Human Anatomy: Male Internal-External Genital Organs (Lecture Notes)

HUMAN ANATOMY
MALE INTERNAL-EXTERNAL GENITAL ORGANS
(Lecture Notes)

Necdet Ersöz
Gazi University Medical School

Primary Sex Organs

Testes (testicles):

ü  Produce the gametes or spermatozoa

ü  Also produce androgen/sex hormones involved in secondary sex organ development (physique, body hair, voice, pitch etc.)

Secondary Sex Organs

ü  Sperm transport ducts: epididymis, ductus deferens, ejaculatory ducts & urethra

ü  Accessory glands: seminal vesicles, prostate gland & bulbourethral glands

ü  Copulatory organ: penis

ü  Scrotum

ü  Ejaculatory duct: connection between ductus ductus deferens & seminal vesicle

ü  Seminal vesicles secrete fructose-rich fluid to aid in spermatozoa viability (60% ejaculatory volume, heavily  innervated by the sympathetic nervous system)

ü  Prostate gland: glandular tissue encased by smooth muscle (secretes alkaline buffer to neutralize vaginal acids, 40% ejaculation volume, heavily innervated by the sympathetic nervous system)

ü  Bulbourethral glands (Cowper’s glands): superficial to the pelvic diaphragm (secrete mucus rich solution to neutralize urethra & lubricate penis prior to coitus)

Testis

The testis is a firm, ellipsoid organ, measuring approximately 4 x 3 x 2.5 cm. The longest diameter is between the rounded superior and inferior poles, and this axis is titled slightly anteriorly and laterally. The testis, convex and smooth on all surfaces, is slightly flattened from side to side, presenting rounded anterior and posterior borders and more extensive lateral and medial surfaces. The epididymis is applied to the posterior border and protrudes from it laterally; it is in contact with the testis from its superior to its inferior pole.

The testis and the epididymis invaginate the tunica vaginalis from behind. Therefore, the visceral lamina of the tunica covers the testis and epididymis everywhere except along their posterior border and along the posterior part of the area of contact between the two. Anteriorly a deep grove, the sinus epididymis, intervenes between the testis and the epididymis, and is lined by the tunica vaginalis. The tunica vaginalis also covers the anterior surface of the spermatic cord for a variable distance above the testis.

Subjacent to the tunica vaginalis, the testis is invested by a dense layer of fibrous tissue, the tunica albuginea which is thinner over the mediastinum. Small septa (septula testis) extend from the deep surface of the tunica albuginea into the testis and subdivide it into 200 to 300 roughly pyramid shaped compartments or lobules. The apex of each lobule points towards the mediastinum and within the lobule lie one to three seminiferous tubules. These tubules are 0.1 mm to 0.3 mm in diameter and measure nearly 1 m in length. Most of the tubule packed into the lobule is highly convoluted (tubuli seminiferi contorti), but one or both ends of all tubules pointing toward the mediastinum become straight (tubuli seminiferi recti). In the mediastinum these straight seminiferous tubules terminate in a labyrinth of the intercommunicating channels that form the rete testes. As the rete passes through the tunica albuginea, it links up with 10 to 20 efferent ductules.

The appendix testis is a sessile cyst 2 or 3 mm in diameter attached to the upper pole of the testis within the tunica vaginalis. It is part of the remains of the paramesonephric duct. Scattered among of the cells of the connective tissue between the tubules (outside them) are the interstitial cells (of Leydig). Larger than fibroblasts, they constitute the endocrine portion of the testis, secreting testosterone, the male sex hormone necessary for spermatogenesis.

Blood Supply

The testicular artery, from the aorta, runs in the spermatic cord, gives off a branch to the epididymis, and reaches the back of the testis, where it divides into medial and lateral branches. These do not penetrate the mediastinum testis, but sweep around horizontally within the tunica albuginea. Branches from these vessels penetrate the substance of the organ. Venules reach the mediastinum, from which several veins pass upwards in the spermatic cord and surround the testicular artery with a mass of intercommunicating veins, the pampiniform plexus. On its way to the testis and on the surface of the organ before entering it, the artery and its branches are intimately related to the venous plexus in order to provide a countercurrent heat exchange; for spermatogenesis the testis has to function at a temperature 2-4 C degree lower than rectal temperature. Varicocele (varicosities of the pampiniform and cremasteric veins) occurs much more frequently on the left side than the right, for reasons which are obscure. The only valves in the plexus and main are at the upper ends of the veins through the left vein is more often valveless than the right.

