Respiratory System

Question 1

Breathing

Answer 1

• Inhalation is an active process requiring energy expenditure.
• Negative-Pressure Breathing: The diaphragm flattens and the external intercostal muscles contract to increase Intrathoracic Volume. This causes the Intrapleural Volume to increase first, which leads to a decrease in Intrapleural Pressure (according to Boyle’s Law; P₁V₁ = P₂V₂). Since the gas in the lungs at atmospheric pressure is now higher than the pressure in the intrapleural space, the lungs expand into the intrapleural space, and the pressure in the lungs drops, forcing air into the lower-pressure lungs from the higher-pressure outside environment.
• Expiration is not an active process during calm states and occurs entirely due to the elastic recoil of the lungs and the musculature. During more active states, the internal intercostal muscles and abdominal muscles can be used to force air out in speed up the process of ventilation.
• Ventilation is primarily regulated by the Ventilation Center in the medulla oblongata to cause regular contraction of respiratory muscles. These neurons contain chemoreceptors that are primarily sensitive to carbon dioxide concentration. Respiratory rate increases in response to Hypercapnia (high partial pressure of carbon dioxide) to exhale more carbon dioxide.

Question 2

Gas Exchange

Answer 2

• When blood arrives at the alveoli, it has a relatively low partial pressure of oxygen and a relatively high partial pressure of carbon dioxide, facilitating transfer of each down its respective concentration gradient; thus, no energy is required for gas exchange.

Question 3

Control of pH

Answer 3

• The lungs control the pH of blood by adjusting carbon dioxide levels.
• Acidemia (low blood pH or high H⁺ concentration) shifts the bicarbonate buffer system to the left, increasing the CO₂ concentration. Acid-sending chemoreceptors (responding to acidemia) and ventilation center chemoreceptors (responding to hypercapnia) cause increase in respiratory rate to blow off CO₂, which helps shift the bicarbonate buffer system to the left to decrease H⁺ concentration.
• If the blood is too basic (Alkalemia), the body will seek to increase acidity by slowing down the respiratory rate so that more CO₂ can be retained, which shift the bicarbonate buffer system to the right to produce more hydrogen ions and bicarbonate ions.
• Hyperventilation blows off a lot of carbon dioxide, reducing its concentration in the blood and shifting the bicarbonate buffer system to the left. This decreases the concentration of hydrogen ions in the blood, resulting in Respiratory Alkalosis (elevated blood pH).
• Hypoventilation retains a lot of carbon dioxide, raising its concentration in the blood and shifting the bicarbonate buffer system to the right. This increases the concentration of hydrogen ions in the blood, resulting in Respiratory Acidosis (low blood pH).