Transport of Gases: Oxygen and Carbon Dioxide

Oxygen Transport

Methods of Transport

• Bound to Hemoglobin
  • Oxygen binds to the iron atom in hemoglobin.
  • Constitutes 98-99% of oxygen transport.
  • Each hemoglobin molecule can carry four oxygen molecules.
• Dissolved in Blood Plasma
  • Only 1-2% due to low solubility in water.

Hemoglobin Forms

• Oxyhemoglobin: Hemoglobin fully saturated with oxygen.
• Deoxyhemoglobin: Hemoglobin after oxygen is released to tissues.

Oxygen Binding and Release

• Binding shape change facilitates more oxygen binding.
• Oxygen loading and unloading influenced by:
  • Partial pressure of oxygen
  • Temperature
  • Blood pH
  • Partial pressure of CO2
  • 2,3-Bisphosphoglycerate (BPG)

Partial Pressure of Oxygen

• Arterial Blood
  • Partial pressure: ~100 mmHg, 98% saturation, 20 ml O2/100 ml blood.
• Venous Blood
  • Partial pressure: ~40 mmHg, 75% saturation.
• Venous Reserve
  • Oxygen remaining in venous blood after tissue delivery.

Influences on Hemoglobin Saturation

• Temperature: Increased temperature lowers saturation.
• pH and CO2: High acidity (low pH) and high CO2 decrease affinity.
• BPG: Increases with low oxygen, reduces affinity for oxygen.

Carbon Dioxide Transport

Methods of Transport

• Dissolved in Plasma: 7-10% transported this way.
• Chemically Bound to Hemoglobin
  • Forms carbaminohemoglobin.
  • Binds to amino acids, not iron.
• As Bicarbonate Ions
  • Main transport form.
  • CO2 enters RBC, forms bicarbonate ions via carbonic anhydrase.

Chloride Shift

• Systemic Capillaries: Bicarbonate leaves RBC, chloride enters.
• Pulmonary Capillaries: Bicarbonate re-enters RBC, chloride exits.

Haldane Effect

• Lower oxygen pressure increases CO2 carrying capacity of hemoglobin.

Buffering and Blood pH

Carbonic Acid-Bicarbonate Buffer System

• Maintains Blood pH: Range of 7.35-7.45.
• Acts as base (bicarbonate ion) or acid (carbonic acid) to balance pH.

Respiratory Rate Influence

• Slow breathing retains CO2, lowers pH (more acidic).
• Rapid breathing releases more CO2, raises pH (more basic).

Types of Hypoxia

• Anemic Hypoxia
• Ischemic Hypoxia
• Histotoxic Hypoxia
• Hypoxemic Hypoxia
• Carbon Monoxide Poisoning
  • Causes inadequate oxygen delivery to tissues.