Generality
The gonads are the primary sexual organs of the reproductive system of the human being.
Belonging to the category of endocrine glands, the gonads have the important function of secreting the gametes - that is, the sex cells for reproduction - and the sex hormones - necessary for the development of secondary sexual characteristics and for the control of the reproductive system.
Figure: Testicle
Figure: Zoom of the Ovary
The male gonads are the testes, while the female gonads are the ovaries.
The gametes produced by the male gonads are the spermatozoa; the gametes secreted by the female gonads are the egg cells.
Among the male sex hormones, testosterone is noted; Among the female sex hormones, estrogen and progesterone deserve a mention.
The production of hormones by the gonads is under the control of two important organs: the hypothalamus and the pituitary.
What are the gonads?
The gonads are the primary sexual organs of the human reproductive (or genital) system.
They are endocrine glands, which have the important function of secreting:
- gametes, i.e. the sex cells necessary for reproduction,
- the sex hormones, fundamental for the development of secondary sexual characteristics and for the control of the genital apparatus.
The gonads of men and women are different: the male gonads are the testes, while the female gonads are the ovaries (in the singular ovary, but also ovary or ovary).
TESTICLES: NOTES OF ANATOMY
The testicles, or didymes, are two and reside in the scrotum, a sac of fibro-muscular tissue that originates at the base of the penis and takes place between the man's thighs.
In an adult male, the testicles measure 3.5-4 centimeters in length and 2.5 centimeters in width, have an anterior-posterior diameter of about 3 centimeters, and ultimately weigh about 20 grams.
From a histological point of view, each testicle has two main components:
- Interstitial Leydig cells (or more simply Leydig cells), which secrete male sex hormones.
- The seminiferous tubules, which constitute 90% of the weight of a mature testicle and are organized into two distinct cell lines: the so-called germ cells and the so-called Sertoli cells.
Germ cells are the testicular cells responsible for the production of male gametes.
The Sertoli cells, on the other hand, have the task of supporting the germ cells in their action, supplying the latter with nutrients (lipids, glycogen and lactate) and regulatory substances of the spermatogenesis process.
OVARIES: NOTES OF ANATOMY
Two in number and similar in shape to a bean, the ovaries reside on the sides of the uterus and thus represent the most important organs of the female genital system.
Ovaries and uterus are connected to each other by means of important tubular structures, called the fallopian tubes.
The precise location of the ovaries is called the ovarian fossa.
The ovaries are whitish in color and typically measure 2-4 centimeters in length, 2-3 centimeters in width and 1-2 centimeters in thickness in an adult woman.
From a histological point of view, the ovaries are made up of various cellular elements, including:
- The cells of the germinal epithelium of the ovary. They are the cells that cover the ovaries externally.
- The germ cells of the ovary. These are the cells that give rise to female gametes.
- The stromal cells of the ovary. They are the cells used to support the germ cells and the secretion of female sex hormones
Sex Hormones
The sex hormones produced by the gonads belong to the category of steroid hormones. Steroid hormones are derivatives of cholesterol.
The male gonads produce sex hormones which are, in large part, different from the sex hormones secreted by the female gonads: this can be appreciated in the effects that the male sex hormones and the female sex hormones have on the development of the secondary characters, respectively, of men. and woman.
Also known by the name of androgens (where "andro" derives from the Greek word "andròs", ἀνδρός, meaning "man"), the male sex hormones are:
- Testosterone. It is the most important and representative male sex hormone.
- Androstenedione. It is the hormonal precursor of testosterone and estrogen, which are the main female sex hormones. Its presence in men and women confirms that a small part of male sex hormones are equivalent to female ones.
- L "androstenediolo
- The dehydropiandrosterone
- The androsterone
- Dihydrotestosterone
Female sex hormones, on the other hand, are:
- Estrogen. As stated, they are the most important and representative female sex hormones.
