The World of Pregnancy

What Hormones Are Secreted By The Testicles?

Testicles are an important part of the male reproductive system. These are mixed glands, secreting hormones and sperm. Spermatozoids together with the secretions of spermatic ways and adjacent glands form sperm.

Hormones Secreted By The Testicles

Anatomy & Structure

The weight of a testicle is of around 40 g and its length of around 4.5 cm. The testicle has at the exterior a thick –walled capsule known as tunica albuginea. These form the testicular mediastinum at the posterior side, which sends fibrous sepals by dividing around 250 testicular lobules. Among these sepals, there are some that are incomplete, the testicular lobules communicating between them.

Each lobe has 1 to 4 seeded tubers which are inserted in a network of lax connective fibers, interstitial cells known as Leydig cells, Sertoli cells, Totally, a testicle has around 900 tuberous sinuous trunks.

The seminiferous tubes will secrete spermatozoids and the interstitial cells will secrete testicular androgens. – Check this!

The testicles appear and then develop retroperitoneally, and then along the fetal period, they migrate to the scrotum. Throughout the migration, they are “dressed” in the vaginal tunic.

The testicles are located in the scrotum, where the constant temperature is 1° or 2° Celsius lower than the body`s temperature, this being very important for spermatogenesis.

Role & Functions

Sertoli cells have the following roles:

  • Endocrine role through secretion and inhibition synthesis which has an important role in regulating androgen secretion and inhibition of follicle-stimulating hormone
  • Paracrine role by synthesis of an androgen binding protein which will bind testosterone, dihydrotestosterone (DHEA) and estradiol.
  • It offers blood testicular barrier.
  • It`s a support for germ cells.
  • It secretes a fluid in the sperm circulation.

Hormones Secreted by the Testicles

Androgens & Hormones

1. Testosterone

It`s mainly secreted by Leydig cells and is seen as the most important testicular hormone despite the fact that a large of its amount is transformed in dihydrotestosterone. In the adult male, testosterone is synthesized on a daily basis, around 4 to 9 mg. The maximum level is synthesized in the morning and the minimal level in the evening, around midnight.

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The largest amount of testosterone (around 98%) is under a form related to sex-steroid-binding globuline and albumine.

The testosterone plasma concentration is of 650 nanograms/dl (in adult males). This acts mostly after is transformed in dihydrotestosterone by 5-alpha-reductase.

2. DHEA

  • Its virilizing power is higher than the one of testosterone.
  • 80% comes from the peripheral conversion of testosterone.
  • 20% is synthesized by Leydig cells.

3. DHEA & Androstenedione

Dihydrotestosterone is produced only by the adrenal cortex, while the androstenedione has mixed origins. The 2 hormones account for less than 10% of circulating androgens.

Estrogen Hormones

Estrogen hormones come mostly from the flavor of androstenedione and testosterone, but they are also secreted by the testicle, and a small amount is produced by the adrenal cortical.

  1. Corticolibrin, vasopressin, angiotensin II, beta-endorphins, oxytocin, growth factors: having a role of local regulation of all testicular functions secreted by Leydig cells.
  2. Activin, mullerian inhibition factor, inhibin, transferin. Activin stimulates the secretion of follicle-stimulating hormone as well as erythropoiesis.

Physiological effects of testicular hormones:

  • Initiating and maintaining primary and secondary male sexual characteristics.

The masculinizing role of testosterone is manifested in a different way depending on the period:

1. Fetal development period

Testosterone is secreted in intrauterine life starting with the week 7 of pregnancy, right after firming Leydig cells under the action of human chorionic gonadotropin hormone.

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Fetal testosterone is the one inducing the formation of the penis, scrotum, testicles as well as all the other attachments of the male reproductive system.

In the last 2 or 3 pregnancy months, the secretion of testosterone is intensifying, resulting in the testicles lowering their position in the scrotum.

2. Extrauterine period

During childhood, the level of testosterone is quite low. Around 11 years, GnRH isn`t inhibited anymore as it used to be by now, and the testosterone plasma levels start to decrease.

In puberty as well as adolescence, the physiological effects of these testicular hormones start to manifest:

  • They start stimulating the growth of the waist;
  • They develop the male phenotype;
  • They cause the occurrence of male secondary characteristics (developing thick tone, facial hair or larynx).

Anabolic testicular hormone effects:

  • They stimulate protein synthesis;
  • They cause retention of renal water, calcium, Na, K;
  • They stimulate hematopoiesis.

Testicular hormone effects on regulatory cells:

  • Inhibins inhibit the gonadotropin-releasing hormone and follicle-stimulating hormone secretion;
  • Testosterone inhibits luteinizing hormone and reduces gonadotropin-releasing hormone.
  • Activins stimulate the secretion of follicle-stimulating hormone.

Adjusting the testicular functions by age:

  • During fetal life, the testicular function is generally controlled by human chorionic gonadotropin, which is secreted by the placenta throughout the entire 9 months;
  • During childhood, there`re hypothalamic inhibitory circuits which will cause a very small amount of gonadotropin-releasing hormone;
  • During puberty, the male starts his adult sexual life;
  • Climacteric: it appears due to the result of progressive decrease in the ability of all the testicles of secreting androgenic hormones due to the result of changes in the testicles with age.

Pathology Associated to Testicles

  1. Deficiency of androgen hormone secretion
  • It occurs due to the damage of a link of hypothalamic pituitary-testicular chain;

Causes:

  • Enzymatic defects;
  • The genetic inability of the hypothalamus of secreting gonadotropin-releasing hormone;
  • Changes in cellular androgen receptors.

Depending on the period in which the clinical aspect occurs, is different if:

  • It occurs in the intrauterine life: the clinical picture is o male pseudohermafroditism (the occurrence of a female genital tract in the XY chromosomal fetus);
  • It occurs during childhood: eunucoid syndrome (narrow shoulders, sterility or female sex characteristics);
  • It occurs during adulthood: specific somatocomportamental symptoms with slow regression of male sexual characteristics.
  1. Hypersecretion of androgenic hormones

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It`s different depending on the period when it occurs:

  • During childhood: it leads to early puberty;
  • After puberty: it`s rather hard to put a diagnosis, because the effects overlap with the physiological effects of testosterone.

Testicular Tests

1. Clinical tests:

  • The occurrence of the genitals;
  • Anamnesis;
  • Secondary sexual characters.

2. Lab tests

  • Karyotype;
  • Spermogram;
  • Barr-Bertram test (it highlights the sex hormone, normally absent).

Hormonal Dosage

  • Urinary doses of 17 ketosteroids (most part of plasma testosterone is metabolized in the liver in 17KS); normal 10 to 20 mg/dl/24 hours;
  • Pituitary gonadotropin dosing (differential diagnosis between primary testicular insufficiency and one of pituitary causes);
  • Testicular stimulation test with human chorionic gonadotropin (differentiates between primary or secondary hypogonadism);
  • Plasma testosterone dosing;
  • Gonadotropin-releasing hormone stimulation test (diagnosis of pituitary gonadal insufficiency).
Image courtesy of medicalnewstoday.com
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