Sexual differentiation in the embryo

Question 1

What part of the Y chromosome is responsible for sex differention?

Answer 1

SRY region which coded for testis determining factor

Question 2

Where on the Y chromosome does the SRY region lie?

Answer 2

Close to the end of the short arm of the Y chromosome.

Question 3

What makes up the bipotential tissue that both male and female gonads are formed from?

Answer 3

Somatic mesenchymal tissues (Genital ridge)

Primordial germ cells

Question 4

Where do the primordial germ cells lie initially in the developing embryo? Where do they move to?

Answer 4

In the epithelium of the yolk sac near the base of the developing allantois. They then migrate (thought to be guided by chemotaxis) to the gonadal ridge.

Question 5

What happens in the male embryo at around 6 weeks in terms of sex development?

Answer 5

1. Vigorous proliferation of sex cord cells which incorporate most of the primordial germ cells and develop into the definitive testis cords. These will give rise to the seminiferous tubules of the adult. In these the primordial germ cells will give rise to spermatazoa and the mesodermal cells will give rise to sertoli cells.
2. Between the cords the loose mesenchyme vasculaarizes and develops as stromal tissue, within which cells condense in clusters to for endocrine units (will become Leydig cells)

Question 6

What cells express the SRY gene?

Answer 6

Sertoli cells

Question 7

In the female what do the mesenchymal cells give rise to?

Answer 7

The granulosa cells

Question 8

The initial decision of whether to make an ovary or a testis depends on the presence of the SRY gene. What is it dependent on after this for further development?

Answer 8

A population of normal germ cells.

Question 9

Describe how turners syndrome affects development and causes infertility?

Answer 9

• Will initially develop an ovary due to the absence of SRY.
• After this normal oocyte growth depends on the activity of both X chromosomes, with the activity of only one resulting in death of the oocytes.
• This causes death of the follicles and ovarian dysgenesis resulting in a streak ovary.

Question 10

Describe how klienfelters syndrome affects development and causes infertility?

Answer 10

• Testes will form normally initially due to the presence of the SRY region
• However the germ cells die when the enter meiosis due to the presence of more than one X chromosome.

Question 11

What two hormones are essential for male development in the fetus? What structures secrete them?

Answer 11

Androgens from the Leydig cells

Anti mullerian hormone from the sertoli cells

Question 12

Does female development require the influence of hormones?

Answer 12

No

Question 13

What do the mullerian ducts develop into?

Answer 13

Oviducts
Uterus
Cervix
Upper vagina

Question 14

What do the wolffian ducts develop into?

Answer 14

Epididymis
Vas deferens
Seminal vesicles

Question 15

What are the primordial structures for the internal genitalia?

Answer 15

Wolfiaan Duct

Mullerian Duct

Question 16

What is the differences between the primordial tissue for the gonads, the internal and the external genitalia?

Answer 16

Gonads: One indifferent and bipotential structure (Gonadal ridge)
Internal Genitalia: Two separate sets on unipotential primordial (Mullerian and Wolffian Ducts) 
External genitalia ( One bipotential precursor)

Question 17

What is the name given to the structure that attaches the testis to the posterior abdominal wall

Answer 17

Gabernaculum

Question 18

How does the gabernaculum assist in the descent of the testis?

Answer 18

It does not elongate as the fetus grows which means the relative position of the testis becomes increasingly caudal

Question 19

Describe what the testis are doing in pre pubertal life?

Answer 19

Testis size is increasing slowly but steadily

Prospermatogonial cells are undergoing very limited mitotic proliferatiom

Question 20

What happens to the testis at puberty?

Answer 20

Sudden increase in testicular size and activity
Germ cells resume mitotic activity and begin the process of spermatogenesis.
Endocrine secretion by the leydig cells increases sharply

Question 21

What attaches the ovary to the posterior abdominal wall

Answer 21

The mesovarium