Development of male genital system (MBBS)

Development of male genital system for mbbs 2nd year reproductive system module taught in pakistani medschool. The content is as laid down by the PMDC for the year 2024

1. Development of Male Genital System

2. Development of Genital System The sex determination of embryo is possible at the of fertilization but the early development of genital system is similar. In both the sexes, this early development of embryo up to 7 th is called as indifferent period. The sex determination of embryo occurs after 7 th week. The genital system which develops during this period is called as GONADS

3. Development of Gonads The gonads mean the testis or ovary These are develop from the three sources Mesothelium (Mesoderm) lining the posterior abdominal wall Underlying mesenchyme (Embryonic connective tissue) Primordial Germ cells

4. First Indication The first for development of male genital system is migration of epiblastic cells to the wall of yolk cells

5. Migration of Epiblastic Cells

6. Indifferent Gonads During the 5 th week of development there is thickening of mesoderm on posterior abdominal wall due to proliferation of mesothelial cells. Proliferation of mesothelial cells with underlying mesenchymal cells result in formation of longitudinal genital on medial site of mesonephric duct on each side of vertebral column.

7. Genital Ridge Initially the genital ridge consists of blastema, than these blastema differentiated to form the cords of cells. These cords of cells extending from the surface to the deep. The arrangement of cords will differentiate the blastema into outer cortex and inner medulla. Upto this stage the development of genital system is similar in two sex. The developing testis secrets the testosterone .

8. Male Gonads Y – chromosome SRY  TDF ( Testes Determining Factor) if Produced  development of testis Usually from 7 th week If not produced Development of ovary Usually from 12 th week Called as waiting period

9. Indiferent Stage Both sexes has same first stage coelomic epithelium primary germ cords primordial germ cells mesonephric duct (Wollfian) and tubules paramesonephric duct

10. Development of Gonads Endodermal cells, called primordial germ cells, migrate from the wall of the yolk sac near the allantois to the dorsal wall of the abdominal cavity during the 5 th week. The primordial germ cells enter the gonadal ridges that parallel the mesonephros. Each ridge has a thick epithelium continuous with columns of cells called primary sex cords that extend into the center (medulla) of the ridge. At this gender indifferent stage , male embryos are indistinguishable from female embryos.

11. Sex Differentiation If the embryo is going to develop into male than this will control by a factor, the TDF ( testes determining factor) which regulate by a genome which is present on the short on the short limb of Y chromosome. This factor responsible for the sex differentiation and development of male sex organ (Testis)

12. Development of the Testes The primary sex cords in the male proliferate and the germ cells migrate into the sex cords. The resulting testis cords produce the seminiferous tubules. Connections develop between the arching testis cords and the adjacent mesonephric tubules. The mesonephric tubules later degenerate, but the seminiferous tubules remain connected to the mesonephric duct. Primary sex cords under influence of TDF are secreted the Testosterone which helped in formation seminiferous tubules from primary sex cords in medulla while primary sex cords in cortex degenerated.

13. Development of the Ovaries The primary sex cords in the female embryo degenerate and the primordial germ cells migrate into the outer region (cortex) of the genital ridge that will become the ovary .

14. Development of Genital Ducts in the Male In male 8 to 10 mesonephric in thoracic region persists and connected to upper pole testes forming efferent ductules. Remaining all mesonephric ductules degenerate. Mesonephric duct on each side persists and developed in male ducts:

15. Development of Genital Ducts in the Male The mesonephric duct on each side developed in following ducts in successive order. Mesonephric duct at caudal end open in cloaca. Epididymis Ductus Deferens Seminal vesicle Ejaculatory duct

16. Development of Seminal Vesicles Lateral outgrowths from the caudal end of each mesonephric duct gives rise to the seminal glands (vesicles). The part of the mesonephric duct between the duct of this gland and the urethra becomes the ejaculatory duct .

17. Caudal Opening of Mesonephric Duct

18. Division of Cloaca

19. Development of Prostate Multiple endodermal outgrowths arise from the prostatic part of the urethra and grow into the surrounding mesenchyme . The glandular epithelium of the prostate differentiates from these endodermal cells, and the associated mesenchyme differentiates into the dense stroma and smooth muscle of the prostate.

20. Development of Prostate

21. Bulbourethral Glands These pea-sized structures develop from paired outgrowths from the spongy part of the urethra. The smooth muscle fibers and the stroma differentiate from the adjacent mesenchyme. The secretions of these glands contribute to the semen. Bulbourethral Glands

22. Genital Tubercle

23. Development of External Genitalia Up to the seventh week, the external genitalia are similar in both sexes. Distinguishing sexual characteristics begin to appear during the 9th week, but the external genitalia are not fully differentiated until the 12th week.

24. Development of Male External Genital System Early in the fourth week, proliferating mesenchyme produces a genital tubercle in both sexes at the cranial end of the cloacal membrane. Labioscrotal swellings and urogenital folds soon develop on each side of the cloacal membrane. The genital tubercle soon elongates to form a primordial phallus .

25. Development of Male External Genitalia When the urorectal septum fuses with the cloacal membrane at the end of the sixth week, it divides the cloacal membrane into a dorsal anal membrane and a ventral uerogenital membrane . The urogenital membrane lies in the floor of a median cleft, the urethral groove , which is bounded by the urethral folds . The anal and urogenital membranes rupture a week or so later, forming the anus and urogenital orifice, respectively.

26. Development of Male External Genitalia During the 12th week, a circular in-growth of ectoderm occurs at the periphery of the glans penis. When this ingrowth breaks down, it forms the prepuce (foreskin) a covering fold of skin. The corpora cavernosa and corpus spongiosum of the penis develop from mesenchyme in the phallus. The labioscrotal swellings grow toward each other and fuse to form the scrotum. The line of fusion of these folds is clearly visible as the scrotal raphe . Agenesis of the scrotum is an extremely rare anomaly.

27. Reproductive Organs Male Genitalia Female Genitalia Scrotum The scrotum develops from an out-pouching of the skin of the anterior abdominal wall. Clitoris The clitoris is an erectile organ located where the labia minora meet anteriorly. Penis This is the male organ of copulation. It is the common outlet for urine and semen. Vestibule The vestibule is the space surrounded by the labia minora into which the orifices of the urethra and vagina and the ducts of the greater and lesser vestibular glands open The Glans Penis Distally, the corpus spongiosum penis expands to form the conical glans penis. Bulbs of Vestibule The bulbs of the vestibule are paired masses of elongated erectile tissueThe bulbs are homologous with the bulb of the penis of the corpus spongiosum .