Chapter 7: Gas exchange in humans

Question 1

Mucus-secreting cells

Answer 1

• Secretes mucus
• Traps dust particles and microorganisms in inhaled air
• Moisten the inhaled air to prevent drying up of the moist respiratory surface

Question 2

Ciliated epithelial cells

Answer 2

Cilia beat to sweep the mucus towards the pharynx
The mucus is either coughed up or swallowed → most microorganisms are killed by stomach acid

Question 3

Hairs in nostrils

Answer 3

Trap large dust particles in air

Question 4

Rich supply of blood

Answer 4

Warm the inhaled air

Question 5

Pharynx

Answer 5

Common passage for air and food

Question 6

Larynx

Answer 6

• Contains two folds of tissues caled the vocal cords → sound is produced when air passes through them and causes them to vibrate
• Mainly made up of cartilage → prevent the larynx from collapsing due to pressure changes while breathing
• Raised and pressed against the epiglottis while swallowing to prevent food from entering the respiratory tract

Question 7

Trachea

Answer 7

• C-shaped cartillage → prevents the trachea from collapsing due to pressure changes while breathing + opening lies next to the esophagus to allow the esophagus to expand while swallowing
• Walls contain smooth muscles and elastic fibres? regulate the diameter of the airway and hence the airflow
• mucus-secreting cells (goblet cells) + ciliated epithelial cells + rich supply of blood → warm, moisten and clean the inhaled air

Question 8

Bronchi

Answer 8

• Cartillage → prevents the trachea from collapsing due to pressure changes while breathing
• Walls contain smooth muscles and elastic fibres → the contraction and relaxation of the smooth muscles helps regulate the diameter of the airway and hence airflow
• mucus-secreting cells (goblet cells) + ciliated epithelial cells + rich supply of blood → warm, moisten and clean the inhaled air
• Ensure even distribution of volume of inhaled gas to each bronchus to prevent overloading of the lungs

Question 9

Why does the smooth muscles of the bronchi relax during exercise?

Answer 9

• When the smooth muscles relax, the diameter of the lumen of the bronchus increases.
• More air can enter the lungs for gas exchange
• so [more oxygen can be transported to muscle cells for respiration / more carbon dioxide can be removed] during exercise.

Question 10

Bronchioles

Answer 10

• Directs gas to the air sacs
• Walls are mostly made up of smooth muscles and elastic fibres
• No cartilage (bronchioles are highly affected by the contraction and relaxatioon of smooth muscles and elastic fibres)
• Larger bronchioles are lined with mucus-secreting cells and ciliated epithelial cells

Question 11

Adaptive features of air sacs for gas exchange

Answer 11

• Large number of air sacs → increases the surface area for gas exchange
• Thin (one-cell thick) wall of air sacs and wall of blood capillaries → shortens the diffusion distance for the diffusion of gases
• Secretes watery fluid to form water film in the inner surface of air sacs → allow gases to dissolve in the water film for gas exchange for diffusion to occur [THIS IS A MUST]
• Rich supply of blood capillaries → allows dissolved gases in air sacs to be rapidly transported away from air sacs → maintain steep conc gradient for the diffustion of gases in and out of the air sacs
• Highly folded → provide a large surface area for diffusion

Question 12

Diffusion of oxygen in inhaled air

Answer 12

Oxygen from inhaled air diffuses across the residual air
Oxygen from inhaled air dissolves in the water film lining the inner surface of the air sacs
Oxygen dissolves across the water film, wall of the air sacs and the walls of the blood capilaries into the blood

Question 13

Uptake of oxygen by RBCs

Answer 13

• Oxygen in the blood combines with haemoglobin to form oxyhaemoglobin
• Blood becomes oxygenated
• Oxygenated blood returns to the heart through the pulmonary vein
• The heart pumps the oxygenated blood to different body parts