Male reproductive system consists of parts for production of gametes and copulation. The male gonads are testes situated in scrotum, a pouch of pigmented skin arising from lower abdominal wall. Its wall consists of smooth muscles called dartos tunic muscles. It is divided into two compartments right and left by muscles septum. Each compartment encloses a testis, epididymis and a testicular end of a spermatic cord. It lies below the public symphysis in front of upper part of thigh and behind the penis. Scrotum protects testes and acts as thermo-regulator i.e. regulates temperature for proper functioning of testis. Testes are soft, smooth, pinkish oval organs about 4.5 cm long, 2.5 cm wide and 3 cm thick. Testes are mesodermal in origin and located outside the abdomen in scrotum i.e. extra abdominal sac by spermatic cord. Each testis is connected to the wall of scrotum by short fibromuscular band called gubernaculum.
During early foetal life, the testes develop in the lumbar region of the abdominal cavity just below the kidney. During seventh month of development, they descend permanently into the respective scrotal sacs through a passage called inguinal canal. Along with testes, peritoneum, blood vessels, lymph vessels, nerves and vasa deferentia also descend down in scrotal sacs. Hence peritoneum covering testes i.e. tunica vaginalis is an indication of abdominal origin of testis. The peritoneum eventually surrounds the testes in the scrotum, becoming detached from abdominal peritoneum. Failure of testis to descend from abdomen into scrotum leads to sterility called cryptorchidism.
In each testis, there are 200 to 300 lobules. In each lobule there are 1 to 4 convoluted loops called seminiferous tubules. These tubules converge towards posterior surface and form a network of irregular tubules called rete testis. Testes descend into the scrotum along with peritoneum, blood vessels and vas deferens.
Histology of Testis :
Testis is externally covered by fibrous connective tissue called tunica albuginea. It is covered internally by tunica vascularis formed by capillaries and externally by an incomplete peritoneal covering called tunica vaginalis.
Seminiferous tubules are lined by cuboidal germinal epithelial cells. The germ cells undergo the process of spermatogenesis.
Transverse section of testis shows different stages of spermatogenesis like spermatogonia, primary and secondary spermatocytes, spermatids and sperms.
Few large pyramidal cells present interrupted between germinal epithelium are Sertoli cells. Sperm bundles get attached to Sertoli cells with their heads.
Sertoli cells provide nourishment to the sperms till maturation. Between seminiferous tubules are present a few groups of cells called interstitial cells or cells of Leydig. These cells secrete the hormone testosterone after puberty.
Vasa efferentia :
From the rete testis, 15 to 20 fine convoluted ductules, vasa efferentia, pierce the tunica albuginea to enter the caput or head of the epididymis.
Epididyms :
These are a pair of "C" shaped structures lying along the posterior border of each testis. Each shows presence of highly coiled duct, about 6 meters long, which is differentiated in three regions:-
1) Upper wider head or caput epididymis that receives vasa efferentia.
2) Middle narrower body or corpus epididymis.
3) Lower duct is also wider called tail or cauda epididymis.
In the head of epididymis, the sperms undergo physiological maturation, acquiring increased motility and fertilizing capacity. In the tail, sperms are stored for short period and then enter the vas deferens.
Spermatozoa are produced irrespective of whether ejaculation takes place or not. The spermatozoa not ejaculated are reabsorbed in the vas deferens.
Vasa deferentia :
These are a pair of tubular structures arising from cauda epididymis. Each vas deferens is about 40 cm long and entering into abdominal cavity through the inguinal canal, medially towards the posterior wall of the urinary bladder. Here it is joined by the duct from seminal vesicle to form ejaculatory duct.
Ejaculatory duct :
These are a pair of ducts each about 2 cm long. It is formed by joining of vas deferens and a duct of seminal vesicle. Both ejaculatory ducts open into urethra in the region of prostate gland. They carry seminal fluid and spermatozoa to the urethra.
Urethra :
The male urethra provides a common pathway for the flow of urine and secretion of male reproductive organs called semen. The urethra includes three parts:-
1) The first part is surrounded by prostrate gland and is called the prostatic urethra which carries urine only.
2) The second part is the membranous urethra, which is situated between the end of prostate gland and root of penis. It carries both urine and semen.
3) The third part is penile urethra which is situated in the penis. It carries both urine and semen. The urethra has two sphincters internal sphincter of smooth muscle fibres as its beginning and external sphincter of striated muscles.
Penis :
It is cylindrical, erectile and pendulous organ suspended in public region in front of scrotum. Urethra passes throughout the length of penis. It contains three columns or erectile tissues. Ordinarily, it remains small and limp but on sexual arousal, it becomes long, hard and erect. Erectile tissue has abundant blood sinuses. Blood flows in the sinuses and makes penis erect.
The penis contains two postero-lateral tissues called corpora cavernosa and a median corpus spongiosum. Urethra passes through corpus spongiosum. Urethra passes through corpus spongiosum. Hence, it is also called spongial urethra. Near the tip of the penis, the corpus spongiosum is enlarged to form a soft and highly sensitive glans penis. It is covered by a loose retractable fold of skin called prepuce or foreskin.
Penis functions as a copulatory organ.
ACCESSORY SEX GLANDS :
Seminal vesicles :
The seminal vesicles are two small fibro-muscular pouches present on the posterior side of the urinary bladder. Seminal duct joins with vas deferens and forms ejaculatory duct.
Seminal vesicles secrete a viscus fluid fructose, fibrinogen and prostaglandins. It contributes about 60% or the total volume of the semen.
Fructose provides energy to sperms for swimming. The prostaglandins stimulate contractions in the female reproductive tract to help the process of fertilization. The fibrinogen helps in coagulation of semen after ejaculation.
Prostate gland :
It consists of 20 to 30 separate lobes which open separately into the urethra. The prostatic fluid is a whitish liquid forming about 30% of total volume of semen.
The prostatic secretion neutralizes the acidity of vaginal secretion. At pH 6.0 to 6.5, sperms become motile and facilitate the process of fertilization.
Cowper's glands :
These are also known as bulbo-urethral glands. They are pea-sized and situated on either sides of membranous urethra. These glands secrete an alkaline viscous fluid. which neutralizes acids that may be present in the penile urethra due to previous urination and also lubricates the vagina of female genital tract.
Fructose is present in seminal fluid and is not produced elsewhere in the body. Hence it provides a proof for forensic test in case of rape. Its presence in the female genital tract confirms sexual intercourse.
Artificial insemination- It is a technique to make a female pregnant by artificially introducing semen into the vagina.
Semen :
It is ejaculated during sexual intercourse, known as coitus. It is a whitish fluid which contains spermatozoa and a mixture of secretions from seminal vesicles, prostate gland and Cowper's gland. A single ejaculation releases 3 to 4 ml of semen which contains about 300 million sperms. However, only one sperms. The release of a large number of sperm ensures the process of fertilization.