Session 6: The Male Reproductive System Flashcards
What does the male reproductive system consist of?
The male reproductive system consists of (1) the paired testes which produce spermatozoa (sperms) and contains cells that produce the sex hormones, (2) a duct system which transports the spermatozoa to the urethra, (3) accessory sex glands that supply the fluid components to the semen and (4) the pelvis.
Describe the scrotum
[*] The scrotum is a cutaneous fibro-muscular sac for the testes and associated structures. Developed from labioscrotal folds and contains the testis, epididymis and first part of the spermatic cord (vas deferens).
[*] It is situated posteroinferior to the penis and inferior to the pubic symphysis.
[*] The bilateral embryonic formation of the scrotum is indicated by the mid-line scrotal raphe, which is continuous on the ventral surface of the penis with the penile raphe.
[*] Internally, deep to the scrotal raphe, the scrotum is divided into two compartments, one for each testis, by the septum of the scrotum.
Describe the Testes
[*] The testes are paired, ovoid reproductive glands.
[*] The testes are suspended in the scrotum by the spermatic cords.
[*] The surface of each testis is covered by the visceral layer of the tunica vaginalis, except where the testis attach to the epididymis and spermatic cord.
[*] The parietal layer of the tunica vaginalis is adjacent to the internal spermatic fascia, is more extensive than the visceral layer and extends superiorly for a short distance onto the distal part of the spermatic cord.
[*] There is a small amount of fluid between the two layers, in the cavity of the tunica vaginalis, allowing the testis to move freely in the scrotum.
[*] The testis is a compound tubular gland, enclosed in a thick fibrous capsule, the tunica albuginea.
- Posteriorly, the tunica albuginea capsule thickens into a ridge, forming the mediastinum testis that contains many interconnected channels, which provide passageways for the sperms to enter the duct system. From this internal ridge, fibrous septums (invaginations of tunica albuginea) extend inward between lobules of long and highly coiled seminiferous tubules (deep to the tunica albuginea, strong connective tissue septa extend into the testis, dividing it into about 250 pyramid-shaped lobules)
- Each lobule contains between one and four highly convoluted seminiferous tubules, in which spermatozoa are produced.
[*] The testes are contained within the scrotal sac. The scrotum consists of a layer of skin and superficial fascia; the superficial fascia contains the dartos muscle. Dartos acts to regulate the temperature of the scrotum. It does this by contracting to wrinkle the scrotal skin. This reduces the surface area available for heat loss. Temperature regulation is important for optimal spermatogenesis.
Describe the arrangemet of the sertoli cells and spermatogenic cells deep to the tunica albuginea
[*] Underneath the thick tunica albuginea, sections of seminiferous tubules are evident. Each seminiferous tubule is surrounded by a layer of connective tissue, with flattened myofibroblasts and an inner basement membrane.
The tubules are lined by a complex stratified epithelium, the seminiferous epithelium, consisting of 2 kinds of cells – the Sertoli cells (supporting cells) and the spermatogenic cells (the germ cells)
Sertoli cells are fixed to the basement membrane of the tubule, and are far less numerous than the spermatogenic cells. The cytoplasm of each cell forms an elaborate system of processes that extend upward to the luminal surface, surround the spermatogenic cells and fill all the spaces between them.
- Owing to this and the limitations of resolution of the light microscope, the cell boundaries are difficult to visualize.
- The apical region of each cell has complicated recesses into which the head of sperms appear to be embedded.
Spermatogenic cells are arranged in rows between and around the Sertoli cells. The most primitive spermatogonic cells, the spermatogonia, rest on the basement membrane, while the later stages are located at successively higher levels in the epithelium.
- Primary spermatocytes lie adjacent to spermatogonia but nearer the lumen. The nuclei have variable appearances that represent the stages of the first meiotic division.
- Secondary spermatocytes (rarely seen in the seminiferous epithelium because of their short half-life) divide rapidly (second meiotic division) to form spermatids, which have a lightly stained round nucleus located nearer the lumen of the seminiferous tubule.
- The spermatids mature into spermatozoa, the deeply staining heads of which appear to be embedded in the cytoplasm of the Sertoli cells and their tails hang into the lumen of the seminiferous tubule.
Describe the arrangemnet of Leydig cells
[*] Between the seminiferous tubules, there is loose connective tissue containing interstitial (Leydig) cells, which are seen in isolated clusters or in rows along small blood vessels.
- The cells have large spherical nuclei (containing small amounts of peripherally located chromatin and one or two prominent nucleoli) with eosinophilic (stained red in the section).
- Altogether spermatogenesis (in the seminiferous tubules) and steroidogenesis (in the Leydig cells) occur in separate histological compartments within the testis, the compartments are functionally and physiologically interactive.
