Respiratory system Week 5 Flashcards
How are airflow rates measured by
Spirometry
Effective oxygenation and CO2 removal in lungs dependent on
1) Ventilation and gas exchange by diffusion
2) Perfusion of lungs
What are the factors influencing efficiency of diffusion across alveolar capillary border
1) Partial pressure of gases
2) surface area
3) thickness of barrier
What are partial pressures of gasses
Pressure exerted by gas in mixture of gasses
What law does does partial pressure of gasses follow
Dalton’s law
How are partial pressures of gases calculated
% of gas in air x atmospheric pressure
Is the pressure exerted by gas in mixture of gases proportional
Yes
What are the factors of blood flow
Alveoli perfusion, rate of blood flow through alveoli
Why does alveolar gasses take time to diffuse and equilibrate with blood
Different gasses diffuse/equilibrate at different rates
When does gas exchange occur
When blood perfuses capillary
What are the factors influencing rate of gas transfer across alveolar membrane
1) Partial pressure gradients of O2 & CO2
2) Surface area of alveolar membrane
3) Thickness of barrier separating air and blood across alveolar membrane
4) Diffusion constant
What is the major determinant of rate of gas transfer
Partial Pressure gradients of O2 and CO2
What is the relationship between partial pressure gradient and rate of transfer
Greater partial pressure gradient = greater rate of transfer
What is the relationship between surface area and rate of transfer
Greater SA = greater rate of transfer
What happens to the surface area when one exercises
Surface area increases with increased opening of pulmonary capillaries with increased cardiac output and alveolar expansion
What is the relationship between barrier thickness and rate of transfer
Thicker = greater rate of transfer
What are pathological diseases that could cause increased thickness of barrier
Pulmonary edema, pulmonary fibrosis, pneumonia
What is the relationship between diffusion constant and rate of transfer
Greater diffusion constant = greater rate of transfer
How much greater is the diffusion constant of CO2 compared to O2
20x
Why is the diffusion constant of CO2 greater than O2
Helps to offset smaller partial pressure gradient of CO2 and allows for equal amount of CO2 and O2 transfer across membrane
What is the difference between pulmonary and systemic circulation
Pulmonary is normally dilated whereas systemic is normally constricted
What makes the pulmonary circulation unique in terms of its hemodynamic features
Low pressure, low resistance, high volume system
What is the distribution of blood flow in lungs
Non uniform
Do the lungs receive 100% of cardiac output at all times
Yes
What are the differences between systemic and pulmonary arterial pressure
Pulmonary artery >25/15 mmHg
Systemic artery 120/80 mmHg
What are the limited respiratory responses imposed by diseases
Increased dead space and decreased tidal volume
How is the tidal volume affected
Restriction of chest wall/lung movement. Loss of lung elasticity due to fibrosis (scarring) of alveolar walls
What is the differences between apex and base of lung in terms of its ventilation/perfusion ratio (V/Q)
Apex: High V/Q ratio due to greater pO2 and lower pCO2
Base: Low V/Q ratio due to lower pO2 and greater pCO2
How is the distribution of blood flow in perfusion of lungs influenced by
Gravity (Posture): Upright = more blood at bottom
Muscular tone of arterioles (vascular tone): less muscular walls in pulmonary arterioles compared to systemic arterioles
- can distend easier with more blood flow
- vasoconstriction = less blood flow through capillaries
How does the body attempt to do homeostasis of hypocapnia
Receptors detect decreasing PCO2 and increasing pH
Respiratory muscles inhibited
Decrease rate of respiration and decrease PCO2 elimination
Arterial PCO2 increases
How does the body attempt to do homeostasis of hypercapnia
Receptors detect increasing PCO2 and decreasing pH
Respiratory muscles stimulated
Increase rate of respiration and increase PCO2 elimination
Arterial PCO2 decreases
What is residual volume
Volume of air left in lungs after maximum expiration
What is tidal volume
Volume of air entering lungs at each resting breath/exiting lungs on passive expiration
What is expiratory reserve volume
Extra air expelled from lungs with max expiration after passive expiration
What is inspiratory reserve volume
Extra air entering lungs with max inspiration in addition to TV
What factors influence the ventilation volumes
Physical fitness, age, size
What other ventilation volumes does exercise recruit
IRV and ERV
What factors influence the ability to ventilate
Chest wall, lungs, others (pain, abdominal movement restricted)
How is vital capacity calculated
ERV + IRV + TV
What are the chemical controls of breathing
PCO2, PO2, H+
How is H+ and PO2 monitored
Carotid and aortic bodies
When does PO2 activate peripheral chemoreceptors
when arterial PO2 < 60 mmHg
What scenario makes the arterial PO2 < 60 mmHg
Life threatening situation which invokes an emergency response
What does H+ not affect
Central chemoreceptors
What is PCO2 as a chemical control of breathing
Main respiratory regulator
What does PCO2 affect
Mainly affects central chemoreceptors
Weakly affects peripheral chemoreceptors
What does H+ affect
Peripheral chemoreceptors
Can CO2 pass through blood brain barrier
Yes
Can H+ pass through blood brain barrier
No
When does PCO2 affect central chemoreceptors
PCO2 > 70 - 80 mmHg which directly depresses respiratory center and central chemoreceptors
What are the 2 main controls of respiration which increases ventilation
Medullary chemoreceptors (decreasing pH, increasing CO2)
Carotid and aortic body receptors (decreasing O2)
How is minute ventilation calculated
TV x Respiratory rate = x L/min
What causes deviations in minute ventilation
Hypoventilation = decreased ventilation
Hyperventilation = increased ventilation
Tachypnoea = increased rate of respiration
Dyspnea = distressful sensation of breathing
