In which direction does carbon dioxide move during external respiration?

Correct Answer: B

Rationale: During external respiration, carbon dioxide moves from the blood into the lungs. This is because the blood carries carbon dioxide from the body tissues to the lungs to be exhaled. In the lungs, carbon dioxide diffuses from the blood into the alveoli to be eliminated during exhalation. Choice A is incorrect because carbon dioxide does not move from the blood into the tissue cells during external respiration. Choice C is incorrect as carbon dioxide is exhaled into the atmosphere, not the other way around. Choice D is incorrect as carbon dioxide is produced in the tissue cells and needs to be transported back into the blood for removal in the lungs.

Correct Answer: B

Rationale: The correct answer is B because the apneustic centers of the pons provide stimulation to the inspiratory center in the medulla oblongata to promote inhalation. This is essential for regulating the breathing cycle. Choice A is incorrect as the apneustic centers do not inhibit the pneumotaxic and inspiratory centers. Choice C is incorrect as the apneustic centers do not directly monitor blood gas levels. Choice D is incorrect as the apneustic centers do not alter chemoreceptor sensitivity.

Correct Answer: C

Rationale: The primary muscles of inspiration are the diaphragm and external intercostal muscles. The diaphragm contracts and moves downward, increasing the volume of the thoracic cavity, while the external intercostal muscles lift and expand the rib cage. This creates a negative pressure in the lungs, allowing air to flow in. A: Internal intercostal muscles are involved in forced expiration, not inspiration. B: While the diaphragm is a primary muscle of inspiration, internal intercostal muscles are not. D: Rectus abdominis and transversus thoracis are primarily involved in expiration, not inspiration.

Correct Answer: A

Rationale: The correct answer is A: Trachea. The trachea is the windpipe, a tube that carries air to and from the lungs. It is located in front of the esophagus. The trachea is made up of cartilage rings, allowing it to stay open and prevent it from collapsing. The other choices are incorrect because the lungs are the organs where gas exchange occurs, the larynx is the voice box, and the bronchi are the two branches of the trachea that lead to the lungs.

Correct Answer: D

Rationale: The correct answer is D: corniculate cartilage. The corniculate cartilage is the largest of the laryngeal cartilages. It is paired and sits atop the arytenoid cartilages in the posterior aspect of the larynx. The cricoid cartilage (A) is a complete ring of cartilage located just below the thyroid cartilage. The epiglottis (B) is a leaf-shaped cartilage that helps prevent food and liquid from entering the airway during swallowing. The thyroid cartilage (C) is the largest laryngeal cartilage but not the largest overall.