The serous membrane covering the surface of the lungs is called the:

 # The serous membrane covering the surface of the lungs is called the:

 A. Parietal pleura

 B. Mediastinum

 C. Visceral pleura

 D. Pericardium

The correct answer is C. Visceral pleura.

The visceral pleura is the serous membrane that directly covers the surface of the lungs, adhering closely to the lung tissue. The parietal pleura (A) lines the chest wall and diaphragm, not the lung surface. The mediastinum (B) is the central compartment of the thoracic cavity, not a membrane. The pericardium (D) is the membrane surrounding the heart, not the lungs.

The respiratory center in the brain is stimulated primarily by:

 # The respiratory center in the brain is stimulated primarily by:

A. High concentration of carbon dioxide in the blood

B. High concentration of oxygen in the blood

C. Low concentration of oxygen in the blood

D. Low concentration of carbon dioxide in the blood

The correct answer is A. High concentration of carbon dioxide in the blood.

The respiratory center in the brain, located in the medulla oblongata and pons, is primarily stimulated by elevated levels of carbon dioxide (CO₂) in the blood. This is detected through changes in blood pH (caused by CO₂ forming carbonic acid), which triggers the respiratory center to increase breathing rate and depth to expel excess CO₂ and restore pH balance. While low oxygen levels (C) can also stimulate breathing, this is a secondary mechanism primarily mediated by peripheral chemoreceptors, not the primary driver. High oxygen (B) or low CO₂ (D) typically do not stimulate the respiratory center.

Which of the following would cause the oxy-hemoglobin dissociation curve to shift to the right?

  # Which of the following would cause the oxy-hemoglobin dissociation curve to shift to the right?

 A. Decreased pCO2

B. Increased pH

C. Increased levels of 2,3-DPG

D. Decreased body temperature

The correct answer is C. Increased levels of 2,3-DPG.

The oxy-hemoglobin dissociation curve represents the relationship between the partial pressure of oxygen (pO₂) and hemoglobin's oxygen saturation. A right shift in the curve indicates a decreased affinity of hemoglobin for oxygen, meaning oxygen is more readily released to tissues.

• C. Increased levels of 2,3-DPG (2,3-diphosphoglycerate): Increased 2,3-DPG levels, often seen in conditions like hypoxia or high altitude, reduce hemoglobin's affinity for oxygen, promoting oxygen release to tissues. This causes a right shift in the curve.

Other options:

• A. Decreased pCO₂: This would shift the curve to the left (Bohr effect), as lower carbon dioxide levels increase hemoglobin's oxygen affinity.
• B. Increased pH: Higher pH (more alkaline conditions) also shifts the curve to the left, increasing oxygen affinity.
• D. Decreased body temperature: Lower temperatures shift the curve to the left, as hemoglobin holds onto oxygen more tightly.