Chapter 11: Gas Exchange in humans

Question 1

What is gas exchange?

Answer 1

The diffusion of oxygen into the blood and carbon dioxide out.

Question 2

When does gas exchange occur rapidly?

Answer 2

1. There is a large surface area exposed to the gas
2. The distance across which diffusion has to take place is small
3. There is a good blood supply
4. There is good ventilation, creating a steep concentration gradient.

Question 3

How does the lungs have a large surface area?

Answer 3

The presence of millions of alveoli in the lungs provides a very large surface for gaseous exchange.

The many branching filaments in a fish’s gills have the same effect.

Question 4

How is the diffusion distance in the alveoli small?

Answer 4

It has a thin epithelium.
There is only a two-cell layer separating the air in the alveoli from the blood in the capillaries.

One layer: alveolus wall
Other layer: Capillary wall.

Hence the distance for diffusion is very short.

Question 5

How does the lungs get a good blood supply?

Answer 5

The alveoli are surrounded by networks of blood capillaries.

The continual removal of O2 by the blood in the capillaries ling the alveoli keeps its concentration low.

A steep diffusion gradient is maintained, favouring rapid diffusion of oxygen from the air passages.

The continual delivery of CO2 from the blood into the alveoli and its removal from the air passages by ventilation.

Thus, maintaining a diffusion gradient that promotes the diffusion of CO2 from the alveolar lining into the brochioles.

Question 6

Name the key structures of the respiratory tract.

Answer 6

Question 7

Define ventilation.

Answer 7

The movement of the thoracic cavity in order to suck air in and blow it out again.

Question 8

What is ventilation assisted by?

Answer 8

The ribs, the intercostal muscles and the diaphragm.

Question 9

How do you inhale?

Answer 9

The internal intercostal muscles relax and the external intercostal muscles contract, pulling the ribcage upwards and outwards

The diaphragm contracts, pulling downwards.

The volume of the thoracic cavity expands, forcing the lungs to expand and the air pressure inside to decrease.

Air is pushed into the lungs.

Question 10

How do you exhale?

Answer 10

The internal intercostal muscles contract and the external intercostal muscles relax, pulling the ribcage downwards and inwards.

The diaphragm relaxes, moving back upwards.

The volume of the thoracic cavity shrinks causing the lungs to shrink back to their original volume and the air pressure inside to increase

Air is pushed out of the lungs.

Question 11

Tell me the composition of inspired air.

Answer 11

21% oxygen
0.04% carbon dioxide
water vapour: variable

Question 12

Tell me the composition of exhaled air.

Answer 12

16% oxygen
4% carbon dioxide
water vapour: saturated

Question 13

Tell me the test for carbon dioxide.

Answer 13

Limewater turns milky in presence of CO2.

Question 14

What happens to the breathing rate as physical activity increases?

Answer 14

Breathing rate increases
The breathing depth increases

This allows more O2 to move into the blood for aerobic respiration in muscle cells and more carbon dioxide to be removed.

Question 15

How do you calculate breathing rate?

Answer 15

Count the number of breaths in one minute.

Question 16

Tell me about the relationship between CO2 concentration and physical activity.

Answer 16

Increased physical activity increases CO2 concentration.
This lowers the pH of the blood.
The brain detects this increase and instructs the intercostal muscles and diaphragm muscles to contract and relax more rapidly, increasing the breathing rate in order to remove the carbon dioxide faster.

Question 17

What protects the respiratory system?

Answer 17

Nasal hair
Mucous
Goblet and ciliated cells.

Question 18

How does nasal hair protect the gas exchange system?

Answer 18

It filters out any large microbes and dust that enter through the nose.

Question 19

How does the mucous protect the gas exchange system?

Answer 19

It is sticky. It traps smaller dust particles and pathogens.

Question 20

How do goblet cells protect gas exchange?

Answer 20

They secrete mucous that forms a thin film over the internal lining.
This sticky liquid traps pathogens and small particles and pushes them up towards the pharynx.
This prevents pathogens from entering the alveoli.

Question 21

How does ciliated cells protect the gas exchange system?

Answer 21

They continuously beat in order to move the mucous secreted by the goblet cells upwards and way from the lungs.
When he mucus reaches the top of the trachea, it is swallowed into the oesophagus.