If a radioimmunoassay is properly conducted and the amount of radioactive hormone bound to antibody is low, this would indicate which of the following?

Correct Answer: A

Rationale: The correct answer is A: Plasma levels of endogenous hormone are high. When the amount of radioactive hormone bound to the antibody is low in a radioimmunoassay, it indicates that there is a high concentration of non-radioactive, endogenous hormone present in the sample competing for binding sites on the antibody. This competition results in fewer radioactive hormones binding to the antibody. Therefore, the low radioactive hormone binding suggests an abundance of non-radioactive hormone in the sample. Choice B is incorrect because low levels of radioactive hormone binding do not indicate low plasma levels of endogenous hormone. Choice C is incorrect as more antibody wouldn't affect the binding of radioactive hormone if endogenous hormone levels are high. Choice D is incorrect because the amount of radioactive hormone needed is not related to the binding observed in the assay.

Correct Answer: D

Rationale: The correct answer is D: Human chorionic gonadotropin (hCG). During the first 3 weeks of pregnancy, trophoblast cells produce hCG, which is crucial for maintaining the corpus luteum and ensuring the production of progesterone to support the early pregnancy. hCG is also the hormone detected in pregnancy tests. Rationale: A: Estrogen is mainly produced by the ovaries, not trophoblast cells in the early stages of pregnancy. B: Luteinizing hormone is produced by the pituitary gland to trigger ovulation, not by trophoblast cells. C: Oxytocin is produced by the hypothalamus and released by the pituitary gland during labor and breastfeeding, not by trophoblast cells in the early stages of pregnancy.

Correct Answer: A

Rationale: The correct answer is A: Below-normal arterial PO2. In a 12-month-old infant with patent ductus arteriosus, there would likely be a left-to-right shunt causing increased blood flow to the lungs, leading to decreased systemic blood flow. This can result in decreased systemic oxygenation and below-normal arterial PO2 levels. Choices B, C, and D are incorrect because patent ductus arteriosus does not directly affect arterial PCO2, arterial blood pressure, or pulmonary arterial pressure in a way that would lead to those specific outcomes at this age.

Correct Answer: A

Rationale: The correct answer is A: Seminal vesicles. These glands produce fructose, a sugar in semen that provides energy for sperm. Seminal vesicles are located near the base of the bladder and are responsible for producing a significant portion of the fluid in semen. The other choices are incorrect because the bulbourethral gland produces a clear lubricating fluid, the prostate produces a milky fluid that helps with sperm motility and viability, and the epididymis is a coiled tube where sperm mature and are stored, but it does not produce fructose.

Correct Answer: A

Rationale: The correct answer is A: Seminiferous tubules. Sperm production occurs in the seminiferous tubules of the testis through a process called spermatogenesis. This is where germ cells develop into mature spermatozoa. The other choices are incorrect: B: Ejaculatory duct is where sperm and seminal fluid mix before ejaculation, C: Interstitial cells produce testosterone, and D: Rete testis is a network of tubules where sperm travel after being produced in the seminiferous tubules.