43 - Oxygen transport in the blood. Oxyhemoglobin dissocitation curve: Oxygen exchange in the lungs and tissues.

sections

oxygen transport in blood

oxyhaemoglobin dissociation curve

oxygen exchange in lungs and tissues

transport CO2

exchange of CO2 in lungs and tissue

oxygen transport in blood

• Oxygen moves according to its partial pressure gradient by diffusion (high to low) from the alveoli into the capillary blood

• in the blood, it is transported with hemoglobin (98%) forming oxyhaemoglobin.

• Only a small amount of dissolved oxygen is transported in the blood.

• partial pressure of oxygen is higher in the capillaries of peripheral tissues so oxygen to diffuse into the tissues.

• Hemoglobin contains 4 oxygen binding units (Hb), it reacts with 4 molecules of oxygen to form oxyhaemoglobin

oxyhaemoglobin dissociation curve

• Shows the relationship between pO₂ (partial pressure of oxygen) and hemoglobin saturation.

• At low pO₂:

  • Hemoglobin has low affinity for oxygen.

  • Fe²⁺ is not in the best position to bind O₂.

• When one O₂ molecule binds:

  • Hemoglobin changes shape (cooperative binding).

  • Makes it easier for more O₂ to bind.

  • Causes the steep rise in the curve.

• The fourth O₂ binds less easily — curve flattens at the top.

🔄 Curve Shifts – What Affects Oxygen Binding

• Right Shift = Hemoglobin releases O₂ more easily (lower affinity).

• Left Shift = Hemoglobin holds onto O₂ more tightly (higher affinity).

Factors Affecting the Curve:

• Temperature:

  • ↑ Temp → Shift right

  • ↓ Temp → Shift left

• pCO₂:

  • ↑ pCO₂ → Shift right

  • ↓ pCO₂ → Shift left

• 2,3-BPG (2,3-DPG):

  • ↑ 2,3-BPG → Shift right

  • ↓ 2,3-BPG → Shift left

• pH (Bohr effect):

  • ↑ pH (alkaline) → Shift left

  • ↓ pH (acidic) → Shift right

oxygen exchange in lungs and tissues

• In the lungs, oxygen diffuses from the alveoli into the pulmonary capillaries because the partial pressure (PO2) in the alveoli is greater (100mmHg) than the partial pressure in the capillaries (40mmHg).

• In the other tissues of the body, a higher PO2 in the capillaries (100mmHg) than in the tissues (40mmHg) causes oxygen to diffuse into the surrounding cells.

transport CO2 in blood

• Initially Co2 diffuses from the tissue and into the blood Co2 is a lot more soluble in blood than O2, so blood carries more dissolved CO2 than O2.

  • 10% of the CO2 is transported in the dissolved form.

  • hemoglobin bound to CO2 is called carbaminohemoglobin. (30%): CO2 + Hb  HbCO2

  • In the form of bicarbonate (60%)

• carbonic anhydrase

  • CO2 + H2O  H2CO3  HCO3- + H+

  • CO2 is converted into bicarbonate ion (HCO3-) by carbonic anhydrase:

exchange of CO2 in lungs and tissue

• When O2 is used by the cells and becomes CO2

• this increases the intracellular partial pressure of CO2

• CO2 diffuses from tissue cells →capillary blood → lungs. - diffuses →pulmonary capillaries → alveoli →expired.

• CO2 always travels the opposite direction than O2.

• CO2 is more soluble than O2 so diffuses at a faster rate.

• That means that the pressure difference required for diffusion od CO2 is lesser than the pressure difference of O2.