Male Reproductive System of mammals

The male reproductive system consists of paired testes, several accessory glands, a duct system and a mating organ called penis. Testis is the primary male sex organ. It produces spermatozoa and secretes the male sex hormone testosterone. The human male testis measures 5 cm, 3 cm and 2.5 cm respectively, in length, thickness and width.  It is covered by thick connective tissues sheaths which is white fibrous called tunica albuginea. In man, both testes normally remain suspended in a pouch called scrotum outside the abdominal cavity. This keeps the testes at a cooler temperature than the body temperature (2-2.5 degree celcius below the body temperature) which is essential for the maintenance and function of the spermatogenic tissues of the testes. Spermatogenic tissues are responsible for the production of sperms called spermatogenesis. Each testis has about 250 compartments called testicular lobules. Each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced. Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonea) and Sertoli cells. The male germ cells undergo meiotic divisions finally leading to sperms. Sertoli or sustentacular or nurse cells are present in between spermatogenic cells which provide nourishment to developing spermatozoa (sperm cells) and regulate spermatogenesis by releasing inhibin to check FSH overactivity. The functions of the sertoli cells are as follow:

Ø To provide nourishment to the developing spermatozoa,

Ø To absorb the parts being shed by developing spermatozoa,

Ø T release anti-mullerin factor (ANF) to prevent the development of mullerin duct/ovidudct,

Ø To release androgen binding protein.

The region outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydigcells. These Leydig cells constitute the endocrine tissue of the testis to synthesise and secrete testicular hormones called androgens. Other immunologically competent cells are also present. Seminiferous tubules unite to form several straight tubules called tubuli recti which opens into irregular cavities in the posterior part of the testis. It is highly anastomosing (Fused together in a vein-like network) labyrinth of cuboidal epithelium lined channels called rete testis.  Several tubes called vasa efferentia arise from it and conduct spermatozoa out from the testis (Seminiferous tubules to vasa efferentia form intratesticular genital duct system).

The extratesticular duct system consists of tubes which conduct sperms from the testes to the outside. It starts with vasa efferentia which arise from the testis and become confluent to form a folded and coiled tube called epididymis behind each testis. The epididymis consists of three parts namely Caput, Corpus and Cauda. The epididymis stores the sperm temporarily. A  partially coiled tube from the cauda epididymis aise called vas deferens ascends into the abdomen through inguinal canal, passes over the urinary bladder receives the duct from the seminal vesicle behind the urinary bladder to form an ejaculatory duct. The vas deferens dilates to form ampulla before entering prostate gland. The final portion of the ampulla passes through the prostate to open into the urethra shortly after its origin from urinary bladder. The urethra reveives the ducts from the prostate and cowper’s glands, passes through the penis and opens to the outside. Urethra is the common passage for urine and sperms.

PENIS: PENIS is the copulatory organ of man. It is cylindrical and erectile, perpendulous organ suspended from the pubic region in front of scrotum. It is made up of special tissues that help in the erection of the penis to facilitate insemination during copulation. The enlarged end of the penis called glans penis is covered by a loose fold of skin called foreskin. Normally penis remains small and limp (Flaccid) but on sexual arousal, it becomes long, hard, thick and erect. Penis is not at all always remains ready for copulation (Mating or Sex), it only becomes ready for copulation when a man get sexually excited. Normally, human penis measures 3-5cm (on an average) in length but magically it becomes 15cm long (on an average) on sexual arousal. Penis is made up of spongy muscle tissue which, when filled with blood, causes stiffening and erection. In mating, penis enters the vagina and releases sperms in the cervix region. Some people suffer from erectile disfunction of penis and they are not able to penetrate in the vagina during sex. This may occur due to many disease or unhealthy practices like masturbation. Masturbation gives pleasure but leaves its harmful effects for life long. Sometime, a man become sexually disfunctinal for lifetime due excessive masturbation.

Testes descend in the scrotal sac when foetus is about 7 months old and occurs under the influence of Follicle Stimulating Hormone (FSH) and testosterone. If it fail to descend, it is called CRYPTORCHITISM and leads to sterility. Scrotum remain connected with abdomen or pelvic cavity the inguinal canal. Blood vessels, nerves and conducting tubes passes through it. Cremaster muscles and connective tissue form spermatic cord and surround all the structures passing through inguinal canal. Cremaster muscles and dartos muscles help in the positioning of the testes. Whenever the outside temperature is low, these contract to move the testes clos to abdominal cavity or pelvic cavity. When outside temperature is high, these relax moving the testes away. In some seasonally breeding mammals, testes descend to the scrotum in breeding season only and ascend back to the abdomen in the non-breeding season. E.g. Rats.