The Morphology of Human Sperms

1. Head - 4.0 μm
2. Neck - 0.3 μm
3. Middle piece - 7 μm
4. Principal piece - 40 μm
5. End piece - 5-7μm
6. Approximately 58.3μm

• As it is released from the wall of the seminiferous tubule into the lumen, the spermatozoon is non-motile but structurally mature.
• Its expanded head contains little cytoplasm and is connected by a short constricted neck to the tail.
• The tail is a complex flagellum and is divided into middle, principal and end pieces.
• The head contains the elongated flattened nucleus with condensed, deeply staining chromatin and the acrosomal cap anteriorly, which contains acid phosphatase, hyaluronidase, neuraminidase and proteases necessary for fertilisation.
• In the centre of the neck, is a well formed centriole, corresponding to the proximal centriole of the spermatid from which it differentiated The axonemal complex is derived from the distal centriole.
• A small amount of cytoplasm exists in the neck covered by plasma membrane continuous with that of the head & tail.
• The middle piece - a long cylinder - consists of an axial bundle of microtubules, the axoneme, outside which is a cylinder of nine dense outer fibres, surrounded by a helical mitochondrial sheath.
• The annulus is an electron - dense body at the caudal end of the middle piece.
• The principal piece - motile part of cell - The axoneme and the surrounding dense fibres are continuous from the neck region through the whole length of the tail except for its terminal 5-7μm, in which the axoneme alone persists.
• The end piece has a typical structure of a flagellum, with a simple nine plus two arrangement of microtubules.

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