The Male Reproductive System - 2 Sperm and Hormone Production

Jennifer Carbrey Ph.D. Department of Cell Biology Testis Structure

epididymis

testis

Spermatogenesis occurs in the testes.

Spermatogonia (stem cells) can divide continuously throughout the life of the male. image by KDS444 (modified), http://commons.wikimedia.org/wiki/File:Rete_testis.jpg, Creative Commons Attribution-Share Alike 3.0 Unported license Sperm Production FSH

Sertoli Cells make androgen binding protein convert testosterone to estrogen

LH

Leydig Cells secrete testosterone secrete DHT (dihydrotestosterone, contain 5-a- reductase) (for 2° male characteristics) image by Uwe Gille (modified), http://commons.wikimedia.org/wiki/File:Germinal_epithelium_testicle.svg, Creative Commons Attribution-Share Alike 3.0 Unported license Sperm Production

FSH initiates sperm differentiation.

Testosterone needed to mature the sperm.

Number of sperm in semen (200-400 million/5ml) depends on proliferation rate and frequency of ejaculation.

<20 million sperm/ml = infertile!

Maturation = 90 days.

Capacitation requires contact with female oviduct epithelium. Androgens

Testosterone is responsible for gonadotropin (GnRH) feedback, spermatogenesis and embryonic differentiation.

Dihydrotestosterone (DHT) is most important for external virilization and secondary sexual characteristics.

Steroids delivered by carrier in the blood. Act by changing gene expression (activate transcription).

Anabolic actions (promoting increased muscle mass).

Excess testosterone can decrease the size of the testes and decrease sperm count but will increase the size of the prostate. Androgen Dependent Tissues

• Seminal vesicles - provide fructose rich liquid which is 60% of semen volume.

• Prostate - alkaline secretion provides 20% of semen volume - enlarges under influence of DHT

• Secondary sex traits: inc. muscle mass, inc. facial hair, deep voice Estrogen & the Male Skeleton

Bone expresses aromatase

Estrogen and testosterone stimulate longitudinal growth of the skeleton.

Estrogen induces epiphyseal growth plate closure at end of puberty.

Males with estrogen receptor inactivation or aromatase inactivation have continual growth of skeleton.

Key Concepts

Local synthesis of testosterone is required for differentiation of sperm and embryonic sexual differentiation. DHT is most important for secondary sexual characteristics.

At the end of puberty, estrogen acts at the epiphyseal plate to limit linear growth of the long bones.