Question

38. Shortly after fertilization has occurred, the ovum undergoes a number of mitotic divisions that

transforms it into a ____________, this stage of development occurs in the _________

A) Trophoblast: Endometrium

B) Blastocele: Ovaries

C) Morula: Fallopian Tube

D: Chorian: Uterus

E) Ovary: Amnion

41. The presence of both dihydrotestosterone and __________ in the fetus will further the development of

the _________ into the male reproductive tract.

A) Estrogen: Wolffian ducts

B) Mullerian-promoting substance : Mullerian ducts

C) Wolffian-promoting substance: Wolffian ducts

D) Wolffian-inhibiting substance : Mullerian ducts

E) Mullerian-inhibiting substance : Wolffian ducts

42. Which of the following is not a function of granulosa cells?

A) Secreting chemical messengers that target the oocytes

B) Transporting nutrients to the oocyte’s interior

C) Secreting a protein called inhibin

D) Serving as an intermediary between the oocytes and sperm

E) All of the above are functions of granulosa cells

Answer 1

1) After the zygote formation, typical mitotic divisions of the nucleus occurs by producing two blastomeres. The two cell stage is reached approximately 30 hours after the fertilization. The blastomeres continue to divide by binary division through 4,8,16 celled stage until a cluster of cells is formed and is called MORULA in the FALLOPIAN TUBE. Morula after spending about 3 days in fallopian tube enters the Uterine cavity in the 16-64 celled stage. The central cell of the morula is called inner cell mass which forms the embryo proper and the outer cell mass is formed by peripheral cells. The cells now on the outer side of morula become trophoectoderm (trophoblast) and the inner cells become inner cell mass. Trophoectoderm differentiates into chorion and inner cell mass into embryo.

Option a) Trophoblast is formed in the endometrium. But it is a very late feature.

b) Blastocele is the cavity when morula differentiate into outer trophoblast and inner cell mass. It also occurs in endometrium. No part after fertilization occurs inside ovaries.

c) Serial mitotic divisions of zygote forms Morula in the fallopian tube. (ANSWER).

d) Chorion is formed from trophoblast in uterus. But it is a very late feature.

e) Amnion is formed along with chorion. It also occurs in uterus not in ovaries.

2) The testis of the fetus has Sertoli cells and Leydig cells. Sertoli cells secrete MULLERIAN INHIBITING FACTOR (MIF) and Leydig cells secrete testosterone which promotes the growth of WOLFFIAN DUCT and is converted into Dihydrotestosterone which forms the male external genitalia. Therefore Option E is the answer.

3) Granulosa cells are flat, spindle shaped cells in follicles which surround the oocyte. They have the receptors for FSH. Granulosa cells become columnar later in the menstrual cycle and becomes multi-layered stratum granulosum. At the time of ovulation, the follicle ruptures and only secondary oocyte surrounded by zona pellucida is released. Functions of granulosa cells:

• Provide nourishment to the developing oocyte by transporting the nutrients inside the oocyte.
• Secrete estrogen, Inhibin-B.
• When estrogen levels become 200picograms and is sustained for 48 hours, LH becomes maximum which resumes the Meiosis-I in which primary oocyte was arrested and secondary oocyte is formed. So it is also regarded as a function of granulosa cells.
• After ovulation, the released mature ovum consists of oocyte surrounded by inner layer of zona pellucida and on outer side by Corona radiata consisting of granulosa cells arranged in multi-layers. Hence it forms an intermediary between the Ovum and sperm.

All are the functions of granulosa cells. Option E is the answer.