Hiccup is due to

Correct Answer: B

Rationale: The correct answer is B because hiccups are caused by the irritation of the phrenic nerve, which controls the diaphragm muscle responsible for breathing. When the nerve is irritated, it causes the diaphragm to contract involuntarily, leading to the characteristic sound of hiccups. Choice A (Increased inspiration) is incorrect as hiccups are not caused by increased inspiration but rather by involuntary contractions of the diaphragm. Choice C (Expanded stomach) is incorrect as hiccups are not directly related to the size of the stomach but rather to nerve irritation. Choice D (Acidity in the stomach) is incorrect as hiccups are not primarily caused by stomach acidity, but by nerve irritation leading to diaphragm contractions.

Correct Answer: A

Rationale: The correct answer is A because even though the patient has normal hemoglobin levels, the significantly decreased SaO2 and PaO2 levels indicate that the hemoglobin is not effectively carrying oxygen to the tissues. This leads to a situation where the tissue demands for oxygen may be met at baseline, but the patient will be unable to respond to physiological stressors that require increased oxygen delivery. Choice B is incorrect because it focuses on short-term oxygen needs and CO2 expulsion, which are not directly related to the implications of the oxyhemoglobin dissociation curve in this case. Choice C is incorrect because decreased SaO2 and PaO2 levels would lead to tissue hypoxia, which would likely result in sensations of shortness of breath or labored breathing as the body tries to compensate for the lack of oxygen. Choice D is incorrect because decreased PaO2 levels would not lead to respiratory alkalosis. The body would likely try to compensate by increasing respiratory rate to improve oxygenation.

Correct Answer: D

Rationale: The correct answer is D: anatomic dead space. Anatomic dead space refers to the air in the conducting passages (such as trachea, bronchi) that does not reach the alveoli for gas exchange. This space only serves as a pathway for air to move in and out of the lungs. Vital capacity (A) is the maximum amount of air that can be exhaled after a maximum inhalation. Minimal volume (B) is not a recognized term in respiratory physiology. Residual volume (C) is the amount of air left in the lungs after a maximal exhalation and is not specifically related to the air in conducting passages.

Correct Answer: A

Rationale: The correct answer is A, during external respiration. Oxyhemoglobin forms when oxygen binds to hemoglobin in the lungs during external respiration. This process occurs in the alveoli where oxygen diffuses from the air sacs into the blood, binding with hemoglobin to form oxyhemoglobin. Choices B, C, and D are incorrect because oxyhemoglobin formation specifically happens during external respiration, not immediately after carbon dioxide enters the blood, when the chloride shift occurs, or during pulmonary ventilation. These processes are important in respiration but do not directly involve the formation of oxyhemoglobin.

Correct Answer: B

Rationale: The correct answer is B: the precentral motor gyrus. This area is primarily responsible for voluntary motor control, not for altering the activity of respiratory centers. Cortical association areas (A), the limbic system (C), and the hypothalamus (D) can influence respiratory centers through emotional responses, autonomic control, and regulation of breathing patterns, respectively. The precentral motor gyrus is not directly involved in modifying respiratory activity.