Carbonic anhydrase in the RBC is the fastest enzyme and it decomposes in one second for fast action. Its concentration in the blood is due to the presence of

Correct Answer: D

Rationale: The correct answer is D: Hemoglobin. Carbonic anhydrase is an enzyme found in red blood cells that rapidly catalyzes the conversion of carbon dioxide into bicarbonate ions. Hemoglobin plays a crucial role in transporting carbon dioxide in the blood. The high concentration of hemoglobin in red blood cells allows for efficient binding and transport of carbon dioxide, leading to the need for a rapid enzyme like carbonic anhydrase to facilitate its conversion. Plasma (choice A) does not directly influence the concentration of carbonic anhydrase. Carbon dioxide (choice B) is the substrate for carbonic anhydrase, not the reason for its concentration. Sodium ions (choice C) do not directly affect the action of carbonic anhydrase in red blood cells.

Correct Answer: B

Rationale: The correct answer is B: Decreased diffusion capacity for oxygen. With age, respiratory dead space increases, leading to a mismatch between ventilation and perfusion in the lungs. This results in a decrease in the ability of the lungs to effectively transfer oxygen into the bloodstream, reducing the diffusion capacity for oxygen. This physiological change can lead to decreased oxygenation of tissues and organs. Summary: A: Increased diffusion of gases - Incorrect. Increased dead space does not enhance gas diffusion; instead, it impairs gas exchange. C: Decreased shunting of blood - Incorrect. Shunting refers to blood bypassing oxygenation in the lungs, which is not directly affected by dead space. D: Increased ventilation - Incorrect. While dead space may lead to increased ventilation efforts, it does not directly improve oxygen diffusion capacity.

Correct Answer: D

Rationale: The correct answer is D: Bronchioles. Bronchioles are the smallest airways in the lungs and play a crucial role in determining pulmonary resistance. They have smooth muscle surrounding them, which can contract or relax to regulate airflow and resistance. Constriction of bronchioles increases resistance, while dilation decreases it. Visceral and parietal pleura (A) are membranes that cover the lungs and chest wall, not directly involved in determining pulmonary resistance. The trachea (B) and bronchi (C) are larger airways that mainly serve as conduits for air passage and do not have as significant an impact on resistance as the bronchioles do.

Correct Answer: C

Rationale: The correct answer is C because as the SCUBA diver rises too fast, the pressure decreases rapidly. This causes the nitrogen gas that was dissolved in the blood at high pressure to form bubbles, leading to decompression sickness. Choice A is incorrect because carbon dioxide rushing into cells is not the cause of decompression sickness. Choice B is incorrect because it refers to carbon dioxide forming bubbles in the blood, which is not the mechanism of decompression sickness. Choice D is incorrect because it focuses on excess air from the SCUBA tank entering the blood, which is not the primary reason for decompression sickness.

Correct Answer: B

Rationale: Step 1: Understand the term - Hypercapnia means increased levels of CO2 in the blood. Step 2: Elevated PCO2 directly relates to increased CO2 levels. Step 3: This condition can lead to respiratory issues due to excess CO2. Step 4: Therefore, choice B, elevated PCO2, is the correct answer. Summary: Choices A, C, and D are incorrect as hypercapnia specifically refers to increased CO2 levels, not the cessation of breathing, elevated PO2, or an increase in pH.