Testicular hormones: Androgens
The endocrine activity of the male gonads is primarily associated with the production of androgens. The main representative of this group is testosterone and its active metabolites, in particular dihydrotestosterone. These hormones have a complex effect on the entire male body, not limited solely to the reproductive system.
The key effects of androgens can be divided into two broad groups:
- Metabolic effects. Male sex hormones actively intervene in metabolism. They trigger lipolysis, which is the mobilization of fat from tissue depots. Simultaneously, a powerful anabolic effect manifests, consisting in the stimulation of protein synthesis in skeletal muscle and other tissues.
- Morphogenetic effects. Testosterone is specifically responsible for the formation and development of secondary male sex characteristics.
Ovarian hormones: general principles and Estrogens
The endocrine function of the female gonads is characterized by strict periodicity. Hormone production here is subordinated to the menstrual cycle, and their action is directed strictly at specific target organs: the uterus, mammary glands, and pituitary gland.
The first group of female hormones is estrogens (including estradiol and its metabolites). Their main source is maturing as well as atretic ovarian follicles. Globally, estrogens are responsible for the development of secondary female sex characteristics, but their activity throughout the cycle has clear points of application:
- Uterus. Following the end of menstruation, estrogens trigger the active regeneration and restoration of the endometrium.
- Mammary glands. Under the influence of estradiol, growth and branching of the excretory ducts occur.
- Pituitary gland. The negative feedback principle is implemented: high levels of estrogens inhibit the further production of follicle-stimulating hormone (FSH).
Progestins: hormones of the corpus luteum
The second phase of the cycle is controlled by progestins, the main one being progesterone. This hormone begins to be actively produced in the premenstrual phase, and its primary source is the corpus luteum formed in the ovary. The biological significance of progesterone comes down to preparing the female body for potential pregnancy.
The effect of progesterone on target organs:
- Uterus. Under the influence of progesterone, the endometrium swells, and the uterine glands begin to actively secrete mucus. A crucial factor in maintaining pregnancy is the ability of progesterone to reduce the sensitivity of the myometrium (the muscular layer of the uterus) to oxytocin. This prevents premature uterine contractions.
- Mammary glands. Unlike estrogens, which stimulate duct growth, progesterone causes the development of terminal secretory units—the alveoli.
- Pituitary gland. Via a feedback mechanism, progesterone suppresses the secretion of luteinizing hormone (LH) by the anterior pituitary.
Briefly: answers to topical questions
Which cells of the testes synthesize testosterone?
Testosterone in the testes is synthesized by Leydig cells (interstitial endocrinocytes).
They develop from mesenchyme and are located in the interstitial tissue of the organ. The process of testosterone production by these cells is directly stimulated by luteinizing hormone (LH), which is secreted by the anterior pituitary gland. The resulting hormone enters the blood and lymph, and also acts locally on spermatogenic cells and Sertoli cells, ensuring the development of male sex characteristics and maintaining spermatogenesis.
Which cells of the ovarian follicle produce estrogens?
Estrogens in the growing follicle are produced by follicular cells (granulosa cells) with the participation of theca cells.
Synthesis proceeds in cooperation between two cell types:
- Theca cells, under the influence of LH, synthesize androgens: cholesterol → progesterone → testosterone; testosterone diffuses into neighboring follicular cells.
- Follicular cells, under the influence of FSH, take up testosterone and convert it into estradiol via aromatization of androgens.
The resulting estradiol accumulates in the follicular antrum and is secreted into the blood.
From which ovarian structures does the corpus luteum form?
The corpus luteum forms from the ovulated follicle; the sources explicitly indicate the luteinization of granulosa cells.
After ovulation, under the influence of LH, granulosa cells undergo luteinization: their cytoplasm volume increases and lipid inclusions appear. As a result, the corpus luteum is formed—a transient hormonally active structure that produces progesterone.
Estrogens build the "roads" (mammary ducts) and "foundation" (endometrial regeneration). Progesterone prepares the "rooms" (alveoli) and "soft bed" (endometrial swelling, contraction blocking).
Class and exam questions
Where are estrogens synthesized?
They are produced in maturing and atretic ovarian follicles.
Which hormone is responsible for the growth of alveoli in the mammary gland?
Progesterone is responsible for the development of the terminal secretory units (alveoli).
What is the feedback mechanism for estrogens?
High levels of estrogens inhibit the production of follicle-stimulating hormone (FSH) in the pituitary gland.
Why is progesterone called the hormone of pregnancy?
It prepares the endometrium for implantation and reduces the sensitivity of the myometrium to oxytocin, preventing miscarriage.
What else to study on this topic
- Cellular composition of maturing and atretic follicles
- Structure and stages of development of the corpus luteum
- The negative feedback mechanism in the pituitary-gonadal axis
- Histological structure of the endometrium and myometrium
- Synthesis of testosterone and its derivatives
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