Respiratory System Notes PT 2

Three Basic Steps of Respiration

• Pulmonary Ventilation:

  • Exchange of gases between the atmosphere and the lungs, a fundamental process ensuring that oxygen enters the bloodstream and carbon dioxide is expelled.

  • Includes two distinct phases:

    • Inhalation: The active phase involving the diaphragm and intercostal muscles contracting to expand the thoracic cavity, allowing air to flow into the lungs.

    • Exhalation: The passive phase, often relying on the elastic recoil of lung tissue and the relaxation of respiratory muscles to expel air from the lungs.

• External Respiration:

  • The crucial gas exchange process occurring in the alveoli, where oxygen diffuses from the air in the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli to be exhaled.

  • This process is heavily influenced by the surface area of the alveoli, the thickness of the respiratory membrane, and the partial pressures of the gases involved.

• Internal Respiration:

  • Refers to the exchange of gases between the blood in the capillaries and the tissues of the body.

  • Oxygen is delivered to cells for metabolic processes while carbon dioxide, a byproduct of metabolism, enters the bloodstream to be transported back to the lungs for expulsion.

Diffusion in the Respiratory System

• Alveoli and Capillaries:

  • Gas exchange occurs across the thin walls of the alveoli into the adjacent pulmonary capillaries, leveraging differences in concentration and partial pressures.

  • Partial Pressure:

    • This concept drives diffusion; gases will move from regions of higher partial pressure (e.g., more oxygen in the alveoli) to lower partial pressure (e.g., oxygen-poor blood) until equilibrium is reached.

    • Factors enhancing the diffusion rate include increased surface area of alveoli, reduced diffusion distance (thin alveolar walls), and lighter molecular weight of gases involved, aiding in swift gas exchange.

Gas Laws Relevant to Respiration

1. Dalton’s Law (Law of Partial Pressures):

   • Each gas in a mixture exerts its own pressure independently, known as its partial pressure.

   • The sum of all partial pressures equals the total pressure of the gas mixture.

   • Example: Atmospheric pressure = 760 mmHg, comprised largely of:

     • 78.6% nitrogen (partial pressure approximately 597 mmHg)

     • 20.9% oxygen (partial pressure approximately 159 mmHg)

     • 0.04% carbon dioxide (partial pressure approximately 0.03 mmHg)

2. Henry’s Law:

   • Relates to the solubility of gases in liquid and states that at a constant temperature, the amount of a gas that dissolves in a liquid is proportional to its partial pressure above the liquid.

   • Example: Under physiological conditions, carbon dioxide is 24 times more soluble in plasma than oxygen, which has significant implications for transport and gas exchange.

   • Soda can analogy:

     • When a soda can is sealed, carbon dioxide is under pressure, dissolving into the liquid. Upon opening, this pressure releases, allowing gas to escape until equilibrium is re-established with atmospheric pressure.

External Respiration

• Gas Movement:

  • Oxygen (O₂) moves from the alveoli, where its concentration is high, into the blood, where its concentration is lower; conversely, carbon dioxide (CO₂) moves from the blood, where its concentration is higher, into the alveoli to be expelled.

• Factors Affecting Rate:

  • The rate of gas exchange is influenced by the differences in partial pressures of O₂ and CO₂, the total surface area available for gas exchange (larger area facilitates more gas exchange), and the molecular weights of the gases involved (lighter gases diffuse more easily).

Oxygen Transport in Blood

• Plasma:

  • Oxygen is not very soluble in plasma; only about 0.3 ml O₂ per 100 ml of blood is transported in this form, representing a mere 1.5% of the total blood's oxygen-carrying capacity.

• Red Blood Cells:

  • Hemoglobin significantly increases oxygen transport capacity;

    • Each hemoglobin molecule can bind up to four O₂ molecules.

    • Total oxygen carried by hemoglobin can reach 19.7 ml per 100 ml of blood (98.5% of capacity).

