The iron-containing protein that carries oxygen in the blood is:

A. A pneumothorax occurs when there is a collapse of the lung due to air entering the pleural cavity, but this is not directly related to the lungs dropping below atmospheric pressure.
B. Air flows out of the lungs when the pressure inside the lungs is higher than atmospheric pressure (e.g., during exhalation).
C. When the pressure in the lungs drops below atmospheric pressure, it creates a vacuum effect, causing air to flow into the lungs during inhalation. This is how normal breathing works.
D. Bronchiolar constriction can cause respiratory distress, but it is not directly linked to a drop in lung pressure. Instead, constriction happens due to factors like asthma or allergies, not pressure changes.

A. The hilum is the region on the medial side of the lung where the bronchus, blood vessels, and nerves enter and exit the lung.
B. The epiglottis is a flap of tissue that covers the trachea during swallowing to prevent food from entering the airways, but it is not related to the entry of structures into the lung.
C. The nares are the nostrils through which air enters the respiratory system, not the area where the bronchus and vessels enter the lung.
D. The conchae (also known as turbinates) are structures inside the nasal cavity that help warm and humidify air, not related to the lung’s entry point.