Male reproductive system | Anatomy

The male reproductive system consists of the testes which produces sperm that are then transported through the epididymis, ductus deferens, ejaculatory ducts and urethra; as well as accessory glands like the seminal vesicles, prostate and bulbourethral glands whose secretions play vital roles in reproduction.

Testes

They are the male gonads. They lie in the scrotum suspended by the spermatic cord and dartos muscle. Each testis is surrounded by an outer tunica vaginalis, which has visceral and parietal layers, and an inner tough, tunica albuginea. Septae from the tunica albuginea divide the testes into about 300 lobules. Each lobule consists of 1-4 tightly coiled structures called seminiferous tubules, which are the site of spermatogenesis. The seminiferous tubules are lined by germinal epithelium and has two specialized cells called Sertoli cells and spermatogenic or germ cells. Spermatozoa are released into the lumen of the seminiferous tubules.

Sertoli cells: They are elongated columnar cells with characteristic ruffled apical and lateral surfaces and oval nuclei. They extend all the way from the basement membrane to the lumen. They surround the germ cells and nourish and support them, hence they are also called sustentacular cells. They are joined together by tight junctions leading to the formation of the blood-testis barrier. They secrete inhibin, mullerian inhibitory factor and androgen binding protein, phagocytose dying germ cells and excess cytoplasm and have receptors for FSH.
Spermatogenic or Germ cells: These cells undergo spermatogenesis to produce the spermatozoa or sperm. Spermatogonia are located basally along the basal membrane, are round, pale or dark with prominent nucleoli. Primary spermatocytes have granulated nuclei. Spermatids have very little cytoplasm and dark, round nuclei. Dark type A spermatogonia are the source of stem cells while pale, type A spermatogonia differentiate into type B spermatogonia which then undergo spermatogenesis.

The narrow terminal portions of the seminiferous tubules form the straight tubules or tubuli recti. The straight tubules empty into the rete testes which are located posteriorly at a ridge like structure called the mediastinum of the testis. About 15-20 efferent ductules connect the rete testis to the epididymis. The efferent ductules are lined by ciliated columnar cells and microvilli and are surrounded by a circular layer of smooth muscle.

Leydig cells or interstitial cells are located in the connective tissue in between the seminiferous tubules. They are acidophilic (stain pink with H and E stain), large polygonal cells with a prominent smooth endoplasmic reticulum and highly refractive, rod shaped cytoplasmic crystals of Reinke. Leydig cells have receptors for LH. They secrete testosterone.

The testes are supplied by testicular arteries which are a branch of the abdominal aorta. They run in the spermatic cord. The testes are also supplied by the cremasteric branch of the inferior epigastric artery and the artery to the ductus deferens. The small veins draining the testes form a network of veins called the pampiniform plexus which lies in the spermatic cord. It continues as the testicular vein at the deep inguinal ring. The right testicular vein drains into the IVC while the left testicular vein drains into the left renal vein at a right angle. The right angle of joining and also longer length of the left testicular vein puts it at greater risk of varicoceles. Lymphatic drainage is to the lateral aortic and pre-aortic nodes. Autonomic nerve supply is from the tenth and eleventh thoracic spinal nerves through the renal and aortic plexuses.

Epididymis

It is situated along the superior and posterior margins of the testes. Sperm complete their maturation process in the epididymis. It is connected to the efferent ductules at one end and the ductus deferens or vas deferens at the other. The epididymis is a highly coiled duct with a head, body and tail regions. It is lined by pseudostratified columnar epithelium with principal cells and basal or stem cells. The principal cells have well developed rough endoplasmic reticulum, Golgi apparatus and characteristic stereocilia. Stereocilia contain actin filaments and they increase the surface area of the epididymis to facilitate absorption and secretion. Ductus deferens and hair cells of the inner ear are the only other areas to have stereocilia. The head and body of the epididymis have circular smooth muscle layer while the tail region has inner longitudinal, middle circular and outer longitudinal layers, which help in the movement of sperm towards the ductus deferens.

Ductus deferens or vas deferens

It is a tube like structure that begins at the inferior pole of the testes, enters the spermatic cord which passes through the inguinal canal. It dilates to form the ampulla at its distal end and joins the duct of the seminal vesicle to form the ejaculatory duct. In a vasectomy, the vas deferens is cut and ligated as a form of surgical sterilization. Epithelium and three layer muscle coat is similar to the epididymis.

Ejaculatory ducts

It is formed by the joining of the duct leading from the ampulla of the vas deferens with the duct of the seminal vesicle. It passes through the prostate and opens into the prostatic urethra at the seminal colliculus or verumontanum. It lacks a muscle coat.

Seminal vesicles

These paired saccular glands are located posterior to the bladder, between the bladder and the rectum. It is the major contributor of seminal fluid. The secretion of the seminal fluid contains fructose which is an energy source for sperm, choline, prostaglandins for viability and motility of sperm and proteins which undergo coagulation after ejaculation. Muscular coat comprised of an inner circular and outer longitudinal layer is present in the wall which is important during ejaculation to move the seminal fluid into the ejaculatory duct. Semen contains sperm and secretions from the seminal vesicles, prostate and bulbourethral glands.