Epididymal, vas deferens and prostate function are the cornerstones of male health

Anatomy and Physiology of Male Reproductive Organs

Epididymis

(1) Anatomy: The epididymis is crescent-shaped, closely attached to the upper end and posterior border of the testis, and slightly lateral. The upper end is enlarged to form the head of the epididymis, the middle part is the body of the epididymis, and the lower end is narrow to form the tail of the epididymis. The tail of the epididymis bends inward and upward to become the vas deferens. After the efferent ductules of the testis enter the epididymis, they bend and coil to form the enlarged head of the epididymis. The ends of the efferent ductules merge into an epididymal duct. The epididymal duct is tortuous and coiled, forming the body and tail of the epididymis, and the end of the duct sharply turns upward to become the vas deferens.

(2) Physiology: The epididymis is not merely a sperm passage and container; its main function is to provide a suitable environment for sperm development and maturation. After sperm enter the epididymis, they are directly nourished by the epididymal fluid, acquiring various abilities and gradually maturing. Sperm usually remain in the epididymis for 2-3 weeks. Due to the spontaneous rhythmic contractions of the efferent ducts of the testis and the epididymal duct, coupled with the pressure of the epididymal secretions, sperm are facilitated to be transported to the vas deferens. If not expelled in time, they are mainly digested and absorbed in the epididymis.

Vascular Deferens, Ejaculatory Ducts, and Spermatic Cord

(1) Anatomy: The vas deferens is a direct continuation of the epididymal duct, about 50 cm long, with thick walls and well-developed muscle layers, while the lumen is small. It feels like a round cord when touched and has a certain firmness. The vas deferens has a long course and can be divided into four parts according to its route: the testicular part, the spermatic cord part, the inguinal part, and the pelvic part. Its course is as follows: it enters the spermatic cord from the posterior border of the testis, enters the pelvis through the inguinal canal, and runs inward and downward along the lateral wall, crossing the end of the ureter to reach the posterior part of the bladder base. At this point, the two vas deferens gradually approach each other and dilate in a fusiform shape, forming the ampulla of the vas deferens. Absence of the vas deferens is one of the causes of clinical infertility. The ampulla of Vas Deferens tapers at its lower end and merges with the seminal vesicle duct at the base of the prostate to form the ejaculatory duct. The ejaculatory ducts are paired on the left and right, approximately 2 cm long, penetrating the base of the prostate and opening on either side of the urethral crest in the prostatic urethra. The spermatic cord is a nearly circular cord-like structure suspending the testis and epididymis. It originates at the internal inguinal ring and runs obliquely inward and downward, passing through the inguinal canal and subcutaneous ring into the scrotum, ending at the posterior border of the testis. It is composed of the cremaster muscle, vas deferens, internal spermatic artery, external spermatic artery, vas deferens artery, pampiniform plexus, spermatic nerve, lymphatic vessels, and covering fascia. The left internal spermatic vein directly drains into the left renal vein at nearly a right angle; therefore, 99% of varicocele cases occur on the left side.

(2) Physiology: Testicular spermatogenesis requires a suitable temperature. The venous dispersion within the spermatic cord and the contraction and relaxation of the cremaster muscle ensure a constant testicular temperature. Arterial supply, venous return, and lymphatic return of the scrotal contents, as well as sperm transport, all pass through the spermatic cord. Therefore, the spermatic cord's function is twofold: to ensure the spermatogenesis of the testes and to ensure the transport of mature sperm. The vas deferens is the channel for transporting sperm. It mainly relies on the ciliated cells within the lumen and its own peristalsis to propel sperm forward, transporting semen and motile sperm from the testes to the ejaculatory duct. The main physiological function of the ejaculatory duct is ejaculation. It relies first on the highly contractile columnar epithelial cells lining the lumen, and also on the combined contraction of the seminal vesicle, vas deferens, prostate, and corpus spongiosum to complete the ejaculation process, expelling semen from the urethra.

Seminal Vesicles

(1) Anatomy: The seminal vesicles are located behind the base of the bladder, lateral to the ampulla of the vas deferens. They are a pair of elongated oval sac-like organs, mainly composed of tortuous tubules. Their excretory ducts merge with the end of the ampulla of the vas deferens to form the ejaculatory duct, and the secreted fluid constitutes semen.

(2) Physiology: The seminal vesicles store semen and secrete a pale yellow, viscous, alkaline fluid called seminal vesicle fluid, which is the main component of semen, accounting for about 60%. Its main components are fructose and prostaglandins. It has a nourishing effect on sperm.

Prostate

(1) Anatomy: The prostate is slightly flattened chestnut-shaped, wide at the upper end and pointed at the lower end. Its transverse diameter is about 4 cm, longitudinal diameter is about 3 cm, anteroposterior diameter is about 2 cm, and it weighs about 20 grams. It is divided into anterior, middle, posterior, and lateral lobes. The base of the prostate is adjacent to the base of the bladder, the seminal vesicles, and the ampulla of the vas deferens. Anteriorly, it is bordered by the pubic symphysis, and posteriorly, it is close to the rectal ampulla. The posterior part of the prostate can be palpated through the rectum. Normally, there is a shallow prostatic sulcus. When enlarged, the posterior part is significantly raised, and the prostatic sulcus becomes shallower or disappears. Enlargement of the middle lobe can easily cause difficulty in urination. The prostate gland is covered by a loose connective tissue outer layer containing a rich network of blood vessels, beneath which lies a fibrous sheath formed by the pelvic fascia. The inner layer is a muscle layer; these three layers together constitute the prostatic capsule.

The prostate has an ample blood supply. There are three arteries: the inferior vesical artery, the middle hemorrhoidal artery, and the internal pudendal artery. The inferior vesical artery is the primary one, dividing at the junction of the bladder and prostate into the superior and inferior prostatic capsule arteries. The latter enter the gland at the 5 o'clock and 7 o'clock positions (lithotomy position). During surgical treatment, attention should be paid to bleeding at these two points. The prostatic venous plexus runs between the pubis and the prostate, along the prostatic ligament, merging with the deep dorsal vein of the penis, and then draining into the internal iliac vein via the inferior vesical vein and lateral ligament.

(2) Physiology: The prostate gland is the largest accessory gland in men. Its main physiological function is to secrete prostatic fluid, also known as seminal plasma, which is an important component of semen, accounting for about 1/3 of the volume of a single ejaculation. It is a milky white, acidic serous fluid with a pH of 6.45. Prostatic fluid contains a large number of inorganic and organic substances and enzymes, such as sodium, potassium, calcium, zinc, magnesium, citric acid, protein, starch, hyaluronidase, and prostaglandins, which have an important influence on sperm motility and physiological function.