7.2 The mammalian gaseous exchange system

Question 1

where does gas exchange take place

Answer 1

in the lungs

Question 2

describe the nasal cavity

Answer 2

• large surface area (warms air to body temperature)
• hairy lining (secretes mucus to protect from infection by trapping dust+bacteria)
• moist surfaces (increase humidity of incoming air, reducing evaporation)

Question 3

describe the trachea

Answer 3

• main airway carrying clean,warm,moist air from nose to chest
• supported by incomplete rings(so food moves down oesophagus) of strong,flexible cartilage = stops from collapsing
• linked with ciliated epithelium with goblet cells between/below epithelial cells

Question 4

explain the function of the ciliated epithelium and goblet cells

Answer 4

• goblet cells = secrete mucus onto lining to trap dust
• cilia = beat and move the mucus away from the lungs and to the throat
• cigarettes stop cilia from beating

Question 5

describe the bronchus

Answer 5

• left bronchus leads to the left lung
• right bronchus leads to the right lung
• similar to trachea but smaller
• same supporting rings of cartilage

Question 6

describe the bronchioles

Answer 6

• smaller bronchioles have no cartilage
• diameter <1mm
• walls contain smooth muscle (contract = bronchioles constrict / relax = bronchioles dilate)
• lined with thin layer of flattened epithelium (some gas exchange is possible)

Question 7

describe the alveoli

Answer 7

• tiny air sacs which are the main gas exchange surface
• diameter = 200-300um
• layer of thin, flattened epithelial cells+collagen+elastic fibres
• elastic recoil = stretch as air is drawn in/return to resting size to help squeeze air out
• inner surface is lined with a thin layer of a solution of water, salts and lung surfactant = keeps alveoli inflated

Question 8

how are the alveoli adapted to their function

Answer 8

• large SA (300-500 million alveoli and each SA=50-75m2)
• thin layers (alveoli and capillaries have single epithelial cell walls so diffusion distance is short)
• good blood supply (constant flow through millions of capillaries maintains steep conc gradients)
• good ventilation (breathing helps maintain steep diffusion gradients)

Question 9

describe the structure of the lungs

Answer 9

• rib cage = semi-rigid case where pressure can be lowered with respect to air outside
• diaphragm = broad, domed sheet of muscle forming thorax floor
• external/internal intercostal muscles = between ribs
• pleural membranes = line thorax and surround lungs
• pleural cavity = space between pleural membranes and filled with thin layer of lubricating fluid so membranes can slide over each other easily

Question 10

explain the process of inspiration

Answer 10

(energy using process)

1. diaphragm contracts (flattening+lowering)
2. external intercostal muscles contract (ribs move upwards+out)
3. volume of thorax increases
4. pressure in thorax is reduced (lower than atmospheric air)
5. air is drawn into the lungs
6. pressure inside/outside the chest is equalised

Question 11

explain the process of expiration

Answer 11

(passive process)

1. diaphragm relaxes (up into domed shape)
2. external intercostal muscles relax (ribs move downwards+in)
3. elastic fibres in alveoli return to normal length
4. volume of thorax decreases
5. pressure in thorax is greater than atmospheric air
6. air moves out of the lungs
7. pressure inside/outside the chest is equalised

Question 12

explain the process of expiration by force

Answer 12

(energy using process)

1. internal intercostal muscles contract)
2. ribs are pulled down hard and fast
3. abdominal muscles contract
4. diaphragm is forced to increase pressure in the lungs rapidly