Lymph Drainage

Within the testis, lymphatic capillaries lie between, not within, the seminiferous tubules. Lymphatics run back with the testicular artery to para-aortic nodes lying alongside the aorta at the level of origin of the testicular arteries (L2 vertebra), i.e. just above the umbilicus. The  testicular lymph therefore does not drain to inguinal nodes, although the overlying scrotal skin does.

Nerve Supply

The testis is supplied by sympathetic nerves. Most of the connector cells in T10 segment of the cord. Passing in the greater or lesser splanchnic nerve to the coeliac ganglion the efferent fibres synapse there. Postganglionic grey fibres reach the testis along the testicular artery. Sensory fibres (testicular sensation) share the same sympathetic pathway. They run up along the testicular artery and through the coeliac plexus and lesser splanchnic nerve and its white ramus to cell bodies in the posterior root ganglion of T10 spinal nerve. There is no parasympathetic supply to the testis.

Efferent Ductules

The sperm are transported out of the testis and into the epididymis through a series of efferent ductules.

Ductus Deferens (Vas Deferens)

The ductus deferens also known as vas deferens, conveys spermatozoa and secretions produced by the testis to ejaculatory ducts. The deferent duct commences behind the lower pole of the testis as the continuation of the epididymis and terminates in the pelvis just above the prostate by forming the ejaculatory duct. The deferent duct ascends in scrotum behind the testis and then in the spermatic cord, entering the inguinal canal through the superficial ring and leaving it through the deep ring. At the deep ring, the duct bends sharply medially and, embedded in the pelvic fascia, pursues its intrapelvic course toward the prostate. The deferent duct can be identified as a 2 mm to 3 mm thick palpable cord when the neck of the scrotum is rolled between finger and thumb. The lumen of the is quite narrow, and its thickness is due to the smooth muscle in its walls. The duct is usually filled with spermatozoa; contraction of its walls, induced by sympathetic activity, discharges the spermatozoa into the ejaculate.

Spermatic Cord

 The ductus deferens and accompanying structures are conventionally considered as passing through the deep inguinal ring and along the inguinal canal to the superficial ring, picking up coverings from the layers of the abdominal wall as they do so (but as far as the passage of semen is concerned, the movement is of course in the opposite direction). All these structures make up the spermatic cord, whose components may be considered under two headings: the three coverings of the cord, and its six (groups of) constituents. Of the three coverings, the internal spermatic fascia is the investment derived from the transversalis fascia at the deep inguinal ring.

As the cord passes through the ring into the inguinal canal, it picks up a second covering, the cremasteric fascia and cremaster muscle, from the internal oblique and transversus aponeuroses and muscles. The transverse muscle fibers spiral down the cord and return behind it to become attached to the pubic tubercle. The internal oblique fibres, a larger contribution, also spiral around the cord and some return to pubic tubercle but most return to the internal oblique itself. The third covering is from the crura of the superficial ring (external oblique aponeurosis), the external spermatic fascia. Strictly speaking the cord is only complete as it acquires this outer covering on emerging from the superficial ring.

The cremaster muscle can elevate the testis towards or even into the inguinal canal; although the fibres are skeletal the action is reflex rather than voluntary. This cremasteric reflex is particularly active in the infant and child and must be borne in mind when examining the scrotum in the young, to avoid an erroneous diagnosis of undescended testis. The constituents of the cord consists of:

ü  The ductus deferens, which usually lies in the lower and posterior part of the cord.

ü  Arteries, the largest of which is the testicular artery with the artery to the ductus and the cremasteric artery (from the inferior epigastric, to the coverings).

ü  Veins – the pampiniform plexus

ü  Lymphatics, essentially those accompanying the veins from the testis to para-aortic nodes, but including some from the coverings which drain to external iliac nodes.

ü  Nerves, in particular the genital branch of the genitofemoral nerve which runs among the coverings to supply the cremaster muscle, and is classified as part of the spermatic cord and not as a separate structure running through the inguinal canal. Other nerves are sympathetic twigs which accompany the arteries.

