Male external genital organs

Male external genital organs

Male genital organs are situated both outside the pelvic cavity and within the pelvic cavity. As lower temperature is required for parthenogenesis, the testes are placed outside the pelvic cavity in the scrotal sac. Since urethra serves both the functions of urination and ejaculation, there is only one tube enclosed in the urogenital triangle.

Root of penis : The penis is the male organ of copulation.It is made up of : A root or attached portion, and a body or free portion. The root of the penis is situated in the superficial perineal pouch. It is composed of three masses of crectile tissue, namely the two crura and one bulb. Each crus is firmly attached to the margins of the pubic arch, and is covered by the ischiocavernosus.The bulb is attached to the perineal membrane in between the two crura. It is covered by the bulbospongiosus. Its deep surface is pierced (above its centre) by the urethra, which traverses its substance to reach the corpus spongiosum (located in the body). This part of the urethra within the bulb shows a dilatation in its floor, called the intrabulbar fossa.

Body of penis

The free portion of the penis is completely enveloped by skin. It is continuous with the root in front of the lower partof the pubic symphysis. It is composed of three elongated masses of erectile tissue. During erection of the penis these masses become engorged with blood leading to considerable enlargement. These masses are the right and left corpora cavarnosa, and a median corpus spongiosum. The penis has a ventral surface that faces backwards and downwards, and a dorsal surface that faces forwards and upwards. The two corpora cavernosa are the forward continuations of the crura. They are in close apposition with each
other throughout their length.The corpora cavernosa do not reach the end of the penis.Each of them terminates under cover of the glans penis in a blunt conical extremity. They are surrounded by a strong fibrous envelope called the tunica albuginea. The tunica albuginea has superficial longitudinal fibres enclosing both the corpora, and deep circular fibres that enclose each corpus separa tely,and also from a median septum.The corpus spongiosum is the forward continuation of the bulb of the penis. Its terminal part is extended to from a conical enlargement; called the glans penis. Throughout its whole length it is traversed by the urethra. Like the corpora, it is also surrounded by a fibrous sheath. The basa of the glans penis has a projecting margin, the corona glandis, which overhangs an obliquely grooved constriction,known as the neck of the penis.Within the glands the urethra shows a dilatation (in its roof) called the navicular fossa. The skin covering the penis is very thin and dark in colour. It is loosely connected with thefascial sheath of the organ. At the neck is folded to from the prepuce or foreskin which covers the glans to a varying extent and can
be retracted backwards to expose the glans. On the undersurface of the glans there is a median fold of skin called the frenulum.The potential space between the glans and the prepuce is known as the preputial sac. On the corona glandis and on the neck of thepenis there are numerous small preputial or sebaceous glands which secrete a sebaceous material called the smegma, which collects in the preputial sac.The superficial fascia of the penis consists of very loosely arranged areolar tissue, completely devoid of fat. It may contain a few muscle fibres. It is continuous with the membranous layer of superficial fascia of the abdomen above and of
the perineum below. It contains the superficial dorsal vein of the penis. The deepest layer of superficial fascia is membranous and is called the fascia of the penis or deep fascia of penis, or buck's fascia. It surrounds all three masses of erectile tissue, but does not extend into the glans. Deep to it there are the deep dorsal vein, the dorsal arteries and dorsal nerves of the penis. Proximally, it is continuous with the dartos and with the fascia of the urogenital triangle.

