Week 4 - Physiology Flashcards
Pulmonary mechanics is similar to
heart mechanics - gas flow instead of blood flow
Respiration is used to primarily control
CO2 - because it’s super important to control blood pH
define Gauge Scale
Any scale of measurement the has an arbitrary 0 other than the absolute
True or False - If something measures twice as much on a gauge scale, then it is twice as much
False - because zero on a gauge scale is not absolute zero
what are the two gauge scales used in pulmonary physiology?
mmHg and cmH2O
What is defined as 0 on the two gauge scales used in pulmonary physiology
atmospheric pressure = 0
A negative pressure indicates what?
that the pressure is less than atmospheric
Define the following pressures: PB, PA, PP
PB - bariatric (atmospheric) pressure… always 0, it’s the arbitrary defined 0 of the gauge scale
PA - pressure in the alveoli. Is also 0 because it is connected to PB
PP - Pressure of the pleural space
The pariaetal and plural membrane lubricate the lungs for what purpose?
to allow the membranes to easily slide along the lungs as the lungs are constantly expanding and contracting
What is the typical pressure in the PP (pleural space) and why
-5cmH2O, because the lungs and thorax are both elastic structures trying to pull away from the pleural space, thus decreasing pressure
What happens to each pressure as muscles expand the thoracic space
1) thoracic cavity increases in size, causing pleural space to expand
2) PP changes from -5 cmH2O to -10 cmH2O
3) PT increases from 5 to 10, causing slight negative in alveoli as they expand
4) air from outside flows from 0 to the slight negative in the alveoli, filling lungs with air.
Exhaling is the exact same order of steps, but opposite direction of movement and pressures
What formula is used to determine the pressure differential across the alveolar wall (PT)
PT=PA-PP
ie, at rest Pa=0 PP=-5 -> 0-(-5)=5
What drives inspiration and expiration?
PP
define lung compliance ( C )
C=ΔV/ΔP
V=volume
P=pressure
A normal graph of the relationship between pressure and volume in the longs described in terms of compliance follows what slope?
low compliance -> high compliance -> low compliance
low slope -> steep slope -> low slope
With Fibrosis, what would you expect to happen to the lung compliance curve
lower compliance
In a high compliance lung you need (more/less) pressure to reach the same volume as a normal compliance lung.
less
Emphysema is associated with what kind of lung compliance
high compliance
Rank the following in order of most to least pressure needed to achieve the same lung volume: normal compliance, low compliance, high compliance
low compliance -> normal -> high compliance
What are the partial pressures of gases in the atmosphere?
PO2=160mmHg
PCO2= 0 (used to define the partial pressure gauge scale)
Assuming constant ventilation of the alveoli, what are the gas partial pressures in the alveoli?
P02 = 100 mmHg PCO2 = 40 mmHg
True or false, given constant breathing, the partial gas pressures in arterial blood are the same is in the alveoli
True
what are the partial pressures of gasses in venous blood
PO2 = 40 mmHg PCO2 = 45 mmHg
What three things drive the rate of gas flow?
- partial pressure differential
- surface area
- diffusion distance
What determines the direction of the flow of gases
gas partial pressure differentials (higher pressure to lower pressure)
True or false, concentration of gases affects the direction in which a gas will diffuse
false
Increasing the rate of ventilation has what effect on the gas partial pressures in the alveolus?
PO2 increases
PCO2 decreases
Decreasing the rate of ventilation has what effect on the gas partial pressures in the alveolus?
PO2 decreases
PCO2 increases
What controls the gas partial pressures in the alveolus
the rate of ventilation/breathing
Define Henry’s Law
the amount of gas in a solution is equal to it’s partial pressure of the gas outside the solution times it’s solubility.
Which gas has higher solubility, CO2 or O2?
CO2
O2 is only 0.003 mLO2/dLblood/mmHg
Why is hemoglobin so important?
Blood can only carry 0.3mL O2 per dL of blood, however the body needs 200mL O2 per minute…
what is the storage capacity of hemoglobin?
