Week 9 Flashcards
Conducting Zone
Anatomical Dead Space
- No gas exchange
- Reinforced with cartilage
- Smooth Muscle regulates diameter
Respiratory Zone
- Gas Exchange
- little cartilage or smooth muscle
Regions in the conducting zone
Larynx, Trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles and terminal bronchioles
Regions in the respiratory zone
Respiratory bronchioles, alveolar sacs
tidal volume
Volume of single breath
Vital Capacity
Limit for inhalation/exhalation
Residual Volume
Conducting zone (about 150 mL) plus minimum volume in alveoli (1L)
Total lung capacity
Vital Capacity + residual volume
Functional Residual Capacity
Volume of conducting zone and alveoli after normal exhalation
How is the fresh air that enters the lungs with each breath determined
tidal volume - dead space volume = about 350 mL at rest
How does functional residual capacity impact the PO2 and PCO2 relative to the outside air
- FRC (about 2000mL at rest) is old air that already underwent gas exchange
- only small fraction of alveolar air is being replaced with each breath because FRC»_space; Vt-Vd
- Causes lower O2 pressure and higher CO2 pressure compared to outside
Calculating total ventillation
Total volume of air flow into the lungs and airways per minute
= tidal volume x breathing frequency
In humans, about 6L/min = 500 mL x 12 / minutes
Calculating Alveolar Ventilation
Total air flow into the alveoli per minute (anatomical dead space doesn’t participate in gas exchange)
= (Vt-Vd) x fR
In humans, 4.2 L/min = (500mL-150mL) x 12/min
How does alveolar ventilation determine gas exchange
- Determines alveolar partial pressures, and thus diffusion rates
- Increasing AV increases the rate at which fresh air enters the FRC in alveoli
Does tidal volume or breathing frequency lead to a greater improvement in gas exchange
Increasing tidal volume produces a greater increase in gas exchange
What muscles are involved in breathing
Diaphragm, intercostal and abdominal muscles
What muscles are involved in inspiration
- Diaphragm contracts, expanding the thoracic cavity downwards
- External intercostal rotate ribs outward and upward
What muscles are involved in expiration
- Passive respiration relies on recoil force
- Active expiration involves the internal intercostals contracting, rotating the ribs in and downward, abdominals push organs against diaphragm to compress thoracic cavity upward
Pleural sac
- Pleural membranes encase the lungs and lines the inside of the thoracic cavity
- The intrapleural space is fully enclosed and fluid filled, creating a flexible lubricated connection between the lungs and chest wall, held together by negative pressure
- connection between thorax and lungs ensuring lungs follow size changes
What creates the negative force in the intrapleural space
the opposing elastic recoil forces of the lungs and the chest walls
Def: elasticity
The tendency of a structure to resume its normal shape after being stretched
Why are there opposing recoil forces between the chest wall and lungs
- Pleura holds structures together
- The lungs are larger than they would normally be
- Chest wall is smaller than normal
- causes recoil forces proportional to the magnitude of stretch applied to these structures
- Fluid in intrapleural space prevents recoiling (hard to compress/expand)
Pneumothroax
Conditions in which air accumulates within the intrapleural space
how will pneumothorax affect intrapleural pressure, lung volume, ventilation and the chest wall?
- Intrapleural pressure = 0 relative to atmosphere
- Decrease in lung volume
- Increase in chest wall
- Intrapleural space increase in size
- Ventilation would stop - no mechanism to increase lung volume
When does inhalation stop based on force vectors
- Force of muscle causes expansion
- As expansion occurs, force of lung recoil increases and force of chest recoil decreases
- When the force of muscle + the chest recoil force = lung recoil force, inhalation will stop
Transpulmonary pressure
The transpulmonary pressure difference (Palv- Pip) is the force that expands the lungs above its resting volume, opposing the recoil force
What pressures drive airflow in/out of the lungs
The pressure difference between the atmosphere and alveoli
Airflow= (Patm-Palv)/flow resistance
What are the changes in pressure and volume throughout inhalation
- Increase force to expand chest
- Decrease in intrapleural pressure
- Increase in the transpulmonary pressure
- increase force to expand lungs
- Decrease in alveolar pressure
- inhalation
- Increase in lung volume
What are the changes in pressure and volume throughout exhalation
- Decrease force to expand chest
- Increase in intrapleural pressure
- Decrease in transpulmonary pressure
- Increase in alveolar pressure
- exhalation
- decrease in lung volume
How will increase in airway resistance affect breath volume over time
Increase in resistance causes a decrease in flow
What determines the compliance of the lungs
The elastic forces that lead to recoil
1. Lung tissue: primarily due to elastin and collagen
2. Surface tension of fluid lining lungs
What determines compliance of the lungs
the change in lung volume as a result of changes in pleural pressure
Surface tension
The cohesion of liquid molecules at air interface
- Tends to reduce lung volume, so increasing lung volume requires transpulmonary pressures that overcome inward force due to surface tension
Surfactant
- Secreted by alveolar type II cells
- a detergent-like mix of phospholipids and proteins that reduces surface tension
- more concentrated in smaller alveoli, further reducing surface tension and preventing collapse (P=2T/r - greater surface tension due to smaller radius)
Lymphatic System and Intrapleural Pressure
The lymphatic pump creates a negative pressure within lymph vessels that sucks fluid out of the intrapleural space and reduces intrapleural pressure
