Respiratory 5 Flashcards
What exists between alveoli and pulmonary capillaries at all time
Partial pressure gradient for O2 and CO2
What determines the O2 and CO2 diffusion rate between alveoli and capillaries
Gas composition in alveoli
In alveoli what remains relatively constant during quiet respiration assuming perfusion is normal
PO2 and PCO2
What is perfusion
Blood flow
O2 entering alveoli is equal to what
O2 uptake from pulmonary capillaries
What can alter partial pressures of O2 and CO2 and alter diffusion
Alterations in ventilation rate independent of changes in CV system
Ex) hyperventilation or hypoventilation
What can cause hypoventilation
Alcohol, drugs
What happens during hypoventilation
Slow breathing
- increased PCO2, not ventilating as much CO2 out
- decreased PO2 bringing in less O2
What happens during hyperventilation
Breathing rapidly, deeply
- bringing in more O2 than being taken up by capillaries
- O2 builds up in alveoli, alveolar PO2 increases
- exhaling CO2 faster then being brought to pulmonary capillaries, PCO2 decreases
- increased diffusion of O2 and CO2
What must happen so one organ system does not work harder then it needs to
Ventilation and alveolar blood flow (perfusion) must match
What must happen for external respiration
- Bringing O2 from atmosphere into alveoli
- Blood flow must be high enough to pick up available O2
- Matched ventilation/perfusion
What is local regional control to match perfusion and ventilation in lungs?
Gravity
How does gravity affect blood flow in lungs
- blood flow is higher at base of lung and decreases up to apex during rest
- low pressure circuit and right ventricle doesn’t create enough pressure to go against gravity
- pressure of pumping and downward pressure causes perfusion in base
How does gravity affect ventilation
- highest at base and decreases as move up
- entire lung not -3 mmHg, more positive at base
Why is the intrapleural pressure more negative at the apex
Bigger space between the pleura because gravity
What does a more negative intrapleural pressure do to the alveoli at the apex
Partially open and filled with air even at rest and therefore do not take much air during ventilation
What does not innervate the pulmonary arterioles like it does the systemic arterioles
Autonomic innervation
What are the two local controls for smaller areas of the lungs
Pulmonary arterioles influenced by O2
Bronchioles sensitive to CO2
What can affect blood flow in pulmonary arterioles
Decreasing O2 levels around
Decrease causes constriction
Why do the pulmonary arterioles constrict in response to low O2
Increases resistance so blood flow can be diverted to ventilated arterioles that have adequate O2
What causes constriction to low O2 in pulmonary arterioles
O2 sensitive K+ channels close
What affects air flow in bronchioles
Increase CO2 causes dilation, reduces resistance so more CO2 exhaled
Decrease CO2 causes constriction, not over ventilating and no excessive removal of CO2
What happens when one alveoli is blocked and air cannot move in
- at first blood will continue to flow by, from CO2 and CO2 will increase in alveoli and region
- O2 will decrease, no fresh O2 and everything in alveoli picked up
- increase CO2 causes dilation of bronchiole
- decrease O2 will cause arterioles to constrict
- blood will take path of least resistance
What are 3 local control of arterioles and bronchioles
PCO2 increases - bronchioles dilate
PCO2 decreases - bronchioles constrict
PO2 decreases - pulmonary arteries constrict
What happens during a blockage in a pulmonary vessel (blood clot) in alveoli
Alveolar PO2 increases (fresh O2 being brought not picked up)
Alveolar PCO2 decreases (continuing to ventilate removing CO2 but no perfusion with new)
What happens in region when there’s a vessel blockage
Tissue PO2 increases
Tissue PCO2 decreases
Bronchiole smooth muscle constricts diverting flow
What is hypoxia
Too little oxygen
What causes hypoxia
Impaired diffusion from alveoli to blood or impaired blood transport
- inadequate amounts of O2 reaching alveoli
What is hypoxia often paired with
Hypercapnia
- excess CO2
- low levels ventilation or improper diffusion
What do the sensors in the arterial blood to avoid hypoxia and hypercapnia respond to
- Oxygen - ATP production
- Carbon dioxide - CNS depressant/ acid precursor
- PH - denaturing of protein
What is normal PO2 in arterial and venous blood
95 and 40 mmHg
What is normal PCO2 in arterial and venous blood
40 and 46 mmHg
What is normal pH in arterial and venous blood
7.4 and 7.37 (CO2 causes slight drop)
What direction do gases diffuse
Down partial pressure gradients
When does O2 and CO2 diffuse until
Equilibrium
Ex) PO2 cells 40 mmHg = venous 40 mmHg blood
What 3 things is alveolar gas exchange influenced by
- O2 reaching the alveoli
- Gas diffusion between alveoli and blood
- Adequate perfusion of alveoli
Two causes of low alveolar PO2 assuming perfusion remains constant
- Inspired air has low O2 content
- Alveolar ventilation
When is inspired air low in O2
As increase elevation, PO2 decreases
- PO2 at sea level is ~160 mmHg, in Denver (1600m above) PO2 132 mmHg
When does alveolar ventilation cause low alveolar PO2
- Ventilation issue (hypoventilation)
- increase airway resistance, decrease lung compliance, or CNS issue decrease rate or depth of breathing