The Leydig cells secrete testosterone
Recap the descent of the testes
[*] The testes arise in the Mesonephric ridge in the upper lumbar (posterior abdominal) regions, at the lower pole of the kidneys. The testes descend through the abdomen.
[*] They are tethered to the labioscrotal folds (Genital swellings, future scrotum), by the Gubernaculum.
[*] As the body grows, the relative position of the testis becomes more caudal.
[*] A musculo-fascial layer evaginates into the scrotum as it develops, together with peritoneal membrane to form the Processus Vaginalis.
[*] As the testes descend they cross the inguinal canal and exit the anterolateral abdominal wall – they follow the course of the inguinal canal and end up close to the labioscrotal folds.
[*] Above the testis the fascia and peritoneum become closely apposed. The fascial layers, obliterated stem of the processus vaginalis, vas deferens, testicular vessels and nerves, form the spermatic cord, which occupies the inguinal canal in males.
[*] The scrotal ligament is the vestigial remnant of the gubernaculum in the male.
Describe the arterial supply and venous drainage of the testes
[*] The arterial supply to the testes is direct from the abdominal aorta. The long, Testicular Arteries, arise just inferior to the Renal Arteries.
- They pass retroperitoneally (posterior to the peritoneum) and cross over the ureters and the inferior part of the external iliac arteries to reach the deep inguinal rings.
- The arteries then pass through the inguinal canal, emerging through the superficial inguinal rings and enter the spermatic cords.
[*] The venous drainage of the testes is asymmetrical. The veins emerging from the testis and epididymis form the Pampiniform Venous Plexus. This plexus is part of the thermoregulatory system of the testis, helping to keep the gland at a constant temperature.
- The Right Testicular Vein drains into the Inferior Vena Cava (IVC); Testes => Pampiniform Venous Plexus => Right Testicular Vein => IVC
- The Left Testicular Vein drains into the Left Renal Vein; Testes => Pampiniform Venous Plexus => Left Testicular Vein => Left Renal Vein
- The blood from the abdominal aorta is cooled as it passes through the testicular artery, as it is wrapped in the testicular vein (pampiniform plexus of veins)
Describe the innervation and lymphatic drainage of the testes and the scrotum
[*] Innervation
- Lumbar plexus – anterior surface (of the scrotum)
- Sacral plexus – posterior and inferior surfaces (of the scrotum)
[*] Lymphatic drainage (different as it is related to where they developed)
- Testes drain to paraaortic nodes. If you have a malignancy of the testis and metastases occurs, the nodes won’t be palpable until you have substantial disease burden as the paraaortic nodes are quite deep.
- Scrotum drains to superficial inguinal nodes.
What makes up the duct system?
[*] The seminiferous tubules are joined by straight tubules to the interconnected passageways (rete testis) (a network of canals) in the mediastinum of the testis and the sperm enter a series of coiled ductules (ductuli efferentes), which emerge, on the posterior surface of the testis. These join to form a long, single convoluted tube, ductus epididymis which is continuous with a straight, thick-walled ductus deferens (vas deferens) that forms part of the spermatic cord.
Describe the Epididymis
[*] Epididymis: anatomically the epididymis has a head (caput), body (corpus) and tail (caudal) segments.
- It is located on the superior and posterolateral surface of the testis.
- It is connected to seminiferous tubules via efferent ductules and the rete testis.
- Its main function is sperm transport, maturation and storage.
- During their passage through the epididymis, the sperms undergo structural maturation and become motile. This is essential for successful fertilisation.
- They are then stored in the tail segment until ejaculation
- The ductus epididymis is lined by a tall, pseudostratified columnar epithelium. On the inner surface of the basement membrane, small basal cells form a discontinuous layer.
The tall columnar cells have tufts of non-motile cytoplasmic processes called stereocilia projecting into the lumen.
Near the lumen, the cytoplasm of the tall cells contains occasionally dark-staining granules.
The basement membrane is surrounded on the outside by a highly developed network of capillaries and a circular layer of smooth muscle fibres.
Describe the Ductus Deferens
[*] Ductus Deferens (Vas Deferens)
- Straight muscular tube that emerges from the caudal epididymis.
- It is contained within the spermatic cord and its main function is to transport the sperms rapidly to the prostatic urethra.
- Its terminal portion (called the ampulla) and the duct of the seminal vesicle form the ejaculatory duct, which opens into the prostatic urethra.
- Rich autonomic innervation of the smooth muscle fibres of the ductus deferens permits rapid contractions, which propel the tube’s contents towards the ejaculatory ducts.
- During ejaculation, the ejaculatory duct and the duct of the seminal vesicle dilate to facilitate the entry of the sperms and seminal gland secretions into the prostatic urethra.
- The ductus deferens ascends in the spermatic cord, traverses the inguinal canal, tracks around the pelvic side wall, passes between the bladder and ureter before forming a dilated ampulla and opening into the ejaculatory duct.
