The outside layer of the oocyte is the _____.

Correct Answer: C

Rationale: The correct answer is C: zona pellucida. The zona pellucida is the glycoprotein layer surrounding the oocyte. It plays a crucial role in fertilization by binding sperm and facilitating the acrosome reaction. The theca interna and externa are layers surrounding the ovarian follicle, not the oocyte itself. The antrum is a fluid-filled cavity within the follicle, not the outer layer of the oocyte. Therefore, the correct choice is C as it directly relates to the outer layer of the oocyte.

Correct Answer: C

Rationale: The shedding and bleeding of the decidua during menses is directly caused by low levels of sex steroids. Sex steroids, specifically estrogen and progesterone, play a crucial role in maintaining the uterine lining. When levels of these hormones drop, it triggers the shedding of the decidua, leading to menstrual bleeding. FSH and LH are pituitary hormones that regulate the menstrual cycle but do not directly cause the shedding of the decidua. GnRH is a hypothalamic hormone that stimulates the release of FSH and LH.

Correct Answer: B

Rationale: The correct answer is B: Cord blood stem cells. Umbilical cord blood contains stem cells that are collected from the blood in the umbilical cord and placenta after a baby is born. These stem cells are known as cord blood stem cells, which are multipotent and have the potential to develop into various types of cells in the body. Pluripotent stem cells (choice A) refer to stem cells that can differentiate into almost any cell type, which is not specifically present in the umbilical cord. Blood stem cells (choice C) are found in bone marrow and are responsible for producing blood cells, but they are not the primary type of stem cells found in umbilical cord blood. Choice D is incorrect because umbilical cord blood indeed contains cord blood stem cells.

Correct Answer: B

Rationale: LH (luteinizing hormone) stimulates Leydig cells to secrete testosterone by binding to its receptor on the Leydig cells, triggering the production and release of testosterone. GnRH (choice A) stimulates the release of LH, not testosterone directly. Inhibin (choice C) inhibits FSH secretion but does not directly stimulate testosterone production. DHT (choice D) is a metabolite of testosterone and does not stimulate Leydig cells to produce testosterone.

Correct Answer: B

Rationale: The correct answer is B: Testosterone. Testosterone promotes the final step of spermatogenesis, which is the maturation of spermatids into spermatozoa. Testosterone is essential for the development and maintenance of male reproductive tissues and secondary sexual characteristics. Choice A, Relaxin, is not involved in spermatogenesis. Choice C, Inhibin, regulates FSH secretion but does not directly promote the final step of spermatogenesis. Choice D, Estrogen, is a female sex hormone and not directly involved in spermatogenesis.