How does the body compensate for large airflow, small blood flow
Decreasing CO2
- increased contraction of local airway smooth muscle
- increased constriction of local airways
- increased air resistance
- decreased airflow
Increasing O2
- relaxation of local pulmonary arteriolar smooth muscle
- blood vessel dilation
- decreased vascular resistance
- increased blood flow
How does the body compensate for small airflow, large blood flow
Increasing CO2
- decreased contraction of local airway smooth muscle
- local airways dilation
- decreased air resistance
- increased airflow
Decreasing O2
- increased contraction of local pulmonary arteriolar smooth muscle
- blood vessel constricted
- increased vascular resistance
- decreased blood flow
What is the difference between apex and base of lung
Apex: ventilation > perfusion
Base: perfusion > ventilation
What is CO2 excretion associated with
H+ elimination
What happens when CO2 excretion and H+ elimination increases
Arterial PCO2 decreases
What factors affect amount of O2 carried by Hb
Partial pressure of O2 (PO2) in blood
Concentration of Hb in blood
pH
Temperature
2,3-diphosphoglycerate (2,3-DPG)
When partial pressure of O2 (PO2) increases in blood, what happens to O2 binding to Hb
Increased O2 binding to Hb up till saturation capacity of Hb
What is oxygenation
When each Fe atom binds reversibly to one O2 molecule
The transport of O2 to tissues are dependent on
CVS, Blood, Respiratory system
How is O2 transported in the blood
98% bound to Hemoglobin (Major carrier)
2% dissolved in plasma
Which O2 exerts partial pressure in blood
O2 dissolved in plasma
How is CO2 transported in the blood
7% dissolved in plasma
23% bound to proteins including Hb and forms carbamino compounds
70% converted to bicarbonate ion
What enzyme converts CO2 to H2CO3
Carbonic anhydrase
Why should we measure forced expiratory volumes of the lungs
Detects changes in airway resistance & elasticity of lungs
What does FVC mean
Forced vital capacity
What does FVC measure
Total volume expired forcefully after full inspiration
What does FEV1 mean
Forced expiratory volume of air exhaled in 1 sec after full inspiration
What hormones simulates production of 2,3-DPG
Epinephrine, Growth Hormone, Thyroid hormone
What is 2,3-DPG
A by-product of RBC glycolysis
How can O2 be released quicker
Increased 2,3-DPG
Increased temperature
Decreased pH
When temperature increases, what happens to the sigmoidal curve
Shifts to the right
When temperature decreases, what happens to the sigmoidal curve
Shifts to the left
When pH increases, what happens to the sigmoidal curve
Shifts to the left
When pH decreases, what happens to the sigmoidal curve
Shifts to the right
When 2,3-DPG increases, what happens to the sigmoidal curve
Shifts to the right
When 2,3-DPG decreases, what happens to the sigmoidal curve
Shifts to the left
What is formed when Co2 binds to Hb
Carbamino Hb
What is formed when H+ binds to Hb
HHb
What is the function of HHb
Buffer pH
What is the purpose of bicarbonate ion swapping out for Chloride ion
Shift maintains electrical neutrality
What does compliance mean
The measure of stretchability
Change in lung vol/unit change in airway pressure
What does decreased compliance of the lung mean
There is decreased stretchability and more work is needed for breathing
what is the causes of decreased compliance
fibrosis, lack of surfactant, edema of alveolar walls
What are the factors that influence the diffusion of gases
Difference in partial pressure of gases between alveoli & blood
Diffusion barrier
Area available for diffusion
Different properties of gases
If the pressure difference increases, does the diffusion increase?
Yes
If the diffusion barrier is thicker, what happens to the diffusion
Slower diffusion
If the area available for diffusion decreases, what happens to the diffusion
diffusion decreases
the greater the solubility in blood, the greater the diffusion?
Yes
Is the diffusion of Co2 > o2?
Yes
How does high altitude influence diffusion
Decreased difference in partial pressure causes decreased diffusion
How does fibrosis and edema influence diffusion
Abnormal thickening of alveolar-capillary border = decreased diffusion
How does pneumonia influence diffusion
Decreased alveolar volume/number of functional alveoli = decreased surface area for diffusion
Does increased blood flow mean greater gas exchange?
No. One could have decreased alveoli with thickened membranes which negates this. Another could be exercise where there is increased blood flow but less time for gas to equilibrate
what is the purpose of surfactant
decrease alveolar surface tension by lowering surface tension proportionally
what is surfactant made of
lipids, proteins, phospholipids
What does a lack of surfactant lead to
Alveoli collapse such as infant respiratory distress syndrome in newborns
What can surfactant be found
along the surface of alveolar epithelium
Why is surface tension not constant
alveoli of different diameters cannot coexist due to instability and air will flow from one to another and not the other way
what is the major determinant of compliance of lungs
surface tension of alveoli
what is the issue of smaller alveoli
greater tendency to collapse
Does reducing tension lead to increased compliance
Reducing tension = reducing pressure = increased compliance
What contributes to increased resistance by airway narrowing
Decreased lung volume
mucus accumulation
bronchoconstriction (contraction of smooth muscles of bronchioles)
What are the sources of airway resistance
trachea, bronchi, bronchioles
What are the factors of bronchodilation
Hormones - epinephrine
sympathetic simulation - minimal effect
increased co2 concentration - local chemical control
what are the factors of bronchoconstriction
pathological - allergy induced spasm of airway. histamine, slow reactive substance of anaphylaxis (leukotrieves)
physiological - parasympathetic stimuli, decreased CO2 concentration (local chemical control)
Physical blockage of airway - airway collapse, edema of walls, excess mucus