- The progesterone
- The androstenedione
Note: men have minimal amounts of estrogen and progesterone. Similarly, women have modest amounts of testosterone.
Hence, there is no clear-cut division between male sex hormones and female sex hormones.
FUNCTIONS OF MALE SEXUAL HORMONES
Male sex hormones, testosterone in primis, control the development of the secondary sexual characteristics of man, ie they regulate:
- Growth of the penis and testicles;
- The appearance of pubic, skin and beard hair;
- The strengthening of the muscles;
- The widening of the shoulders;
- Enlargement of the prostate.
FUNCTION OF FEMALE SEXUAL HORMONES
Female sex hormones, estrogen in the lead, control the development of a woman's secondary sexual characteristics, in other words they govern:
- Breast and pubic hair growth
- The maturation of the uterus and vagina;
- The enlargement of the pelvis;
- The typically female distribution of adipose tissue in the hips, legs and breasts;
- The onset of menstruation and all changes in the uterus during the menstrual cycle.
Hormonal regulation
The secretion of sex hormones by the gonads depends on other hormones, released by two important anatomical structures, located inside the skull and known as the hypothalamus and pituitary.
The mechanism by which the hypothalamus and pituitary regulate the secretion of sex hormones by the gonads is as follows:
- Nervous organ, but with endocrine functions, the hypothalamus releases a series of hormones of a protein nature, known as releasing hormones (relasing hormones) or RH hormones.
Among the RH hormones, there is also a hormone known as GnRH or gonadotropin releasing hormone. - The function of GnRH is to stimulate the pituitary, located at the base of the skull, to secrete the so-called gonadotropins, another class of protein hormones.
There are two gonadotropins produced by the pituitary gland: follicle-stimulating hormone (or FSH) and luteinizing hormone (or LH). - FSH and LH are the hormones that have the task of interacting with the gonads and stimulating them to produce sex hormones.
In summary, the hormonal activity of the gonads depends on the hormones FSH and LH, secreted by the pituitary, whose production is stimulated by another hormone, the GnRH, secreted by the hypothalamus.
The above scheme is also known as the hypothalamus - pituitary - gonadal axis.
In endocrinology, hormones that regulate the release of other hormones, such as the gonadotropins FSH and LH, take the generic name of tropic hormones.
CONTROL A FEEDBACK NEGATIVE
Control of sex hormone secretion by the gonads is an example of regulation a feedback negative.
In the controls a feedback negative, the initial stimulus receives a stop signal from the final response that the same initial stimulus provoked.
In the case of the hypothalamus - pituitary - gonads axis, the initial stimulus is the release of GnRH by the hypothalamus.
Indeed, as described above, GnRH induces the pituitary gland to produce FSH and LH, which, in turn, induce the gonads to secrete sex hormones.
Sex hormones represent the final response to the initial stimulus. Part of them, circulating in the blood, has the task of interacting with the hypothalamus and the pituitary, inhibiting their secretory activity (as regards GnRH, FSH and LH).
Figure: Negative feedback control of the release of sex hormones.
FUNCTIONS OF FSH AND LH ON THE MALE AND FEMALE GONADES
In humans, FSH stimulates the production and maturation of male gametes by the testes.
In women, however, it induces the maturation of the ovarian follicle, inside the ovaries.
By passing to LH, in man, the luteinizing hormone stimulates the testicles to secrete the sex hormones testosterone and so on.
In women, on the other hand, it induces the ovaries to produce estrogen and progesterone; moreover, it stimulates the ovulation process, ie the release of the mature egg cell in the fallopian tubes.
Gametes
Male gametes are the so-called spermatozoa; the process of production of spermatozoa by the male gonads is called spermatogenesis.
The female gametes, on the other hand, are the so-called egg cells or oocytes; the process of egg cell production by the female gonads is known as oogenesis or oogenesis.
While the male gonads produce 100-200 million spermatozoa per day, the female gonads ripen only one egg cell every 28 days (menstrual cycle).
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