ü  The processus vaginalis, the obliterated remains of the peritoneal connexion with the tunica vaginalis of the testis (and the constituent of the cord most commonly forgotten). When patient it forms the sac of an indirect inguinal hernia.

Prostate Gland

This glandular organ lies beneath the bladder and above the urogenital diaphragm, and is penetrated by the proximal part of the urethra. It is normally broader than it is long (like the caecum), approximately 4 x 3 x 2 cm, and roughly the size and shape of a chestnut. It is clasped on each side by the lavator prostatae part of levator ani. Its female homologue is the small group of paraurethral glands (of Skene). The prostate provides about 30% of the volume of seminal fluid (most comes from the seminal vesicle).

The prostate has a base and an apex, and anterior, posterior and inferolateral surfaces. The base is the upper surface (unlike the bladder, whose base is its posterior surface), fused with the neck of the bladder and perforated by the urethra which transverses the whole length of the gland. The blunt apex is the lowest part and the prostatic urethra emerges from the front of the apex to become the membranous urethra which penetrates the urogenital diaphragm. The anterior surface is at the back of the retropubic space and is connected to the bodies of the pubic bones by the puboprostatic ligaments.

The inferolateral surfaces are clasped by the levator prostatae parts of levator ani, while the posterior surface, which has a vertical median groove palpable on rectal examination is in front of the lower rectum but separated from it by the rectovesical fascia. The ejaculatory ducts pierce the posterior surface just below the bladder and pass obliquely through the gland for about 2 cm to open into the prostatic urethra about halfway down. The prostate's own ducts also open into this part of the urethra.

A thin layer of connective tissue at the periphery of the gland forms the 'true capsule' of the prostate, and outside this there is a condensation of pelvic fascia forming the 'false capsule'. Between these two capsules lies the prostatic plexus of veins. A third or 'pathological capsule' is described when tumour tissue compresses the normal surrounding part; if benign, the growth can be 'shelled out' from this compressed capsule.

The gland consists of acini of varying shapes and sizes embedded in a fibromuscular stroma — a mixture of connective tissue and smooth muscle; this is the characteristic histological feature. Numerous small ducts open into the prostatic urethra. It is customary to consider the gland as being made up of five lobes — anterior, middle, posterior and two lateral — but there is usually no clear distinction between them. The anterior lobe is the small area in front of the urethra; it is unimportant, consisting almost entirely of stromal tissue with few acini.

The middle lobe is the region between the ejaculatory ducts and the proximal urethra, and is of great importance since, when affected by benign hypertrophy (the common 'enlarged prostate' of the over 50s), it elongates and obstructs the urethra. Minor degrees of hypertrophy of this lobe without urethral obstruction cause a small swelling (the uvula vesicae) at the apex of the trigone of the bladder. The rest of the gland at the back and sides forms the combined posterior and lateral lobes, which are best regarded simply as right and left lobes, and again are important not only because of simple enlargement but as the commonest sites of cancerous change.

Enlargement of the lateral lobes may be detected on rectal examination but middle lobe enlargement extending forwards into the bladder will not be. Benign hypertrophy of the prostate is usually not a generalized enlargement but a local adenomatous proliferation in the 'internal zone' or central region of any of the lobes adjacent to the urethra — the region of the so-called mucosal or periurethral glands. The acini in the much larger outer or peripheral zones of any lobe are the ones affected by carcinoma.

The prostatic urethra extends from the internal urinary meatus to the apex of the prostate and is the widest part of the urethra. It is characterized posteriorly by a midline longitudinal ridge, the urethral crest. In the middle of the crest is a small swelling, the seminal colliculus (verumontanum), on which opens the prostatic utricle (utriculus masculinus), an embryonic remnant about 0.5 cm long resulting from union of the caudal ends of the paramesonephric (Mullerian) ducts; it is thus the homologue of the uterus. Alongside it, on the urethral crest, the ejaculatory ducts open. The prostatic ducts open on the crest and in the sulcus on each side.

Blood Supply

The main arterial supply is from the prostatic branch of the inferior vesical artery, with some small branches from the middle rectal and internal pudendal vessels passing to the lower part, but sometimes the middle rectal provides the major supply. The veins run into a plexus between the true and false capsules and this joins the vesicoprostatic plexus receives the deep dorsal vein of the penis, and drains backwards into the internal iliac veins.