Describe the Spermatic Cord
- The spermatic cord contains the structures running to and from the testes – the neurovascular and duct systems. It runs from the deep inguinal ring, lateral to the inferior epigastric vessels, to the posterior border of the testis via the inguinal canal and superficial inguinal ring.
- In a section of the spermatic cord, the ductus deferens is a thick muscular tube. The smooth muscular coat consists of inner and outer longitudinal layers and an intermediate layer of circular muscle. The epithelium lining the lumen is pseudostratified columnar, and the cells usually have stereocilia.
- The epithelium lies on a thin lamina propria containing a large number of elastic fibres. As a result, in fixed preparations, the mucous membrane is thrown into numerous folds.
- Surrounding the ductus deferens is a collection of small veins (pampiniform plexus), which are the most bulky constituents of the spermatic cord. Also present in the cord are numerous arteries, lymphatic vessels and nerves.
What are the contents of the Spermatic Cord?
- Testicular artery, cremasteric artery, artery to vas deferens (deferential artery)
- Paminiform Plexus
- Genital branch of Genitofemoral nerve (nerve to cremaster), testicular nerves (sympathetic nerves) (and the ilio-inguinal nerve runs along the outside of the spermatic cord)
- Vas deferens
- Lymphatics
- Tunica vaginalis (remains of the processus vaginalis)
NB: testes’ temperature is lower than that of body temperature
The cord is enclosed by a discontinuous layer of longitudinally-oriented strands of striated muscle, the cremaster muscle.
The pampiniform plexus, testicular artery, artery of the ductus deferens, lymphatic vessels, testicular nerves and ductus deferens all run deep to the internal spermatic fascia.
The genital branch of the genitofemoral nerve, cremasteric artery and ilioinguinal nerve all run on the superficial surface of the external spermatic fascia.
What are the coverings of the spermatic cord?
The coverings of the spermatic cord come from the anterolateral abdominal wall:
- External spermatic fascia: aponeurosis of external oblique
- Cremasteric muscle and fascia – internal oblique and transversalis
- Internal spermatic fascia – transversalis fascia
What are the Accessory Male Sex Glands
[*] The seminal vesicles, the prostate gland and the bulbourethral glands form the bulk of the seminal fluid (semen) in which sperms are suspended.
[*] During sexual arousal and ejaculation, the secretions are emitted in a controlled sequence commencing with the bulbourethral glands, then prostate, followed by spermatozoa and finally, the seminal vesicles. The structural and functional integrity of these glands is dependent upon adequate levels of male sex hormones
Describe the Seminal Vesicles
- 2 small glands lying posterior to the prostate gland, between the bladder and rectum.
- NOT a storage site
- Diverticulum (derived from) of vas deferens
- The gland body consists of a single, highly convoluted tube that joins the ampulla of the ductus deferens to form the ejaculatory duct
- The mucous membrane forms an elaborate system of thin, branched anastomosing folds that project into the lumen. The large lumen of the gland contains coagulated secretion.
- The epithelium lining the mucous membrane varies from simple columnar to pseudostratified. The lamina propria is surrounded by a smooth muscle coat divided into an inner circular and a very thin outer longitudinal layer.
- The secretions from the seminal vesicles account for 70-80% of the volume of the ejaculate
- Duct of each seminal vesicle combines with vas deferens to form ejaculatory duct into the prostatic urethra.
Describe the zones of the prostatic gland
The prostate gland surrounds the urethra at its origin from the bladder. It has several very important anatomical relationships and can be divided into zones or lobes.
- Base: neck of bladder
- Apex: urethral sphincter and deep perineal muscles
- Muscular anterior surface: urethral sphincter
- Posterior: ampulla of rectum
- Inferior-lateral: leveator ani
Zones: central zone (surrounding the urethra) and peripheral zone
A DRE permits size and consistency examination of the prostate
- The gland is surrounded by a fibro-muscular capsule from which branching septae divide into numerous, but separate, compound alveolar glands, from which excretory ducts originate and open independently into the prostatic urethra. The septae are characterized by discrete bundles of smooth muscle fibres interweaving with the connective tissues.
The secretion of the gland forms about a third of the ejaculate volume and contains prostaglandins, proteolytic enzymes and citric acid.
The epithelium lining the glands varies from low cuboidal to simple or pseudostratified columnar and the cells have pale-staining cytoplasm.
The epithelium rests on a very thin lamina propria
- Blebs of secretion may be seen attached to the free cell surfaces and are often seen in the lumen of the glands.
Also present in the lumina are concentrically lamellated eosinophilic bodies, the prostatic concretions (corpora amylacea), some of which may be calcified.
