Why do we need testosterone and progesterone?

Sex glands

Olga Smirnova, Post-science

To begin with, let's look at the differences between the ovaries and testes and the features of their work. Let's start with the ovaries. The body of a woman and other female mammals works cyclically, observing ovarian cycles, which mean the alternate work of two hormone-producing units in the ovary.

During the first half of the cycle, a woman prepares for fertilization. This half of the cycle is called the follicular phase of the cycle. At this time, follicles develop that produce estrogens – sex hormones. In each cycle, several follicles enter the hormone-dependent stage of development. The egg of the best follicle after its rupture enters the fallopian tube and is sent for fertilization. The ruptured follicle turns into a yellow body – the endocrine element of the ovaries, which produces the pregnancy hormone progesterone. gestation – "pregnancy"). The second half of the cycle, the woman's body is preparing for pregnancy. If pregnancy does not occur, everything starts over, so follicles that produce estrogens and progesterone work alternately in the ovaries to prepare the mother's body for pregnancy.

Now let's deal with the follicles. During the first cycle, the best follicle is selected by the number of estrogens produced, which together with other hormones support the development of the oocyte. Due to the large amount of estrogens and other hormones, the oocyte in this follicle becomes ready for fertilization. At the moment of follicle rupture, when the oocyte enters the abdominal cavity and is captured by the fallopian tubes, estrogens act on pituitary cells that secrete luteinizing hormone. This hormone causes the rupture of the follicle, the release of the egg, stimulates differentiation into cells of the corpus luteum (Lat. corpus luteum).

In the second phase of the cycle, progesterone is produced, which prepares the mother's body for pregnancy. Progesterone stimulates the growth of the endometrium of the uterus to create a folding that will delay and implant the embryo. Progesterone causes the endometrium of the uterus to develop glands for the secretion of viscous mucus, which helps to delay and implant the embryo into the uterus. Also, this hormone acts on the mammary glands to stimulate the beginning of their branching and increase the number of alveoli that produce milk. As a result of these processes, every second half of the cycle, the mammary glands develop significantly, swell, and then return to the previous level, to the beginning of a new cycle. Such alternating work of two ovarian units allows you to prepare a woman first for fertilization, then for pregnancy. Progesterone also acts on the vagina to facilitate the advancement of sperm into the vagina and then choose the best sperm that will pass all barriers and fertilize the egg. 

The breeding strategies of male and female individuals differ. The strategy of males is the number and diversity of offspring. The strategy of female – the quality of offspring. Out of three hundred thousand sperm that enter the female genital tract, one is selected. This choice is made under the control of the ovarian hormones – estrogen and progesterone. All hormones create barriers for sperm, through which the best sperm will pass. As a result, only one sperm fertilizes one egg. If we talk about the peculiarities of the female body and ovaries, it remains a mystery why, in the presence of two ovaries, women are more likely to have one child. It would seem that the concentration of hormones in the blood throughout the cycle is the same: in the first phase – estrogen, in the second – progesterone. These hormones enter the bloodstream. The selection of the dominant follicle should be equally good in both ovaries, as well as ovulation. Therefore, both fallopian tubes should catch the egg and start fertilization, but this happens only in one. This question remains unresolved because mammals with a large number of young have both ovaries working.

Now let's move on to the testes. The cellular composition of the testes is similar to the ovaries, but in the male body, the center of the hypothalamus, which is responsible for cyclic changes in the ovaries of a woman, is blocked by androgens. If a woman's ovary works cyclically, then the testis in men – constantly. The rate of spermatogenesis is a genetic component that is not regulated by hormones. Hormones regulate the quality of spermatozoa, depending on the quality of seminal fluid. There are two types of cells in the testes. The first type is Leydig cells, which produce testosterone. Testosterone is also produced by teka cells, which are located on the follicle membrane. Teka cells and Leydig cells are cells of homologous origin. The second type is Sertoli cells, which line the seminal tubules. In the niches of Sertoli cells, spermatozoa mature from the early stages to mature spermatozoa. Homologues of Sertoli cells in follicles are granulosa cells that create the environment in which the oocyte matures. In their work, the testes are similar to the ovaries in the follicular phase of development.

Sertoli cells convert androgens into estrogens, which better support sperm viability. Sertoli cells are affected by pituitary hormone – follicle stimulating hormone. In women, this hormone stimulates the development of follicles, and in men it supports the work of Sertoli cells and stimulates the development of tight contacts between them. Contacts between Sertoli cells give birth to a hemato-testicular barrier, which is necessary for comfortable growth of spermatozoa in their environment and protection of spermatozoa from external signals. A man's body is unfamiliar with the environment in which spermatozoa mature. If the hemato-testicular barrier breaks and proteins enter the blood of a man, immune or allergic reactions occur. Fifteen years ago, methods of male contraception were practiced, which consisted in ligation of the spermatic cord. This method increased the pressure in the excretory ducts, and tight contacts were torn. The consequence of this method of contraception was immune reactions in men, so it was abandoned. This is an example of how well the body is prepared to protect spermatozoa from the external environment, which is the rest of the male body.

The glands producing seminal fluid are also affected by androgens. For example, the prostate is an androgen–dependent organ that supplies elements of seminal fluid. Without androgens, the prostate decreases in size, but excessive production of androgens can lead to diseases such as hyperplasia, adenoma or prostate cancer. A large amount of androgens in the blood increases the division of prostate cells. If these cells are normal, it is good, if they have malignant degeneration, it is bad. All prostate diseases are treated with antiandrogens that block the division of all prostate cells. Thanks to the work of the testes, the spermatozoa first mature under the action of the hormones of the testes, then grow in the seminal fluid of the correct composition, maintaining mobility and all the properties so that it is easy to choose the best one in a woman's body. 

Olga Smirnova – Doctor of Biological Sciences, Professor of the Department of Human and Animal Physiology, Head of the Laboratory of Endocrinology of the Faculty of Biology of Lomonosov Moscow State University.

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