Respiratory System: Structure, Function, and Physiology (Module Quiz Study Notes)

Respiratory System: Structure, Function, and Physiology

Main Functions of the Respiratory System

The respiratory system is essential for gas exchange and maintaining homeostasis in the body. It consists of various anatomical structures that work together to ensure efficient oxygen intake and carbon dioxide removal.

• Gas Exchange: The primary function is the exchange of oxygen and carbon dioxide between the air and the bloodstream. Oxygen is absorbed into the blood, and carbon dioxide is expelled from the body.

• Regulation of Blood pH: By controlling the levels of carbon dioxide in the blood, the respiratory system helps maintain the acid-base balance (pH) of body fluids.

• Protection and Filtration: The respiratory tract filters out dust, pathogens, and other particles from inhaled air, protecting the body from infection and irritation.

Anatomical Names for Marked Parts:

• Part A: Trachea (windpipe) – the main airway conducting air to the lungs.

• Part B: Lung – the primary organ for gas exchange, containing alveoli where oxygen and carbon dioxide are exchanged.

Mechanism of Inspiration (Inhalation) and Boyle's Law

Inspiration is the process of drawing air into the lungs. It involves coordinated muscular and pressure changes, explained by Boyle's Law.

• Muscular Action: The diaphragm contracts and moves downward, while the intercostal muscles contract to lift the rib cage upward and outward.

• Volume and Pressure Changes: As the thoracic cavity volume increases, the pressure inside the lungs (intrapulmonary pressure) decreases below atmospheric pressure.

• Boyle's Law: This law states that at a constant temperature, the pressure of a gas is inversely proportional to its volume:

$P_1V_1 = P_2V_2$

• As lung volume increases during inspiration, pressure decreases, causing air to flow into the lungs.

Example: When you inhale, the diaphragm flattens, increasing thoracic volume and decreasing pressure, so air rushes in.

Pulmonary Ventilation Rate (Minute Volume)

Pulmonary ventilation rate, or minute volume, is the total volume of air entering (or leaving) the lungs per minute. It is calculated by multiplying the tidal volume (the amount of air inhaled or exhaled in a single breath) by the respiratory rate (number of breaths per minute).

• Formula:

$\text{Minute Volume} = \text{Tidal Volume} \times \text{Respiratory Rate}$

• Given: Tidal Volume = 400 mL (0.4 L), Respiratory Rate = 12 breaths/min

• Calculation:

$\text{Minute Volume} = 0.4\,L \times 12\,\text{breaths/min} = 4.8\,L/\text{min}$

Example: Mrs Tee's pulmonary ventilation rate is 4.8 litres per minute.

Respiratory Volumes and Graph Interpretation

Respiratory volumes are measured to assess lung function. The graph provided typically shows the following:

• Tidal Volume (TV): The volume of air inhaled or exhaled in a normal breath (labelled on the graph, often as the height of the regular wave).

• Inspiratory Reserve Volume (IRV): The additional air that can be inhaled after a normal inspiration.

• Expiratory Reserve Volume (ERV): The additional air that can be exhaled after a normal expiration.

• Residual Volume (RV): The air remaining in the lungs after maximal exhalation.

Label	Volume Name	Description
A	Inspiratory Reserve Volume (IRV)	Maximum volume of air that can be inhaled after a normal inspiration
B	Tidal Volume (TV)	Volume of air inhaled or exhaled in a normal breath
C	Expiratory Reserve Volume (ERV)	Maximum volume of air that can be exhaled after a normal expiration
D	Residual Volume (RV)	Volume of air remaining in the lungs after maximal exhalation
E	Functional Residual Capacity (FRC)	Volume of air remaining in the lungs after a normal expiration

Additional info: The exact labels may vary depending on the graph, but these are standard respiratory volumes assessed in pulmonary function tests.