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Steroid Hormones

Steroid hormones: Types and Functions

Steroid hormones are small lipid-soluble molecules – chemical messengers of the body derived from a single source: cholesterol. The four primary types of steroid hormones are:

  • Androgens
  • Corticoids
  • Estrogens
  • Progestins

Steroid hormone formation occurs in different areas of the body, primarily in the following endocrine glands:

  • Women: adrenal glands, ovaries, placenta (incomplete)
  • Men: adrenal glands, testes

Another source of some steroid hormones is the nonendocrine peripheral tissue, including:

  • Brain
  • Fat
  • Intestine
  • Kidneys
  • Liver
  • Skin

Although LDL cholesterol has long been vilified, it is the actual precursor to critical steroid hormones. Without enough cholesterol, the body will not have enough material to create essential hormones. Maintaining a healthy HDL to LDL cholesterol ratio is crucial to hormone homeostasis (balance).

According to dictionary sources, the steroid hormones definition is that of having a characteristic ring structure of steroids which are formed from cholesterol. These vital functions are critical to a well-functioning body. Too much or too little of any steroids can alter bodily homeostasis, leading to an array of possible medical issues.

Proper function of steroid hormones is crucial for the heart, as red blood cell production, blood pressure regulation, electrolyte balance, metabolism, insulin regulation, and cholesterol regulation are all associated with various steroids.

Steroid hormones are crucial to the body and help to maintain homeostasis and proper functions.

How Steroid Hormones Work

When steroid hormones enter the bloodstream, they must bind to proteins to carry them to their appropriate receptor cells. Because they are lipids, steroid hormones are fat-soluble rather than water-soluble. They cannot move through the bloodstream on their own. Sex hormone-binding globulin (SHBG) is the primary transporter of testosterone, estradiol, and DHT. Albumin can bind to all steroids, although the connection has a low affinity, making the hormones readily available to their receptors. The SHBG binding is high affinity, requiring increased steps for the release of the hormones to their receptor cells. The protein corticosteroid-binding globulin (CBG) transports the corticosteroids, 17a-hydroxyprogesterone, and progesterone through the bloodstream.

Unbound steroids bind with their receptors to create the mechanisms of action we will explain in the next section.

Steroid hormones benefits consist of the following types of actions:

  • Reproduction
  • Metabolism
  • Blood pressure regulation
  • Stress responses
  • Red blood cell production
  • Muscle development
  • Bone mineralization
  • Brain function support
  • Behavior and emotional actions
  • Electrolyte regulation

By looking at that list, it might be easy to place hormones that are not steroids into that category due to anabolic-like tendencies. After all, muscle and bone strengthening are considered anabolic functions. To that end, which of the following hormones is a steroid, and which is not?

  • Testosterone
  • Growth hormone
  • Insulin growth factor 1

Of that list, only testosterone is a steroid. Although growth hormone and IGF-1 accomplish anabolic-like functions of helping build lean muscle mass and bone density, they are peptide hormones, not steroids.

Steroid hormones work to support many crucial functions in the body, including reproduction, metabolism, and stress responses.

Steroid Hormone Mechanism of Action

Every hormone in the body has a unique function and receptor cells. A hormone typically cannot bind to another hormone’s receptors, except in limited cases. There are also differences in how hormones interact with their receptors. Some hormones bind to receptors on the outside of cells. In the case of steroid hormones, they must first pass through the cellular plasma membrane of the receptor and enter the cytoplasm to form a receptor-hormone complex.

How do steroid hormones work once they form the receptor-hormone complex?

The next step involves entering the nucleus where a second binding occurs, this time to a receptor on the chromatin to trigger a process called gene transcription resulting in the production of messenger RNA molecules that are then modified and transported back into the cytoplasm where they carry out their functions by activating production of proteins.

Using cholesterol as a base, a series of steps occurs where various enzymes, encoded by different genes, converts the source cholesterol into different hormones. Pregnenolone is the first of the steroid hormones to come from the cholesterol source. Adrenocorticotropin hormone (ACTH) produced in the pituitary gland stimulates the conversion of cholesterol in the adrenal glands, and luteinizing hormone begins the process in the testes and ovaries. Once formed, pregnenolone is then available for enzymatic conversion into the other types of steroid hormones.

The peptide hormones responsible for steroid hormone synthesis are:

  • Adrenocorticotropin hormone (ACTH): cortisol
  • Luteinizing hormone (LH): progesterone and testosterone
  • Follicle-stimulating hormone (FSH): estrogen (also responsible for sperm production)

Androgen hormones can come from the adrenals, testes, and ovaries, but only the adrenal glands can produce the corticoids – also called corticosteroids. Estrogen hormones come from the ovaries and testes. The placenta is an incomplete source of endocrine hormones as it lacks cholesterol-forming enzymes. It can form pregnenolone using maternal and fetal cholesterol, which it then converts to progesterone. Since there are no enzymes for future conversion, the placenta uses maternal and fetal precursors to produce estrogens.

