Pre-Embryonic Phase of Development MCQs

When the zona pellucida is lost, the blastocyst is able to release proteolytic enzymes that allow it to penetrate the uterine wall. The uterine mucosal lining also aids in promoting enzyme release. The acrosome reaction is not related to implantation in that it occurs before fertilization. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 29

The divisions that occur during cleavage are always mitotic, producing daughter cells with a diploid number of chromosomes. However, in cleavage there is no period of cell growth between divisions, so that the originally oversized ovum is fractionalized through cleavage into cells, called blastomeres, of normal size. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 29

If none of the above are not true, then all are true, which is true. Syncytiotrophoblast extends processes into the endometrium at the end of the 1st week, and spaces called lacunae or sinusoids appear within this syncytium during the 2nd week. Maternal blood leaking into the lacunae initiates uteroplacental circulation. Primary villi form near the end of 2 weeks as cytotrophoblast invades syncytium. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 43

Ans. is 'd' i.e.,Trophoblast [Ref Singh IB, Human embryology Stile p. 38] Blastocyst possesses an inner cell mass called embryoblast which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast, which helps to provide nutrition to the embryo.

The trophoblast gives rise to both the syncytiotrophoblast and the cytotrophoblast, as well as the extraembryonic mesoderm. The ectoderm is a derivative of the epiblast, and the secondary yolk sac comes from endoderm cells that line the exocoelomic cavity or the primitive yolk sac. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 43

Ans. is 'b' i.e., 5 -7 days [Ref: Text book of Human embryology - 286] Contact of blastocyst with endometrium occurs at the time of implantation. Implantation occurs at around 6 -7 days. 11. Haploid number of chromosomes is seen in ? a) Spermatogonia b) Primary spermatocytes c) Secondary spermatocyte d) None Correct Answer - C Ans. is 'c' i.e., Secondary spermatocyte [Ref Ganong 23'd% p. 403, 404] Diploid means that cell contains 46 chromosomes (diploid of 23) and haploid means that cell contains 23 chromosomes. Development of sperm is as follows : - Spermatogonia(Diploid-46) → Primary spermatocyte (Diploid-46) Primary spermatocyte (Diploid-46) is of 2 types-

Fertilization occurs in the upper third of uterine tube, a region called the ampullary region. The sperm are transported there primarily by muscular contractions and by action of the cilia in the uterine tube. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 29

The inner cell mass of the blastocyst becomes the embryoblast and then eventually the embryo and fetus while the outer cell mass becomes trophoblast and then eventually the placenta. Reference - Textbook of Langman's, 12th Edition, General Embryology Page number - 29