( sperm = seed; zoon = animal )
It is microscope, elongated haploid motile male gamete or paternal gamete measuring about 0.055 mm ( 60 μ ) in length. Sperm remains viable for seventy-two hours, but can fertilize the ovum in first 12 to 14 hours only.
Head :
It is flat and oval region consisting of large nucleus and an acrosome. Acrosome secretes hydrolytic enzymes like hyaluronidase which helps in penetration of the egg during fertilization. The acrosome and anterior half of nucleus is covered by a fibrillar sheath.
Neck :
It is a very short region having two centrioles. The proximal centriole plays a role in first cleavage of zygote. The distal centriole gives rise to the axial filament of the sperm.
Middle piece :
It serves as power house for sperm. It has many mitochondria spirally coiled ( Nebenkern ) around the axial filament. The mitochondria provide energy for the movement of the sperm in the female genital tract. Posterior half of nucleus, neck, middle piece of sperm are covered by a sheath.
Tail :
The tail is long, slender and tapering structure formed of cytoplasm. A fine thread, the axial filament arises from the distal centriole and traverses the middle piece and tail.
Sperms
* The sperms was first discovered by Leeuwenhock.
* Spermatozoon this term is given by Von Baer.
* Each day about 300 million sperm complete the process of spermatogenesis.
* A sperms is about 60 um long and contains several structures that are highly adapted for reaching and penetrating a secondary oocyte.
* The major parts of a sperm are the head and the tail.
* The flattened, pointed head of the sperm is about 4-5 um long.
* It contains a nucleus with 23 highly condensed chromosomes.
* Covering the anterior two - thirds of the nucleus is the acrosome, a caplike vesicle filled with enzyme that help a sperm to penetrate a secondary oocyte to bring about fertilization.
* Among the enzymes are hyaluronidase and proteases.
* The tail of sperm is subdivided into four parts : neck, middle piece, principle piece and end piece.
* The neck is the constricted region just behind the head that contains centrioles.
* The centrioles form the microtubules that comprise the remainder of the tail.
* The middle piece contains mitochondria arranged in a spiral, which provide the energy (ATP) for locomotion of sperm to the site of fertilization and for sperm metabolism.
* The principal piece is the longest portion of the tail and the end piece is the terminal, tapering portion of the tail.
* Once ejaculated, most sperm do not survive more than 48 hours within the female reproductive tract.