Biosynthetic pathways and enzymatic regulation
The synthesis of sex steroids in the body occurs via two main pathways:
- Testicular pathway: characteristic of the male reproductive system. Under the influence of follicle-stimulating hormone (FSH), testicular cells produce testosterone.
- Adrenal pathway: the adrenal cortex serves as an important source for the synthesis of both androgens and estrogens.
Enzymatic regulation plays an important role in steroid biochemistry. There are specific drugs known as aromatase inhibitors. Their mechanism of action consists in blocking the pathways that convert precursors (including androgens supplied by the adrenal cortex) into estrogens. The main effect of such inhibitors is a pronounced decrease in the level of circulating estrogens in the blood.
Main female sex hormones
The key regulators of the female reproductive system are estrogens and progesterone.
Estrogens (estradiol, estrone, estriol) are synthesized by granulosa cells. Their main functions include:
- Control of the proliferative phase of the ovarian-menstrual cycle.
- Ensuring puberty, breast growth, and female-pattern distribution of adipose tissue.
- Stimulation of bone tissue development and ossification of epiphyseal cartilages.
- Moderate anabolic effect, retention of nitrogen, salts, and water in the body.
- Influence on psycho-emotional state.
During pregnancy, the concentration of estrogen increases approximately 30-fold, with about 90% of the pool consisting of estriol, which is actively secreted by the placenta.
Progesterone is produced predominantly by the corpus luteum, and starting from the second trimester of pregnancy, the placenta takes over this function. It is responsible for:
- Regulation of the secretory phase of the cycle and preparation of the endometrium for implantation.
- Maintenance of pregnancy and structural remodeling in the uterus and mammary glands.
- Increase in basal body temperature and acceleration of basal metabolism.
Androgens and inhibins
In addition to estrogens and progesterone, the regulation of reproductive function involves:
- Androgens: synthesized in the ovaries and adrenal cortex. They provide anabolic processes in the body and stimulate libido.
- Inhibins: hormones that, via a feedback mechanism, block the production of gonadotropin-releasing hormone and pituitary FSH.
Hormonal dynamics at the end of the ovarian cycle
In the final stage of the cycle, the hormonal background undergoes drastic changes. Atretic follicles retain their endocrine activity and continue estrogen production until they transform into atretic bodies.
At the end of this period, the function of the corpus luteum and atretic follicles ceases completely. This triggers a sharp drop in the concentration of sex hormones in the systemic circulation. The most critical factor in this process is the rapid decline in progesterone levels.
Effect on the immune system
Metabolism is closely linked to immunity. Metabolic disorders can provoke underdevelopment of the thymus (thymus gland), leading to weakened immune responses and the development of immunodeficiency.
Hormones are divided into two groups based on their effect on immunity:
- Immunosuppressants (suppress responses): these include glucocorticoids and all major sex hormones (estrogens, androgens, progesterone).
- Immunostimulants (activate responses): growth hormone (somatotropin), insulin, and thyroxine (thyroid hormone).
Estrogens stand for Proliferation (building tissues and bones, retaining water). Progesterone stands for Secretion (preparing the endometrium, warming the body).
Class and exam questions
How do aromatase inhibitors affect the hormonal background?
They block the enzymatic pathway converting androgens into estrogens. As a result, the level of circulating estrogens in the blood decreases significantly.
Which estrogen predominates in women during pregnancy?
The overall level of estrogens increases 30-fold, with about 90% of their amount represented by estriol, which is actively secreted by the placenta.
Why does a sharp drop in hormones occur at the end of the ovarian cycle?
This is due to the cessation of the endocrine function of the corpus luteum and atretic follicles. Of critical importance during this period is the sharp drop in progesterone levels.
How do sex hormones affect immunity?
Androgens, estrogens, and progesterone act as immunosuppressants. They suppress immune responses, unlike growth hormone or insulin, which stimulate them.
What else to study on this topic
- Mechanism of action of aromatase inhibitors at the biochemical level
- Biosynthesis of testosterone in testicular cells under the influence of FSH
- The role of atretic follicles in maintaining estrogen levels
- The relationship between metabolic disorders and thymic involution
- Feedback mechanism: how inhibins block GnRH and FSH
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