Pelvic Cavity LO6
6. Understand the gross anatomy of the male reproductive tract, scrotum, and penis.
Scrotum & testes:
The scrotum is a cutaneous expansion suspended from the perineum and inferior portion of the proximal body of the penis. The scrotum contains the testes, which are suspended by the spermatic cords. The layers of the scrotum and spermatic cord are homologous and contiguous with many of the layers of the anterior abdominal wall. The scrotum consists of two major layers: skin & subcutaneous layer. The subcutaneous is also known as the dartos proper (consisting of smooth muscle and fascia). Deep to the dartos is the spermatic cord and its coverings. The dartos divides to form the septum of scrotum, which separate the testes.
The testis is enveloped by the tunica vaginalis, a serous membrane derived from peritoneum. The tunica vaginalis is comprised of two layers: a parietal layer (which adheres to the internal spermatic fascia) and a visceral layer (which invests the spermatic cord and testis). Between the parietal and visceral layers of the tunica vaginalis is a dynamic potential space (cavity). This dynamic potential space allows the testes to move within the scrotum. If serous fluid accumulates within the layers of the tunica vaginalis, it is known as hydrocele. If remnants of the tunica vaginalis persist in the spermatic cord, hydrocele may also present there as well.
Each testis is encapsulated by the tunica vaginalis and the tunica albuginea. The tunica albuginea is a dense, white layer which surrounds and compartmentalizes segments of the seminiferous tubules. Spermatozoa travel from the coiled seminiferous tubules through straight tubules into the rete testis. From the rete testis, spermatozoa move into the epididymis before traveling to the ductus (vas) deferens. The epididymis is comprised of a head and body (which receive spermatozoa from the rete testis) and tail. Spermatozoa travel from the head → body → tail of the epididymis.
To review the pathway of spermatozoa: Seminiferous tubules → Rete testis → Epididymis head → E. body → E. tail → Ductus deferens
Superficial to the septum, and continuous with the raphe of the penis, is the raphe (ridge, seam) of the scrotum. The raphe of the scrotum runs from the raphe of the penis to the anus.
The spermatic cord consists of three layers of tissues that envelop contents. The three basic layers of the sheath portion of the spermatic cord (and associated homologs) are the:
- external spermatic fascia (= external oblique m. fascia),
- cremaster m. & fascia (= internal oblique m. & fascia), and
- internal spermatic fascia (= transversalis fascia).
The major contents of the sheath are the:
- ductus (vas) deferens,
- testicular a., &
- pampiniform plexus (of veins).
The contents also include the:
- artery of ductus deferens (from the inferior vesical a.),
- cremasteric a. (from the inferior epigastric a.),
- genital br. of the genitofemoral n.,
- autonomic fibers:
- sympathetics follow the arteries,
- parasympathetics follow the ductus deferens,
- lymphatics, &
- processus vaginalis vestige (a thread-like connection that may connect the tunica vaginalis of the testis to the peritoneum).
External to the spermatic cord, you may observe anterior scrotal nn., which are continuations of the ilio-inguinal n. On a female donor, these are known as the anterior labial nn., and they accompany the round ligament of the uterus.
An enlargement or dilation of the pampiniform plexus (of veins) is known as varicocele. More frequent on the left side (due to draining into the left renal v. versus directly into IVC), these dilations can cause some discomfort, and may even affect the health of the ipsilateral testis.
Ductus (vas) deferens:
The ductus (vas) deferens conducts spermatozoa from the testis, through the spermatic cord (and through the inguinal canal) to the deep ring, and travels posteriorly to the bladder, superior to the ureter, ultimately joining the seminal vesicle to form the ejaculatory duct.
The ligation or embolization of the ductus (vas) deferens in known as a vasectomy, a common surgical procedure to prevent male fertility.
The prostate gland is extraperitoneal, and sits inferior and in close association with the neck of the bladder. The prostate gland surrounds and conducts the prostatic urethra to the membranous urethra. The prostate gland receives the ejaculatory ducts. The prostate was previously thought to be comprised of five anatomical lobes, yet only three lobes (2 lateral, 1 median) are distinguishable for most of a male’s life. The glandular substance of the prostate is divided among three zones: peripheral (most of the substance), central (some of the substance), and transitional (very little of the substance).
There is an elevation of mucosa, the uvula of the bladder, near the internal urethral meatus and intramural part of the urethra. With benign prostatic hyperplasia (BPH), glandular cells of the transitional (peri-urethral) zone may multiply, and exert pressure upon the prostatic urethra, which can make voiding the bladder difficult. A common treatment for BPH is transurethral resection of the prostate (TURP), a procedure involving the passing of a resectoscope through the urethra, and removing portions of the prostate gland in order to maintain patency for urine flow. Distal, and somewhat continuous with the uvula, another elevation of mucosa, the seminal colliculus, hosts the openings of the ejaculatory ducts into the prostatic urethra.
The prostate gland may be palpated through the anterior wall of the rectum.
The penis consists of a root (that anchors the penis to the perineum) and body (that serves as the intromittent organ). The root of the penis consist of the three masses of erectile tissue within the superficial perineal space (the crura and bulb of the penis). Three tubes of erectile tissue internally traverse the penis: laterally paired corpora cavernosa and a single corpus spongiosum. In standard anatomical position (SAP), the penis is in its erect state. The side of the penis in SAP that may contact the anterior abdomen is the dorsum (dorsal surface) of the penis. Opposite from the dorsum is the urethral surface.
The distal end (tip) of the body is the glans penis, a bulbous, skin-covered elaboration of corpus spongiosum. The rounded, circumferential border of the glans penis is the corona of glans. While the penis is in a flaccid state, an elaboration of the skin surrounding the body, the prepuce (foreskin), covers the glans penis. A slight reflection of prepuce on the urethral surface proximal to the glans penis, the frenulum, connects the prepuce to the glans. The spongy (penile) urethra is transmitted by the corpus spongiosum and terminates at the external urethral meatus of the glans penis.