MCV 90 fL, low reticulocyte production index. Most possible cause of anemia?

Correct Answer: C

Rationale: The correct answer is C, Aplastic anemia. Aplastic anemia is characterized by pancytopenia, which includes low red blood cell count (MCV 90 fL) and low reticulocyte production index. Thalassemia (A) would typically present with microcytic anemia, not normocytic. Vitamin B12 deficiency (B) would present with macrocytic anemia. Iron deficiency anemia (D) would present with microcytic anemia. Therefore, based on the given data, the most likely cause is aplastic anemia.

Correct Answer: D

Rationale: The correct answer is D because iron is better absorbed in the ferrous form compared to the ferric form. Ferrous iron is more soluble and readily absorbed by the body through the duodenum and upper small intestine. Intrinsic factor is needed for the absorption of vitamin B12, not iron (Choice B). Ascorbic acid actually enhances iron absorption by reducing ferric iron to the more absorbable ferrous form, so Choice C is incorrect. Large intestine absorption (Choice A) is not a significant route for iron absorption in the body.

Correct Answer: C

Rationale: Platelets play a crucial role in the process of hemostasis after vascular injury. When a blood vessel is damaged, platelets adhere to the site and change shape to form a plug, a process known as platelet aggregation. This is important for stopping bleeding. Vasodilation (choice A) typically occurs after vasoconstriction to help with blood flow. Clotting factors (choice B) are essential in the coagulation cascade but not directly involved in platelet aggregation. Serotonin (choice D) is released by platelets during aggregation but does not directly stimulate the process. Therefore, the correct answer is C as platelets changing shape is a key step in platelet aggregation during vascular injury.

Correct Answer: D

Rationale: The correct answer is D: Thymus. The thymus is a primary lymphoid organ where T lymphocytes mature. It plays a crucial role in the development of the immune system. Lymph nodes (A), spleen (B), and Peyer's patches (C) are considered secondary lymphoid organs where immune responses are initiated but not where lymphocytes mature. Thymus is the only choice that fits the criteria of being a primary lymphoid organ.

Correct Answer: A

Rationale: The correct answer is A: Antibodies are opsonins. Antibodies are proteins produced by B-cells that can bind to antigens, marking them for destruction by phagocytic cells. Opsonins enhance phagocytosis by promoting the binding of pathogens to phagocytes. This statement is correct because antibodies can act as opsonins. B: B-cells can't recognize naive antigen - Incorrect. B-cells can recognize and respond to naive antigens through their B-cell receptors. C: T-cells recognize naive antigen - Incorrect. T-cells also recognize and respond to naive antigens through their T-cell receptors. D: T-helper cells not important for cytokines - Incorrect. T-helper cells play a crucial role in orchestrating the immune response by producing cytokines that regulate immune cell activities.