Respiratory Physiology (Part 2) Flashcards
What are the 3 muscles of inspiration?
- diaphragm
- external intercostal
- accessory muscles such as the sternocleidomastoid
*diaphragm is the most important
What drives expiration?
It is a passive process driven by the reverse pressure gradient between the lungs and atmosphere
What muscles drive forced expiration?
- abdominal muscles
- internal intercostal muscles
The compliance of what 2 structures are of primary interest in the respiratory system?
the lungs and chest wall
What does compliance describe?
The change in lung volume for a given change in pressure, which can be defined as the system’s distensibility
The compliance of the lungs and chest wall are inversely correlated with what?
their elastic properties, or elastance
The greater the amount of elastic tissue, the greater the elastic force, but the _____ the compliance
lower
Pressures equal to atmospheric pressure are ____.
zero
Pressures higher than atmospheric pressure are ____.
positive
Pressures lower than atmospheric pressure are ____.
negative
What does the slope of the pressure-volume loop equal?
the compliance of the lung
As pressure outside of the lungs becomes more negative, the lung ____ and its volume _____.
inflates
increases
What is the negative pressure outside of the lungs that causes them to inflate called?
expanding pressure
The lungs fill with air along the _____ limb of the pressure-volume loop
insipration
Once the lungs are expanded maximally, the pressure outside of the lungs is made gradually ____ negative, causing the lung volume to decrease along the _____ limb of the pressure-volume loop
less
expiration
Describe the phenomenon of hysteresis
The slopes of the inspiration and expiration limbs are different
Which limb on the pressure-volume loop is greater for a given outside pressure? Why?
the expiration limb, because compliance is higher during expiration than during inspiration
Compliance is measured on the _____ limb
expiration
Why are the inspiration and expiration limbs of the lung compliance curve different?
Because of the surface tension at the liquid-air interface
As surfactant density increases, surface tension decreases which causes a(n) _____ in compliance
increase
As surfactant density decreases, surface tension increases which causes a(n) _____ in compliance
decrease
What is created when air is introduced into the intrapleural space?
a pneumothorax
Normally the intrapleural space has a _____ pressure
negative
What creates this negative intrapleural pressure?
2 opposing elastic forces pulling on the intrapleural space: the lungs tend to collapse and the chest wall which tends to spring out
When a pneumothorax is introduced, the normal negative intrapleural pressure becomes ____.
zero
What are the 2 consequences of a pneumothorax?
1) the lungs collapse
2) the chest wall springs out
What is the problem keeping small alveoli open?
The attractive forces between adjacent molecules of liquid creates surface tension. As the molecules of liquid are drawn together, the surface area becomes as small as possible, forming a sphere. The surface tension generates a pressure that tends to collapse the sphere
What does the Law of Laplace state?
The pressure tending to collapse an alveolus is directly proportional to the surface tension generated by the molecules of liquid lining the alveolus and inversely proportional to alveolar radius
A large alveolus will have a ___ collapsing pressure, and therefore will require ____ pressure to keep it open
low
minimal
A small alveolus will have a ___ collapsing pressure, and therefore will require ____ pressure to keep it open
high
more
So, why are alveoli so small if they have a higher tendency to collapse?
They need to be as small as possible to increase their total surface area for gas exchange
How do small alveoli remain open under high collapsing pressures?
surfactant
What is surfactant?
a mixture of phospholipids that line the alveoli
How does surfactant reduce the collapsing pressure for a given radius?
By reducing surface tension
What is another advantage surfactant provides for pulmonary function?
It increases lung compliance, which reduces the work of expanding the lungs during inspiration
How do you calculate airflow?
Q = ΔP/R
Q = Airflow ΔP = Pressure gradient R = Airway resistance
What is the driving force for airflow?
pressure difference
What is the site of highest airway resistance?
the medium-sized bronchi
What innervates bronchial smooth muscle?
parasympathetic cholinergic nerve fibers
Parasympathetic stimulation of bronchial smooth muscle produces _____.
constriction
Sympathetic stimulation of bronchial smooth muscle produces _____.
relaxation
High lung volumes ____ airway resistance, whereas low lung volumes ____ airway resistance.
decreases
increases
What are the 3 phases of the breathing cycle?
- rest
- inspiration
- expiration
What does alveolar pressure equal at rest?
zero (atmospheric pressure)
What does intrapleural pressure equal at rest?
It is negative at approximately -5
What happens to alveolar pressure during inspiration?
It becomes negative (lower than atmospheric pressure)
What happens to intrapleural pressure during inspiration?
it becomes even more negative than at rest (approximately -8)
What happens to alveolar pressure during expiration?
It becomes positive (higher than atmospheric pressure)
What happens to intrapleural pressure during expiration?
It begins to return to the value at rest (-5) so it becomes more positive
What does gas exchange in the respiratory system refer to?
Diffusion of O2 and CO2 in the lungs and in the peripheral tissues
The transfer of gases across cell membranes or capillary walls occurs by way of what?
simple diffusion
Net diffusion of a gas is dependent on what?
the concentration gradient
What does gas pressure in a mixture of gases equal?
