Spermatogonium

Types of spermatogonia

• Type A cells, with dark nuclei. These cells are reserve spermatogonial stem cells which do not usually undergo active mitosis.
• Type A cells, with pale nuclei. These are the spermatogonial stem cells that undergo active mitosis. These cells divide to produce Type B cells.
• Type B cells, which undergo growth and become primary spermatocytes.
• These 3 different subtypes get distinguished based on nuclear morphology Adark has a homogeneously dense, deeply stained chromatin with at least one chromatin-free cavity, occasionally presenting nuclear rarefraction zones. Apale have a less dense chromatin, while type B spermatogonia can be recognized by nucleolar localization, their position to the basement membrane and the presence of several flakes or granules.

  Spermatogenesis

• Spermatogenesis occurs in the germinal epithelium of the seminiferous tubules. Spermatogonia undergo meiosis to produce spermatids that later mature into spermatozoa. The spermatogonia duplicate their DNA to obtain 46 chromosomes in preparation for the primary division. At this stage, the germ cells are now referred to as primary spermatocytes.
• The primary spermatocytes undergo a primary division, yielding two secondary spermatocytes each with 23 chromatids. The secondary spermatocytes then undergo a second division to produce two spermatids, each with 23 chromosomes.
• The spermatids are currently surrounded by Sertoli cells, which nourish the sperm and produce inhibin, an inhibitor of the follicle-stimulating hormone.
• The last step of spermatogenesis is spermiogenesis. During this process, the spermatids are transformed into spermatozoa, mature sperm. At this point, no other division occurs. The sperm is released from the Sertoli cells and transported to the epididymis through peristalsis. While in the epididymis, the sperm is stored and begins maturation. Once the sperm has fully matured, it will reach its spermatozoan phase.

  Male hormones

• Gonadotropin-releasing hormone : Secreted by the hypothalamus, GnRH triggers the release of the luteinizing hormone and follicle-stimulating hormone.
• Follicle-stimulating hormone : FSH is in charge of stimulating Sertoli cells with testosterone to produce regulatory molecules and nutrients needed for the cells. The nutrients are a needed factor for the maintenance of spermatogenesis.  
• Luteinizing hormone : LH stimulates Leydig cells to produce testosterone.
• Testosterone: Testosterone is an important hormone that helps mature sperm through the process and gives rise to male secondary characteristics.
• Inhibin: Inhibin is secreted by Sertoli cells. It participates in regulating and inhibiting FSH.

  Sperm structure

• Head: As the head of the sperm, it is an ovular shape consisting of the nucleus and the acrosome.
• * Acrosome: The Acrosome covers two-thirds the head's outside area; it contains hydrolytic enzymes needed to penetrate the oocyte for fertilization.
• * Nucleus: The nucleus consists of conjugated DNA with proteins. The chromatin is tightly compacted with no visible chromosomes.  
• Midpiece/neck: The midpiece consists of the mitochondria where ATP is produced.  
• Tail: The tail consists of a long flagellum made up of microtubules. It arises during the spermatid stage and allows motility.

  Infertility

Diseases that cause infertility

• Cystic fibrosis
• * Cystic fibrosis is a genetic condition that changes proteins in the body. It causes mucus to become thick and sticky leading to blockages and damage as it builds up.
• * The vast majority of Men with cystic fibrosis suffer from infertility issues. The main cause of infertility is due to obstructive azoospermia. OA is a condition where there is a blockage in a male's reproductive tract, resulting in a lack of sperm in a male's ejaculate. This is mostly due to an absence of the vas deferens, which is thought to be caused by CFTR mutations. In most males with CF, spermatogenesis does occur, but the males have a lower ejaculate volume. 
• Klinefelter syndrome
• * Klinefelter syndrome is the most common chromosomal abnormality associated with male infertility. Klinefelter's is due to a trisomy of XXY on the 23rd chromosome, giving males an extra X chromosome. The cause of infertility is related to the replacement of normal testicular architecture with tubular atrophy, sclerosis, or maturation arrest, which degenerates into fibrosis.

Anticancer drugs

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