Correct Answers:

Explanation: The presence of cartilaginous rings is a defining characteristic of the trachea. Bronchi have a continuous epithelial lining, but lack the prominent cartilaginous rings. Bronchioles have less cartilage and thinner epithelium than bronchi. Alveoli are the key structures for gas exchange and are easily identifiable as thin-walled sacs. The pseudostratified columnar epithelium with cilia and goblet cells is characteristic of the respiratory tract lining, aiding in mucus clearance.

The gas exchange system relies on maintaining a clean and moist surface area for efficient gas exchange. Ciliated epithelial cells, goblet cells, and mucous glands all play crucial roles in this process.

Ciliated Epithelial Cells: These cells line the bronchi and bronchioles of the lungs. Their primary function is to transport mucus, containing trapped dust, pathogens, and other debris, upwards towards the pharynx to be swallowed or coughed out.

• Structure: Ciliated cells have numerous tiny hair-like structures called cilia projecting from their apical surface. These cilia beat rhythmically in a coordinated fashion.
• Function: The coordinated beating of the cilia propels the mucus layer upwards, effectively clearing the airways of contaminants. This prevents infection and maintains the integrity of the gas exchange surface.

Goblet Cells: Goblet cells are specialized epithelial cells found throughout the respiratory tract, particularly in the lining of the bronchi and bronchioles. They are responsible for secreting mucus.

• Structure: Goblet cells are modified epithelial cells that store and release mucus.
• Function: The mucus produced by goblet cells traps inhaled particles, including dust, pollen, bacteria, and viruses. This acts as a physical barrier, preventing these substances from reaching the alveoli. The mucus also helps to keep the respiratory surface moist, preventing the delicate alveolar lining from drying out.

Mucous Glands: These glands are distributed throughout the respiratory tract and secrete mucus. They contribute significantly to the overall mucus production in the airways.

• Structure: Mucous glands are specialized secretory cells that produce and release mucus. They can be submucosal glands (located beneath the epithelium) or embedded within the epithelium.
• Function: Mucous glands provide a continuous supply of mucus to the respiratory lining. This mucus, secreted by goblet cells and mucous glands, traps inhaled particles and pathogens, contributing to the defense mechanism of the respiratory system. The mucus is then moved upwards by the action of cilia.

In summary, these three cell types work together to maintain a healthy respiratory system by trapping and removing foreign particles and pathogens, and by maintaining a moist surface for efficient gas exchange. Damage to any of these cell types can impair the respiratory system's ability to defend itself.

Surfactant is a lipoprotein substance produced by Type II pneumocytes within the alveoli. Its primary role is to reduce the surface tension of the fluid lining the alveoli. Surface tension is the force that causes the alveoli to collapse, particularly at the end of exhalation.

Importance of Surfactant: Without surfactant, the alveoli would tend to collapse during exhalation, significantly reducing the surface area available for gas exchange. This collapse would impair the efficiency of gas exchange, making it difficult to obtain sufficient oxygen and remove carbon dioxide. Surfactant reduces surface tension by inserting itself between the water molecules in the alveoli, disrupting the cohesive forces that cause them to attract each other. This allows the alveoli to remain open and inflated, maintaining a large surface area for gas exchange.

Consequences of Surfactant Deficiency: Neonatal Respiratory Distress Syndrome (NRDS), also known as hyaline membrane disease, is a condition that occurs in premature infants due to a deficiency of surfactant. In infants with NRDS, the alveoli collapse during exhalation, leading to:

• Increased Respiratory Effort: The infant has to work harder to breathe to keep the alveoli open.
• Reduced Oxygen Uptake: The reduced surface area for gas exchange leads to inadequate oxygen uptake.
• Increased Carbon Dioxide Retention: Inefficient carbon dioxide removal leads to a buildup of carbon dioxide in the blood.
• Potential Lung Damage: Prolonged respiratory distress can damage the lungs.

Treatment for NRDS typically involves administering artificial surfactant to help keep the alveoli open.