The gonads are the guarantor glands of the morphological and behavioral development of each sex, male or female. They intervene in the embryonic stage and are energetically activated during puberty. They fulfill a double function: reproductive and endocrine.


What are gonads?

Gonads are the glands that provide genital differentiation to humans and other vertebrate animals. They are also called sex glands and mixed glands , due to their dual function: reproductive and endocrine. There are two types of gonads : Male, represented by the testicles; and the feminine ones, constituted by the ovaries. Exceptionally, a vertebrate animal has a hermaphroditic gonadal structure, with characteristics typical of both sexes.

  • Gonads characteristics
  • Function of the testicles
  • Function of the ovaries
  • Gonad-related diseases
  • Importance of the gonads

Gonads characteristics

According to their typologies, the gonodes can have the following characteristics:


Male gonads:

The testicles are part of the male reproductive system . There are two of them, they are located outside the abdomen, at the base of the penis. They are ovoid-egg-shaped and white in color. They are surrounded by a fibrous layer of connective tissue that gives them strength and elasticity. In childhood they are between 2 and 3 centimeters long, while at puberty they reach twice the size and about 3 or 4 centimeters wide.

Each testicle is supported by a spermatic cord that comes from the abdomen and passes through the inguinal canal. They settle side by side, although not always on the same level. The right is usually a little higher than the left. They are not attached to any other surface, so they can move inside the scrotum , the sac that surrounds them.

The testes are made up of seminiferous ducts, in which spermatogenesis occurs. And by excretory sperm ducts, made up of Haller’s network, efferent ducts and the epididymis. The albuginea or membranous layer that surrounds the testicle completes its structure. In addition to the set of arteries, veins and lymphatic vessels. In the vascular part of the albuginea are the interstitial cells of Leydig, which produce testosterone.

The scrotum is one of the seven layers that line the male sex glands . There are also the dartos, the subcutaneous cell layer, the external spermatic fascia, the cremaster, the internal spermatic fascia and the vaginal tunica or serous layer of the testicle. All responsible for keeping the glands at a temperature commensurate with the efficient production of sperm (between 1 and 3 degrees lower than body temperature.) Only one testicle (monorchidism) or none (anorchidism) rarely develops.

Female gonads:

The ovaries make up, together with the fallopian tubes, uterus, vagina and external genitalia, the female reproductive system . There are two of them, they have an ovoidal shape -slightly flattened- and a greyish-white color.

They are attached to both sides of the uterus, in the lower abdomen. They are attached to the fallopian tubes, uterus, and abdominal wall through ligaments. Among them are the Tubo-ovarian, meso-ovarian, uterus-ovarian and suspensory cords, which support the sexual gland from the abdominal wall.

They are about 3 centimeters long, 2 wide, and about 1 centimeter thick. This is due to its cortex or albuginea area, made up of dense connective tissue, stroma and follicles. It is in the ovarian follicles , complex spherical structures, where the oocytes or germ cells are found.

They complete the ovarian structure, a tissue provided with vessels and nerve endings, known as the medulla. Also the hilum, the ovarian network in which the androgen-producing cells are found . It is characteristic of the gonads to produce both female and male hormones.

Ovarian activity is cyclical , in women it is called the menstrual cycle and is characterized by at least two particular stages: follicular and luteal or secretory. In the middle of these two phases the process of ovulation or release of the ovum occurs.

Function of the testicles

Both types of gonads – male and female – have reproductive and endocrine functions.

Spermatogenesis occurs in the testes , the production of sperm, gametes or reproductive cells of man. This process begins in the hypothalamus, with the action of gonadotropin-releasing hormone, which stimulates the placement of germ cells. The spermatogonia are stationed in the tissue of the seminiferous tubules, existing in numbers of 500 in each testicle.

In man, gamete production lasts an average of 70 days, from placement to spemiogenesis or sperm maturation. In an ejaculation, the fertile man can produce up to 250 million spermatozoa; and in the rest of life, about 500 billion.

What hormones do the testicles produce?

The endocrine function of the testes starts from the albuginea. Interstitial Leydig cells – stimulated by luteinizing gonadotropic hormone – produce androgens . Among them, one of great potency, testosterone. The male sex hormone is responsible for genital differentiation in the fetal stage. Also of the appearance of secondary sexual characteristics from puberty and complete fertility, once adolescence is over.

