Nokea
RU486 causes abortion if it is administered before or soon after implantation. What is the specific effect of RU486?
- A. It binds to luteinizing hormone receptors, stimulating the secretion of progesterone from the corpus luteum
- B. It blocks progesterone receptors so that progesterone has no effect within the body
- C. It blocks the secretion of follicle-stimulating hormone by the pituitary
- D. It blocks the effects of oxytocin receptors in the uterine muscle
Correct Answer: B
Rationale: The correct answer is B, as RU486 blocks progesterone receptors, preventing progesterone from exerting its effects. Progesterone is crucial for maintaining the uterine lining to support a pregnancy. By blocking progesterone receptors, RU486 causes the uterine lining to break down, leading to the expulsion of the embryo and ultimately causing abortion.
Choice A is incorrect because RU486 does not bind to luteinizing hormone receptors or stimulate progesterone secretion.
Choice C is incorrect because RU486 does not block the secretion of follicle-stimulating hormone; its mechanism of action is specific to progesterone receptors.
Choice D is incorrect because RU486 does not block the effects of oxytocin receptors in the uterine muscle; its primary action is on progesterone receptors.
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The pregnancy period is:
- A. 120 days;
- B. nine weeks;
- C. 280 weeks;
- D. 280 days;
Correct Answer: D
Rationale: The correct answer is D: 280 days. The pregnancy period, also known as gestation, typically lasts around 280 days from the first day of the last menstrual period to the birth of the baby. This duration is calculated based on the average length of a full-term pregnancy, which is approximately 40 weeks. It is important to note that individual pregnancies may vary slightly in duration, but the standard reference is 280 days.
Explanation of other choices:
A: 120 days - This is too short for a full-term pregnancy.
B: Nine weeks - This is only around 63 days, which is far less than the average gestation period.
C: 280 weeks - This is equivalent to around 1960 days, which is much longer than a typical pregnancy duration.
Which of the following is the site of fertilization?
- A. Ureters
- B. Urethra
- C. Uterine tubes
- D. Ovaries
Correct Answer: C
Rationale: The correct answer is C, Uterine tubes. Fertilization occurs in the uterine tubes, also known as Fallopian tubes, where the sperm and egg meet to form a zygote. The uterine tubes provide a suitable environment for fertilization to take place.
A: Ureters - Incorrect, ureters are tubes that carry urine from the kidneys to the bladder, not involved in fertilization.
B: Urethra - Incorrect, the urethra is a tube that carries urine from the bladder out of the body, not involved in fertilization.
D: Ovaries - Incorrect, ovaries release eggs but fertilization does not occur in the ovaries; rather, it occurs in the uterine tubes.
The main structures in erectile tissue responsible for maintaining an erection are the:
- A. pacinian corpuscles
- B. peripheral nerves
- C. helicine arteries
- D. Acrosome phase
Correct Answer: C
Rationale: The correct answer is C: helicine arteries. Helicine arteries are the main structures in erectile tissue responsible for maintaining an erection. They dilate in response to signals from the nervous system, allowing increased blood flow into the penis, leading to an erection. Pacinian corpuscles (A) are sensory receptors for touch and pressure, not involved in erectile function. Peripheral nerves (B) transmit signals between the brain and the penis but are not directly responsible for maintaining an erection. Acrosome phase (D) is a term related to sperm structure and not relevant to erectile tissue function.
The development strategy where the young develop within their mother's uterus and obtain nourishment from the mother via placenta is best described as
- A. Oviparity.
- B. Viviparity.
- C. Semelparity.
- D. Ovoviviparity.
Correct Answer: B
Rationale: The correct answer is B: Viviparity. Viviparity refers to the development strategy where young develop within the mother's uterus and receive nourishment through the placenta. This is the best description for the scenario provided.
A: Oviparity involves laying eggs externally.
C: Semelparity is a reproductive strategy where an organism reproduces only once in its lifetime.
D: Ovoviviparity is a combination of oviparity and viviparity, where eggs are retained within the mother's body until they hatch.
Which structure is the site of sperm production?
- A. Vas deferens
- B. Seminiferous tubules
- C. Albuginea
- D. Epididymis
Correct Answer: B
Rationale: The correct answer is B: Seminiferous tubules. These tubules are located within the testes and are the specific structures where sperm production occurs through a process called spermatogenesis. Sperm cells are produced within the seminiferous tubules and then mature as they move through the epididymis (choice D) and vas deferens (choice A). The albuginea (choice C) is the tough outer covering of the testes and does not play a direct role in sperm production. Therefore, the seminiferous tubules are the primary site for sperm production in the male reproductive system.