Questions: 2. Differentiate between negative pressure and positive pressure and what happens in inhalation and exhalation of the lungs.

Negative pressure and positive pressure are terms used to describe the pressure differences relative to atmospheric pressure, particularly in the context of respiratory physiology.

Negative Pressure:

• Negative pressure occurs when the pressure inside a space is lower than the atmospheric pressure outside. In the context of the lungs, negative pressure is crucial for inhalation.
• During inhalation, the diaphragm contracts and moves downward, and the intercostal muscles contract to expand the chest cavity. This expansion increases the volume of the thoracic cavity, leading to a decrease in intrapleural pressure (the pressure within the pleural cavity surrounding the lungs). As a result, the pressure inside the lungs becomes lower than the atmospheric pressure, creating a negative pressure gradient. This causes air to flow into the lungs to equalize the pressure.

Positive Pressure:

• Positive pressure occurs when the pressure inside a space is higher than the atmospheric pressure outside. In the context of the lungs, positive pressure is involved in exhalation.
• During exhalation, the diaphragm relaxes and moves upward, and the intercostal muscles relax, causing the chest cavity to decrease in volume. This reduction in volume increases the intrapleural pressure, making it higher than the atmospheric pressure. Consequently, the pressure inside the lungs becomes greater than the atmospheric pressure, creating a positive pressure gradient. This causes air to flow out of the lungs to equalize the pressure.

Summary:

• Inhalation involves creating negative pressure in the lungs by expanding the thoracic cavity, allowing air to flow in.
• Exhalation involves creating positive pressure in the lungs by reducing the thoracic cavity's volume, pushing air out.