Reproductive System Session 1 Origin of the Sexes Lecture 1 Development of Male and Female Reproductive System 1

The genital system LANGMAN”S Medical Embryology Indifferent Embryo • Between week 1 and 6, female and male embryos are phenotypically indistinguishable, even though the genotype (XX or XY) of the embryo is established at fertilization. • By week 12, some female and male characteristics of the external genitalia can be recognized. • By week 20, phenotypic differentiation is complete.

4 Indifferent Embryo • The indifferent gonads develop in a longitudinal elevation or ridge of intermediate mesoderm called the urogenital ridge ❑ Initially…. gonads (as a pair of longitudinal ridges, the genital or gonadal ridges). ❑ Epithelium + Mesenchyme. ❑ Germ cells …… do not appear …… until the sixth week of development. • Primordial germ cells arise from the lining cells in the wall of the yolk sac at weeks 3-4. • At week 4-6, primordial germ cells migrate into the indifferent gonad. ➢ Male germ cells will colonise the medullary region and the cortex region will atrophy. ➢ Female germ cells will colonise the cortex of the primordial gonad so the medullary cords do not develop.

5 6 The genital system

7 8 • Phenotypic differentiation is determined by the SRY gene (sex determining region on Y). • which is located on the short arm of the Y chromosome. The Sry gene encodes for a protein called testes- determining factor (TDF). 1. As the indifferent gonad develops into the testes, Leydig cells and Sertoli cells differentiate to produce Testosterone and Mullerian-inhibiting factor (MIF), respectively. 3. In the presence of TDF, testosterone, and MIF, the indifferent embryo will be directed to a male phenotype. 4. In the absence of TDF, testosterone, and MIF, the indifferent embryo will be directed to a female phenotype.

9 10 ❑The components of the indifferent embryo that are remodeled to form the adult female and male reproductive systems are: 1. Gonads 2. Paramesonephric (Mullerian) duct 3. Mesonephric (Wolffian) duct 4. Phallus 5. Urethral folds 6. Genital swellings

11 12 Indifferent Embryo Adult Female Adult Male Testes, Seminiferous Ovary, Primordial Gonads Tubules, Tubuli Recti, Follicles, Rete Ovarii Leydig Cells, Sertoli Cells Uterine Tubes, Uterus, Paramesonephric Cervix, Upper Third of Appendix Testes Ducts Vagina*, Hydatid of Morgagni Epididymis, Ductus Appendix Vesiculosa, Duct Deferens, Seminal Mesonephric Ducts of Gartner Vesicles, Ejaculatory Duct, Appendix Epididymis Efferent Ductules, Mesonephric Tubules Epoophoron, Paroophoron Paradidymis Glance and Body of the Phallus Clitoris Penis Ventral Aspect of the Urethral Folds Labia Minora Penis Genital Swellings Labia Majora, Mons Pubis Scrotum • * Lower two-thirds develops from vaginal plate of urogenital sinus • Structures written by red color refers to vestigial structures Genital Ducts in the Sixth Week A: Male; B: Female

Genital ducts in the sixth week in the male A and female B. The mesonephric and paramesonephric ducts are present in both. Note the excretory tubules of the mesonephros and their relation to the developing gonad in both sexes.

14 A:Genital ducts in the female at the end of the second month B: Genital ducts after descent of ovary

Genital ducts in the female at the end of the second month. Note the paramesonephric (müllerian) tubercle and formation of the uterine canal. B. Genital ducts after descent of the ovary. The only parts remaining from the mesonephric system are the epoophoron, paroophoron, and Gartner’s cyst. 15 Formation of the Uterus and Vagina A. 9 weeks, B. At the end of the third month, C. Newborn

• A. 9 weeks. Note the disappearance of the uterine septum. • B. At the end of the third month. Note the tissue of the sinovaginal bulbs. • C. Newborn. The fornices and vagina are formed by vacuolization of the the upper portion of the • paramesonephric tissue, and the lower portion of the vagina is formed by vacuolization 16 • of the sinovaginal bulbs. Formation of the Uterus and Vagina A. 9 weeks, B. At the end of the third month, C. Newborn

17 Main Abnormalities of the Uterus and Vagina

18 A: Genital ducts in the male in the fourth month. B: Genital ducts after descent of the testis.

19 Descent of the Ovary and Testes

• The ovaries and testes develop within the abdominal cavity but later descend into the pelvis and scrotum, respectively. • This descent involves the gubernaculum (a band of fibrous tissue) and the processus vaginalis (an invagination of peritoneum).

20 Testes

1. The gubernaculum extends from the testes to the genital swellings (forming the gubernaculum testes in the adult male, which anchors the testes within the scrotal sac). 2. The processus vaginalis forms the tunica vaginalis in the adult male. 3. Cryptorchidism???

21 Descent of the testis: A. During the 2nd month; B. In the middle of the 3rd month; C. In the 7th month; D. Shortly after birth.

22 Drawing showing the coverings of the testes that are derived from constituents of the abdominal wall

23 Ovary

1. The gubernaculum extends from the ovary to the junction of the uterus and uterine tubes (forming the ovarian ligament in the adult female) and the continues into the labia majora (forming the round ligament of the uterus in the adult female). 2. The processus vaginalis is obliterated in the adult female

24 25 Development of Prostate Gland

❑The prostate gland develops from multiple outgrowths of the prostatic urethra.

❑Dihydrotestosterone (DHT) is the main mediator of prostatic growth in males.

26 External Genitalia Indifferent Stage A. Approximately 4 weeks; B. Approximately 6 weeks

27 External Genitalia in the Male A. Development of external genitalia in the male at 10 weeks; B. Transverse sections through phallus during formation of penile urethra; C. Newborn

28 Hypospadias and Epispadias Hypospadias showing the various Epispadias combined with exstrophy of locations of abnormal urethral orifices the bladder. Bladder mucosa is exposed

29 Development of the External Genitalia in the Female:- A: at 5 months; B: in the newborn

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