In peripheral tissues, steroid hormones are synthesized from enzymes. The androgens testosterone and androstenedione undergo aromatization as part of their conversion to estradiol and estrone – two forms of estrogen. Aromatase, an enzyme produced by fat, converts these androgens into the estrogen hormones. The more fat a person has, specifically in the abdominal region, the greater the incidence of conversion. That is also why people who are overweight have an increased risk of developing testosterone deficiency and estrogen dominance as the testosterone to estrogen ratio in the body changes. DHT (dihydrotestosterone) is another example of a steroid hormone produced in peripheral tissue, this one in the skin by the enzyme 5-alpha reductase.

In the adrenal glands, steroid hormones are produced by the adrenal cortex and the adrenal medulla. The cortex is the outer part of the adrenal glands, and the medulla is the inner part. The adrenal cortex features three separate zones, each producing different hormones:

  • Zona Fasciculata
  • Zona Glomerulosa
  • Zona Reticularis

The Zona Reticularis is the area of the adrenal glands responsible for additional androgen steroid production of DHEA, androstenedione, and testosterone.

Steroid hormone mechanism of action begins with the conversion of cholesterol in a series of enzymatic processes.

Types of Steroid Hormones

The ovaries, testes, and adrenal glands are the primary producers of steroid hormones. There are two adrenal glands, one on top of each kidney. The ovaries and testes make up the gonads – the female and male reproductive organs and endocrine glands.

The adrenal glands are responsible for producing the following types of steroid hormones:

  • Corticoids:
    • Mineralocorticoids
    • Glucocorticoids
  • Androgens
    • Androstenedione
    • DHEA
    • DHEAS
    • Testosterone

The steroid hormones list of the gonads (ovaries and testes) includes many hormones, including the three most common:

  • Estrogen
  • Progesterone
  • Testosterone

One of the primary differences in gonadal steroids is the difference between males and females. Although testosterone and estrogen are both vital for all adults, their levels are not the same. Males have significantly higher testosterone levels than females, who have more estrogen in their bodies. However, because estrogen and testosterone have vital functions for the brain, bones, muscles, reproduction, and more, their levels must remain in proper balance.

The anabolic properties of androgen hormones help to prevent problems such as osteoporosis from occurring in later years of adulthood.

Various types of steroid hormones are produced in the adrenal glands and gonads, some in both areas.

Adrenal Gland Hormones

The adrenal glands consist of an outer layer called the cortex and an inner layer called the medulla – each responsible for the secretion of different steroid hormones. The hormones of the adrenal cortex, broken down by each zone, include:

  • Zona Glomerulosa: The outermost layer of the adrenal cortex is the producer of mineralocorticoids:
    • Aldosterone: action is exerted on the kidneys, salivary glands, stomach, and sweat glands
      • Increases sodium reabsorption and excretion of potassium and hydrogen ions by the kidneys to maintain PH balance in the blood
      • Long-term blood pressure regulation
    • Corticosterone: the precursor hormone to aldosterone, corticosterone levels increase after stress
      • Exerts effects on long-term memory, including stress effects on memory due to stress disrupting reconsolidation of emotional memory
  • Zona Fasciculata: The adrenal cortex layer between the glomerulosa and reticularis responsible for producing the glucocorticoid hormones cortisol as well as corticosterone:
    • Cortisol: a primary stress hormone also known as hydrocortisone
      • Stress hormone that helps prepare the body to handle a stressful situation
      • Regulating the following:
        • blood pressure
        • blood glucose levels by inhibiting muscle and fat cell uptake of glucose
        • metabolism (releasing amino acids, stimulating lipolysis)
      • Suppresses inflammation
      • Increases water retention
      • Strengthens cardiac muscle contractions
      • Provides immune system support
      • Decreases bone formation
      • Regulates sleep/wake cycle
  • Zona Reticularis: The adrenal cortex innermost layer responsible for androgen hormones:
    • DHEA and DHEA-S: precursors to androstenedione, testosterone, and estrone (estrogen)
    • Androstenedione: precursor for testosterone and estrogen
    • Testosterone: primary male sex hormone
    • Estrogen: primary female sex hormone

What are steroid hormones from the adrenal medulla?

