Question

Pressure between the inside chest wall and the outside of the lungs normally remains negative. Explain how pressure inside the lungs can become positive (to cause exhalation) without muscle action.

Short answer

The pressure can be positive because of alveoli surface tension.

Step-by-step solution

Conceptual Introduction

Fluid statics, often known as hydrostatics, is a branch of fluid mechanics that investigates the state of balance of floating and submerged body, as well as the pressure in a fluid, or imposed by a fluid, on an immersed body.

Breathing process in humans

With each breath, the pressure inside the lungs rises and falls. When you inhale, the pressure drops below atmospheric pressure (negative gauge pressure), allowing air to enter into the lungs. When you exhale, the pressure rises above atmospheric pressure(positive gauge pressure), forcing air out.

Lung pressure is regulated by a number of ways. Inhalation requires muscular movement in the diaphragm and rib cage; this muscle action increases the capacity of the lungs, lowering the pressure within them.

When pressure becomes positive/negative

A positive pressure opposes inhalationdue to surface tension in the alveoli.

By allowing surface tension in the alveoli to produce its own positive pressure, you may exhale without using your muscles. When you blow up a balloon, blow out a candle, or cough, muscle activity can contribute to the positive pressure and cause forced exhalation.

If the lungs were not linked to the interior of the chest wall via liquid adhesion, they would collapse owing to surface tension in the alveoli.

During exhale and inhalation, the gauge pressure in the fluids connecting the lungs to the interior of the chest wall is therefore negative, ranging from 4 to 8 mm Hg.If air is let into the chest cavity, the bond between the lungs is broken, and one or both lungs may collapse.To re-establish negative pressure and inflate the lungs, suction is delivered to the chest cavity of surgical patients and trauma victims.

The lungs of a person are pliable by nature. The fluid (carbon dioxide) is exhaled out of the chest during the exhalation process. As a result, the lungs' volume shrinks.

If one exhales, surface tension in the alveoli provides its own positive pressure, the pressure within the lungs can become positive without the need of muscles. The pressure within the lungs can be raised by this motion.

Therefore, the pressure is said to be positive due to the alveoli surface tension