Human Physiology

Lesson 26 : Male Reproductive System-II

Functions of Male Genital Tract and Semen Ejaculation

The spermatozoa are synthesized in the tests after attainment of puberty age and continue until death of animal. After leaving the testes they spend about 3-4 days in epididymis where they undergo further maturation and attain motility and fertility. Testicular sperms are not capable of fertilizing ovum. In the epididymis several structural and biochemical changes occurs that makes the sperms fertilizable.

Just at the time of copulation or mating with female, epididymis contracts and pushes spermatozoa into ductus deferens and urethra for deposition into female genital tract. The process of passage of spermatozoa or semen out of male genital tract is termed as ejaculation. Before ejaculation, the spermatozoa are also mixed with fluid secreted from various accessory glands. The fluid portion is known as seminal plasma and sperms are suspended in it. Semen is the term given to secretion of male genital tract and it contains spermatozoa and seminal plasma. Approximately 3.5 ml semen is discharged with every ejaculation and one milliliter of semen contains about 100 millions spermatozoa. On volume basis, sperms constitute just 1% of semen volume.

Composition of semen: Semen is whitish viscous discharge of male genital tract. It contains a fluid called seminal plasma and spermatozoa in varying number (sperm concentration). Semen composition is described in terms of volume of ejaculate (i.e. volume of semen discharged per ejaculate) and sperm concentration (i.e. billions of sperms present in one milliliter of semen). Seminal plasma also contains some specific bio-molecules that are required for sperm metabolism. Some such compounds are citric acid, inositol, fructose ergothionine, glyceryl phosphoryl choline. Usual components of blood plasma such as electrolytes, glucose, enzyme, hormones and other organic compounds are also found in semen.

Structure of Sperm: Spermatozoa (singular spermatozoon) are specialized gametic cells possessing own motility. Typical spermatozoon has two distinct portions, the Head and the Tail. Head is oval shaped in structure and encloses nuclear material containing haploid chromosomes. Anterior part contains modified golgi bodies with stored enzymes for helping in penetration of ovum. This portion is called acrosome . Tail is long cylindrical process attached to posterior end of head and it arises from centriole. Tail is further subdivided into Mid piece, Chief or main piece and End piece. Mid piece consists of spirally arranged densely packed mitochondria which provide energy for mobility of main piece. Main and end piece contains axonemal contractile filaments for sperm motility. Motility of sperm is visible under ordinary microscope in diluted semen sample.