Lecture 15 Flashcards
Where does gas exchange primarily occur in the lungs?
In the alveolar sacs, which contain Type 1 alveolar cells that are fused with capillaries for efficient diffusion.
What is the role of Type 1 alveolar cells in gas exchange?
They have thin walls (~0.2 microns) and are fused with capillaries, allowing rapid diffusion of oxygen and carbon dioxide.
What are the main components of the respiratory zone where gas exchange occurs?
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
Why does carbon dioxide diffuse faster than oxygen, despite having a lower partial pressure gradient?
Because CO₂ is 20 times more soluble in water than O₂, so it diffuses more quickly even with a smaller gradient.
According to Fick’s Law, what four factors influence the rate of gas diffusion?
Partial Pressure Difference (ΔP) – Gases move from high to low pressure.
Surface Area (A) – Larger surface area = faster diffusion.
Solubility (S) – CO₂ is 20x more soluble than O₂.
Distance (d) – The thinner the diffusion distance, the faster the exchange.
How is most oxygen transported in the blood?
98% of oxygen is bound to hemoglobin (Hb), forming oxyhemoglobin (HbO₂). The remaining 2% dissolves in plasma.
How does Dalton’s Law relate to gas exchange in the lungs?
Dalton’s Law states that each gas in a mixture exerts its own partial pressure. In the lungs, oxygen moves from areas of high PO₂ (104 mmHg) to low PO₂ (40 mmHg) in blood.
How does air humidification in the lungs affect partial pressure calculations?
Water vapor pressure (~47 mmHg) reduces the total available pressure for gases, lowering alveolar PO₂ from 160 mmHg to ~150 mmHg.
What does the oxygen-hemoglobin dissociation curve show?
It shows how oxygen binds to and is released from hemoglobin based on PO₂ levels. More oxygen is released in areas with low PO₂ (like tissues).
What factors cause a right shift in the oxygen-hemoglobin dissociation curve? What does this mean?
↑ CO₂
↑ Temperature
↓ pH (Bohr Effect)
↑ 2,3-BPG
A right shift means hemoglobin releases oxygen more easily, which is useful during exercise or high metabolism.
Why does fetal hemoglobin (HbF) have a left-shifted oxygen dissociation curve compared to adult hemoglobin?
Fetal hemoglobin has a higher affinity for oxygen so it can extract O₂ from the mother’s blood.
What are the three ways CO₂ is transported in the blood?
As bicarbonate (HCO₃⁻) – 70%
Bound to hemoglobin (HbCO₂) – 23%
Dissolved in plasma – 7%
What enzyme catalyzes the conversion of CO₂ into bicarbonate (HCO₃⁻) in red blood cells?
Carbonic anhydrase (CA).
What happens to CO₂ transport in the lungs, according to the Haldane Effect?
In the lungs, oxygen binds to hemoglobin, causing CO₂ to be released and exhaled.
This enhances CO₂ removal from the blood.
A patient with chronic lung disease has difficulty exhaling CO₂. How does this affect blood pH?
If CO₂ is not exhaled, it accumulates, forming more carbonic acid (H₂CO₃), which lowers blood pH, causing respiratory acidosis.
During hyperventilation, what happens to CO₂ levels and blood pH?
CO₂ levels decrease, reducing H₂CO₃, which raises blood pH, leading to respiratory alkalosis.
If a patient has a right-shifted HbO₂ dissociation curve, what does this mean for oxygen delivery to tissues?
Hemoglobin is releasing oxygen more easily, meaning more O₂ is delivered to tissues, which is beneficial during exercise or fever.
If alveolar PO₂ drops from 104 mmHg to 60 mmHg (as in high altitude), how will this affect oxygen loading in the lungs?
Hemoglobin will not reach full saturation in the lungs, leading to less oxygen being delivered to tissues. This can cause hypoxia.
Explain why gas exchange is still efficient during exercise, even though blood moves faster through pulmonary capillaries.
Oxygen diffuses rapidly, and equilibrium is reached within 0.25 seconds, while blood transit time is 0.75 seconds at rest. Even during exercise, equilibrium is achieved before blood exits the lungs.
