Generality
The gonads are the primary sexual organs of the reproductive apparatus of the human being.
Belonging to the category of endocrine glands, the gonads have the important function of secreting gametes - that is, sex cells for reproduction - and sex hormones - necessary for the development of secondary sexual characteristics and the control of the reproductive apparatus.
Figure: Testicle
Figure: Zoom of the Ovary
The male gonads are the testicles, 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 reported; among female sex hormones, estrogens 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 gland.
What are the gonads?
The gonads are the primary sexual organs of the human reproductive (or genital) apparatus.
They are endocrine glands, which have the important function of secreting:
- the gametes, that is the sex cells necessary for reproduction,
- sex hormones, fundamental for the development of secondary sexual characteristics and for the control of the genital apparatus.
The gonads of man and woman are different: the male gonads are the testicles, while the female gonads are the ovaries (in the singular ovary, but also the ovary or ovary ).
TESTICLES: NOTES OF ANATOMY
The testicles, or didimis, 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, possess an antero-posterior diameter of about 3 centimeters and, finally, they weigh about 20 grams.
From the histological point of view, each testicle has two main components:
- Leydig's interstitial cells (or more simply Leydig's 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 substances that regulate the process of spermatogenesis.
OVAI: NOTES OF ANATOMY
In number of two and similar in shape to a bean, the ovaries reside on the sides of the uterus and with this represent the most important organs of the female genital apparatus .
Ovaries and uterus are connected to each other, by means of important tubular structures, called Fallopian tubes .
The precise site of the ovaries is called the ovarian fossa .
The ovaries are whitish in color and, in an adult woman, generally measure 2-4 centimeters in length, 2-3 centimeters in width and 1-2 centimeters in thickness.
From a histological point of view, the ovaries are composed 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 . They are the cells that give rise to female gametes.
- The stromal cells of the ovary . They are the cells used to support germ cells and the secretion of female sex hormones
Sexual 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 that are, in large part, different from the sex hormones secreted by the female gonads: this can be appreciated in the effects that male sex hormones and female sex hormones have on the development of secondary characters, respectively, of man and woman.
Also known as androgens (where "andro" comes 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 estrogens, which are the main female sex hormones. Its presence in men and women is confirmation that a small proportion of male sex hormones are equivalent to female ones.
- The androstenediol
- Dehydropiandrosterone
- The androsterone
- Dihydrotestosterone
Female sex hormones, however, are:
- Estrogens . As stated, they are the most important and representative female sex hormones.
- Progesterone
- androstenedione
Please note: humans have minimal amounts of estrogen and progesterone. Similarly, the woman has modest amounts of testosterone.
Thus, there is no clear division between male sex hormones and female sex hormones.
FUNCTIONS OF MALE SEXUAL HORMONES
The male sex hormones, testosterone in the first place, control the development of the secondary sexual characteristics of man, that is they regulate:
- Penis and testicles growth;
- The appearance of pubic, cutaneous and beard hairs;
- Strengthening of the musculature;
- Shoulder enlargement;
- Prostate enlargement.
FUNCTION OF FEMALE SEXUAL HORMONES
The female sex hormones, estrogen in the head, control the development of the woman's secondary sexual characteristics, in other words they govern:
- Breast and pubic hair growth;
- The maturation of the uterus and vagina;
- Basin enlargement;
- The typically female distribution of adipose tissue, in the hips, legs and breast;
- 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 hypothalamus and pituitary glands .
The mechanism through which hypothalamus and pituitary gland regulate the secretion of sex hormones, by the gonads, is the following:
- Nervous organ, but with endocrine functions, the hypothalamus releases a series of proteic hormones, known as relasing hormones or RH hormones .
Among RH hormones, there is also a hormone known as GnRH or gonadotropin-releasing hormone .
- The function of GnRH is to stimulate the pituitary gland, located at the base of the skull, to secrete the so-called gonadotropins, another class of protein-based hormones.
Gonadotropins, produced by the pituitary gland, are two in all: the follicle-stimulating hormone (or FSH ) and the 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 gland, whose production is stimulated by another hormone, GnRH, secreted by the hypothalamus.
The above described scheme is also known as the hypothalamus axis - pituitary - gonads .
In endocrinology, the hormones that regulate the release of other hormones, such as the gonadotropins FSH and LH, take the generic name of tropic hormones .
CHECK A NEGATIVE FEEDBACK
The control of sex hormone secretion by the gonads is an example of negative feedback regulation.
In negative feedback controls, the initial stimulus receives a stop signal from the final response that the initial stimulus itself has caused.
In the case of the hypothalamus - pituitary - gonadal axis, the initial stimulus is the release of GnRH, from the hypothalamus.
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 gland, inhibiting its secretory activity (as regards GnRH, FSH and LH).
Figure: negative feedback control of the release of sex hormones.
FUNCTIONS OF FSH AND LH ON MALE AND FEMININE GONADES
In humans, FSH stimulates the production and maturation of male gametes by the testicles.
In women, however, it induces the maturation of the ovarian follicle, inside the ovaries.
Moving on to LH, in humans, the luteinizing hormone stimulates the testes to secrete testosterone sex hormones, etc.
In women, however, it causes the ovaries to produce estrogen and progesterone; in addition, it stimulates the ovulation process, ie the release, in the fallopian tubes, of the mature egg cell.
Gameti
The male gametes are the so-called spermatozoa ; the process of sperm production by male gonads is called spermatogenesis .
Female gametes, on the other hand, are the so-called egg or egg cells ; the process of making egg cells, by female gonads, is known as oogenesis or oogenesis .
While the male gonads produce 100-200 million spermatozoa per day, the female gonads bring to maturity only one egg cell every 28 days (menstrual cycle).