Sum of the “Partial Pressures” of Individual Gases
What are the 2 factors that determine the partial pressure of a gas dissolved in a fluid?
- Concentration
- Solubility coefficient of the gas
Partial pressure of a gas dissolved in fluid is _____ related to concentration of the dissolved gas and _____ related to the solubility coefficient
directly
inversely
For a given concentration, the less soluble the gas, the _____ the partial pressure
greater
The total gas concentration in solution is the sum of what 3 things?
- Dissolved gas
- Bound gas
- Chemically modified gas
In solution, only _____ gas molecules contribute to the partial pressure
dissolved
Where does gas exchange occur?
Between alveolar gas and the pulmonary capillary
__ diffuses from alveolar gas into pulmonary capillary blood, and __ diffuse from pulmonary capillary blood into alveolar gas.
O2
CO2
What is the PO2 and PCO2 in dry inspired air?
PO2 is approximately 160 mmHg
PCO2 is zero, because there is no CO2 in dry inspired air
In humidified air the air is fully saturated with what?
water vapor
What happens to PO2 when air is humidified in the trachea?
It is reduced, because O2 is “diluted” by water vapor and equals approximately 150 mmHg
What is the PCO2 in humidified air in the trachea?
PCO2 is zero, because there is no CO2 in dry inspired air
What is the PO2 and PCO2 in alveolar air?
PO2 is 100 mmHg
PCO2 is 40 mmHg
Why does PO2 decrease and PCO2 decrease in the alveoli?
Because O2 leaves alveolar air and is added to pulmonary capillary blood, and CO2 leaves pulmonary capillary blood and enters alveolar air
Blood entering the pulmonary capillaries is essentially ___ ____ blood
mixed venous blood
What does PO2 and PCO2 equal in the mixed venous blood of the pulmonary capillaries? Explain the reasoning behind each
PO2 is 40 mmHg because the tissues have taken up and consumed O2
PCO2 is 46 mmHg because the tissues have produced CO2 and added it to venous blood
The blood that leaves the pulmonary capillaries will become ___ ____ blood
systemic arterial blood
What is the PO2 and PCO2 in system arterial blood?
PO2 is 100 mmHg
PCO2 is 40 mmHg
What are the 2 forms in which O2 is carried in blood?
- dissolved
- bound to hemoglobin
Dissolved O2 accounts for approximately _% of the total O2 content of blood
2%
Dissolved O2 produces what?
partial pressure
Is the amount of dissolved O2 sufficient enough to meet the demands of the tissues?
No
O2 bound to hemoglobin accounts for approximately _% of the total O2 content of blood
98
Describe the structure of hemoglobin
It is a globular protein that consists of 4 subunits, in which each contains a heme moiety made up of an iron-binding porphyrin and a polypetide chain, which is designated as either alpha or beta
What is adult hemoglobin called?
alpha2beta2
How many molecules of O2 can bind to a single hemoglobin molecule?
4, one per subunit
In order for hemoglobin to bind O2 it must be in what state?
the ferrous (Fe2+) state
What are 3 variants of the hemoglobin molecule?
- Methemoglobin
- Fetal hemoglobin
- Hemoglobin S
When is hemoglobin considered methemoglobin?
When the heme moieties is in the ferric state (Fe3+)
Does methemoglobin bind oxygen?
No, because it is not in the ferrous state, it is in the ferric state
Describe the fetal hemoglobin variant
The 2 beta chanins are replaced by gamma chains, giving it the designation of alpha2gamma2
What is the physiologic consequence of the fetal hemoglobin modification?
It has a higher affinity for O2
Hemoglobin S is an abnormal variant of hemoglobin that causes what disease?
sickle cell disease
Which subunits are abnormal in hemoglobin S?
the beta subunits
The deformation of hemoglobin S in its deoxygenated form can result in what?
occlusion of small blood vessels
The O2 affinity of hemoglobin S is ___ than the O2 affinity of hemoglobin A.
less
What is O2-binding capacity?
The maximum amount of O2 that can be bound to hemoglobin per volume of blood, assuming hemoglobin is 100% saturated
What is O2 content?
The actual amount of O2 per volume of blood
How is O2 content calculated?
O2 content = O2 binding capacity x % Saturation + Dissolved O2
What determines O2 delivery to tissues?
Blood flow and the O2 content of blood
What are the 2 ways O2 delivery to tissues can be calculated?
= Cardiac output x O2 content of blood
= Cardiac output x (Dissolved O2 + O2 bound to hemoglobin)
If 4 molecules of O2 are bound to heme groups than saturation is __%
100%
If 3 molecules of O2 are bound to heme groups than saturation is __%
75%
If 2 molecules of O2 are bound to heme groups than saturation is __%
50
If 1 molecules of O2 are bound to heme groups than saturation is __%
25
Percent saturation of hemoglobin is a function of what?
PO2