1 g of Hb can store 1.36mL O2
How much Hb does a typical young male have? How much O2 total is in his blood?
15 g Hb per dL blood
- 36mL O2/gHb x 15gHb/dL blood = 20.4mL O2/dL blood
- 4+0.3 (from plasma)=20.7mL O2/dL blood
Why is CO2 so important?
CO2+H2O H+ + HCO3-
controlling the level of CO2 is the main method of controlling blood pH
Explain how bicarbonate ends up in the plasma
CO2 forms H+ and HCO3+ when dissolved in water, however red blood cells use carbonicanhydrase to rapidly dissociate all CO2, and then the cells expel only CO3+. At the lungs it is reformed, but during transport red blood cells insure CO2 is carried as CO3+ in the blood
Controlling ventilation controls CO2 levels which in turn controls ____
blood pH
Increased ventilation results in acidosis/alkalosis
alkalosis
Decreased ventilation results in acidosis/alkalosis
acidosis
What is the importance of increased H+ production resulting from breakdown of CO2?
H+ is used to dissociate/release O2 from hemoglobin allowing O2 to be distributed to cells
Why is such a high partial pressure of O2 in the lungs important?
As PO2 increases the saturation of O2 binding sites that are used up rapidly increases, thus maximizing the O2 content of the blood.
What factors decrease O2 affinity for Hb (right shift in Hb Dissociation Curve)
decrease in pH
increase in temperature
increase in CO2
What is another name for a right shift in the Hb Dissociation Curve as a result of CO2, and why is this concept important?
Bohr effect.
The increase in the presence of CO2 helps drive the release of O2 from Hb, allowing it to be released to tissues and cells.
Describe the differences in the values for the formula Q=ΔP/R in systemic vs pulmonary
pulminary: Q=5 ΔP=25-5=20 therefor R=4 Systemic: Q=5 ΔP=100-0=100 therefore R=20
Why is low resistance in pulmonary circulation important?
low resistance allows lower driving pressure to maintain flow of blood equal to systemic circulation, thus helping prevent edema in the lungs.
Which organ is the only organ to receive close to 100% of cardiac output (in fact, it’s often rounded to 100%)?
the lungs, which is why it is a prime location to modify the blood as with harmones, and very important for angiotensin/renin system.
Where are receptors located to detect the presence of O2, and what are they called?
in the carotid and aortic arch. they are called peripheral chemoreceptors
At what PO2 do the O2 receptors signal the brain to increase ventilation?
> 60 mmHg of O2
what gas does the body monitor to determine minute to minute breathing rate
CO2
True of False: As with O2, the body has direct receptors for detecting the presence of CO2
False
How does the body determine CO2 levels?
Central Chemoreceptors: detect H+ in CSF
What allows measure of H+ in CSF to be an accurate measure of CO2
The blood brain barrier. It does not allow H+ to cross, but does allow CO2 to cross, which can then dissociate to H+ and CO3- on the other side
CO2 in the blood is loosely/tightly regulated at 40mmHg
very tightly, it is one of the only substance your body tightly regulates and will almost always be seen right at 40mmHg
Why is CO2 preferred for regulation over O2
O2 is rarely ever a limiting factor
Besides O2, what else does Peripheral Chemoreceptors detect?
Significantly high levels of arterial H+ (metabolic acidosis)
What happens in Emphysema?
breakdown of alveolar walls
- decrease surface area
- decrease cross sectional area (increases resistance)
- increase in lung compliance due to loss of elasticity from loss of structure
The increased resistance in pulmonary circulation results in what for the heart, and what for the lungs?
increase work/load on the heart, resulting in heart problems
increase filtration in the lungs resulting in edema
In emphysema is is easy/difficult to inspire and easy/difficult to expire
easy inspire/difficult expire
Is emphysema a restrictive or obstructive disease?
obstructive - the destruction of alveolar walls results in less pull keeping airways open, so airways become floppy and prone to collapse (obstruction)