Lymph Drainage

The lymphatics of the prostate pass across the pelvic floor to internal iliac and sacral nodes but some may reach the external iliac nodes.

Nerve Supply

The acini receive parasympathetic (cholinergic) innervation from the pelvic splanchnic nerves, but this is much less important than the muscle fibres of the stroma which contract to empty the glands during ejaculation and which are under sympathetic (adrenergic) control from the inferior hypogastric plexus.

Seminal Vesicle

The seminal vesicle is a thin-walled, elongated sac, like a lobulated, blind-ending tube much folded on itself. The pair produce about 60% of the seminal fluid, and are applied to the base of the bladder above the prostate. They are covered behind by the rectovesical fascia, and their tips are just covered by the peritoneum of the rectovesical pouch.

Each lies lateral to the ampulla of the ductus deferens of its own side, and at the lower end of the ampulla behind the prostate the duct of the seminal vesicle joins the ductus to form the ejaculatory duct.

They secrete fructose to provide an energy source for sperm and alkalinity to enhance sperm mobility. The duct of each seminal vesicle joins the ductus deferens on that side to form the ejaculatory duct.

Blood Supply

The artery to the ductus deferens is a branch of the superior vesical (or sometimes the inferior vesical artery). It accompanies the ductus to the lower pole of the epididymis and anastomoses with the testicular artery. The seminal vesicles are supplied by branches from the inferior vesicle and middle rectal arteries.

Lymph Drainage

Lymphatics accompany the blood vessels to the nearest iliac nodes.

Nerve Supply

The smooth muscle of the ductus and seminal vesicles receives fibres from the pelvic plexus. The sympathetic fibres run in the branch from the first lumbar ganglion and are motor; their division produces sterility, for the paralysed muscle cannot contract to expel the stored secretion and spermatozoa, i.e. there is no emission or ejaculation.

Ejaculatory Ducts

There are two ejaculatory ducts. Each receives sperm from the ductus deferens and the secretions of the seminal vesicle on its own side. Both ejaculatory ducts empty into the single urethra.

Bulbourethral Glands

The bulbourethral glands are also called Cowper’s glands are located below the prostate gland and empty into the urethra. The alkalinity of seminal fluid helps neutralize the acidic vaginal pH and permits sperm mobility in what might otherwise be an unfavourable environment.

External Male Genital Organs

Penis

The penis has as its main parts the root, body and glans. The root of the penis is attached to the inferior surface of the perineal membrane and consists of the (central) bulb of the penis with a cms on each side. Each crus is attached to the angle between the perineal membrane and the everted margin of the pubic ramus, receives the deep artery of the penis near its anterior end, and continues forwards to become the corpus cavernosum. The bulb is the posterior end of the corpus spongiosum. At the front of the root area, below the subpubic angle, the two corpora cavernosa are bound together side by side with the corpus spongiosum behind them (when the penis is dependent, but ventral to them when erect) to form the body of the penis. The penile urethra runs through the whole length of the corpus spongiosum from the bulb at the back to its expanded opposite end which is the glans penis. The urethra enters near the front of the bulb so that most of the bulge of the bulb is behind and below the urethra. The bulb has a slight (palpable) midline notch on its under surface and extends back towards the perineal body. The arteries of the bulb enter it near the urethra, which in this region receives the ducts of the bulbourethral glands.

The corpus spongiosum and the two corpora cavernosa are each surrounded by a tough fibrous membrane, the tunica albuginea of the corpus (not to be confused with the tunica albuginea of the testis); that of the corpus spongiosum enlarges distally to enclose the glans. The fibrous sheaths of the corpora are fused together; between the corpora cavernosa this connective tissue forms a septum with vertical comb-like strands. In some mammals a bone (os penis) lies here. The fused sheaths are attached to the under surface of the pubic symphysis by a triangular sheet of fibrous tissue, the suspensory ligament of the penis.

The three corpora thus fused together are loosely surrounded by the fascia of the penis (Buck's fascia), a cylindrical prolongation of Colles' fascia   beneath which lie the midline deep dorsal vein with a dorsal artery on each side and more laterally a dorsal nerve. The skin is hairless and prolonged forwards in a fold, the prepuce, which invests the corona of the glans (its slightly projecting lower margin) and some or all of the rest of the glans. Beneath the skin in the midline is the superficial dorsal vein which is accompanied by lymphatics from skin and the anterior part of the urethra.

