movement n exchnage gasses

Pathway of Inhaled Air

  • Inhalation draws atmospheric air into the lungs through a specific respiratory pathway.

  • Sequential anatomical pathway of inhaled air:

    • Nasal cavity

    • Trachea

    • Bronchi

    • Bronchioles

    • Alveoli

  • Gas composition of air reaching the alveoli:

    • Rich in oxygen (O2O_2)

    • Poor in carbon dioxide (CO2CO_2)

Mechanism of Gas Exchange in the Lungs

  • Gaseous exchange occurs within the lungs through the physical process of diffusion.

  • Definition of diffusion: The movement of substances from an area of higher concentration to an area of lower concentration.

  • Concentration gradient of oxygen in the alveolus:

    • Inhaled air inside the alveolus contains a higher concentration of oxygen compared to the concentration of oxygen in the blood capillaries.

  • Pathway of oxygen diffusion across respiratory membranes:

    • Diffuses through the wall of the alveolus.

    • Diffuses through the wall of the surrounding blood capillaries.

    • Enters the blood stream.

Haemoglobin and Oxygen Transport

  • Red blood cells contain a dark red-coloured compound known as haemoglobin.

  • Combination of oxygen and haemoglobin:

    • Haemoglobin combines with oxygen to form oxyhaemoglobin.

    • Chemical formula representation: Haemoglobin+Oxygen→Oxyhaemoglobin\text{Haemoglobin} + \text{Oxygen} \rightarrow \text{Oxyhaemoglobin}

    • Key characteristics of oxyhaemoglobin:

    • Unstable chemical compound.

    • Bright red in colour.

  • Circulation of oxygenated blood:

    • Blood containing oxyhaemoglobin is transported from the lungs to the heart.

    • The heart pumps the oxygenated blood to all other parts of the body.

  • Release of oxygen at target tissues:

    • Body cells and surrounding tissue fluid maintain a low concentration of oxygen.

    • Due to its unstable nature, oxyhaemoglobin decomposes upon reaching environments with a low oxygen concentration.

    • Decomposition releases oxygen molecules into the surrounding tissues and converts the compound back into dark red haemoglobin.

Cellular Respiration and Carbon Dioxide Removal

  • Oxygen uptake by body cells:

    • Released oxygen diffuses from red blood cells across capillary walls into the body cells.

  • Process of cellular respiration:

    • Diffused oxygen oxidizes glucose molecules inside body cells to yield energy.

    • Chemical equation for cellular respiration: Glucose+Oxygen→Carbon Dioxide+Water+Energy\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy}

  • Concentration gradient of carbon dioxide:

    • Continuous cellular respiration creates a higher concentration of carbon dioxide in the body cells than in the blood capillaries.

  • Diffusion and removal pathway of carbon dioxide:

    • Carbon dioxide diffuses out of body cells into the blood capillaries down its concentration gradient.

    • Transported via blood back to the alveoli in the lungs.

    • Excreted from the lungs into the atmosphere during exhalation.

Structural Adaptations of Alveoli for Gas Exchange

  • Specific structural adaptations of alveoli increase efficiency and maximize gas exchange:

    • Very Thin Walls:

    • Both the alveolar wall and blood capillary wall are extremely thin, composed of only one layer of cells.

    • Shortens diffusion distance, thereby facilitating and increasing the rate of gas diffusion.

    • Moist Alveolar Wall:

    • The inner surface wall of the alveolus is kept moist.

    • Allows respiratory gases to dissolve in moisture prior to diffusing across into blood capillaries.

    • Large Surface Area:

    • The human lungs contain millions of individual alveoli.

    • Provides a vast total surface area dedicated to gaseous exchange.

    • Compact Network of Capillaries:

    • Each alveolus is surrounded and covered by a dense, compact network of blood capillaries.

    • Maximizes contact area and increases the rate of gas exchange between alveoli and blood capillaries.

Factors Influencing the Rate of Diffusion

  • Gas concentration differential across respiratory membranes directly dictates diffusion rates:

    • The difference in concentration of a gas between the alveoli and blood capillaries is a primary driving factor.

    • The greater the difference in concentration of a gas between the alveoli and blood capillaries, the higher the rate of diffusion of that gas.