Topic 6.4 Gas Exchange

Question 1

6.4.1 Distinguish between ventilation, gas exchange and cell respiration.

Answer 1

Ventilation: the repeated filling of lungs with air and then breathing that air out; i.e. exchange of gas between lungs and outside air

Gas exchange: the movement (diffusion) of gases; in lungs, O₂ typically diffuses into bloodstream & CO₂ typically diffuses into lung tissue; exchange of gas between alveoli, capillaries and body cells (internal respiration)

Cell respiration: exchange of gases in mitochondria that produce energy (O₂ is a reactant, CO₂ is a product)

Question 2

6.4.2 Explain the need for a ventilation system.

Answer 2

• we are too thick (1 mil. cells thick in some places), so need ventilation system to move enough O₂ around our bodies
• conc’n of respiratory gases within lungs encourages diffusion of each gas in a direction that is beneficial to the body
  
  • continuous action of breathing replenishes [O₂] in lungs
  • keeps O₂ in lungs at high level in comparison to O₂ levels in blood capillaries in the lungs ∴ O₂ diffuses into capillaries & CO₂ diffuses into lung tissue

Question 3

6.4.3 Describe the features of alveoli that adapt them to gas exchange.

Answer 3

Alveoli:

• have spherical shape (shape with highest SA:V ratio): provides large surface area for respiratory gases to diffuse through
• are one cell thick: easier diffusion because respiratory gases don’t have to diffuse through many layers
• have a moist inner lining: allows gases to dissolve for easier, efficient diffusion
• are surrounded by capillaries: gases don’t need to diffuse far to reach capillaries and bloodstream
• are very small: provide short distance for diffusion
• millions in each lung: increase surface area

Question 4

6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli.

Answer 4

also pharynx (where the mouth and nose tube meet near top) and larynx (looks like a square U somewhere in the neck)

Question 5

6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostals muscles, the diaphragm and abdominal muscles.

Answer 5

1. at resting, pressure inside = pressure outside
2. when inhaling:
   
   • diaphragm contracts, flattens and moves down
   • external intercostal muscles contract, moving ribs up and out
   • volume ↑, pressure ↓
   • pressure inside < pressure outside ∴ air passively flows into lungs from outside
3. when exhaling:
   
   • abdominal muscles contract, pushing diaphragm up into dome shape
   • internal intercostal muscles contract (external intercostal muscles relax), moving ribcage down and in
   • volume ↓, pressure ↑
   • pressure inside > pressure outside ∴ air flows out from lungs to outside body