 Dissection          
From the superficial inguinal ring, makes a longitudinal incision downwards through the skin of the anterolateral aspects of the scrotum till its lower part. Reflect the skin alone if possible otherwise reflect skin, dartos and the other layers together till the testis enveloped in its tunica vaginalis is visualised.Lift the testis and spermatic cord from the scrotum .Cut through the spermatic cord at the superficial inguinal ring and remove it together with the testis and put it in a tray of water. Incise and reflect the coverings if any, e.g remains of external spermatic fascia cremaster muscle,cremasteric fascia and internal spermatic fascia. Separate the various structures of supermatic cord. Feel ductus deferens as the important constituent of spermatic cord. Make a transverse sectionthrough the testis to visualise its interior. Identify the epididymis capping the superior pole and lateral surface of the testis. The slitlike sinus of epididymis formed by tucking-in of the visceral layer of peritonuem between the testis and the epididymis is seen onthe anterolateral aspect of the testis.Cut through and reflect the skin along the dorsum of the penis from the symphysis pubis to theend of the prepuce. Find the extension of the membranous layer of the superficial fascia of the abdominal wall on to the penis ( fundiform ligament ). The superficial dorsal vein of the penis lies in the superficial fascia. Trace it proximally to drain into any of thesuperficial external pudendal veins of thigh. Deep to this vein is the deep fascia and suspensory ligament of the penis. Divide the deep fascia in the same line as the skin incision. Reflect it to see the deep dorsal vein with the dorsal arteries and nerves on each side.Make a transverse section through the body of the penis, but leave the two parts connected by the skin of urethral surface or ventral surface. Identify two corpora cavernosa and single corpus spongiosum traversed by the urethra.
Structure of the testis : The glandular part of the testis consists of 200 to 300 lobules. Each lobule contains two to three seminiferous tubules. Each tubule is highly coiled on itself. When stretched out, each tubule measures about 60 cm in length, and is about 0.2 mm in diameter.The tubules are lined by cells which represent stages in the formation of spermatozoa.The seminiferous tubules join together at the apices of the lobules to from 20 to 30 straight tubules which enter the mediastinum. Here they anastomose with
each other to from a network of tubules, called the rete testis. In its turn, the rete testis gives rise to 12 to 13 efferent ductules which emerge near the upper pole of the testis and enter the epididymis. Here each tubule becomes highly coiled and forms a lobe of the head of the epididymis. The tubules end in a single duct which is coiled on itself to from the body and tail of the epididymis. It is continuous with the ductus deferens. The testes develop in relation to the developing mesonephros, at the level of segments T10 to12. Subsequently, they descend to reach the scrotum. Each testis begins to descend during the second month of intrauterine life. It reaches the iliac fossa by the 3rd month, rests at the deep inguinal ring from the 4th to the 6th month, traverses the inguinal canal during the 7th month. reaches the superficial inguinal ring bu the 8th month and the bottom of the scrotum by the 9th month. An extension of peritoneal cavity called the processus vaginalis precedes the decent of testis into the scrotum,into which the testis invaginates. The processus vaginalis closes above the testis.          

Clinical anatomy

Due to laxity of skin and its dependent position, the scrotum is a common site for oedema. Abundance of hair and of sebaceous glands also makes it a site of sebaceous glands also make it a site of sebaceous cysts. As the scrotum is supplied by widely separated dermatomes (L1,S3) spinal anaesthesia of the whole scrotum is diffcult to achieve. The scrotum is bifid in male-pseudoherma-phroditism. Unilateral absence of testis -monorchism or bilateral absence of testis -anorchism. The testis may occupy anabnormal position due to deviation from the normal route of desent. It may be under the skin of the lower part of the abdomen, under
the skin of the front of the thigh, in the femoral canal, under the skin of the penis, and in the perineum behind the scrotum. Hermaphroditism or intersex is a condition in which an individual shows some features of a male and some of a female. In true hermaphroditism, both testis and ovary are present. In pseudohermaphrodition,the gonad is of one sex while the external or internal genitalia are of the opposite sex.Varicocoele is produced by dilatation of the pamainiform plexus on veins. It is usually left-sided; possibly because the left testicular vein is longer than the right, enters the left renal vein at a right angle and is crossed by the colon which may compress it when loaded. The testis and epididymis may be the site of various infection and of tumours. The commoncauses of epididymitis and epididymoorchitis are tuberculosis,filariasis, the gonococcal and other pyogenic infections. Testis may be palpated to check any nodules, or any irregularity or size or consistency. Tapping a hydrocele is a procedure for removing the excess fluid from tunica vaginalis. If a swelling is purely scrotal one can get above the level of swelling is due to inguinal hernia, it is not possible to get above the swelling.

External genitalia : As early as 3rd week of development, the mesenchymal cells from primitive streak migrate around the cloacal membrane. These from raised cloacal folds.Cranially the folds fuse to from genital tubercle. During 6th week of development cloacal folds are divided into urethral folds anteriorly a pair of swelling, the genital swelling appear. Gential swellings from the scrotum.