Question

1. Describe the different functions of the conducting zone and respiratory zone and relate those to differences in their histology.

2. State whether hyperventilation and emphysema would raise or lower each of the following—the blood Po2, Pco2, and pH—and explain why.

Answer 1

Question 1:

Functions of conducting zone and respiratory zone:

• Conducting portion of respiration is made of nasal cavities, nasopharynx, larynx, trachea, bronchi and bronchioles
• Bronchioles further branch to terminal bronchioles and further to respiratory bronchioles which leads to alveoli.
• Respiratory portion is made of respiratory bronchioles. Alveolar ducts, alveolar sacs and alveoli.

Conducting zone:

Trachea

• Trachea has smooth muscles, hyaline cartilage and fibroelastic tissue. They allow flexibility during inspiration and expiration.
• Respiratory mucosa and sub mucosa is used to moisten the air and trap particles in the air.
• Respiratory mucosa is made of epithelium and supporting lamina propria.
• Epithelium is columnar pseudostratified with cilia and goblet cells.
• Lamina propria contains elastin which has significant role in inspiration and expiration.
• Sub mucosa has mucous glands. These mucous glands humidify the inhaled air. Traps the dust particles in air and transfers it outside to keeps the lungs clean.

Bronchi:

Trachea branches to bronchi. It has less cartilage and smooth muscles.

Bronchioles:

• Bronchioles are 1mm diameter and are made of ciliated columnar cells, non ciliated in smaller bronchioles. Goblet cells are absent. Secretary clara cells are present.
• Terminal bronchioles are lined by smooth muscles.

Respiratory zone:

• The respiratory bronchioles lead into alveolar ducts, which lead into the alveolar sacs. These have several alveoli, surrounded by blood vessels - from the pulmonary system.
• Respiratory zone consist of branching air spaces with pulmonary capillaries. The air spaces are within 0.2 µm of blood, thus causes efficient way to exchange of oxygen through diffusion.

Alveoli:

Alveoli has 2 types of cells type I pneumocytes and type II pneumocytes.

• Type I pneumocytes has large flattened cells for diffusion of gases. They are connected to each other by tight junctions.
• Type II pneumocytes these cells secrete surfactant that reduce surface tension of the thin alveolar walls.

Question 2:

State whether hyperventilation and emphysema would raise or lower each of the following – the blood Po2, Pco2, and pH, explain why?

PO2 and PCO2 are the partial pressure of oxygen and carbon dioxide.

Hyperventilation

• Raise blood PO2 slightly because hemoglobin is already 97% saturated in normal breathing.
• PCO2 will decrease significantly since the body expels its faster than the body generates it.
• This will increase pH and lead to alkalosis – alkaline condition of the body tissue and fluids

Emphysema

• Emphysema causes shortness of breath, due to over-inflation of the alveoli.
• Less surface area is available for gas exchange, thus decreasing PO2 in blood.
• PCO2 rise because it is not properly expelled out.
• This lowers pH, producing acidosis – acidic condition of the body tissue and fluids.