What happens when the bronchioles in the lungs dilate?
They increase their volume and lower the pressure inside the lungs, moving air in
What does the parietal pleura secrete?
What is the purpose of the fluid secreted by the parietal pleua?
The surface tension adheres the two pleural layers together
What is the parietal pleura attached to?
The chest wall
What is the result of the parietal pleura being attached to the chest wall?
When the chest wall expands, the parietal pleura moves wtih it, as does the visceral pleura
What is the visceral pleura attached too?
What is the result of the attachment of the visceral pleura to the lung?
When the chest wall expands, the lung expands
What do the external intercostal muscles do?
Elevate the ribs in a 'bucket handle' type movement
How much of chest expansion is the chest wall responsible for during quiet respiration?
What does the diaphragm do to expand the chest?
Contracts and descends
How much of chest expansion is the diaphragm responsible for during quiet respiration?
What muscles are involved in inhalation during quiet breathing?
- External intercostals
What muscles are involved in exhalation during quiet breathing?
What muscles are involved in inhalation during forced breathing?
- External intercostals
- Pectoralis minor
- Serratus anterior
What muscles are involved in exhalation during forced breathing?
- Internal intercostals
- Innermost intercostals
- Abdominal muscles
What happens to blood flowing through alveolar capillaries?
It picks up oxygen and loses carbon dioxide by diffusion of those gases across the alveolar wall
What is the rate of gas exchange in the alveolar capillaries determined by?
- Area available for gas exchange
- Resistance to diffusion
- Gradient of partial pressure
In a normal lung, what is the exchange area?
What creates the large area for exchange in the lungs?
The huge number of alveoli
In normal lungs, is the area available for exchange a limiting factor on gas exchange?
What provides resistance to diffusion in the alveoli?
Although the diffusion pathway is short, there are several structures between the alveolar as and the alveolar capillary blood
What must the alveolar gas diffuse through to reach the alveolar capillary blood?
- Gas in the alveoli
- The alveolar epithelial cell
- Interstitial fluid
- Capillary endothelial cell
- RBC membrane
5 cell membranes, 3 layers of intracellular fluid and 2 layers of extracellular fluid
How long is the diffusion distance between alveolar gas and alveolar capillary blood?
Less than 1 micron
What gases must diffuse through the barrier between alveolar gas and alveolar blood?
Oxygen and carbon dioxide
What is the rate of diffusion across the alveoli affected by for most of the barrier (the cells, membranes, and fluid)?
Solubility of gas in water
How does the diffusion rate of carbon dioxide differ from that of oxygen?
It diffuses 21 types as fast for a given gradient
Why does carbon dioxide diffuse across the alveoli faster than oxygen?
Because it is more soluble
How much faster than oxygen does carbon dioxide diffuse for a given gradient?
21 times as fast
What is the result on gas exchange at the alveoli of carbon dioxide diffusing much faster than oxygen?
Anything affecting diffusion will only change oxygen transport, as that is limiting (if there is a problem affecting the exchange of gases, oxygen will be affeted first)
What must be true of the partial pressure if the tissues of the body are to be properly supplied with oxygen and carbon dioxide?
The partial pressure of oxygen and carbon dioxide in the alveolar gas must be kept very close to their normal values
What is the normal partial pressure of oxygen in the lungs?
What is the normal partial pressure of carbon dioxide in the lungs?
How is the maintenance of normal partial pressures of oxygen and carbon dioxide in the lungs achieved?
Exchange of gas between alveolar gases and atmospheric air brought close to it through the airways of the lung through the process of ventilation
How is air driven through the airways of the lungs?
By the pressure changes produced by increases and decreases in the volume of air spaces next to the alveoli
What effect does the movement of breathing have on pressure in ther teminal and respiratory bronchioles during inspiration?
It lowers it
What is the result of the movement of breathing during inspiration lowering pressure in the terminal and respiratory bronchioles?
Air flows down the airways to them
What is the effect of the movement of breathing during expiration?
It increases pressure in the terminal and respiratory bronchioles, so air flows back out again
Does fresh atmospheric air enter the alveoli?
If fresh atmospheric air doesn't enter the alveoli, how does exchange of oxygen and carbon dioxide occur?
By diffusion between alveolar gas and atmospheric air in the terminal and respiratory bronchioles
How can the movement of air during breathing be measured?
What are the types of lung volume?
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Residual volume
What is meant by tidal volume?
The lung volume that represents the amount of air that is displaced between normal inspiration and expiration, when extra effort is not applied
What is meant by inspiratory reserve volume?
The extra volume that can be breathed in when extra effort is applied
What is meant by expiratory reserve volume?
The extra volume that can be breathed out when extra effort is applied
What is meant by residual volume?
The volume left in the lungs at maximal expansion
Can residual volume be measured with a spirometer?
How must residual volume be measured?
By helium dilution
What are the types of lung capacity?
- Vital capacity
- Functional reserve capacity
- Inspiratory capacity
What is meant by vital capacity?
The biggest breath that can be taken in
What is vital capacity measured as?
From the max inspiration to the max expiration
What is vital capacity in a typical adult?
Why is vital capacity clinically important?
Becasue it changes a lot in disease
What is meant by functional residual capacity?
The volume of air in the lungs at resting expiratory level
What is functional reserve capacity equal to?
Expiratory reserve volume + residual volume
What is functional residual capacity in a typical adult?
What is meant by inspiratory capacity?
The biggest breath that can be taken from resting expiratory level (lung volume at the end of quiet expiraton)
What is inspiratory capacity in a typical adult?
Draw a diagram illustrating all lung capacities and volumes
What is meant by serial (anatomical) dead space?
The volume of the conducting airways
Normally, what is serial dead space in an adult?
Why must we consider serial dead space
Air enters and leaves the lungs by the same aiways, so the last air in is the first air out, and does not reach the alveoli, and is therefore unavailable for gas exchange
How is serial dead space measured?
By the nitrogen washout test
What happens in a nitrogen washout test?
- The patient takes a maximum inspiration of 100% oxygen
- The oxygen that reaches the alveoli will mix with alveolar air, and the resulting mix will contain nitrogen (there is 79% nitrogen in air)
- However, the air in the conducting airways (dead space) will still be filed with pure oxygen
- The person exhales through a one way valve that measures the percecntage of nitrogen in and volume of air expired
- Nitogen concentration is initially zero, as the patient exhales the dead space oxygen
- As alveolar air begins to move out and mix with dead space air, nitrogen concentration gradually climbs, until it reaches a plateau where only gas is being expired
How can the results of a nitrogen washout test be interpreted to determine the dead space volume?
A graph can be drawn, plotting nitrogen % against expired volume
Draw a typical graph of the results of a nitrogen washout test
What is alveolar (or distributive) dead space?
The volume of air in alveoli not taking part in gas exchange
Why does alveolar dead space exist?
Some alveoli receive insufficient blood supply; others are damaged by accident or disease, so that even in the air that reaches the alveolar boundary, there is a proportion that fails to exchange
What is physiological dead space equal to?
Anatomical dead space + alveolar dead space
How is physiological dead space determined?
Measuring pCO2 or pO2 of expired alveolar air
Why can physiological dead space be determined by measuring the pCO2 or pO2 of expired alveolar air?
Because the alveolar air is diluted by dead space to form the expired air, and the degree of dilution is a measurement of physiological dead space
What is meant by alveolar ventilation rate?
The amount of air that actually reaches the alveoli
How is alveolar ventilation rate calculated?
Pulmonary ventilation rate (tidal volume x RR) - dead space ventilation rate (dead space volume x RR)