The Male Reproductive System - 2
Sperm and Hormone Production
Jennifer Carbrey Ph.D.
Department of Cell Biology
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The Male Reproductive System: Sperm and Hormone Production, Study notes of Cell Biology
An in-depth exploration of the male reproductive system, focusing on sperm and hormone production. Topics covered include the role of stem cells in spermatogenesis, the structure of the testes and its components, the functions of Leydig and Sertoli cells, and the process of sperm maturation and production. Additionally, the document discusses the role of androgens and estrogen in the male body, including their effects on various tissues and the skeleton.
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2021/2022
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The Male Reproductive System - 2
Sperm and Hormone Production
Jennifer Carbrey Ph.D. Department of Cell Biology
Spermatogenesis occurs in the testes. Spermatogonia (stem cells) can divide continuously throughout the life of the male.
Testis Structure
testis
epididymis
image by KDS444 (modified), http://commons.wikimedia.org/wiki/File:Rete_testis.jpg, Creative Commons Attribution-Share Alike 3.0 Unported license
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.
Sperm Production
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.
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.