Gas Exchange in Humans (IGCSE)

Introduction

• Channel: IGCSE Study Buddy
• Topic: Gas Exchange in Humans
• Purpose: Revise biology topics from the Cambridge IGCSE syllabus

Key Features of Gas Exchange Surfaces

• Large surface area: Increases space for diffusion
• Thin surface: Reduces diffusion distance, allowing faster rate
• Good blood supply: Maintains concentration gradients
• Good ventilation with air: Maintains concentration gradients of CO2 and O2

Parts of the Breathing System

• Larynx: Contains vocal cords
• Trachea: Windpipe connecting throat to lungs
• Lungs: Main organs for gas exchange
• Diaphragm: Flat muscle under lungs, changes chest volume during breathing
• Bronchi: Tubes from trachea to lungs
• Bronchioles: Smaller tubes from bronchi to alveoli
• Alveoli: Tiny air sacs for gas exchange, surrounded by capillaries
• Capillaries: Blood vessels around alveoli
• Ribs: Bones protecting lungs
• Intercostal muscles: Control rib movements during breathing
  • External: Outside the rib cage
  • Internal: Inside the rib cage

Function of Cartilage in the Trachea

• Strengthens and supports trachea, keeping it open

Ventilation (Breathing)

• Inspiration (Inhalation): Breathing in
  • External intercostal muscles contract, internal relax
  • Rib cage moves up and out
  • Diaphragm contracts and flattens
  • Volume of thorax increases, pressure decreases
  • Air moves into lungs
• Expiration (Exhalation): Breathing out
  • External intercostal muscles relax, internal contract
  • Rib cage moves down and in
  • Diaphragm relaxes and domes up
  • Volume of thorax decreases, pressure increases
  • Air moves out of lungs

Differences in Inspired and Expired Air

• Oxygen: 21% in inspired air, 16% in expired air
• Carbon Dioxide: 0.04% in inspired air, 4% in expired air
• Water Vapor: Less in inspired air, more in expired air
• Reason: Gas exchange at alveoli; O2 diffuses into blood, CO2 out

Investigating Physical Activity's Effect on Breathing

• Procedure:
  • Measure breaths per minute and chest expansion at rest
  • Exercise for fixed time (e.g., 3 mins)
  • Measure breaths per minute and chest expansion post-exercise
• Outcome: Increase in both rate and depth of breathing
• Reason: Faster respiration in cells, more CO2 detected, brain signals increased breathing rate

Protection from Pathogens and Particles

• Mucus: Traps pathogens and particles
• Goblet cells: Produce mucus lining the respiratory tract
• Cilia: Tiny hairs on ciliated epithelial cells, push mucus to throat to be swallowed

Conclusion

• Summary: Chapter 11 covers the human gas exchange system, its components, and mechanisms
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