Describe the Bulbourethral Glands
These glands are located within the urogenital diaphragm and contain tubular and alveolar-type glands. Just prior to ejaculation, these glands produce a clear watery secretion that may lubricate the urethra.
What does the penis consist of?
[*] The penis consist of a root, body and glans. It’s internal structure consist of a pair of Corpora Cavernosa dorsally and a single Corpus Spongiosum ventrally (3 cylindrical structures).
[*] The corpora are a network-like trabeculae of fibromuscular tissue ramified by spaces which become filled with blood during erection.
[*] In the flaccid condition of the organ, the cavernous spaces contain little blood and appear as collapsed irregular clefts. The corpora are surrounded by a thick band of connective tissue.
Describe the arterial supply and venous drainage of the penis
[*] Blood supply to the penis is via the branches of the internal pudendal artery
- Abdominal aorta => Common Iliac => Internal Iliac => Anterior division of internal iliac => internal pudendal artery
- The internal pudendal artery gives off 3 branches which supply the penis: dorsal arteries of the penis, deep arteries of the penis and bulbourethral artery.
- The helicine arteries of penis are found in the corpora cavernosa ‘cavernous arteries’ and are involved in erection. These arteries have 2 unique features: an intimal cushion and valves. Sympathetic stimulation maintains a tonic contractile state of the intimal cushion, smooth muscle lying in the centre of the artery. This keeps the artery coiled and little blood flow occurs, instead routing to arteriovenous shunts to the deep dorsal vein. Parasympathetic stimulation removes the tonic state and allows vasodilation of the intimal cushion. Blood now pools in the corpora cavernosa, resulting in erection. The valves prevent backflow in the now-tortuous route through the cavernosa.
[*] Blood from the cavernous spaces drain into a venous plexus that joins the Deep Dorsal Vein of the Penis. The vein drains into the prostatic venous plexus, which in turn drains into the Internal Iliac Vein, Common Iliac Vein and Inferior Vena Cava.
What are the roles of the bulbospongiosus and ischiocavernosus in the perineum?
Bulbospongiosus: helps to expel last drops of urine and maintain erections.
Ischiocavernosus: compresses veins, therefore helps maintain erections
What is Hydrocoele, Haematocoele, Varicocoele, Spermatocoele and Epididymitis?
[*] Hydrocoele: collection of serous fluid in tunica vaginalis (remnant of processus vaginalis)
[*] Haematocoele: collection of blood in tunica vaginalis
[*] Varicocoele: varicosities of the Pampiniform plexus
[*] Spermatocoele: retention cyst within the epididymis, aka epididymal cyst. Light can be shined through a spermatocoele (transillumination, indicating that the mass is not a solid tumour but more likely a benign cyst)
[*] Epididymitis: inflammation of the epididymal cyst (collection of fluid within the epididymis)
Compare a direct to an indirect hernia
[*] Direct Hernia
- Hernia directly into the inguinal area
- Medial to the inferior epigastric vessels
[*] Indirect
- Hernia indirectly into the inguinal area, via the inguinal canal + could pass out through the superficial ring and the scrotum.
- Lateral to the inferior epigastric vessels.
- Reopening of the Processus vaginalis gives potential continuity between the peritoneal cavity and tunica vaginalis (abdomen => scrotum)
What is testicular torsion?
Testicular torsion is twisting of the spermatic cord, giving the risk of necrosis of the testis (leading to loss of testis or infertility so it is a surgical emergency). The twisting usually occurs just above the upper pole of the testis. The testes is normally tethered at its lower end to the scrotum by the remnant of the gubernaculum.
Compare Benign Prostatic Hyperplasia and prostatic enlargement due to malignancy
The Prostate Gland enlarges in old age.
[*] Benign prostatic hyperplasia is sex hormone dependent and occurs mainly in the central zone/middle lobule of the prostate. Due to the zone’s close proximity to the urethra, benign prostatic hyperplasia can cause dysuria, nocturia and urgency due to obstruction of internal urethral orifice.
[*] Prostatic cancer is the second most common cause of cancer-related deaths in men; genetic, hormonal, environmental, etc. factors are implicated in its pathogenesis. Malignancies tend to occur mainly in the peripheral zone of the prostate. The malignancies need to get very large before they compress the urethra => causing urinary symptoms, so present late.
- The malignancies metastasise via the lymphatic route (internal iliac and sacral nodes) and venous route (internal vertebral plexus to vertebrae and brain)
Blood levels of prostatic-specific antigen (PSA) produced by normal or abnormal prostatic epithelial cells are often elevated in prostatic disorders. This finding is one of a range of diagnostic tests used to assess and differentiate between prostate hyperplasia, prostatitis (inflammation) and carcinoma
The prostate can be examined via Digital Rectal Examination (DRE) for size and consistency. This exploits the anatomical relation of the prostate to the rectum.
