The partial pressure of carbon dioxide in venous blood is approximately

Correct Answer: B

Rationale: The correct answer is B (45 mm Hg) because the partial pressure of carbon dioxide in venous blood is typically around 40-45 mm Hg. This value represents the amount of CO2 dissolved in the blood plasma. Option A (40 mm Hg) is slightly on the lower side and may not fully reflect the average value. Option C (50 mm Hg) is higher than the usual range for venous blood CO2 levels. Option D (70 mm Hg) is significantly higher than the normal range and is more characteristic of arterial blood CO2 levels. Therefore, option B is the most accurate representation of the partial pressure of CO2 in venous blood.

Correct Answer: C

Rationale: Emphysema is the correct answer because it is characterized by the destruction of alveolar walls and connective tissues in the lungs, leading to reduced respiratory surface area. Asthma is characterized by airway inflammation and bronchoconstriction. Bronchitis is inflammation of the bronchial tubes. Tuberculosis is a bacterial infection affecting the lungs. Emphysema best fits the description provided in the question.

Correct Answer: C

Rationale: The correct answer is C: Smoking. Smoking is a risk factor for developing heart failure because it damages the blood vessels, increases blood pressure, and reduces oxygen delivery to the heart. Regular exercise (A) is actually beneficial for heart health. Low blood cholesterol levels (B) are generally considered a positive factor for heart health. Adequate sleep (D) is important for overall well-being but is not a direct risk factor for heart failure. In conclusion, smoking (C) stands out as the correct answer due to its harmful effects on the cardiovascular system.

Correct Answer: C

Rationale: The larynx consists of 9 cartilages, including the thyroid, cricoid, and epiglottis. These structures provide support and protection to the vocal cords and are essential for phonation and breathing. Choice C is correct because it accurately reflects the number of cartilages in the larynx. Choices A, B, and D are incorrect as they do not correspond to the anatomical structure of the larynx. It is important to understand the specific components of the larynx to correctly identify the number of cartilages present.

Correct Answer: A

Rationale: Step 1: Pleura is a thin membrane that surrounds the lungs and lines the chest cavity. Step 2: There are two layers of pleura - visceral (inner layer covering the lungs) and parietal (outer layer lining the chest cavity). Step 3: The correct answer is A (2), because there are only two layers of pleura. Summary: Choice B and C are incorrect because they each represent only one layer of pleura, whereas the correct answer A encompasses both layers. Choice D is incorrect because it includes all options, which is not accurate in this case.