week 5 - Gas exchange & transport

What four factors determine how much O₂ reaches alveoli?

Ventilation, the amount of oxygen in the air, the amount of water in the air, the solubility of oxygen in water

What is Dalton's Law?

Total pressure equals sum of all partial pressures

How does humidity affect partial pressures?

Water vapour ‘dilutes’ air

What is Henry's Law?

Amount of gas in solution is proportional to partial pressure BUT also depends on solubility

What are the pressure gradients in the lungs during gas exchange?

• O₂: 100 mm Hg (alveoli) → 40 mm Hg (pulmonary capillaries)

• CO₂: 46 mm Hg (pulmonary capillaries) → 40 mm Hg (alveoli)

What are the pressure gradients at the tissue during gas exchange?

• O₂: 100 mm Hg (systemic capillaries) → 40 mm Hg (cells)

• CO₂: 46 mm Hg (cells) → 40 mm Hg (systemic capillaries)

What factors influence gas transfer between alveoli and blood?

Oxygen reaching the alveoli, structural characteristics of the alveoli, the matching of alveolar ventilation to pulmonary blood perfusion

How is oxygen transported in blood?

• Dissolved in plasma: <2%

• Bound to hemoglobin: >98%

What is hemoglobin structure and function?

4 subunits, each with:

• Globin molecules: Bind CO₂ and H⁺

• Heme groups: Contain iron, bind O₂

4 heme groups → each Hb binds 4 O₂ molecules

What is the oxygen-hemoglobin dissociation curve?

• At 100 mm Hg (alveoli): Hb ~100% saturated (4 O₂ per Hb)

• At 40 mm Hg (tissues): Hb ~75% saturated (3 O₂ per Hb)

• During exercise (20 mm Hg): Hb ~25% saturated (1 O₂ per Hb)

What factors shift the O₂-Hb curve to the RIGHT (lower O₂ affinity)?

Bohr effect - curve shifts RIGHT in conditions indicating high metabolic demand:

• Lower pH (high H⁺)

• Higher CO₂

• Higher temperature

How is fetal hemoglobin different?

• Fetal Hb curve shifted LEFT compared to maternal Hb

• Higher O₂ affinity than maternal Hb

• Enables O₂ transfer from mother to fetus across placenta

What are the three ways CO₂ is transported in blood?

Dissolved in plasma (7%), Bound to haemoglobin (23%), Dissolves in water to form bicarbonate ions (70%)