen, the mammary glands develop, leading to the formation of breasts. It is one of the first visible signs of puberty in girls.
- Pubic and axillary hair growth: Sex hormones stimulate hair growth in the pubic region and underarms, signaling the start of puberty.
- Body fat distribution: Estrogen affects fat distribution, often leading to increased fat around the hips and thighs.
- Widening of the hips: Puberty often induces a widening of the pelvis, contributing to the characteristic female silhouette.
- Start of menstrual cycle: The onset of menstruation is a key secondary sexual characteristic, marking potential reproductive capacity.
At men's :
- Breast growth: Although less pronounced than in women, a small amount of breast tissue may develop in men during puberty.
- Growth of facial and body hair: Testosterone stimulates the growth of hair on the face, legs, chest and other areas of the body.
- Widening shoulders and jawline: Testosterone promotes muscle development, often leading to shoulder widening and increased jaw definition.
- Growth of Adam's apple: A cartilaginous protrusion called the Adam's apple becomes more pronounced in men during puberty.
- Enlargement of the genitals: Puberty induces the growth of the external genitalia , including the penis and testicles .
- Voice change: Testosterone causes the vocal cords to thicken, causing a significant drop in voice during puberty.
Secreted by the ovaries and testes, sex hormones therefore regulate the menstrual cycle , spermatogenesis and therefore the process of sperm development, and are essential for reproduction. The ovaries, in women, produce estrogen and progesterone, regulating puberty, ovulation and the menstrual cycle .
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Thyroid hormones: architects of metabolism
Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), secreted by the thyroid gland , orchestrate metabolism. They influence energy consumption, growth and development of organs, ensuring hormonal balance and the proper functioning of the body. Thyroid hormones are also essential for brain development during gestation.
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Peptide hormones: rapid regulators
Peptide hormones, such as insulin and adrenaline , secreted by the pancreas and adrenal glands, regulate glucose metabolism, the stress response, and other processes. The pancreas, through insulin, regulates blood sugar levels , while the adrenal glands produce adrenaline, triggering the "fight or flight" response in cases of acute stress.
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Derived hormones: specific origins
Certain hormones, such as melatonin produced by the pineal gland, have particular origins. They influence the circadian cycle, regulating sleep and wakefulness. These derived hormones, often linked to the nervous system, illustrate the diversity of hormonal sources in the human body.
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Endocrine gland: master of hormones
Endocrine glands , including the thyroid, adrenal glands, and pancreas , mediate the secretion and release of hormones . As a hormonal command center, they constantly adjust hormonal levels to meet the body's physiological needs.
The hypothalamus and pituitary gland , key components of the endocrine system , regulate hormone secretion and maintain hormonal balance.
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Growth hormone: development accelerator
Growth hormone, produced by the pituitary gland or in other words the pituitary gland , stimulates the growth and development of tissues. It plays a crucial role in the growth of children and tissue regeneration in adults. Growth stimulation mainly occurs during deep sleep.
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Steroid hormones: key players in the endocrine system
Steroid hormones , such as cortisol and sex hormones , are derived from cholesterol . Secreted by the adrenal glands and gonads , they regulate various functions, from stress response to metabolism regulation. Sex hormones, such as testosterone , are responsible for the development of secondary sexual characteristics .
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Hormone therapy and gender transition
Transgender people have a gender identity that differs from their sex assigned at birth. For many transgender people, access to gender-affirming hormone therapy (GAHT) is an important and medically necessary step in their gender transition.
For transmen, masculinizing hormone therapy consists of testosterone treatment. Testosterone can be given by injection under the skin or into the muscle, by application of gel or by skin solution. Sometimes other hormonal treatments may be prescribed.
For transwomen, feminizing hormone therapy consists of:
- Anti- androgens , by tablets and more rarely by injections, to reduce male hormones .
- Estrogen
- Progesterone
The choice of treatment is made according to the doctor's recommendations as well as the patient's preferences. There is no evidence that one approved way of administering treatment is more effective than another.
What are the physical effects of hormones?
Hormones induce physical changes that are consistent with gender identity.
Most changes are observed over a period of 2 years. The speed and quality of changes vary from one person to another.
Feminization and masculinization diets are safe when used within established hormonal protocols and are associated with significant improvements in mental health outcomes, including reductions in depression, anxiety, and depression. gender dysphoria.
What are the effects of hormone therapy on the skin?
The effects on the skin vary depending on the type of transition, and therefore the hormone therapy favored.
Hormonal therapy can have two major consequences on your skin:
- An epidermis that produces fewer lipids, and therefore less fat: the skin is drier, and problems linked to oily or combination skin (blackheads, adult acne , etc.) tend to decrease. This is often the result of the inhibition of male hormones in favor of female hormones ;
- Or, on the contrary, a greater production of sebum, linked to an increase in male hormones in the body. The skin thickens, becomes oilier, imperfections can appear.
In transmen, increased body hair can cause problems with ingrown hairs: the skin then reddens locally, inflammation occurs, and in some cases, a small hard lump appears under the skin.
How to care for the skin during gender transition?
The beauty routine remains generally the same:
- Cleanse your skin twice a day to remove impurities
- Moisturize the face with a treatment adapted to skin changes: a rich cream for dry skin and a mattifying anti-imperfection cream for skin that becomes oily.
- Perform a scrub and a purifying exfoliating mask once or twice a week to stimulate cell renewal and refine skin texture.
You can favor certain assets:
- Salicylic acid for its immediate exfoliating action on the stratum corneum, which reduces the number of imperfections
- Zinc gluconate to regulate sebum production upstream, reduce shine and eliminate blackheads
As for dry skin, apply a cream rich in lipids and ceramides.
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Hormone replacement therapy
Hormone replacement therapy (HRT) involves supplementing women with hormones that are lost during the menopausal transition. To relieve symptoms associated with menopause , conventional HRT includes an estrogen and progesterone component to mimic the hormones produced by the human ovary. There are many estrogen-based therapies, including those naturally occurring in the human ovary , such as estradiol and estriol. Other estrogenic compounds include conjugated equine estrogen (CEE), the most commonly prescribed estrogen in the United States. They are not identical in their effect on the human body but share the same FDA indications.
Conclusion
Hormones, controllers of homeostasis, direct a sophisticated ballet in the human body. Each category of hormones, whether sexual, thyroid , peptide, derived, endocrine , growth or steroid, contributes uniquely to the maintenance of physiological balance. Secretion , stimulation, and reception by hormone receptors are crucial elements in this complex chemical dance, illustrating the subtlety of hormonal regulation. This in-depth understanding is essential to appreciate the sophistication of endocrine systems and their implications for overall health.
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