mechanics of breathing Flashcards
What is the basic principle behind the mechanics of breathing?
Breathing, or pulmonary ventilation, is a mechanical process that depends on volume changes in the thoracic cavity. Volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure.Volume is the space the lungs take up.
Pressure is the force exerted by the air molecules inside the lungs.
They are related in that a change in volume causes a change in pressure, which drives the flow of air (gases) into and out of the lungs.
Volume change causes pressure change.
Increased volume = decreased pressure.
Decreased volume = increased pressure.
analogy for mechanics of breathing
Small room = low volume. The furniture is packed tightly together, which is similar to high pressure in the lungs (air molecules are compressed and close together).
Bigger room = higher volume. The furniture now has more space and isn’t as tightly packed, which is similar to low pressure in the lungs (air molecules are spread out).
How This Relates to Breathing:
When the volume of the thoracic cavity increases (like making the room bigger), the pressure decreases (because the air molecules have more space to spread out, just like the furniture in the room).
When the volume decreases (like making the room smaller), the pressure increases (because the air molecules are more compressed, just like the furniture being packed closer together).
So, in your analogy, the room expanding is like the lungs expanding during inhalation, and when the room gets smaller, it’s like the lungs shrinking during exhalation, which increases the pressure inside.
I hope that makes sense! Let me know if you need more clarification.
How does the volume of a container affect the pressure of a gas?
: According to Boyle’s Law, when the volume of a container increases, the pressure of the gas decreases because the molecules are spread farther apart and collide less often. Conversely, when the volume decreases, the pressure increases because the molecules are closer together and collide more frequently.
how volume changes relate to the two phases of breathing
— inspiration, when air is flowing into the lungs, and expiration, when air is leaving the lungs
Inspiration
When the inspiratory muscles, the diaphragm and external intercostals, contract, the size (volume) of the thoracic cavity increases. As the dome-shaped diaphragm contracts inferiorly, the superior-inferior dimension (height) of the thoracic cavity increases (Figure 13.7a). Contraction of the external intercostals lifts the rib cage and thrusts the sternum forward, which increases the anteroposterior and lateral dimensions of the thorax. The lungs adhere tightly to the thorax walls (because of the surface tension of the fluid between the pleural membranes), so they are stretched to the new, larger size of the thorax. As intrapulmonary volume (the volume within the lungs) increases, the gases within the lungs spread out to fill the larger space. The resulting decrease in gas pressure in the lungs produces a partial vacuum (pressure in the lungs is less than atmospheric pressure outside the body), which causes air to flow into the lungs (down the pressure gradient). Air continues to move into the lungs until the intrapulmonary pressure equals atmospheric pressure (Figure 13.8a). This series of events is called inspiration (inhalation).
Expiration
Expiration (exhalation) in healthy people is largely a passive process that depends more on the natural elasticity of the lungs than on muscle contraction. As the inspiratory muscles relax and resume their initial resting length, the rib cage descends, the diaphragm relaxes superiorly, and the lungs recoil (Figure 13.7b). Thus, both the thoracic and intrapulmonary volumes decrease. As the intrapulmonary volume decreases, the gases inside the lungs are forced more closely together, and the intrapulmonary pressure rises to a point higher than atmospheric pressure (see Figure 13.8a). This causes the gases to passively flow out to equalize the pressure with the outside.
What happens during forced expiration in conditions like asthma, chronic bronchitis, or pneumonia?
In forced expiration, the internal intercostal muscles contract to depress the rib cage, and the abdominal muscles contract to force air out of the lungs by pushing the abdominal organs upward against the diaphragm. This becomes necessary when the respiratory passages are narrowed or clogged, making normal expiration harder.
What happens if the intrapleural pressure becomes equal to atmospheric pressure?
Normally, the intrapleural pressure is negative (lower than the pressure inside the lungs), which prevents the lungs from collapsing. If the intrapleural pressure becomes equal to atmospheric pressure, the lungs will recoil and collapse, as the pressure difference is lost, and the lungs cannot stay inflated.
What happens during atelectasis (lung collapse) and how does pneumothorax play a role?
: Atelectasis occurs when the lung collapses and becomes useless for ventilation. This happens if air enters the pleural space (e.g., through a chest wound or rupture of the visceral pleura), causing pneumothorax. The air in the intrapleural space disrupts the fluid bond between the pleurae, causing the lung to collapse.Pneumothorax is reversed by drawing air out of the intrapleural space with a chest tube, which allows the lung to reinflate and resume its normal function.
