This drug can potentiate the effect of prostacyclins to antagonize platelet stickiness and therefore decreases platelet adhesion to thrombogenic surfaces.

Correct Answer: B

Rationale: The correct answer is B: Dipyridamole. Dipyridamole works by inhibiting the enzyme phosphodiesterase, leading to an increase in cyclic adenosine monophosphate (cAMP) levels. This increase in cAMP levels potentiates the effect of prostacyclins, which inhibit platelet stickiness and decrease platelet adhesion to thrombogenic surfaces. Rationale: A: Sulfinpyrazone is a uricosuric agent, not a platelet anti-aggregant. C: Ticlopidine and D: Clopidogrel are both antiplatelet agents but work by different mechanisms (ADP receptor antagonists). They do not potentiate prostacyclins and do not directly affect cAMP levels.

Correct Answer: D

Rationale: Correct Answer: D Rationale: 1. During the mesoblastic phase of erythropoiesis in the yolk sac, only erythroblasts develop. 2. Erythroblasts are precursors of red blood cells and are responsible for producing hemoglobin. 3. Other choices (A, B, C) mention specific types of hemoglobins or cells that are not directly related to the mesoblastic phase. 4. Hb F, Hg A2, Hg A are adult hemoglobin types, Gower 1 and Gower 2 are embryonic hemoglobins, and Portland Hgb is an abnormal hemoglobin. 5. Therefore, the correct answer is D because only erythroblasts develop from yolk sacs during the mesoblastic phase.

Correct Answer: D

Rationale: The correct answer is D because the transferrin receptor is responsible for transporting transferrin-bound iron into cells, particularly erythrocytes. This process allows for the delivery of iron to cells for various biological functions, such as hemoglobin synthesis. Choice A is incorrect as iron is typically absorbed into duodenal cells, not transported out. Choice B is incorrect as it does not align with the role of the transferrin receptor in importing iron. Choice C is incorrect as the transferrin-bound iron in the plasma is not directly handled by the transferrin receptor but rather serves as a carrier for iron transport.

Correct Answer: B

Rationale: The correct answer is B: Improper disposal of phlebotomy equipment. This is the most frequent cause of needle punctures because if needles are not disposed of properly, they can pose a risk of accidental needle sticks to healthcare workers. Patient movement during venipuncture (A) can lead to complications but is not the most frequent cause of needle punctures. Inattention during needle removal (C) and failure to attach needle firmly to the tube holder (D) are also important factors to consider, but improper disposal of needles presents a higher risk of needle punctures.

Correct Answer: B

Rationale: The correct answer is B: P. ovale. P. ovale can cause relapses of malaria due to the presence of dormant liver stages (hypnozoites) that can reactivate weeks to years after the initial infection. P. falciparum, P. malariae, and P. knowlesi do not have hypnozoites and therefore do not cause relapses. P. falciparum is known for its severe manifestations, P. malariae has a long incubation period but does not cause relapses, and P. knowlesi mainly infects monkeys and rarely causes human malaria.