Summary Notes: Gas Exchange in Humans

Human Respiratory System

Key Structures

• Lungs: Main organs for gas exchange.
• Ribs and Intercostal Muscles: Protect lungs and heart; aid in breathing by expanding/contracting the rib cage.
• Larynx: Contains vocal cords.
• Trachea: Connects throat to bronchi; supported by C-shaped cartilage rings.
• Bronchi: Carries air from trachea to lungs; branches into left and right lungs.
• Bronchioles: Smaller branches from bronchi leading to alveoli.
• Alveoli: Site of gas exchange; oxygen diffuses into blood, carbon dioxide diffuses out.

Ventilation

• Breathing In:
  • Internal intercostal muscles relax; external muscles contract.
  • Ribs move up and out; diaphragm flattens.
  • Thorax volume increases, causing air to diffuse into lungs.
• Breathing Out:
  • Thorax volume decreases, increasing pressure to push air out.
  • Generally passive, but can involve muscle contraction when forced.

Composition of Air

• Inhaled air: Higher oxygen content.
• Exhaled air: More carbon dioxide and water vapor.

Impact of Exercise

• Increases rate of respiration and demand for oxygen.
• Produces more carbon dioxide, prompting faster breathing and heart rate.

Adaptations of Exchange Surfaces

• Large Surface Area: Facilitates efficient diffusion.
• Thin Surface: Short diffusion distance for rapid exchange.
• Good Blood Supply: Maintains concentration gradient.
• Good Ventilation: Ensures efficient gas exchange.
• Moisture: Allows gases to dissolve and diffuse effectively.

Protection from Pathogens

• Goblet Cells: Secrete mucus to trap pathogens.
• Cilia: Move mucus towards throat.
• Stomach Acid: Destroys swallowed pathogens.