43- Oxygen transport in the blood. Oxyhemoglobin dissocitation curve: Oxygen exchange in the lungs and tissues.53- Transport of CO2 in the blood. Exchange of CO2 in the lungs and tissues.

- Oxygen transport in the 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% of blood oxygen is bound to haemoglobin) forming oxyhaemoglobin.

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

• The partial pressure of oxygen (Pₒ₂) is higher in arterial blood (capillaries) than in peripheral tissues.

• This difference allows oxygen to diffuse from the capillaries into the tissues, down its concentration gradient.

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

oxyhaemoglobin

Oxyhemoglobin dissocitation curve

ability for haemoglobin to bind to oxygen depends on the partial

pressure gradient of oxygen.

Oxyhemoglobin dissociation curve is for normal, average

blood,

factors affects the strengh of oxygen binding to hemoglobin

• Shift to the Right:

  • Represents decreased affinity of hemoglobin for oxygen.

  • Hemoglobin releases oxygen more easily to the tissues.

  • Happens when:

    • ↑ Temperature

    • ↑ pCO₂ (carbon dioxide)

    • ↑ 2,3-Diphosphoglycerate (2,3-DPG)

    • ↓ pH (more acidic)

  • This is useful during exercise or conditions where tissues need more oxygen.

• Shift to the Left:

  • Represents increased affinity of hemoglobin for oxygen.

  • Hemoglobin holds onto oxygen more tightly, less is released to tissues.

  • Happens when:

    • ↓ Temperature

    • ↓ pCO₂

    • ↓ 2,3-DPG

    • ↑ pH (more alkaline)

  • This happens in conditions where oxygen needs to be conserved or uptake in lungs is prioritized.

•When one oxygen binds to a heme, it causes a conformational (shape) change in hemoglobin.

• This shape change increases hemoglobin’s affinity for oxygen at the remaining heme sites.

• As a result, subsequent oxygen molecules bind more easily.

• This cooperative binding causes the steep middle part of the oxyhemoglobin dissociation curve.

• It means oxygen saturation increases rapidly as partial pressure of oxygen rises.

• last heme is hard to bind - bc binding sites are occupied so shape can change less to accomodate it

Oxygen exchange in the 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 of CO2 in the blood

CO₂ Transport in Blood

• CO₂ diffuses from tissues into the blood.

• CO₂ is much more soluble in blood than O₂, so more CO₂ is carried dissolved.

1. Dissolved CO₂:

   • About 10% of CO₂ is transported dissolved in plasma.

2. Carbaminohemoglobin:

   • About 30% of CO₂ binds to hemoglobin, forming carbaminohemoglobin (HbCO₂).

   • Reaction:

     CO₂+Hb↔HbCO2

3. Bicarbonate ion (HCO₃⁻):

   • About 60% of CO₂ is converted to bicarbonate in red blood cells by the enzyme carbonic anhydrase.

   • Reaction:

     CO₂+H₂O↔H₂CO₃↔HCO₃−+H+

Gas exchange

• Cells use O₂ and produce CO₂ as a waste product.

• This increases the partial pressure of CO₂ inside cells.

• CO₂ then diffuses from tissue cells → capillary blood → lungs.

• In the lungs, CO₂ diffuses from pulmonary capillaries → alveoli → expired air.

• CO₂ moves in the opposite direction to O₂ (O₂ goes into tissues, CO₂ out).

• CO₂ is more soluble than O₂, so it diffuses faster.

• Therefore, CO₂ requires a smaller partial pressure gradient to diffuse compared to O₂.