Gases in Alveolus and Blood

Gases in the Alveolus and Blood

  • Alveolus Gas Exchange: Gases present in alveolus: oxygen and carbon dioxide.

  • Partial Pressure:

    • Defined as the pressure exerted by a gas in a mixture of gases.

    • Example:

      • Arterial oxygen partial pressure (PaO2): 40 mmHg.

      • Arterial carbon dioxide partial pressure (PaCO2): 47 mmHg.

      • Alveolar oxygen partial pressure: 100 mmHg.

      • Alveolar carbon dioxide partial pressure: varies, affecting diffusion process.

Blood Flow to Lungs

  • Blood is directed to the lungs for gas exchange through the pulmonary trunk and its branches: left and right pulmonary arteries.

  • From the heart’s right ventricle, deoxygenated blood flows to the lungs.

  • The process is based on the principle of diffusion, where gases move from areas of high partial pressure to low.

Gas Exchange Mechanism

  • Oxygen Movement: Oxygen moves from the alveoli (high pressure - 100 mmHg) into the blood (low pressure - 40 mmHg).

  • The blood becomes saturated with oxygen as it moves toward the heart (now 100 mmHg).

  • Carbon Dioxide Movement: Carbon dioxide moves from the blood (high pressure - 47 mmHg) to the alveoli (lower pressure), resulting in a partial pressure drop to 40 mmHg post-exchange.

Oxygen Delivery to Tissues

  • Blood with oxygen (100 mmHg) is pumped from the left ventricle into the aorta and delivered to body tissues.

  • At tissues, oxygen is utilized, reducing the blood’s oxygen partial pressure to 40 mmHg.

  • Carbon Dioxide Production: During cellular respiration, tissues produce carbon dioxide, increasing its partial pressure in the blood to 47 mmHg before it returns to the lungs.

Importance of Partial Pressures

  • Significance of Numbers: The partial pressures of oxygen and carbon dioxide are crucial; they govern gas exchange efficiency. These numbers (40 mmHg for oxygen in veins and 47 mmHg for carbon dioxide in arteries) are important for medical diagnostics, such as ABG (Arterial Blood Gases) tests.

Respiratory Membrane and Diffusion

  • The respiratory membrane is composed of two cell layers: alveolar type I cells and endothelial cells of blood vessels.

  • Diffusion Process: Gases diffuse across the membrane due to a pressure gradient. Factors affecting diffusion:

    • Difference in Pressure: Greater pressure difference increases diffusion rate.

    • Surface Area: More surface area allows for greater exchange; damage reduces effective area.

    • Solubility: Gases that dissolve well in liquid diffuse more easily through the membrane.

    • Thickness: A thinner membrane promotes easier diffusion, pathogens like smoke can thicken this membrane, hindering efficiency.

Clinical Considerations

  • Hyperventilation: During a panic attack, excessive breathing can deplete carbon dioxide, leaving insufficient stimulation for breathing. To counter this, breathing into a bag helps restore carbon dioxide levels.

  • Oxygen Administration Risks: Providing high levels of oxygen can inadvertently decrease carbon dioxide levels, potentially stopping the breathing stimulus in patients. It’s crucial to monitor patients receiving supplemental oxygen to avoid such complications.

Conclusion and Exam Preparation

  • Familiarize yourself with the concepts of partial pressures, blood gas exchange mechanics, and the factors affecting diffusion.

  • Understanding these concepts is essential for medical terminology and patient care in respiratory physiology.