Blood Supply

The penis receives three pairs of arteries which are all branches of the internal pudendals  .The artery to the bulb supplies the corpus spongiosum, including the glans. The deep artery of the penis supplies the corpus cavernosum, and the dorsal artery supplies skin, fascia and glans. Note the anastomosis, via the continuity of corpus spongiosum and glans, between the artery of the bulb and the dorsal artery; the deep artery remains separate, supplying the corpus cavernosum only and forming a closed system whose sole function is erection.

Venous return from the corpora is partly by way of viens that accompany the arteries and join the internal pudendal veins, but mostly by the deep dorsal vein which pierces the suspensory ligament, passes above the perineal membrane and enters the vesicoprostatic venous plexus. The superficial dorsal vein drains the dorsal skin of the penis and divides to join the superficial external pudendal and great saphenous veins.

Lymph Drainage

Lymphatics from the penile skin pass to superficial inguinal nodes, but the glans and the corpora drain to deep inguinal nodes. In cancerous spread the internal iliac nodes are rarely involved unless the inguinal nodes are first affected.

Nerve Supply

The skin of the penis is supplied by the pudendal nerves via the posterior scrotal and dorsal nerves; the latter supply the glans. The dermatome mainly involved is S2. The bulbocavernosus and ischiocavernosus muscles which contract spasmodically during ejacula­tion are supplied by the perineal nerve (from the pudendal, S2, 3). The sympathetic nerves necessary for the initial stages of ejaculation (p. 411) are derived from LI segment of the spinal cord via the superior and inferior hypogastric plexuses. The pelvic splanchnic nerves (S2, 3) provide the parasympathetic supply to the cavernous tissue of all three corpora and allow increased blood flow for erection.

Scrotum

The scrotum is a pouch of skin containing the testes and spermatic cords. The subcutaneous tissue has no fat, but contains a part of the panniculus carnosus, the dartos muscle which sends a sheet into the midline fibrous septum of the scrotum. The rugosity of the skin is due to contraction of the dartos. The dartos smooth muscle, and is supplied by sympathetic fibres probably carried by the genital branch of the genito­femoral nerve. Deep to dartos is the layer of the superficial fascia (Colles' fascia) attached behind to the posterior edge of the perineal membrane, at the sides to the ischiopubic rami and bodies of the pubic bones, and in front continuous with Scarpa's fascia.

The cremaster muscle consists of skeletal muscle fibers and controls the position of the scrotum and testes. When it is cold or a man is sexually aroused, this muscle contracts to pull the testes closer to the body for warmth.

Blood Supply

The blood supply of the skin is from superficial and deep external pudendal arteries (from the femoral). Posteriorly there are some branches from the internal pudendal artery. Venous drainage is by external pudendal veins, superficial and deep, to the great saphenous vein.

Lymph Drainage

Lymph drainage is to the medial group of superficial inguinal nodes.

Nerve Supply

The anterior axial line crosses the scrotum. The anterior one-third of the scrotal skin is supplied by the ilioinguinal nerve (LI). The posterior two-thirds is supplied by scrotal branches of the perineal nerve (S3), reinforced laterally by the perineal branch of the pos­terior femoral cutaneous nerve (S2).

Dartos Muscle

The dartos muscle is a layer of smooth muscle fibers in the subcutaneous tissue of the scrotum (surrounding the scrotum). This muscle is responsible for wrinkling up the scrotum, in conditions of cold weather, in order to maintain the correct temperature for spermatogenisis.

•      The common method of sterilizing males is a deferentectomy, popularly called a vasectomy.

•      During this procedure, part of the ductus deferens is ligated and/or excised through an incision in the superior part of the scrotum

•      Hence, the subsequent ejaculated fluid from the seminal glands, prostate, and bulbourethral glands contains no sperms.

•      The unexpelled sperms degenerate in the epididymis and the proximal part of the ductus deferens.

•      Reversal of a deferentectomy is successful in favorable cases (patients <30 years of age and < 7 years postoperation) in most instances

•      The ends of the sectioned ductus deferentes are reattached under an operating microscope.

Note: These notes are taken from Gazi University Faculty of Medicine Prof. Dr. Rabet GOZIL’s anatomy lectures.