7.2 Mammalian Gaseous Exchange System

Question 1

What are the key features of the nasal cavity?

Answer 1

Good blood supply - warms air entering the body
Lined with hairs and mucus secreting cells - traps dust and bacteria (protection from disease)
Moist surfaces - increases humidity, reducing evaporation from the lungs

Question 2

What are the key features of the trachea?

Answer 2

Supported by flexible cartilage - prevents collapse
Lined with goblet cells which secrete mucus - traps dust and bacteria
Ciliated epithelium cells - cilia move away from mucus

Question 3

What are the key features of the bronchus?

Answer 3

Cartilage - prevents collapse

Question 4

What are the key features of the bronchioles?

Answer 4

Smooth muscle (and no cartilage) - bronchioles can constrict and dilate to vary the amount of air reaching the lungs
Flattened epithelium cells - some gaseous exchange is possible

Question 5

What are the key features of the alveoli?

Answer 5

Single layer of flattened epithelium cells - short diffusion distance, which increases diffusion rate
Elastic fibres and collagen - enable stretching and elastic recoil during ventilation
Large surface area - increased rate of diffusion
Good blood supply and good ventilation - O2 is supplied to the alveoli and moved to circulatory system quickly and co2 is removed from the lungs quickly, maintains a steep conc. gradient
Covered with layer of surfactant - alveoli remain inflated

Question 6

Describe the process of inspiration

Answer 6

1. External intercostal muscles contract
2. Ribs move up and out
3. Diaphragm contracts and flattens
4. Thorax volume increases
5. Air pressure in the lungs drops below atmospheric pressure
6. Air moves into the lungs

Question 7

Describe the process of expiration

Answer 7

1. External intercostal muscles relax
2. Ribs move down and inwards
3. Diaphragm Rolexes and reverts to its domed shape
4. Thorax volume increases
5. Air pressure in the lungs rises above atmospheric pressure
6. Air moves out of the lungs

Question 8

Process of forced expiration

Answer 8

1. Internal intercostal muscles contract
2. Ribs move down hard and fast
3. Abdominal muscles force the diaphragm back to its domed position

Question 9

How do surfactants work?

Answer 9

Water is present in the inner surface of alveoli
Oxygen dissolves in the water before diffusing across the alveolar epithelium layer.
The alveoli would collapse if only were present
A surfactant (a mixture of phospholipids and protein) prevents alveoli by interfering with hydrogen bond formation between water molecules

Question 10

Why can expiration be a passive process?

Answer 10

The diaphragm relaxes
The rib cage falls due to gravity
The lungs are elastic and recoil

Question 11

How can preventers (e.g. steroids) reduce the likelihood of an asthma attack?

Answer 11

They can reduce the sensitivity of the lining of the airways

Question 12

How can relievers overcome the symptoms of an asthma attack?

Answer 12

They are chemicals similar to the hormone adrenaline
They attach to the active sites on the surface membranes of smooth muscle cells in the bronchioles, making them relax and dilating the airways

Question 13

What are the two main ways of treating asthma?

Answer 13

1. Relievers

2. Preventers