Male Reproductive SystemAnatomy-Histology Correlate

By: Michael Lu, Class of ‘07

NOTE:

- The pelvic diaphragm is shaped like a bowl and attached to the ilium, ischium, pubis, and coccyx bones.

- The sacrotuberal ligament connects the sacrum to the ischial tuberosity, while the sacrospinous ligament connects the sacrum to the ischial spine. Along with the greater and lesser sciatic notches, these two ligaments form the greater and lesser sciatic foramen.

- The piriformis muscle passes through the greater sciatic foramen. Superior to the muscle are the superior gluteal vessels and nerve. Inferior to the muscle are the inferior gluteal vessels and nerve, the sciatic nerve, and the posterior femoral cutaneous nerve. The internal pudendal vessels and nerve and nerve to obturator internus muscle also leave the pelvis via this opening but reenter the lesser sciatic foramen.

- The lesser sciatic foramen also transmits the tendon to the obturator internus muscle. This muscle covers the obturator foramen. Its fascia has a specialized tendinous arch for attachment of the levator ani muscle. The levator ani muscle includes the puborectalis, pubococcygeus, and iliococcygeus muscles. Along with the (ischio-)coccygeus) muscle, these muscles complete the musculature of the pelvic diaphragm.

NOTE:

- The testicular arteries branch off the abdominal aorta near the kidneys. The right testicular vein drains directly into the inferior vena cava, while the left testicular vein drains into the left renal vein and then into the inferior vena cava. Note how the vessels cross over the ureters and enter and exit the inguinal canal with the spermatic cord via the deep and superficial inguinal rings, respectively.

- The arterial supply of the pelvis is supplied by the common iliac arteries, which are the end branches of the abdominal aorta. The common iliac arteries branch into the external iliac arteries (which continue as femoral arteries) and the internal iliac arteries.

- The posterior division of the internal iliac artery gives off the iliolumbar, lateral sacral, and superior gluteal arteries.

- The anterior division gives off the umbilical artery, which further branches off as the superior vesical artery and the medial umbilical ligament (obliterated umbilical artery. The anterior division also gives off the obturator, middle rectal, inferior gluteal, inferior vesical, and internal pudendal arteries.

- The internal pudendal artery enters the perineum and gives off the inferior rectal artery. As the internal pudendal artery continues toward the external genitalia, it gives off the perineal artery superior to the perineal membrane and ends as the posterior scrotal artery. The internal pudendal artery continues deep to the perineal membrane, with its terminal branches ending as the dorsal artery and deep artery of the penis.

- The pudendal nerve gives off the inferior rectal nerve, and continues as the perineal nerve superiorly and ends as the posterior scrotal nerve. The deep branch of the pudendal nerve continues as the dorsal nerve of the penis in the deep perineal space.

- Reminder: The internal pudendal vessels and pudendal nerve exit the greater sciatic foramen and reenter the pelvis through the lesser sciatic foramen.

- Review the contents of the inguinal canal and spermatic cord. Remember the descent of the testes during development, and the various fascial and muscular layers of the scrotum. This process is detailed below.

- Note the testicular artery and vein and the genital branch of the genitofemoral nerve entering the spermatic cord at the deep inguinal ring. The ilioinguinal nerve sends branches to the scrotum (or labia in females) through the inguinal canal, but is not part of the spermatic cord.

- The ductus deferens travels up the spermatic cord in the inguinal canal, exits from the deep inguinal ring and turns towards the prostate gland located below the bladder.

- The testis is covered by a dense collagenous coat called the tunica albuginea. Septa extend into the testis to separate the lobules. In mature testis, there is a prominent vascular layer immediately beneath the tunica albuginea.

- Most of the testis is occupied by highly coiled seminiferous tubules, as seen in most of the bottom panel. The blue arrows point to Leydig cells that secrete testosterone. We will look at these structures more closely in the next slide.

- The abundant seminiferous tubules all lead into the mediastinum of the testis, separated from the rest of the testis by the tunica albuginea as well. The mediastinum includes the rete testis, which lead to the efferent ducts and then the epididymis at the posterior aspect of the testis. The epididymis can be divided into three parts – the head, the body, and the tail.

- The ductus deferens is continuous with the tail of the epididymis. As mentioned before, it passes through the superficial inguinal ring in the spermatic cord, through the inguinal canal, exits the deep inguinal ring, and joins the duct of the seminal vesicle to form the ejactulatory duct.

- The seminiferous tubules are composed of spermatogonia located at the base of the epithelium with large round nuclei.

- Spermatogonia give rise to primary spermatocytes, with larger nuclei midwsay up in the epithelium. The nuclei are round with distinct bundles of dense chromosomes. These cells are in extended prophase of the first meiotic division.

- The primary spermatocytes further develop into spermatids located higher up in the epithelium toward the lumen. The round nuclei become smaller, denser, and change shape into the heads of mature sperm, or spermatozoa.

- Also found within the seminiferous tubules are Sertoli cells, which are large, relatively pale and irregularly shaped. We can see a prominent nucleolus within the Sertoli cell nucleus. These cells primarily support and nourish the germ cells in the testis with long, apical cytoplasmic folds. They contain testosterone and FSH receptors.

- Within the loose connective tissue of the testis, among seminiferous tubules, we can see Leydig cells. They are indicated by the arrow in the bottom panel. These cells secrete the male steroid hormone, testosterone. There may be small capillaries found among the clusters of Leydig cells.

