What is the normal range for the hematocrit value in a healthy adult?

Correct Answer: B

Rationale: The correct answer is B: 40-60%. Hematocrit represents the percentage of red blood cells in the blood. The normal range for hematocrit in a healthy adult is typically around 40-60%. Values below 40% may indicate anemia, while values above 60% may suggest conditions like dehydration or polycythemia. Choices A, C, and D are incorrect because they fall outside the normal range for hematocrit levels in a healthy adult.

Correct Answer: B

Rationale: Barry Marshall drank a pure culture of H. pylori to demonstrate an association between H. pylori infection and gastric ulcers. This is because he wanted to prove the theory that the bacteria is a primary cause of stomach ulcers, contradicting the prevailing belief at the time. Choice A is incorrect because the direct link between H. pylori and gastric cancer was not the primary focus of his experiment. Choice C is incorrect as his goal was to show the bacterial link to ulcers, not to disprove stress as a factor. Choice D is incorrect because only choice B accurately reflects his intended purpose.

Correct Answer: A

Rationale: The correct answer is A: Selectins expressed on endothelial cells. Rolling of neutrophils on endothelial cells is a crucial step in the process of inflammation and immune response. Selectins are cell adhesion molecules expressed on endothelial cells that facilitate the initial interaction between leukocytes (such as neutrophils) and endothelial cells. This interaction allows for the rolling of neutrophils along the endothelial surface, which is essential for the subsequent steps of adhesion and transmigration into the tissues. Integrins (Choice B) are involved in the firm adhesion of leukocytes to endothelial cells, not in the initial rolling process. Chemokines (Choice C) such as CXCL-8 are signaling molecules that help in the recruitment of leukocytes but do not directly mediate the rolling process. TNF (Choice D) is a pro-inflammatory cytokine but is not directly involved in the rolling of neutrophils on endothelial cells.

Correct Answer: C

Rationale: The correct answer is C because secondary lymphoid tissues, like lymph nodes and spleen, are where lymphocytes encounter antigens and become activated. This process leads to the proliferation and differentiation of lymphocytes, enabling them to mount an immune response against specific pathogens. Choices A, B, and D are incorrect because A pertains to primary lymphoid tissues, B describes a localized immune response, and D refers to the process of gene rearrangement that occurs in the primary lymphoid tissues during lymphocyte development.

Correct Answer: C

Rationale: After engagement of pattern recognition receptors, dendritic cells upregulate expression of the B7 molecule, which is essential for co-stimulation of naïve T cells. This step is crucial for activating T cells. MHC class I molecules present antigens to CD8+ T cells, not CD4+ T cells, so choice A is incorrect. Dendritic cells already have high antigen uptake ability, so choice B is not directly related to activation. PAMP-induced proliferation is not a typical response of dendritic cells after pattern recognition receptor engagement, making choice D incorrect.