Lipid exchange between the RBC membrane and the plasma occurs:

Correct Answer: A

Rationale: The correct answer is A: To replace lost lipids in the membrane. Lipid exchange in RBCs is crucial for membrane maintenance and repair. Lipids can be lost due to various factors like oxidative stress or mechanical stress. Replacing lost lipids helps maintain the integrity and functionality of the membrane. Summary of other choices: B: Providing a mechanism for excretion of lipid-soluble waste products is not a primary function of lipid exchange in RBCs. C: Ensuring symmetry between the lipid layers is important for membrane stability but not the primary purpose of lipid exchange in RBCs. D: Providing lipid-soluble nutrients to RBCs is not the main function of lipid exchange; RBCs primarily rely on glucose for energy.

Correct Answer: D

Rationale: The correct answer is D: Inflammation. ESR (Erythrocyte Sedimentation Rate) measures the rate at which red blood cells settle in a tube over a specific period, which can be elevated in conditions causing inflammation. Inflammation triggers the release of acute-phase proteins, increasing the ESR. Osteoarthritis (A) is a degenerative joint disease and does not typically cause significant inflammation. Polycythemia (B) is an increase in red blood cells, not directly related to ESR. Decreased globulins (C) would not lead to an elevated ESR as it is associated with conditions like multiple myeloma or liver disease.

Correct Answer: B

Rationale: The most likely diagnosis for this man is Acute Myeloid Leukemia (AML) based on his symptoms of breathlessness, bone pain, severe infections, hepatosplenomegaly, and gum hypertrophy. AML is characterized by rapid growth of abnormal white blood cells in the bone marrow, leading to bone pain, infections, and organomegaly. The presence of gum hypertrophy is a classic finding in AML due to infiltration of leukemic cells. In contrast, Multiple Myeloma (choice A) presents with bone pain, anemia, and kidney issues; Chronic Lymphocytic Leukemia (choice C) typically manifests with lymphadenopathy and anemia; and Hodgkin Lymphoma (choice D) presents with painless lymphadenopathy, fever, night sweats, and weight loss. Therefore, AML is the most fitting diagnosis in this case.

Correct Answer: D

Rationale: The correct answer is D: an IgG-IgM response to penicillin. 1. The symptoms of fever, rash, and proteinuria are suggestive of a hypersensitivity reaction to penicillin. 2. The timing of 7 days after penicillin initiation is consistent with a delayed hypersensitivity reaction mediated by IgG and IgM antibodies. 3. Recurrence of rheumatic fever typically occurs weeks to months after the initial episode, making choice A incorrect. 4. Choice B is unlikely given the temporal relationship with penicillin therapy. 5. Choice C is incorrect as an IgE response would present as an immediate hypersensitivity reaction, not after 7 days.

Correct Answer: C

Rationale: The correct answer is C because T lymphocytes play a crucial role in the rejection of polyomavirus-induced tumors. This is evident from the fact that nude mice, which lack functional T lymphocytes, develop tumors when infected with polyomavirus, whereas normal mice with intact T lymphocytes do not. Choice A is incorrect because macrophages are not the main players in rejecting these tumors. Choice B is incorrect as natural killer cells alone cannot reject these tumors without the help of T lymphocytes. Choice D is incorrect as B lymphocytes may also contribute to the rejection process, although they are not the primary effector cells in this context.