The mucociliary escalator protects

Correct Answer: C

Rationale: The mucociliary escalator is a defense mechanism in the respiratory tract that traps and removes inhaled particles and pathogens by using cilia to move mucus out of the lungs. This helps to prevent infections and maintain lung health. Choices A and B are incorrect because the mucociliary escalator specifically functions in the respiratory tract, not the gut or skin. Choice D is incorrect because the mucociliary escalator does not protect all of the mentioned sites, only the respiratory tract.

Correct Answer: B

Rationale: The correct answer is B: NK cells. NK cells are part of the innate immune system and can directly kill virus-infected cells, providing early protection against viral infections. They do not require prior exposure to the virus to initiate their killing mechanism, making them crucial for early defense. Eosinophils (A), Neutrophils (C), and Mast cells (D) are not primarily involved in killing virus-infected cells. Eosinophils are more associated with parasitic infections, Neutrophils are primarily involved in bacterial infections, and Mast cells are involved in allergic reactions.

Correct Answer: A

Rationale: Step 1: Hypervariable regions are responsible for antigen binding specificity. Step 2: Complementary Determining Regions (CDRs) are the specific locations within the hypervariable regions. Step 3: As CDRs are part of the hypervariable regions, choice A is correct. Summary: Choices B, C, and D are incorrect because hypervariable regions are not in the constant region, are present in secreted antibodies, and are found in both heavy and light chains.

Correct Answer: D

Rationale: The correct answer is D because cardiac output refers to the amount of blood pumped by the heart into the systemic circulation per minute. It is a crucial measure of heart function. Option A, coronary insufficient circulation, specifically refers to inadequate blood flow to the heart muscle itself, not overall cardiac output. Option B, a defect in heart valves, would affect the efficiency of blood flow but not necessarily the total amount of blood pumped. Option C, a disorder in heart rhythm, relates to irregular heartbeat patterns rather than the volume of blood pumped. Therefore, D is the correct choice as it directly relates to the definition of cardiac output.

Correct Answer: A

Rationale: The correct answer is A: Red blood cell. Red blood cells, also known as erythrocytes, contain hemoglobin that binds to oxygen and carbon dioxide for transport in the bloodstream. They are specifically designed for gas exchange. White blood cells (B) are part of the immune system and fight infections. Platelets (C) are responsible for blood clotting. Hematocrit (D) refers to the proportion of red blood cells in the blood, not a specific type of cell responsible for gas transport.