[6.6] structure of the human gas-exchange system

Question 1

why is the volume of oxygen that has to be absorbed and the volume of carbon dioxide that must be removed large in mammals?

Answer 1

• they are relatively large organisms with a large volume of living cells
• they maintain a high body temperature which is related to them having a high metabolic and respiratory rates

Question 2

what are the key features of the human gas-exchange system? (6)

Answer 2

• lungs
• ribs / rib cage
• trachea
• bronchi
• bronchioles
• alveoli

Question 3

what is the ribcage and the role of ribs?

Answer 3

• a bony box which supports and protects the lungs
• ribs can be moved by the muscles between them
• this means the lungs can be ventilated by a tidal stream of air, thereby ensuring that the air within them is constantly replenished

Question 4

what is the trachea?

Answer 4

• a flexible airway that is supported by rings of cartilage
• the cartilage prevents the trachea collapsing as the air pressure inside falls when breathing in
• tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells

Question 5

what are bronchi?

Answer 5

• two divisions of the trachea, each leading to one lung
• they are similar in structure to the trachea, and, like the trachea, they also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat
• the large bronchi are supported by cartilage, although the amount of cartilage is reduced as the bronchi get smaller

Question 6

what are the bronchioles?

Answer 6

• a series of branching subdivisions of the bronchi
• their walls are made of muscle lined with epithelial cells
• this muscle allows them to constrict so that they can control the flow of air in and out of the alveoli

Question 7

what are the alveoli?

Answer 7

• minute air-sacs at the end of bronchioles
• between the alveoli there are some collagen and elastic fibres
• the alveoli are lined with epithelium
• the elastic fibres allow the alveoli to stretch as they fill with air when breathing in
• they then spring back during breathing out to expel the carbon dioxide-rich air
• alveolar membrane is the gas-exchange surface