- Fully formed spermatozoa leave the seminiferous tubules by straight tubules and enter interconnected channels called rete testis within the mediastinum (bottom left). These flattened channels are lined with low cuboidal epithelium. As mentioned before, the mediastinum contains the dense connective tissue of the tunica albuginea.

- The rete testis lead into the efferent ductules (bottom right) that lead into the head of the epididymis. Efferent ductules have unusual serrated or scalloped epithelial lining. This is due to alternating tall and short cells. Note the cells have cilia, which beat to help move mature sperm to the epididymis.

- Note the efferent ductules located right next to the epididymis. They empty their contents into the head of the epididymis, located outside the testis.

- Note the difference between the epithelia of the efferent ductules and the epididymis. The long and convoluted epididymis is lined by pseudostratified columnar epithelium (bottom right) with stereocilia.

- Sperm is stored in the tail of the epididymis in preparation for ejaculation.

- From there, the sperm enters the ductus deferens.

- As mentioned before, the ductus (vas) deferens runs in the spermatic cord. It has a thick smooth muscle coat (bottom left) and the mucosa is highly folded and lined with pseudostratified epithelium.

- Other contents of the spermatic cord include the testicular artery, the pampiniform plexus of veins, the genital branch of the genitofemoral nerve, and the dartos (smooth) and cremaster (skeletal) muscles.

- The testicular artery surrounded by the pampiniform plexus creates a counter-current heat exchange that cools the blood in the artery as it travels to the testis (bottom right). Continual healthy development of sperm requires a temperature lower than body temperature.

- After the ductus deferens exits the deep inguinal canal, it heads superiorly towards the urinary bladder. After crossing the ureters, the ampulla of the ductus deferens joins the seminal vesicle.

- The seminal vesicle is located on the posterior side of the bladder and lateral to the ampulla of the ductus deferens. It produces seminal fluid including fructose, absorbic acid, and other components that constitute about 50-80% of semen.

- The duct of the seminal vesicle and the ductus deferens join to form the ejaculatory duct that runs through the prostate gland.

- The prostate gland is an exocrine gland located inferior to the bladder. It secretes various components of semen including citric acid and acid phosphatase as the ejaculatory duct passes through it. The opening of the ejaculatory duct is found at the seminal colliculus, where the contents are emptied into the prostatic portion of the urethra.

- Note the inner surface of the urinary bladder. The openings of the ureters are found at the ureteric orifices. In between them is the interureteric crest. Together with the opening to the urethra, we can find the trigone of the urinary bladder.

- The seminal vesicle is shown to the left. Once again, it is a coiled, sacculated tubular structure that is surrounded by a smooth muscle coat (bracket). Generally, this smooth muscle contains inner circular and outer longitudinal layers.

- The highly folded mucosa of the seminal vesicle is illustrated below, lined with high cuboidal to low columnar epithelium. One may also find some variable pseudostratified columnar epithelium.

- The prostate gland is shown to the right. The secretory glands, lined with simple columnar epithelium, differ somewhat in morphology as they move progressively from the urethra toward the gland periphery.

- The glands near the urethra tend to enlarge with age and restrict the urethra, known as benign hypertrophy. Glands near the periphery are subject to carcinomatous change.

- The glands have a characteristic folded appearance. There may also be distinct concretions that are spherical or oval concentrations of glycoprotein.

concretion

- Note again the internal surface of the urinary bladder: the ureteric orifices, the interureteric crest, and the trigone. Note also the fundus, body, and neck of the bladder, where the urethra opens.

- Note the prostate immediately below the bladder, with the seminal colliculus opening at the prostatic urethra, which then leads into the bulbar portion of the urethra followed by the penile portion.

- Note the sphincter urethrae muscle encircling the urethra. It is skeletal muscle that we can voluntarily control to compress the urethra to prevent urination.

- Note the bulbospongiosus muscle surrounding the bulb of the penis. It acts to compress the bulb and spongy (or penile) urethra to expel last drops of urine during urination or semen during ejaculation. The ischiocavernosus muscles surround and compress the crus and corpus cavernosum of the penis. These muscles can be seen above in slide #4.

- As a reminder, the deep artery of the penis branches from the internal pudendal artery and enters the crus of the penis to supply the corpus cavernosum.

- The structure of the penis is detailed in the next slide.

NOTE:

- The glans of the penis at the tip, connected to the bulb via the corpus spongiosum. The corpus cavernosum is on both sides, connected to the ischial tuberosity.

- The superficial dorsal, and lateral superficial veins underneath the skin but outside the tunica albuginea.

- The deep dorsal vein, dorsal artery, and dorsal nerve within the tunica albuginea.

- The deep artery within the corpus cavernosum.

- The urethra within the corpus spongiosum.

- The two corpora cavernosa and single corpus spongiosum form the erectile tissue of the penis. Note on the top left panel the trabeculae and irregular venous spaces. During an erection, blood flow enters the erectile tissue via arteries, fill the venous spaces, and stay there due to obstructed venous outflow.

- The urethra within the corpus spongiosum, with its erectile tissue filled with blood, is shown in the bottom left.

- The urethral epithelium (bottom right) is lined with pseudostratified or stratified columnar epithelium. There is some variability.