Reproductive system 2: Genital ducts and external genitalia

Question 1

From which germ layer are the reproductive and urinary systems derived?

Answer 1

Intermediate mesoderm.

Question 2

What is the urogenital ridge?

Answer 2

Formed by the intermediate mesoderm. Protrudes from the posterior abdominal wall and covered by epithelium.

Question 3

In the male, what eventually forms the genital tract?

Answer 3

Mesonephric duct. Paramesonephric duct degenerates.

Question 4

In the female, what eventually forms the genital tract?

Answer 4

Paramesonephric duct. Mesonephric duct degenerates.

Question 5

Which gene drives the development of the male genital ducts?

Answer 5

SRY gene.

Question 6

How does SRY drive development of the male genital duct?

Answer 6

Encodes testis determining factor - causes differention of epitelial cells into Sertoli cells. Sertoli cells secrete anti-Mullerian hormone (AMH). AMH causes degeneration of paramesonephric ducts.

Question 7

What is the function of Sertoli cells in male genital tract development?

Answer 7

Cause differentiation of mesoderm of the gonad into Leydig cells. These produce testosterone - promotes survival and further development of mesonephric ducts.

Question 8

What is the name of the structures that connect the mesonephric duct to the rete testis? What do they develop into?

Answer 8

Epigenital tubules - efferent ductules.

Question 9

Which structures are ultimately derived from the mesonephric duct?

Answer 9

Seminal vesicle (out-pouching), vas deferens, efferent ductules, epididymis.

Question 10

Which structures are remnants of the paramesonephric ducts?

Answer 10

Utriculus prostaticus and appendix testis.

Question 11

What is the signal for the development of the female reproductive tract?

Answer 11

The absence of the SRY gene.

Question 12

Why does the female reproductive tract develop in the absence of the SRY gene?

Answer 12

No anti-Mullerian hormone - paramesonephric ducts remain. No testosterone - mesonephric ducts degenerate.

Question 13

Describe the derivatives of the paramesonephric ducts.

Answer 13

Cranial and horizontal - uterine tubes. Caudal - uterus.

Question 14

Why are the uterine tubes not attatched to the ovaries?

Answer 14

The paramesonephric duct is not attached to the gonad.

Question 15

Describe the development of the vagina.

Answer 15

Urogenital sinus develops sinovaginal bulbs that fuse with caudal tips of paramesonephric ducts to form vagina.

Question 16

Describe possible remnants of the mesonephric ducts.

Answer 16

Epoophoron, Paroophoron and Gartner’s cyst.

Question 17

What might be the consequences of a failure of paramesonephric ducts to fuse?

Answer 17

Double uterus and double vagina or just double uterus.

Question 18

What might be the consequences of failure of the uterine septum to degenerate?

Answer 18

Bicornate uterus (two-horned), septated uterus, cervical atresia

Question 19

What might be the consequence of failure of one paramesonephric duct to elongate?

Answer 19

Unicornate uterus.

Question 20

What is the cause and the symptoms of anti-Mullerian hormone syndrome?

Answer 20

Mutation in the AMH gene resulting in no AMH production so paramesonephric ducts persist. Both mesonephric and paramesonephric derivatives develop. Normal male external genitalia but may have cryptorchidism

Question 21

From which structure will either the penis or clitoris develop?

Answer 21

The genital tubercule.

Question 22

From which structure are the external genitalia derived?

Answer 22

The cloacal folds.

Question 23

At how many weeks can penile development be seen?

Answer 23

10 weeks

Question 24

How does the penile urethra develop?

Answer 24

Urethral folds pulled forwards and form lateral walls of urethal groove. Urethral groove is lined by epithelium and forms urethral plate. At the end of third month urethral folds close over urethral plate to form penile urethra.

Question 25

What is hypospadias?

Answer 25

Incomplete fusion of urethral folds - urethra opens on ventral surface of penis. 3-5/1000 births. Difficulty urinating. Can be repaired surgically using the foreskin.

Question 26

What is epispadias?

Answer 26

Usually arises as a result of the urethra opening on the dorsal surface of the penis. Often associated with exstropy of the bladder. 1/30,000 births. Results from improper location of the genital sinus - urethral groove located on dorsal surface.

Question 27

What is development of the female external genitalia dependent on? How does it happen.

Answer 27

Oestrogen. Genital tubercule elongate. Urethtral folds DO NOT elongate form labia minora. Genital swellings form labia majora. Urogenital groove remains open.