Mechanics of Breathing Flashcards
Q: What is atmospheric pressure?
A: Atmospheric pressure is the pressure exerted by the weight of the air in the atmosphere of Earth. At sea level, it is typically measured as 760 mmHg. This pressure acts as the baseline or reference point for the other pressures involved in respiration.
the air around us (carbon + nitrogen)
Q: What is intra-alveolar pressure?
in alveoli
Intra-alveolar pressure, also known as intrapulmonary pressure, is the pressure within the alveoli of the lungs. This pressure changes during the breathing cycle:
(70 mm Hg, also more than intrapleural pressure)
During inspiration, intra-alveolar pressure decreases below atmospheric pressure, allowing air to flow into the lungs.
During expiration, intra-alveolar pressure increases above atmospheric pressure, causing air to flow out of the lungs.
Q: What is intrapleural pressure?
A: Intrapleural pressure is the pressure within the pleural cavity, the thin fluid-filled space between the two layers of the pleura (the membrane lining the lungs and chest cavity). This pressure is always slightly less than the intra-alveolar pressure and atmospheric pressure:
(if intraalveolar is 760 mm Hg, intrapleural is 756 mm Hg)
if it was higher, it will exert pressure on lungs and cause lungs to collapse
During inspiration, intrapleural pressure becomes more negative, helping to expand the lungs.
During expiration, intrapleural pressure becomes less negative but remains negative, maintaining lung expansion and preventing lung collapse.
Q: What is the main mechanism by which air flows in and out of the lungs?
A: Air tends to move from an area of high pressure to lower pressure, driven by alternating reversing pressure gradients between the alveoli and the atmosphere created by breathing.
Q: What are the three important pressures involved in breathing?
A:
Atmospheric pressure
Intra-alveolar pressure
Intrapleural pressure
Q: How do the lungs stay in close opposition to the thoracic cavity, which is larger than the lungs?
A: The lungs are held in close opposition to the thoracic cavity by a transmural pressure gradient.
lungs attached to thoracid wall due to attraction og H2O water molecules within pleural cavity
==> H-H bond attaches outer membrane of pleural cavity to our ribcay
Q: What is the transmural pressure gradient?
transmural gradient. = intra alveolar pressure - intrapleural pressure (e.g. 760 mmHg - 756 mmHg = 4 mmHg)
A: The transmural pressure gradient is the difference between the intra-alveolar pressure (pressure within the alveoli) and the intrapleural pressure (pressure within the pleural cavity). The gradient is always positive because the intra-alveolar pressure is higher than the intrapleural pressure. This positive gradient keeps the lungs inflated and adheres to the inner wall of the thoracic cavity
Q: What happens during muscle contraction in inspiration?
A:
inhalation
–> contraction of external intercostal muscle
–> relaxation of internal intercostal muscle
–> pulls sternum upwards + outwards
–> more space so diaphragm flattens, moves downwards
= increasing the volume of the thorax, which decreases intra-alveolar pressure, allowing air to flow into the lungs (high to low
Q: Describe the process of inspiration.
A: During inspiration, the intra-alveolar pressure must be less than atmospheric pressure.
high to low pressure, from the air to when it enters the lungs.
This is achieved by increasing the volume within the lungs, following Boyle’s law
volume increase, pressure decrease
Q: How does muscle contraction during expiration affect pressures?
.
A: During expiration, the external intercostal muscles relax, relaxation of the diaphragm, contraction of internal intercostal muscles, ==> this flattens the ribs and sternum
decreasing the thoracic volume
increasing intra-alveolar pressure, which pushes air out of the lungs
the contraction of abdominal muscles causes diaphragm to be pushed upward, further reducing the thoracic cavity
pressure changes during inspiration/ expiration
a) before inspiration :
- 760 mm Hg in air
- 760 mm Hg in intra alveolar pressure
- 756 mm Hg intrapleural pressure
b) during inspiration
- 760 mm Hg in air
- 759 mm Hg in intra alveolar pressure
- 754 mm Hg intrapleural pressure
entire thoracic cavity expands,due to contraction of inspiratory muscles and lungs stretched to fill the expanded thorax
=volume increase, pressure decreases
c) during expiration
- 760 mm Hg in air
- 761 mm Hg in intra alveolar pressure
- 756 mm Hg intrapleural pressure
entire thoracic cavity shrinks, due to relaxation of inspiratory muscles and lungs recoil
Q: What role does the autonomic nervous system play in airway resistance?
A: The autonomic nervous system regulates airway resistance, with parasympathetic innervation causing bronchoconstriction and sympathetic innervation causing bronchodilation.
sympathetic : fight/flight; need O2 to run away
narrow diameter= increase resistance vice versa (vv)
normal bronchiole : no cartilage, only smooth muscles
asthma bronchiole : more mucus, small diameter, less airflow
Q: What are the three key factors that contribute to the physiological properties of the lungs?
A:
Compliance: The ability of the lungs to stretch.
Elastic recoil: The ability of the lungs to return to their original shape/ elastic tissue in lung
Surface tension: The force exerted by water molecules lining the alveoli.
Alveolar surface tension
The alveoli are lined by water molecules
- O2 must dissolve in water before it can move across the respiratory membrane
- Too much water increases surface tension and increases diffusion distance (thick layer of h2O)
- Tendency for lungs to collapse
- Impaired gas exchange
- cells secrete pulmonary surfactant modulates surface tension :: Counteract this by producing pulmonary surfactant
A: Pulmonary surfactant, produced by type II alveolar cells, reduces surface tension at the air-water interface in the alveoli, preventing lung collapse and aiding in gas exchange.
how does pulmonary surfactant
- Lipoprotein produced by type II alveolar cells
- Reduces surface tension at air-water interface
- Immunoprotective actions
- H2O will join and form water molecules =. collapse lungs
pulmonary surfactant :
- lipoprotein makes it spread out
thin layer around the entire thing
thinner layer allows gas exchange to occur
