Steroid Hormone Structure and Biological Role in Humans

Steroid hormone is a group of hormones, belonging to the class of chemical compounds known as the steroid that is secreted mainly by three steroid glands, which are the adrenal cortex, testes, and ovaries, and placenta during the period of pregnancy. All types of steroid hormones are derived from cholesterol, and they are transported through the bloodstream to the cells of various target organs, to perform and regulate their various range of physiological functions.  

Classification of Steroids

Classification of steroids are done based on their function, with prominent members and examples related to their functions. They are mainly grouped into two classes-  corticosteroids (includes glucocorticoids and mineralocorticoids), and sex steroids (includes progesterone, androgens and estrogens).

Corticosteroids 

They are a class of steroid hormones produced in the adrenal cortex of the vertebrates, as well as synthetic analogues of these hormones. There are two main classes of corticosteroids that are glucocorticoids and mineralocorticoids and they are involved in the various processes of the body, consisting of the stress response, immune response, and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte levels, and behaviour.

• Glucocorticoids (also known as glucocorticosteroids) are a type of steroid hormone that belongs to the corticosteroids family. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor, which can be found in nearly every cell of a vertebrate species. The word "glucocorticoid" is the combination of the (glucose + cortex + steroid) that refers to its role in glucose metabolism control, synthesis in the adrenal cortex, and its steroidal structure. 

Glucocorticoids are part of the immune system's feedback process, which decreases inflammation and other aspects of immune function. As a result, they're used in medicine to treat conditions like allergies, asthma, autoimmune diseases, and sepsis that are exacerbated by an overactive immune system. Since glucocorticoids have a wide range of (pleiotropic) effects, including potentially harmful side effects, they are hardly ever distributed over-the-counter. 

They are also used in some of the abnormal pathways in cancer cells, so they're used to treat cancer at high doses. This involves inhibiting lymphocyte proliferation in the treatment of lymphomas and leukaemias, as well as reducing anticancer medication side effects.

• Mineralocorticoids are a subclass of corticosteroids, which are steroid hormones themselves. Mineralocorticoids are hormones that are produced in the adrenal cortex and maintain salt and water balance in the body (electrolyte balance and fluid balance). Aldosterone is the most primary mineralocorticoid.

Sex Steroid Hormones 

Sex hormones are steroid hormones that bind with vertebrate steroid hormone receptors. They are also classified as sex steroids, gonadocorticoids, and gonadal steroids. Androgens, estrogens, and progestogens are sex hormones. Slow genomic mechanisms, such as nuclear receptors, as well as fast nongenomic mechanisms, such as membrane-associated receptors and signalling cascades, mediate their effects. 

While they play an important role in sex-related functions, the polypeptide hormones luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone are not normally considered sex steroid hormones.

• Progestogens, which can also be written as progestogens or gestagens. They are the class of steroid hormones that bind to and activate the progesterone receptor (PR). The most important progestogen in the human body is progesterone. The name progestogens are given because of their function in maintaining a pregnancy. Even though they are also present at other phases of the estrous and menstrual cycles.

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• Androgen is any natural or synthetic steroid hormone that binds to receptors in vertebrates and regulates the production and maintenance of male characteristics. The embryological development of the primary male sex organs, as well as the development of male secondary sex characteristics during puberty, are included. The testes, ovaries, and adrenal glands are where androgens are produced. Testosterone is the hormone, that contributes to the development and maintenance of the secondary sex characteristics in the man. 

• Estrogen, also known as oestrogen, is a sex hormone that is involved in the production and control of the female reproductive system as well as secondary sex characteristics. Estrone (E1), estradiol (E2), and estriol (E3) are the three main endogenous estrogens of estrogenic hormonal activity. The most powerful and common estrane is estradiol. Estestrol (E4) is another oestrogen that is only released during pregnancy. Estradiol is a hormone that helps to establish and maintain female secondary sex characteristics.

Functions of the Steroid Hormones 

Some of the steroid hormones lists of function are given below:

• Carbohydrate regulation 

• Mineral balance 

• Reproductive functions 

• Inflammatory response

• Stress response

• Bone metabolism 

• Cardiovascular fitness 

• Activates DNA for protein synthesis 

Synthesis of the Steroid Hormones 

The gonads and adrenal glands produce natural steroid hormones primarily from cholesterol. Lipids are hormones in this form as they are fat-soluble, they can move through the cell membrane and bind to steroid hormone receptors (which can be nuclear or cytosolic depending on the steroid hormone) to cause changes within the cell. Steroid hormones are transported in the bloodstream by carrier proteins including sex hormone-binding globulin or corticosteroid-binding globulin. The liver, as well as other "peripheral" tissues and target tissues, undergo additional conversions and catabolism.

Mechanism of Action and Effects 

Steroid hormones have a variety of pathways by which they influence their target cells. All of these various pathways can be categorised as either genomic or nongenomic in nature. Non-genomic pathways are much quicker than genomic pathways, which are slow and result in changes in the transcription levels of specific proteins in the cell.

1. Genomic Pathways

The genomic effects were the first mechanisms of steroid hormone activity to be discovered. Since free form of the steroid hormones are fat-soluble, they must first move through the cell membrane in this pathway. The steroid may can or may not undergo enzyme-mediated changes in the cytoplasm, such as reduction, hydroxylation, or aromatization. The steroid then binds to a massive metalloprotein called a nuclear receptor, which is also known as a steroid hormone receptor. Many types of steroid receptors dimerize in response to steroid-binding: two receptor subunits combine together to form a single functional DNA-binding unit that can reach the cell nucleus. The steroid-receptor ligand complex enters the nucleus and binds to unique DNA sequences, inducing transcription of its target genes. 

2. Non-Genomic Pathways

There are numerous non-genomic pathways because they include any mechanism that is not a genomic effect. All of these pathways, however, are mediated by steroid hormone receptors found on the plasma membrane. Steroid hormones have been shown to influence ion channels, transporters, G-protein coupled receptors (GPCR), and membrane fluidity. GPCR-linked genes are among them and are most common. 

Do You Know?

How to increase steroid hormones naturally? Some of the ways to increase the level of steroid hormones are stated below:

• By doing exercise and lifting weights 

• Eating food right in protein, fat and carbs. 

• Minimising stress and cortisol levels. 

• Taking vitamin D supplement or directly from the sun.

• Get good better quality deep sleep and plenty of full sleep. 

• By consuming some of the natural testosterone boosters. 

• And finally, by following a healthy lifestyle and avoiding estrogen-like compounds.

Conclusion

This is all about steroidal hormones, how they are synthesised and how they function in the human body. Focus on how these hormones act on different tissues and organs of human bodies and understand their functions.