21. Gametogenesis in animals and human. Origin of germ cells. Spermatogenesis. Mammalian sperm cells.
Covers spermatogenesis from puberty onwards, beginning with hormonal control by LH and testosterone production in Leydig cells, then the cellular setting in the seminiferous tubules with Sertoli cell support. It follows the stages from spermatogonial divisions through meiosis to motile spermatids, explains the syncytium idea of shared gene products, and ends with a breakdown of mammalian sperm structure: head, neck, midpiece and tail with its microtubule arrangement.
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Topic 21 of 64 in the MU Sofia syllabus for Biology (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 187 words (1 min of reading).
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Spermatogenesis Overview
Spermatogenesis Overview
Initiation and Hormonal Influence
Starts at puberty.
Takes about 24 hours.
Luteinizing hormone (LH) activates Leydig cells to produce testosterone.
Cellular Environment
Spermatogonia sit near the basement of the testis tubes.
Sertoli cells help and feed the growing sperm cells.
Process of Sperm Formation
Early Stage: Diploid spermatogonia divide many times.
Middle Stage: One becomes a primary spermatocyte, splits into two haploid secondary spermatocytes through meiosis.
Final Stage: Each secondary spermatocyte divides again to form two spermatids, which grow into motile sperm.
Why Sperm Mature Together (Syncytium)
Helps correct genetic errors using the normal versions of genes.
Shares helpful gene products from sex chromosomes.
Mammalian Sperm Cell Structure
Head:
Acrosome: Derived from the Golgi apparatus, essential for penetrating the ovum.
Nucleus: Contains densely packed DNA, where 85% of histones are replaced by protamines for more compact DNA packaging.
Neck:
Centriole: Plays a crucial role in sperm motility.
Midpiece:
Mitochondria: Provide the energy required for sperm motility.
Tail:
Axial Filament: Composed of a centriole-produced axoneme.
Microtubule Structure: Features 2 central microtubules surrounded by 9 doublets, each with dynein arms for movement, and 9 dense fibers for structural support.
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