LEARNING OUTCOME
• List the features of gas exchange surfaces in humans, limited to
large surface area, thin surface, good blood supply and good
ventilation with air
• What makes the lungs an efficient gas exchange surface?
1. Made up of millions of alveoli (air sacs) that provide a large surface
area
2. The wall of the alveoli and the blood capillary have thin surface as
both are made up of only single layer of cells
3. There is a network of capillary under the alveoli that provides a
good blood supply
4. Continuous breathing provides good ventilation (exchange) of air
rich in oxygen and air rich in carbon dioxide
LEARNING OUTCOME
• Name and identify the internal and external intercostal muscles
LEARNING OUTCOME
• State the functions of the cartilage in the trachea
Cartilage – present in the trachea and the bronchi
Prevents these tubes from collapsing while exhaling (breathing out)
LEARNING OUTCOME
• Explain the role of the ribs, the internal and external intercostal
muscles and the diaphragm in producing volume and pressure
changes in the thorax leading to the ventilation of the lungs
• Internal intercostal muscles contract while
the external intercostal muscles relax
• The ribcage contracts back and down
• Diaphragm muscle relaxes and becomes
dome shaped
• Volume of the chest cavity decreases
• Pressure increases
• Air from the lungs at higher pressure is
forced out to lower atmospheric pressure
LEARNING OUTCOME
• State the differences in composition between inspired and expired
air, limited to oxygen, carbon dioxide and water vapour
• Percentage of Nitrogen is the same in both inspired & expired air
• Oxygen is more in the inspired air (21 – 16 = 5% more)
• Carbon dioxide is more in the expired air (4 – 0.04 = 3.96%)
• Explain the differences in composition between inspired and
expired air
LEARNING OUTCOME
• Use limewater as a test for carbon dioxide to investigate the
differences in composition between inspired and expired air
• Carbon dioxide turns limewater, Ca(OH)2 milky or cloudy
• We know, that expired air contains more carbon dioxide
• Air is inhaled though
flask A
• Air is exhaled to
flask B
• Limewater in flask B
turns cloudy faster
• It is because exhaled
air contains more
carbon dioxide
LEARNING OUTCOME
• Explain the link between physical activity and rate and depth of
breathing in terms of the increased carbon dioxide concentration in
the blood, detected by the brain, causing an increased rate of
breathing
• During and after the exercise both the rate (number of breaths per
minute) and the depth (how deep we breathe) increases
Explanation
• During exercise the muscles contract more so they require more
energy
• So the respiration rate increases in the muscles
• More carbon dioxide is produced and diffuses into the blood
• This makes the blood acidic (low pH, as CO2 is acidic)
• This low pH is detected by the brain (hypothalamus)
• So to bring the pH back to normal by removing carbon dioxide
faster, the brain sends impulses to increase the rate of breathing
LEARNING OUTCOME
• Explain the role of goblet cells, mucus and ciliated cells in protecting
the gas exchange system from pathogens and particles
The inner walls of the trachea and the bronchi are lined (covered) by
mucus, ciliated epithelial cells and goblet cells
mucus – keeps the surface moist and traps the dust, pollen and
pathogens that we may inhale
Goblet cells – secretes slimy substance called mucus
Ciliated epithelial cells – sweeps the mucus with the trapped substances
out of the trachea into the food pipe (oesophagus)