Testosterone acts on the development of muscles and the male reproductive system : penis, scrotum (testicles), prostate and seminal vesicles. Activates hair growth, mainly in the facial, genital, armpit and chest areas. It expands the vocal cords, aggravates the voice. Stimulates the secretion of sweat and sebum that lubricates the surface of the skin. Determines the manly character and attraction to the opposite sex.

In addition to testosterone, the testes produce the androgens: androsterone and androstenedione.

Function of the ovaries

The ovaries are producers of the mature ovules, gametes or reproductive cells of the woman. From adolescence to menopause in women, the ovaries – stimulated by the hypothalamus – begin their cycle month by month. Between the 16th and 12th days prior to menstruation, the female gonads secrete estrogens, hormones that prepare the endometrium for the reception of sperm.

When the ovum finally leaves the ovarian follicle, it travels down the fallopian tubes to be fertilized by the sperm, or else die and be excreted as part of menstruation. Unlike the sperm, which lives up to five days waiting to meet the female gamete, the ovum only lives 24 hours in between.

In their fertile life, the ovaries release up to 400 mature ovules, of about 400 thousand primitive ones contained in the follicles of their cortex.

What hormones do the ovaries produce?

In addition to estrogens, produced during the release of the egg, the ovaries produce the hormone progesterone . The steroid hormone takes place during the second stage – luteal stage – of the menstrual cycle. Participates in the embryonic process, the menstrual cycle and the gestation and maintenance of pregnancy.

The concentration of progesterone is relatively high after ovulation and during pregnancy, when it is released through the placenta.

Together with estrogens, it promotes the development of secondary sexual characteristics in women. Progesterone affects the development of the endometrium in the uterus. Also in the growth and elasticity of the vagina, the development of the breasts and the inhibition of milk production. In addition to the growth of pubic hair and in the region of the armpits, widening of the pelvis and distribution of fat around the hips and legs.

Also during the luteal phase, the female gonads secrete the hormone relaxin , which acts directly on the pelvis and uterus. Relaxes or softens the cervix and pelvic ligaments – prevents contractions – during the birthing process. Before, it facilitates the transit of sperm through the uterine region and their penetration into the ovum. In non-pregnant women, it just slows down and menstruation passes.

Gonad-related diseases

Some genetic disorders, the use of medications, chronic diseases, trauma or surgery, can cause gonadal disorders . Among them: Low or no production of sex hormones (hypogonadism), late pubertal development, decreased libido, sexual dysfunction and infertility.

Genetic disorders such as Turner syndrome or Klinefelter syndrome affect the function of the ovaries and testicles, respectively. Also autoimmune diseases , such as type 1 diabetes, reunmatoid arthritis and lupus, compromise the development of the gonads. The same as pathologies that affect the liver, kidneys and thyroid glands.

1 in 2000 women is born without a chromosome, or the normal pair of chromosomes, an irregularity known as Turner syndrome . It causes short stature and lack of sexual maturity, the breasts and pubic hair do not grow, there is no menstruation, nor fertility. It is also associated with other external physical characteristics and malformations of the heart and kidneys. Women with this feature receive hormonal treatment.

In the case of men, the abnormality in the production of sex hormones – of genetic origin – is due to the excess of chromosomes. 1 in 1000 men is born with one or more extra X chromosomes, this is known as Klinefelter syndrome . It causes less hair production at puberty, short stature, little growth of the reproductive organ, and infertility. In some cases breasts or disproportions in the body such as exorbitantly long legs develop. The treatment is hormonal.

Importance of the gonads

Gonads are necessary for normal sexual development and differentiation . From the fourth week of gestation, sexual characteristics begin to form, and two weeks later they present cortex, marrow and germ cells. Differentiation into testicles or ovaries is determined by genetic makeup. The formation of the testes begins from the seventh week of embryonic development, while the ovaries take a little longer.

The primitive embryonic structure presents female phenotypic expression, without the male gene and the testicular determining factor, the gonads would only transform into ovaries. The fetal testicle secretes the hormone antimullerin, which prevents the development of Müllerian ducts. And it produces testosterone, which stimulates the development of the Wolf ducts and the masculinization of the external genitalia.

When in the embryonic structure the genotype is female, the Müllerian ducts develop, which constitute the uterus, the fallopian tubes and the vagina. And the outer lips are also formed. Internal and external genitalia are formed and start their function during the first weeks of gestation .

Furthermore, the gonads not only act in early embryogenesis, they fulfill determining functions during puberty and successive stages of life. They offer the morphology and character of each sex.

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