An inflammatory response is triggered when:

Correct Answer: C

Rationale: The correct answer is C because mast cells release histamine and heparin during an inflammatory response. Histamine causes vasodilation and increased vascular permeability, leading to redness and swelling. Heparin prevents blood clotting to allow immune cells to reach the site of infection. Choices A and B are incorrect because red blood cells do not release pyrogens, and T cells release cytokines, not interferon, in response to infection. Choice D is incorrect because immunosuppressants like cortisone would dampen the immune response rather than trigger an inflammatory response.

Correct Answer: D

Rationale: The correct answer is D because a higher PO2 gradient between alveoli and blood promotes greater oxygen binding to hemoglobin in the lungs. A high PCO2 (choice A) would actually decrease oxygen binding, while a slightly acidic pH (choice B) can affect oxygen dissociation but not loading. Having a PO2 of about 70 mm Hg (choice C) is not optimal for maximum loading as it is lower than what is typically found in the alveoli during normal breathing.

Correct Answer: C

Rationale: The correct answer is C because the Dorsal Respiratory Group (DRG) is involved in both inspiration and expiration, not just forced breathing. During quiet breathing, the DRG primarily controls inspiration, while the Ventral Respiratory Group (VRG) primarily controls expiration. In forced breathing, both the DRG and VRG are activated to increase respiratory effort. Choice A and B are both true statements as the DRG controls inspiration and the VRG controls expiration. Choice D is incorrect as the VRG is involved in both quiet and forced breathing, not just forced breathing.

Correct Answer: A

Rationale: The correct answer is A: visceral and parietal pleurae. The visceral pleura covers the surface of the lungs, while the parietal pleura lines the thoracic cavity. They form a double-layered membrane that helps reduce friction during breathing. Choices B and C are incorrect because the mediastinum is a central compartment in the thoracic cavity, not a layer of the pleura. Choice D is incorrect as it does not provide a valid alternative.

Correct Answer: A

Rationale: The correct answer is A: 500 million alveoli. The adult lung consists of approximately 300 million alveoli at birth, with an additional 200 million alveoli developing postnatally. This total of 500 million alveoli maximizes the surface area for efficient gas exchange in the lungs. Therefore, choice A is correct. Choices B, C, and D are incorrect because they do not accurately represent the estimated number of alveoli in the adult lung based on scientific research and anatomical studies.