Internal Respiration and Gas Exchange Principles

Internal Respiration

• Internal respiration is the gas exchange between systemic capillaries and tissues.
• Oxygen diffuses from blood (high partial pressure) to tissues (low partial pressure).
• Carbon dioxide diffuses from tissues (high partial pressure) to blood (low partial pressure).
• This process deoxygenates the blood returning to the heart.

Gas Exchange Principles

• Gases move passively down pressure gradients across permeable membranes.
• A steeper pressure gradient leads to faster diffusion.
• Dalton's Law: Each gas in a mixture exerts its own partial pressure independently.
• Total pressure is the sum of the partial pressures of all gases.
• Henry's Law: The amount of gas dissolved in a liquid depends on its partial pressure and solubility.
• Carbon dioxide is more soluble in plasma than oxygen.

Gas Transport

• Oxygen has low solubility in plasma. ~97% of oxygen binds to hemoglobin forming oxyhemoglobin.
• Oxygen saturation depends on PO2, pH (Bohr shift), PCO2, and temperature.
• Bohr Shift: Increased CO2 in tissues forms carbonic acid (H2CO3), which dissociates to H+ and HCO3-.
• Elevated H+ lowers blood pH, reducing hemoglobin's oxygen-binding capacity, promoting oxygen release where CO2 levels are high.
• Carbon dioxide transport:
  • 7% dissolved in plasma.
  • 23% binds to hemoglobin (carbaminohemoglobin).
  • 70% converted to bicarbonate ions (HCO3-) in plasma.

Control of Respiration

• Chemoreceptors in the aortic and carotid arteries signal the brain's respiratory center.
• CO2 changes (via H+ and pH effects) are the primary stimuli for chemoreceptors.
• O2 receptors respond to significant O2 level changes.
• Hyperventilation increases breathing rate, expelling CO2, lowering PCO2, and reducing acidity.
• Hypoventilation decreases breathing rate, retaining CO2, increasing PCO2, and raising acidity.

Significance

• Internal respiration provides tissues with oxygen for metabolic processes and removes the waste product carbon dioxide.
• The regulation of respiration ensures adaptability to changing metabolic demands.