SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Sperm production. Coloured scanning electron micrograph (SEM) of a transverse section across several freeze-fractured seminiferous tubules, the site of sperm production in the human testis. The centre of each tubule is filled with the tails (blue) of developing sperm cells. The tubules are lined with a stratified epithelium containing two types of cell: Sertoli cells (orange), which nourish developing sperm, and spermatogenic cells (green), from which the sperm cells form in a process known as spermatogenesis. After this, the sperm cells mature into their mobile form in a process known as spermiogenesis.
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