During the Medullary Phase of hematopoietic development, which bone is the first to show hematopoietic activity?

Correct Answer: D

Rationale: Step 1: The Medullary Phase starts in the 6th week of gestation. Step 2: Hematopoiesis starts in the yolk sac and then moves to the liver, spleen, and bone marrow. Step 3: The clavicle is the first bone to show hematopoietic activity during this phase due to its unique development timeline. Step 4: Other choices like the femur, iliac crest, and skull develop hematopoietic activity later in fetal development. Summary: The clavicle is the correct answer as it is the first bone to exhibit hematopoietic activity during the Medullary Phase, while the other choices develop this activity later in the developmental process.

Correct Answer: B

Rationale: Step-by-step rationale for the correct answer (B): 1. Low Hb (120 g/L) and MCV (69 fL) indicate microcytic anemia. 2. High WCC (14.9 x 10^9/L) suggests an inflammatory response. 3. Ferritin (18 ng/mL) is low, indicating iron deficiency. 4. Symptoms of blood in stools, fatigue, weight loss are concerning for colorectal cancer. 5. Therefore, the correct diagnosis is iron deficiency anemia due to colorectal cancer. Summary of incorrect choices: A: Iron deficiency anemia due to poor diet - Ferritin levels would typically be low in this case, but other results do not support this choice. C: Vitamin B12 deficiency due to pernicious anemia - MCV is low, not high as expected in vitamin B12 deficiency. D: Thalassemia due to genetic mutation - Thalassemia would present with microcytic anemia

Correct Answer: B

Rationale: The most likely diagnosis for the patient is B: Hodgkin lymphoma. The symptoms of fever, night sweats, and painful lumps in the neck/armpits are classic signs of Hodgkin lymphoma. The Reed-Sternberg cells seen in Hodgkin lymphoma are characteristic and differentiate it from non-Hodgkin lymphoma. Infectious mononucleosis typically presents with sore throat and fatigue, not painful lumps. Tuberculosis usually manifests with respiratory symptoms. Non-Hodgkin lymphoma may present similarly, but the presence of Reed-Sternberg cells points towards Hodgkin lymphoma.

Correct Answer: C

Rationale: Step 1: Hypersensitivity to penicillin and poison oak is due to hapten-protein complex formation. Step 2: Haptens are small molecules that bind to proteins, triggering an immune response. Step 3: This immune response can lead to sensitization and subsequent hypersensitivity reactions. Step 4: IgE antibody is typically involved in Type I hypersensitivity reactions, not haptens. Step 5: IgG and IgM antibodies are more associated with Type II and Type III hypersensitivity, not haptens. Step 6: Th-2 cells are involved in Type IV hypersensitivity reactions, not haptens. Summary: Choice C is correct as hypersensitivity to penicillin and poison oak is initiated by haptens, not IgE antibodies (Choice A), IgG and IgM antibodies (Choice B), or Th-2 cells (Choice D).

Correct Answer: D

Rationale: The correct answer is D because a single B lymphocyte can produce antibodies of many different specificities due to the process of somatic hypermutation and class switching. This allows for the generation of a diverse repertoire of antibodies. Plasma cells, on the other hand, are derived from B cells and are typically monospecific, producing antibodies of a single specificity. This is important for maintaining a focused immune response. Explanation of other choices: A: Choice A is correct. Humans can indeed generate antibodies with approximately 10^8 different VH x VL combinations, contributing to the vast diversity of the immune response. B: Choice B is correct. A single B cell can switch from producing IgM antibodies to IgA antibodies through the process of class switching, enhancing the adaptability of the immune response. C: Choice C is correct. Hematopoietic stem cells possess the genetic potential to create over 10^4 immunoglobulin genes, which allows for the production of a wide array of antibodies