The adrenal medulla provides hormones that help during stress, although they are not essential for life. Adrenal medulla hormones are water-soluble and are part of the fight-or-flight response, including:

  • Dopamine: the precursor hormone to adrenaline and noradrenaline
  • Adrenaline: also called epinephrine, adrenaline provides the following functions:
    • Sends blood rushing to the muscles and brain so they can respond to the stressor
    • Rapidly increases heart rate for stress response
    • Assists with converting glycogen stored in the liver into glucose which is then released in the bloodstream to raise blood sugar levels
  • Noradrenaline: also called norepinephrine, noradrenaline works with adrenaline for the following:
    • Narrowing (constriction) of blood vessels for blood pressure increase

The steroid hormones of the adrenal glands help the body in times of stress and are often called the fight-or-flight hormones.

Gonadal Hormones

The gonadal hormones are what people typically think of when they hear the words steroid hormones. Not only are these chemical messengers crucial for reproduction, but they each play other vital roles in a healthy body. The testes in the male and the ovaries in the female are the primary producers of these hormones.

The primary gonadal steroid hormones examples include:

The Progestogens:

  • Pregnenolone: the hormone synthesized from cholesterol:
    • Precursor to all other steroid hormones
    • May help cognitive functions and memory
    • Might protect against schizophrenia
  • Progesterone: synthesized from pregnenolone, the precursor to hormones that lead to testosterone, and subsequently estrogen production:
    • Menstrual cycle regulator
    • Readies the uterine lining for pregnancy
    • Anti-inflammatory
    • Precursor hormone to testosterone
    • Support skin elasticity
    • Normalizes blood clotting
    • Aids nerve functions
    • Exerts protective benefits for damaged brain tissue
    • Balances zinc and copper levels
    • Helps regulate glial cells
    • Assists pancreatic release of insulin

The Androgens:

  • Testosterone: an androgen hormone produced by the Leydig cells in the testes and the thecal cells of the ovaries, functions include:
    • Male sex organ development
    • Spermatogenesis
    • Libido stimulation
    • Production of red blood cells in bone marrow
    • Stimulation of osteoblast (new bone cell) production
    • Muscle protein synthesis
    • Cognitive functions
    • Emotional well-being
  • Dehydroepiandrosterone (DHEA): a precursor hormone to testosterone and estradiol, DHEA functions include:
    • Body and pubic hair development and body odor
    • Serves as a weak estrogen hormone by enabling estrogenic effects through estradiol conversion in the vagina
    • Exerts neurosteroid effects on the central nervous system
  • Androstenediol (A5): metabolite of DHEA involved in gonadotropin secretion
  • Androstenedione (A4): a precursor hormone of testosterone and estrone
  • Androsterone: androgen breakdown creates this chemical byproduct which is synthesized from protein
  • Dihydrotestosterone (DHT): comes from the conversion of testosterone by the enzyme aromatase in the tissues of the prostate gland and seminal vesicles, hair follicles, skin, liver, brain, and epididymis, and functions include:
    • Growth of body, facial, and pubic hair
    • Male genitalia, seminal vesicles, and prostate gland development
    • Excess DHT can lead to balding and increased body and facial hair growth

The Estrogens: four forms in the body:

  • Estradiol: aromatase converts testosterone into estradiol in the testes and ovaries, functions include:
    • Female breast development and hip widening
    • Vaginal lining support
    • Neuroprotective effects on the brain
    • Decreases bone resorption
    • Assists lung functions
    • Protects skin elasticity and thickness
    • Increases cortisol levels
  • Estrone: a precursor to estradiol, elevated levels in men may indicate type 2 diabetes
    • Increases during menopause
    • Promotes production of nitric oxide
    • Protects the brain and heart
    • Neuroprotective benefits following injury
  • Estriol: a pregnancy form of estrogen produced by the placenta, may inhibit certain breast cancer cells and have anti-inflammatory and gut-healing properties
  • Estetrol: pregnancy estrogen synthesized from estriol and estradiol in the fetal liver, function unknown, may influence liver function, lipid metabolism, bone, and growth endocrine parameters

As a supplemental anabolic steroid, testosterone is often abused by athletes and bodybuilders. Anabolic steroids stimulate muscle protein synthesis to increase muscle mass and strength. Although illegal in sports, many males and some females continue the practice of using steroids. At National HRT, we do not approve of that use as there are considerable steroid hormones side effects that could occur. Infertility, heart attacks, aggressive behaviors, depression, and many other risk factors can influence health and well-being.

Maintaining proper hormone balance in the body is crucial. If you suspect hormonal imbalance, please contact National HRT hormone clinic for a confidential telephone consultation at no charge.

Medically reviewed by   Reviewers National HRT Staff - Updated on August 2, 2019

Please note that the information provided in this article is for informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment.