Gas Exchange in Humans

Human gas exchange system

  • Consists of lungs and air passages. This system allows Oxygen to enter the blood and Carbon Dioxide to leave the blood through the alveoli. The lungs are in the chest in the thoracic cavity, protected by the ribcage

  • System is inside the body because:

    • Air isnt dense enough to support and protect the delicate structure

    • The body would lose water and dry out

Pathway of Air

  1. Air enters the trachea

  2. Air travels into the two bronchi, with one bronchus going to each lung

  3. Air travels into smaller airways (bronchioles)

  4. Air travels into cluster of air sacs (alveoli) at the ned of the bronchioles

Cilliated Epithelium

  • Cilliated epithelium is located throughout most of the airways

  • Contains Goblet cells and cilliated epithelial cells

  • Goblet Cells - Produce and secrete mucus traps dust and microbes

  • Ciliated epithelial - These waft the mucus upward to the mouth so it can be swallowed

Structure and Adaptations of Airways

  • Trachea:

    • Reinforced with cartilage to keep airway open

    • Smooth muscles can contract or relax to constrict or dilate the airway and change airway

    • Elastic tissue allows for stretching and recoiling

    • Lined with cilaited epithelial cells and goblet cells

  • Bronchioles

    • No cartilage, can change shape

    • Smooth muscles can contract or relax to constrict or dilate airway and change airflow

    • Elastic tissue allows for stretching and recoiling

Alveoli and Blood Vessels

  • Alveoli - tiny air sacs at the ends of bronchioles. They are surrounded by a network of capillaries so gases can be exchanged between the air in the alveoli and the blood

  • Gas exchange occurs across the alveolar membrane of the alveoli

  • Oxygen diffuses from the alveoli to pulmonary capillaries where it binds to the haemoglobin in the red blood cells

  • Carbon Dioxide dissociates from the haemoglobin and diffuses from the blood into the alveoli

Adaptations of the alveoli for gas exchange

  • One layer of epithelial cell - fast difussion

  • Large surface area - This increase rate of gas exchange

  • Partially Permeable - only certain gases can move across the the wall

  • Surrounded by network of capillaries - These bring blood close to air for gas exchange

  • Elastic fibres - allow for stretching and recoiling

  • Collagen fibres - These contain strong collagen that prevents alveoli from bursting and limits overstretching