Hormones of Male Reproduction

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Role of GnRH, LH, and FSH:

• At puberty, certain hypothalamic neurosecretory cells increase their secretion of GnRH.

• This hormone stimulates anterior pituitary to increase secretions of FSH and LH.

• LH stimulates Leydig cells to secrete testosterone into the blood.

• Testosterone acts in a negative feed-back to suppress secretion of LH.

• In some target cells, such as those in prostate and seminal vesicles, testosterone is converted to dihydrotestosterone (DHT) by 5-aplha-reductase.

• FSH and testosterone act on Sertoli cells to release androgen-binding-protein.

• ABP binds to testosterone keeping its levels high in the seminiferous tubules.

Role of Testosterone:

• Testosterone stimulates final steps in spermatogenesis.

• Once spermatogenesis has been initiated and reached a certain level, Sertoli cells then release inhibin to inhibit FSH.

• Testosterone levels are regulated by a negative feed-back system.

• When testosterone reaches a certain level in blood, the feedback system inhibits the release of GnRH from the hypothalamus.

Testosterone in Developing Male

• Testosterone leads to development of male reproductive system and decent of testes.

• Testosterone is also converted to estrogen in the brain.

• DHT stimulates the formation of external genitals.

• Testosterone and DHT also bring about secondary sexual characteristics in the male.

• Androgens lead to sexual behavior and sex drive in male and female.

• Androgens also lead to increased muscle mass.

GnRH:

• Synthesized in preoptic region of hypothalamus.

• Stimulates release of LH and FSH.

• FSH: acts on Sertoli cells; Sertoli cells' inhibin produces negative feedback for FSH.

• LH: acts on Leydig cell; Leydig cells' testosterone produces negative feedback for LH.

Aromatase:

• Converts testosterone to estradiol.

Testosterone:

• Facilitates spermatogenesis.

• Male androgen controlled by LH.

• DHT: more active testosterone.

• High concentration in testes.

NOTE: both Leydig cells and testosterone are required for spermatogenesis.

Adrenal androgens:

• Weak; controlled by ACTH.

Testosterone Feedback:

• Circulating testosterone provides negative feedback to hypothalamus and anterior pituitary to regulate LH secretion.

Testosterone Function:

• Testosterone facilitates spermatogenesis.

• FSH initiates spermatogenesis.

Estradiol in men:

• 1/3 comes from Sertoli cells.

• 2/3 comes from aromatase induced conversion of testosterone to estradiol.

Male development requires:

• Testosterone, DHT, MIH.

Androgens:

• Stimulate release of GH, IGF-I.

• Growth of long bones, etc.

• Increased muscle mass.

Erection:

• Parasympathetic response.

• Inflow greater than outflow; erection produced.

Emission:

• Sympathetic response.

Ejaculation:

• Somatic motor efferent response.

Additional Readings:

Basic Endocrinology

1. Introduction to Endocrinology
2. Hypothalamic-pituitary system
3. Adrenal Hormones
4. Antidiuretic Hormone (ADH) and ECF Regulation
5. Endocrine Pancreas
6. Growth Hormone
7. Adrenal Medulla
8. Hormonal Control of Calcium and Phosphate
9. Thyroid Hormones
10. Hormones of Male Reproduction
11. Hormones of Female Reproduction
12. Fluid Compartments of the Body
13. Notes on Hypothalamus Anterior Pituitary and Thyroid
14. Additional Notes on Female Reproduction
15. Hormonal Signaling Pathways
16. FAQ on Adrenal Hormones
17. FAQ on Male Reproduction
18. Synthesis and Deficiencies of Adrenal Hormones
19. Significance of Glycosylated Hemoblogin (HbA1c)
20. Significance of Measuring Albumin while with Calcium Levels
21. Stepwise Approach to Treatment of Ascites
22. How to differentiate between Diabetes Insipidus vs Psychogenic Polydipsia

Related Topics

1. Histology of the Endocrine System
2. Histology of the Male Reproductive System
3. Histology of the Female Reproductive System

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