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2. Development and Anomalies of Male and Female External Genitalia

3. Objectives: • Describe and discus the development of the male urethra and the penis. • Describe and discus the development of the vagina, labia majora and labia minora. • Discuss the congenital anomalies of the male urethra and the penis. • Discuss the congenital anomalies of the vagina, labia majora and labia minora.

4. External Genitalia Indifferent Stage: • Cloacal folds form aound the cloacal membrane in the third week Cranial to the cloacal membrane the folds unite to form the genital tubercle. • Caudally the folds are subdivided into urethral folds anteriorly and anal folds posteriorly. • Genital swellings form on each side of the urethral folds. These swellings later form the scrotal swellings in the male and the labia majora in the female. • In the sixth week it is difficult to distinguish between the two sexes.

5. A,B. Indifferent stages of the external genitalia. • A. Approximately 4 weeks. • B. Approximately 6 weeks. • C. In utero photograph of a 56-day embryo showing continued growth of the genital tubercle and elongation of the urethral folds that have not yet initiated fusion. The genital swellings remain indistinct.

6. External Genitalia in the Male: • In male under the influence of androgens secreted by the fetal testes the external genitalia develops. • Rapid elongation of the genital tubercle(phallus) pulls the urethral folds to form the lateral walls of the urethral groove. • This groove will not reach the glans. The endoderrmal epithelial lining of the groove forms the urethral plate.

7. At the end of the third month, the two urethral folds close over the urethral plate, forming the penile urethra. • The distal part of the urethra is formed during the fourth month by ectoderm from the tip of the glans. • The genital swellings, known in the male as the scrotal swellings, arise in the inguinal region then move caudally and for the scrotum.

8. A. Development of external genitalia in the male at 10 weeks. Note the deep urethral groove flanked by the urethral folds. B. Transverse sections through the phallus during formation of the penile urethra. The urogenital groove is bridged by the urethral folds. C. Development of the glandular portion of the penile urethra. D. Newborn.

9. Defects in the Male Genitalia: • In Hypospadias, fusion of the urethral folds is incomplete, and abnormal openings of the urethra occur along the inferior aspect of the penis, usually near the glans, along the shaft, or near the base of the penis. • If fusion of the urethral folds fails entirely, a wide sagittal slit is found along the entire length of the penis and the scrotum. The two scrotal swellings then closely resemble the labia majora. • Epispadias is a rare abnormality in which the urethral meatus is found on the dorsum of the penis. • Although epispadias may occur as an isolated defect, it is most often associated with exstrophy of the bladder.

10. A. Hypospadias showing the various locations of abnormal urethral orifices. • B. Patient with hypospadias. The urethra is open on the ventral surface of the penis. • C. Epispadias combined with exstrophy of the bladder. Bladder mucosa is exposed.

11. External Genitalia in the Female: • Estrogens stimulate development of the external genitalia of the female. • The genital tubercle elongates only slightly and forms the clitoris. • Urethral folds do not fuse, as in the male, but develop into the labia minora. • Genital swellings enlarge and form the labia majora. • The urogenital groove is open and forms the vestibule.

12. A. In utero photograph of the genitalia of a male fetus at 12 weeks. Note that the urethral folds are fusing and that the scrotal swellings are enlarging to merge in the midline. B. Genitalia of a female fetus at 11 weeks. Note that the urethral folds, which will become the labia minora, have not fused and that the genital swellings, that are forming the labia majora, are widely separated.

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