Key Concepts

1. In the testes, luteinizing hormone (LH) controls the synthesis of testosterone by Leydig cells, and follicle-stimulating hormone (FSH) increases the production of

2. androgen-binding protein, inhibin, and estrogen by Sertoli cells.

3. Spermatozoa are produced within the seminiferous tubules of both testes. Sperm develop from spermatogonia through a series of developmental stages that include spermatocytes and spermatids.

4. The sperm mature and are stored in the epididymis. At the time of ejaculation, sperm are moved by muscular contractions of the epididymis and vas deferens through the ejacu-latory ducts into the prostatic urethra. The sperm are finally moved out of the body through the urethra in the penis.

5. LH and FSH secretion by the anterior pituitary are controlled by gonadotropin-releasing hormone (GnRH).

6. Testosterone mainly reduces LH secretion, whereas inhibin reduces the secretion of FSH. The testicular hormones complete a negative-feedback loop with the hypothalamic-pituitary axis.

7. Androgens have several target organs and have roles in regulating the development of secondary sex characteristics, the libido, and sexual behavior.

8. The most potent natural androgen is dihydrotestosterone, which is produced from the precursor, testosterone, by the action of the enzyme 5a-reductase.

9. Male reproductive dysfunction is often due to a lack of LH and FSH secretion or abnormal testicular morphology.

The testes have two primary functions, spermatogenesis, the process of producing mature sperm, and steroidogenesis, the synthesis of testosterone. Both processes are regulated by the pituitary gonadotropins LH and FSH. Testosterone is the primary sex hormone in the male and is responsible for primary and secondary sex characteristics. The primary sex characteristics include those structures responsible for promoting the development, preservation, and delivery of sperm. The secondary sex characteristics are those structures and behavioral features that make men externally different from women and include the typical male hair pattern, deep voice, and large muscle and bone masses.

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