    • Overall, the total oxygen-carrying capacity of blood is roughly 20 ml O₂ per 100 ml blood, highlighting the efficiency of this transport mechanism in meeting the body's metabolic needs.

Affinity Factors for Oxygen

• Affinity:

  • This term refers to how tightly hemoglobin binds to oxygen, which is critical for effective oxygen transport and delivery to tissues.

  • Factors influencing this affinity include:

    • pH Influence:

      • Lower pH (more acidic conditions) reduces oxygen's affinity for hemoglobin (known as the Bohr effect), facilitating O₂ release to tissues that are metabolically active.

    • CO₂ Impact:

      • Increased levels of CO₂ in the blood also decrease hemoglobin’s affinity for oxygen, leading to enhanced O₂ release and correlating with decreased pH levels.

    • Temperature Influence:

      • Higher temperatures, typically experienced during exercise or increased metabolic activity, also decrease affinity, promoting O₂ release to active tissues.

Carbon Dioxide Transport

• Carbon dioxide is more soluble in plasma compared to oxygen (about 24 times more), which plays a significant role in its transport back to the lungs.

• The transport forms of CO₂ include:

  • Dissolved CO₂: About 7% is transported as dissolved gas.

  • Carbaminohemoglobin: Approximately 23% is bound to hemoglobin, forming carbamino compounds.

  • Bicarbonate ions: Roughly 70% of CO₂ is converted to bicarbonate ions (HCO₃⁻) within red blood cells, a critical process that also helps buffer blood pH.

Chemical Regulation of Respiration

• Chemoreceptors:

  • Specialized receptors that monitor levels of CO₂, O₂, and blood pH to help regulate the rate and depth of breathing.

  • Located centrally in the medulla oblongata and peripherally in the aorta and carotid arteries, they are sensitive to changes in these parameters.

• Respiratory Control Centers:

  • These centers, located in the medulla and pons of the brainstem, manage the rhythm and depth of breathing, integrating signals from chemoreceptors and higher brain centers.

• Cortical Influences:

  • Conscious control of breathing can be modified by emotional states (such as stress or relaxation) and voluntary acts (such as speaking, singing, or holding one's breath), allowing for adaptability in respiratory patterns.

Health Impacts of Smoking

• Respiratory Diseases:

  • Smoking damages the respiratory tract's cilia, diminishing their ability to clear mucus and pathogens, leading to chronic cough and mucus production.

  • Inhaled carbon monoxide competes with oxygen for binding to hemoglobin, impairing oxygen transport and thereby affecting tissue oxygenation.

• Cancer Risks:

  • Tobacco smoke contains numerous carcinogens that significantly increase the risk of various cancers, particularly lung cancer, and also contribute to heart disease.

• Other Risks:

  • Chronic smoking can lead to gum disease, increased incidence of blood clotting disorders, emphysema (permanent lung damage), and higher vulnerability to respiratory infections due to compromised immune responses.

Other Respiratory Conditions

• Pneumonia:

  • An inflammatory condition of the lungs, often following viral or bacterial infections, more prevalent in vulnerable populations such as the elderly or those with preexisting health conditions.

• Respiratory Distress Syndrome:

  • Commonly seen in premature infants due to insufficient surfactant levels, leading to difficulty in breathing and increased risk of lung collapse.

• Pulmonary Embolism:

  • Caused by blood clots that obstruct blood flow in pulmonary arteries; this condition is preventable with proper medical care and lifestyle choices, such as regular exercise and avoiding prolonged immobility.

Conclusion

• Overall, the respiratory system performs the essential function of efficiently transporting gases, allowing for proper oxygenation of tissues and removal of carbon dioxide. This process is tightly regulated by a complex interaction of chemical and physical factors, while various conditions—such as smoking and pulmonary diseases—can significantly impede respiratory function. Understanding these mechanisms is vital for promoting respiratory health and making informed lifestyle choices that can mitigate health risks.