Anatomy and Cell Biology 3309 Lecture Notes - Lecture 16: Seminiferous Tubule, Vas Deferens, Epididymis
15 May 2018
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Lecture 16 – Testis
- Testis are the site of production of male germ cells
- Production of spermatozoa takes place in the testis and they leave through a convoluted
duct system called the vas deferens
- Vas deferens channels the spermatozoa into the urethra that opens at the tip of the penis
- There are glands that produce semen in the region where the vas deferns delivers
spermatozoa into the urethra
- Divided into 300 different lobules
- Has a connective tissue capsule
- Sense septations into the testes, dividing the structure into lobules
- Each lobule contains up to 4 highly coiled epithelial tubules (seminiferous tubules)
- Seminiferous tubules are where sperm is generated and they carry spermatozoa into rete
testes (meshwork of channels)
o Designed to produce millions of spermatozoa
o Combined length of seminiferous tubules in both testes averages of 1000 m
o High amounts of cell division occur to generate spermatozoa and it is packaged in a
relatively small space
- Rete testes converge into several tubules that lead into highly coiled epididymis
- Epididymis: where spermatozoa are stored after production in between ejaculations
o Where spermatozoa mature
o Upon demand, they leave through the vas deferns
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- The testis is enclosed by a dense connective tissue capsule (Tunica Albuginea) and contains
250-300 lobules with one to four seminiferous tubules each
- Tunica albuginea:
o Substantial connective tissue capsule (DICT – fibroblasts + blood vessels)
o It is very thick and appears white in real life because of collagen
- Each cross section of tubules represents part of seminiferous tubules that are highly coiled
- Epithelium appears stratified (nuclei are stacked up) but most of the nuclei are not
epithelial cells → they are spermatogenic cells
- Most of the nuclei are spermatogenic cells
- Spermatogenic cells: germ cells at different stages of differentiation
- Sertoli cells: resident epithelial cells
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- In between the sertoli cells, there are differentiating germ cells (spermatogenic cells) which
originally migrate into the epithelium from the yolk sac
- Stem cells are visitors (move into epithelium and start their maturation)
- Amongst the tubules in the connective tissue, there are interstitial (Leydig cells)
- Leydig cells produce testosterone that is delivered to the epithelium because differentiation
requires testosterone
The clonal nature of spermatogenesis
- This occurs in the seminiferous tubules
- Spermatozoa (end product) are clones of dividing stem cells
- Spermatogonia: stem cells
o Cells that migrate into the epithelium
o There are two types
o Stem cells divide and multiply and become precursors for spermatocytes
o Amplification is MITOSIS (cell division and duplication of DNA)
o End product (type B spermatogonium) undergoes meiosis (DNA set is reduced to
haploid set and there is genetic crossover)
- Spermatocytes
o Where meiosis I and meiosis II takes place
o Cells spend a lot of time in prophase of meiosis I (genetic reorganization) → can be
identified very readily in histological section
o The cells are refereed to as primary spermatocytes
o Primary spermatocytes: cells rested in prophase of meiosis I
o After meiosis I, they quickly undergo meiosis II where they just divide without
making more DNA → secondary spermatocytes
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find more resources at oneclass.com
Document Summary
Testis are the site of production of male germ cells. Production of spermatozoa takes place in the testis and they leave through a convoluted duct system called the vas deferens. Vas deferens channels the spermatozoa into the urethra that opens at the tip of the penis. There are glands that produce semen in the region where the vas deferns delivers spermatozoa into the urethra. Each lobule contains up to 4 highly coiled epithelial tubules (seminiferous tubules) Sense septations into the testes, dividing the structure into lobules. Rete testes converge into several tubules that lead into highly coiled epididymis. Epididymis: where spermatozoa are stored after production in between ejaculations: where spermatozoa mature, upon demand, they leave through the vas deferns. The testis is enclosed by a dense connective tissue capsule (tunica albuginea) and contains. 250-300 lobules with one to four seminiferous tubules each: substantial connective tissue capsule (dict fibroblasts + blood vessels)
