During pregnancy, the uterine smooth muscle is quiescent. During the 9th month of gestation the uterine muscle becomes progressively more excitable. What factors contribute to the increase in excitability?

Correct Answer: B

Rationale: The correct answer is B: Progesterone synthesis by the placenta decreases. Progesterone maintains uterine quiescence during pregnancy by inhibiting uterine contractions. As progesterone levels decline towards the end of pregnancy, the uterine muscle becomes more excitable. Placental estrogen synthesis (Choice A) does not directly affect uterine excitability. Uterine blood flow (Choice C) is not a direct factor in uterine muscle excitability. Prostaglandin E2 (Choice D) actually increases towards the end of pregnancy, contributing to uterine contractions rather than decreasing excitability.

Correct Answer: C

Rationale: The correct answer is C: gametes. Gonads produce sex cells, which are haploid cells involved in reproduction. Gametes are the mature, haploid male or female germ cells (sperm or egg) produced by the gonads. Zygotes are formed when gametes fuse during fertilization, not produced by gonads. Interstitial cells are found in the testes and produce hormones, not sex cells. Spermatids are immature male germ cells that develop into sperm, not the primary sex cells produced by gonads.

Correct Answer: D

Rationale: The correct answer is D, follicle-stimulating hormone (FSH). FSH promotes the growth and maturation of primary follicles in the ovary each month. It stimulates the follicles to develop and produce estrogen. LH surge triggers ovulation. A and B are involved in the menstrual cycle, but they do not specifically promote the growth of primary follicles. C is not a hormone involved in the process.

Correct Answer: C

Rationale: The correct answer is C: Primary spermatocyte. Primary spermatocytes are diploid cells that undergo meiosis to produce four haploid cells, which develop into sperm. First, primary spermatocytes undergo meiosis I to form two secondary spermatocytes. Then, meiosis II occurs in each secondary spermatocyte to produce a total of four spermatids, which eventually mature into sperm. Explanation for why other choices are incorrect: A: Spermatids are already haploid cells formed from the division of secondary spermatocytes, not primary spermatocytes. B: Spermatogonium are diploid cells that divide by mitosis to produce primary spermatocytes, not directly giving rise to sperm. D: Ovum is a female gamete that undergoes meiosis to produce one mature egg cell, not sperm.

Correct Answer: C

Rationale: The secretory phase follows ovulation in the menstrual cycle. During this phase, the corpus luteum, formed from the ruptured follicle, secretes progesterone, maintaining the endometrium for potential implantation of a fertilized egg. Choice A is incorrect as ovulation occurs in the preceding phase (ovulatory phase). Choice B is incorrect as the functional layer of the endometrium thickens during the secretory phase to support a potential pregnancy. Choice D is incorrect as the functional layer of the endometrium is not shed during the secretory phase, but rather maintained for pregnancy support.