Male reproductive system:
The male reproductive system of a scrotum,a pair of testes,vasa efferentia, a pair of epididymis,a pair of vasa deferentia,a pair of ejaculatory ducts, a urethra,a penis and certain accessory sex organs.
A spermatic cord connects testis with abdominal cavity.It consists of connective tissue that encloses an artery,a vein,a lymph vessels,a nerve,cremaster muscle and a vas deferens.A testis rests in its chamber over pad called gubernaculum. The scrotal sac of male is homologus to female's labia majora.
Variations in position of testes:
In some mammals (lion,bull,horse),the testes remain permanently in the scrotum and keep functioning throughout the year as in man.In certain seasionally breeding mammals,such as bat,otter and llama,(Insectivora, Tubulidentata and most Rodentia)the testes enlarge,become functional, and descent into the scrotum in the breeding season,but thereafter ascent into abdominal cavity,and become reduced and inactive. In a few cases (elephant,whale,seal)the testes remain permanently in the abdomen as the body temperature is low enough for sperm maturation.Scrotum is absent in such cases.Scrotum is in front of penis in Kangaroo
The testes are the primary sex organs.They are about 4-5cm long, 2.5cm wide and 3cm thick.They are suspended in the scrotal sacs by spermatic cords.Each testes weighs about 10-15 gms.
Each testis has three coverings- tunica vaginalis,tunica albuginea and tunica vasculosa.Ingrowth of the tunica labuginea,called septa, divide the testis into some 200 to 300 lobules.Each testicular lobule contains 1-3 highly convoluted seminiferous tubules,blood vessels and nerve embedded in loose connective tissue.A total of about 750 seminiferous tubules occur in each testis.
Each seminiferous tubule is lined by germinal epithelium,seminiferous tubules is the site of spermatogenesis.The process occurs in waves along the length of the tubule,taking about 9 weeks(63 days) to complete in man. Seminiferous tubules contain 3 types of cells:-
Germ cells or primordial germ cells arise from yolk sac endoderm and enter the testes early in development.These are spermatogenic cells,by mitotic division,produce spermatogonia into the lumen of the seminiferous tubule.The spermatogonia grow into primary spermatocytes which undergo meiosis,producing haploid cells,first secondary spermatocytes and then spermatids. Spermatids differentiate by a process of spermiogenesis into dimorphic haploid sperm(containing X or Y chromosome). Mature spermatozoa lie free in the cavity of the seminiferous tubules.
(ii)Somatic cells/Sertoli cells/Sustentacular cells/ Nurse cells:-
These are supportive nutritive and secrete a polypeptide hormone called inhibin and a steroid oestradiol which interferes with spermatogenic activity and kinetics of sperm production.