Why is gas transport essential in the respiratory cycle?

A. Producing digestive enzymes: The nasal cavity does not have any role in enzyme secretion for digestion. Digestive enzymes are produced primarily by the salivary glands, stomach, pancreas, and small intestine to facilitate chemical breakdown of food. The nose is part of the respiratory and olfactory systems, not the gastrointestinal system.

B. Housing olfactory receptors: The superior portion of the nasal cavity contains the olfactory epithelium, which houses specialized chemoreceptors responsible for the sense of smell. These receptors transmit impulses via the olfactory nerve (cranial nerve I) to the olfactory bulb and cortex, enabling odor detection and discrimination.

C. Filtering and cleaning air: The nasal cavity plays a critical role in air filtration through vibrissae (nasal hairs), mucus secretion, and ciliated epithelium. These mechanisms trap particulate matter, pathogens, and debris, while coordinated ciliary movement propels contaminants toward the pharynx for elimination.

D. Resonating speech sounds: The nasal cavity contributes to speech by serving as a resonating chamber that modifies sound produced by the larynx. Proper nasal resonance is essential for phonation of certain consonants and overall voice quality; obstruction can result in hyponasal or hypernasal speech patterns.

A. Prostaglandins: Prostaglandins are lipid mediators released during inflammation that contribute to vasodilation, pain, and fever. While they play a role in inflammatory responses in the airways, they are not the primary mediator responsible for acute bronchoconstriction during an allergic reaction.

B. Histamine: Histamine is the central mediator released from mast cells during an allergic reaction. It binds to H₁ receptors in the respiratory tract, causing bronchoconstriction, increased vascular permeability, and mucus production, all of which contribute directly to airway obstruction and the clinical manifestations of allergic asthma.

C. Eicosanoid: Eicosanoids, such as leukotrienes and prostaglandins, are involved in the later stages of inflammation and contribute to sustained bronchoconstriction and edema. However, they are secondary mediators compared to histamine in the immediate airway response.

D. Bradykinin: Bradykinin is a peptide that promotes vasodilation, increased vascular permeability, and pain. It plays a minor role in airway inflammation but is not the central mediator responsible for acute airway obstruction in allergic reactions.

E. Omega-3: Omega-3 fatty acids are dietary components with anti-inflammatory properties. They do not function as mediators in allergic responses or cause airway obstruction, and their presence does not trigger mast cell–mediated bronchoconstriction.