1. The respiratory system

2. The respiratory system

3. The nasal passages and lungs
Air is drawn into the body via the nose or mouth. There are advantages to breathing through your nose:
the air is warmed so that it is closer to body temperature
tiny hairs and mucus in the nose filter the air, preventing larger dust and pollen particles reaching the alveoli
mucus moistens the air, making it easier for the alveoli to absorb.
Air then travels through the larynx, trachea (windpipe), bronchi (one bronchus to each lung) and bronchioles to the alveoli, where oxygen passes into the bloodstream.

4. Mechanisms of breathing – inspiration
When you breathe in:
Intercostal muscles pull ribs up and out
intercostal muscles between the ribs contract, pulling the chest walls up and out
the diaphragm muscle below the lungs contracts and flattens, increasing the size of the chest
the lungs increase in size, so the pressure inside them falls. This causes air to rush in through the nose or mouth.
Diaphragm contracts and moves down

5. Mechanisms of breathing – inspiration

6. Mechanisms of breathing – expiration
When you breathe out:
Ribs move in and down
Intercostal muscles between the ribs relax so that the chest walls move in and down.
The diaphragm muscle below the lungs relaxes and bulges up, reducing the size of the chest.
The lungs decrease in size, so the pressure inside increases and air is pushed up the trachea and out through the nose or mouth.
Diaphragm relaxes and bulges up

7. Mechanisms of breathing – expiration

8. Gas exchange at the alveoli
The alveoli are bunches of tiny air sacks inside the lungs.
Each individual sack is called an alveolus.
When you breathe in, they fill with air.
The alveoli are covered in tiny capillaries (blood vessels).
Gases can pass through the thin walls of each alveolus and capillary, and into the blood stream.
Gases can also pass from the blood stream, into the alveolus.

9. Gas exchange at the alveoli

10. Composition of inhaled and exhaled air
Gas
Amount in inhaled air
Amount in exhaled air
Oxygen
Carbon dioxide
Nitrogen
Water vapour
21%
Very small amount
79%
Small amount
17% 3%
79%
Large amount
What are the main differences between inhaled and exhaled air?
Ask the students to compare the relative amounts. Point out that:
The amount of oxygen inhaled is greater than the amount of oxygen exhaled. Consider the efficiency of respiration at the cells.
The amount of carbon dioxide is greater in exhaled air.
The amount of nitrogen is the same.
Mouth to mouth resuscitation works because there is still a lot oxygen left in exhaled air.
Why does mouth-to-mouth resuscitation work?

11. Calculating minute volume
Remember:
Minute volume is the volume of air you breathe in one minute.
You can calculate a person’s minute volume by multiplying the volume of air they breathe in one breath, by their respiratory (breathing) rate.
Question
If you breathe 14 times in one minute (respiratory rate) and you breathe 0.5 litres in each breath, what is your minute volume?
Get students to calculate the answer before revealing it.
Point out that at rest, the volume of air breathed in each breath will be the person’s tidal volume. During extreme exercise, it may be closer to their vital capacity.
Answer:
Minute volume = 14 × 0.5 litres
= 7.0 litres

12. Breathing during exercise
During exercise the muscle cells use up more oxygen and produce increased amounts of carbon dioxide.
Your lungs and heart have to work harder to supply the extra oxygen and remove the carbon dioxide.
Your breathing rate increases and you breathe more deeply.
Heart rate also increases in order to transport the oxygenated blood to the muscles.
Image © 2006 Jupiterimages Corporation

13. Breathing during exercise
Muscle cell respiration increases – more oxygen is used up and levels of CO2 rise.
The brain detects increasing levels of CO2 – a signal is sent to the lungs to increase breathing.
Breathing rate and the volume of air in each breath increase. This means that more gaseous exchange takes place.
The brain also tells the heart to beat faster so that more blood is pumped to the lungs for gaseous exchange.
More oxygenated blood gets to the muscles and more CO2 is removed.

14. Breathing changes during exercise
Look at these statistics for a 16 year-old athlete:
During rest
During exercise
Respiratory rate
14 breaths/ minute
32 breaths/ minute
Volume per breath
0.4 litres
2.4 litres
Minute volume ?
Calculate the athlete’s minute volumes during rest and exercise.
Rest minute volume = 5.6 litres
Exercise minute volume = 76.8 litres

15. The effects of exercise on lung structures
In the long-term, regular exercise strengthens the respiratory system.
The respiratory muscles (the diaphragm and intercostals) get stronger, so they can make the chest cavity larger.
This larger chest cavity means more air can be inspired, therefore increasing your vital capacity.
More capillaries form around the alveoli, so more gaseous exchange can take place.
Relate these facts to improvements in performance. Emphasise that lungs are NOT muscles and therefore do not increase in size – they function more efficiently.
Gas exchange can now take place more quickly meaning exercise can be maintained at a higher intensity for longer.

16. respiration Respiration energy glucose oxygen
Respiration is the process that takes place in living cells which releases energy from food molecules.
Glucose from food is used to fuel exercise.
Oxygen is required to ‘break down’ the glucose to produce energy. This energy is used to make muscles contract.
respiration
glucose
energy
oxygen
Waste products, including carbon dioxide, are produced as a result of the chemical reactions. These must be removed and excreted.

17. Aerobic respiration There are two different types of respiration.
When you exercise at a steady, comfortable rate, the cardiovascular system is able to supply the muscles with all the oxygen they need.
Under these conditions, aerobic respiration takes place.
carbon dioxide
glucose
+ oxygen
energy +
+ water
Aerobic exercise can be maintained for long periods without the performer getting breathless or suffering muscle cramps. Moderate activities like walking, jogging, cycling and swimming use aerobic respiration.

18. Aerobic respiration