The primitive stem cell of spermatogenesis, which is found on the periphery of each seminiferous tubule, is called a ________.

Correct Answer: A

Rationale: The correct answer is A: spermatogonium. Spermatogonium is the primitive stem cell of spermatogenesis located at the periphery of seminiferous tubules. It undergoes mitosis to produce more spermatogonia or differentiate into primary spermatocytes. Spermatid and secondary spermatocyte are later stages in spermatogenesis, not the primitive stem cell. Primary spermatocyte is the immediate progeny of spermatogonium following differentiation.

Correct Answer: B

Rationale: The correct answer is B: oxytocin. Braxton Hicks contractions are irregular, painless contractions of the uterus that occur throughout pregnancy. Oxytocin is the hormone responsible for stimulating contractions during labor. Therefore, the presence of Braxton Hicks contractions indicates the preparation of the uterus for labor under the influence of oxytocin. Choices A, C, and D are incorrect as they do not directly relate to the physiological mechanism of Braxton Hicks contractions.

Correct Answer: D

Rationale: Step-by-step rationale for why the correct answer is D: 1. Testes are the male gonads responsible for producing sperm. 2. The testes function as the primary reproductive organ in males. 3. Sperm production occurs in the seminiferous tubules within the testes. 4. The testes also produce testosterone, the primary male sex hormone. Summary of why other choices are incorrect: A: Producing - While testes do produce sperm, this choice lacks specificity regarding the male gonads. B: Estrogen functions and are called ________ - Estrogen is a female sex hormone, not produced by male gonads. C: Progesterone - Progesterone is a female sex hormone produced mainly by the ovaries, not by male gonads.

Correct Answer: D

Rationale: The correct answer is D: 14 days. During oogenesis, the process of ovulation occurs approximately 14 days prior to the start of the next menstrual cycle. This is crucial for timing fertilization and pregnancy. The other choices are incorrect because: A: an ovum is the mature egg released during ovulation, not directly related to the menstrual cycle. B: 7 days is not a relevant timeframe in the context of oogenesis and menstrual cycles. C: a primary oocyte is the initial stage of egg development and needs further maturation before ovulation, not directly linked to the menstrual cycle timing.

Correct Answer: D

Rationale: The correct answer is D: Sertoli cells. Seminiferous tubules are lined with Sertoli cells, which provide structural support and nourishment to developing sperm cells. These cells also help in the process of spermatogenesis. A: Oocytes are female germ cells found in the ovaries, not in the seminiferous tubules. B: Red blood cells are not found in the seminiferous tubules. They are responsible for carrying oxygen in the bloodstream. C: Leydig cells are found in the interstitial tissue of the testes and are responsible for producing testosterone, not lining the seminiferous tubules. Therefore, the correct choice is D as Sertoli cells play a crucial role in sperm production within the seminiferous tubules.