Physiology · MU Sofia

38. Gas diffusion. Physical basis of gas diffusion. Composition of the atmospheric, inspired, alveolar and expired air. Gas diffusion in the lungs and tissues.

Covers the two stages of gas exchange, ventilation and diffusion between alveolar air and blood, and the physical basis of diffusion through simple diffusion, concentration and partial pressure gradients, and Henry's law on solubility. It describes how water vapour dilutes gas partial pressures, the layers of the respiratory membrane, and oxygen and carbon dioxide movement between blood and tissues. It ends with factors that impair lung diffusion, such as reduced surface area, thickened membrane, anaemia and ventilation-perfusion mismatch, with example conditions.

Inside: 3 sections · 5 labelled pictures · 18 flashcards · 5 min

Topic 38 of 104 in the MU Sofia syllabus for Physiology (Dental Medicine, Year 2). The free AceMed note covers it in 3 sections, about 750 words (5 min of reading), with 18 flashcards.

In this note

  1. Gas diffusion. Physical basis of gas diffusion. Composition of the atmospheric, inspired, alveolar and expired air. Gas diffusion in the lungs and tissues.
  2. Gas Diffusion:-
  3. Physical Basis of Gas Diffusion:-

Gas Diffusion:-

  • Gas exchange occurs in two stages:
  1. 1. Ventilation: This is the exchange of air between the atmosphere and the lungs, a process that helps maintain a steep concentration gradient for gas diffusion.
  2. 2. Diffusion of Gases: This process involves the movement of gases between the alveolar air and the blood. It occurs by simple diffusion across the alveolar membrane, following the principle of moving from an area of high concentration to one of low concentration. This exchange occurs primarily in the respiratory zone of the airways.

Physical Basis of Gas Diffusion:-

  • Law of Simple Diffusion: The physical basis of gas diffusion is the law of simple diffusion. This law states that molecules move from an area of high concentration to an area of low concentration across a semi-permeable membrane.
  • Concentration Gradients: This difference in concentration between two areas is called the concentration gradient. The greater the concentration gradient, the faster the rate of diffusion.
  • Oxygen: Inspired air has a high concentration of oxygen (high PO2), and the blood arriving at the alveoli has a low oxygen concentration (low PO2). Oxygen, therefore, moves from the air into the blood.
  • Carbon Dioxide: Inspired air has a low concentration of carbon dioxide (low PCO2), and the blood arriving at the alveoli has a high concentration of carbon dioxide (high PCO2). Carbon dioxide moves from the blood into the air to be exhaled.
  • Partial Pressure Gradients: The rate of diffusion is also influenced by the partial pressure difference (∆P) of the gases.
  • Henry's Law: According to Henry's law, the concentration of a gas in a liquid is also influenced by its solubility. This means a gas with higher solubility will dissolve more readily in a liquid at a given partial pressure.

Composition of Atmospheric, Inspired, Alveolar, and Expired Air

Water vapor in the air influences the partial pressures of gases by diluting them. When gas molecules are diluted, they exert less pressure in a given area, leading to a reduction in their partial pressure.

Gas Diffusion in the Lungs and Tissues

  • Respiratory Membrane: The respiratory membrane is the thin barrier between the air in the alveoli and the blood in the pulmonary capillaries. It consists of:
  • A film of water and surfactant
  • The alveolar wall
  • The capillary wall
  • An interstitial space
  • Diffusion Pathways: Diffusion takes place through these components:
  • Across the phospholipid membranes of the alveolar and capillary cells
  • Through the thin layers of interstitial fluid and plasma

Continue reading free

The whole note, all 3 sections, is free with an AceMed account, with its 18 flashcards. Premium adds flashcard recall, highlights and Ask AI.

Start freeAlready a member? Open the note