Respiratory system

Question 1

What does respiration include?

Answer 1

Ventilation - getting air into and out of the lungs.
External respiration - gaseous exchange between the lungs and blood.
Transport of gases.
Internal respiration - exchange of gases between the blood in the capillaries and the body cells.
Cellular respiration - the metabolic reactions and processes that take place in a cell to obtain energy from fuels such as glucose.

Question 2

What is the pathway of air?

Answer 2

Air is a mixture of gases and is drawn into the body through the nose.
It passes through the pharynx and onto the larynx, then down the trachea and into the left and right bronchus.
Air moves through each bronchus and they subdivide into secondary bronchi.
These then get progressively thinner and branch into bronchioles and then respiratory bronchioles, which lead into the alveoli.

Question 3

What is the pathway of air (simplified)?

Answer 3

Nose
Pharynx
Larynx
Trachea
Bronchi
Bronchioles
Alveoli

Question 4

What is diffusion?

Answer 4

The movement of gas molecules from an area of high partial pressure to an area of low partial pressure.

Question 5

What is gaseous exchange?

Answer 5

The movement of oxygen from the air into the blood, and carbon dioxide from the blood into the air.

Question 6

How are the alveoli adapted to help gaseous exchange?

Answer 6

Their walls are very thin - only one cell thick - means there is a short diffusion pathway.
This is because there are only two layers of cells from the air in the alveoli to the blood.
An extensive capillary network surrounds the alveoli so they have an excellent blood supply.
They have a large surface area because there are millions of alveoli in each lung, which allows for a greater uptake of oxygen.

Question 7

What are the mechanics of breathing?

Answer 7

The greater the difference in pressure, the faster air will flow.
So for inspiration to occur, the pressure needs to be lower in the lungs than in the atmosphere.
For expiration, air pressure needs to be higher in the lungs than in the atmosphere.
Increasing the volume of the thoracic cavity will reduce the pressure of air in the lungs.
Decreasing the volume of the thoracic cavity will increase the pressure in the lungs, forcing the air out.
The contraction of muscles causes these pressure changes.

Question 8

What happens during inspiration at rest?

Answer 8

Contraction of the external intercostals.
Contraction of diaphragm.
Thoracic cavity volume increases.
Pressure is lower than atmospheric pressure.
Air rushes in.

Question 9

What happens during expiration at rest?

Answer 9

Relaxation of external intercostal muscles and diaphragm.
Thoracic cavity volume decreases.
Pressure increases above atmospheric pressure.
Air rushes out.

Question 10

What happens during inspiration during exercise?

Answer 10

Contraction of external intercostals, diaphragm, sternocleidomastoid and pectoralis major.
Thoracic cavity volume increases further.
Pressure is even lower than atmospheric pressure.
Air rushes in.

Question 11

What happens during expiration during exercise?

Answer 11

Contraction of internal intercostal muscles and abdominals.
Thoracic cavity volume decreases even further.
Pressure increases above atmospheric pressure.
Air rushes out.

Question 12

What is tidal volume?

Answer 12

The volume of air inspired or expired per breath.
At rest this is approximately 0.5L.
This increases during exercise.

Question 13

What is minute ventilation?

Answer 13

The volume of air inspired or expired per minute.
Calculated by: Number of breaths (per min) x tidal volume
Approx. 12 x 0.5 = 6 litres/min.
Big increase during exercise.

Question 14

What is inspiratory reserve volume?

Answer 14

The volume of air that can be forcibly inspired after a normal breath.
Decreases during exercise.

Question 15

What is expiratory reserve volume?

Answer 15

The volume of air that can be forcibly expired after a normal breath.
Slight decrease during exercise.

Question 16

What is residual volume?

Answer 16

The volume of air that remains in the lungs after maximum expiration.
There will still be some air in the alveoli, bronchi and trachea as these are held permanently open by rings of cartilage.
During exercise there is no change.

Question 17

What is a spirometer?

Answer 17

A device used to measure the volume inspired and expired by the lungs.
An individual breathes in and out of a sealed chamber through a mouthpiece.
This makes the chamber inflate and deflate and as this happens, a pen recorder traces the breathing movements onto a chart.
The machine is calibrated so that breathing volumes can be calculated.

Question 18

How does smoking affect the body?

Answer 18

Smoking can cause irritation of the trachea and bronchi.
It reduces lung function and increases breathlessness caused by the swelling and narrowing of the lung’s airways.
Cigarette smoke damages the cells lining the trachea, bronchi and bronchioles.
These tiny cells have microscopic hair-like cilia on their surface which help to push mucus out of the lungs.
When they are damaged, excess mucus builds up in the lung passages, which leads to a smoker’s cough to try to get rid of the mucus.

Question 19

What effect does smoking have on exercise?

Answer 19

Smoking can damage the alveoli as their walls break down and join together forming larger air spaces than normal.
This reduces the efficiency of gas exchange, which also increases the risk of COPD.
Smoking also affects oxygen transport as the carbon monoxide from cigarettes combines with haemoglobin much more readily than oxygen.
This reduces the oxygen-carrying capacity of the blood, which increases breathlessness during exercise.

Question 20

What is partial pressure?

Answer 20

The pressure exerted by an individual gas when it exists within a mixture of gases.
Oxygen only makes up about 21% of air so it therefore exerts a partial pressure.
The partial pressure of oxygen in the blood when diffusing from the alveoli must be lower than in the muscle from the blood.

Question 21

What is the concentration gradient?

Answer 21

The steeper the gradient, the difference between concentration levels at high and low areas, the faster diffusion occurs.

Question 22

How does gaseous exchange occur at the alveoli?

Answer 22

The partial pressure of oxygen in the alveoli (100 mmHg) is higher than the partial pressure of oxygen in the capillaries (40 mmHg).
This is because oxygen has been removed by the working muscles so its concentration in the blood is lower, and therefore its partial pressure.
Oxygen will diffuse from the alveoli into the blood until the pressure is equal in both.

Question 23

How does carbon dioxide diffuse?

Answer 23

The partial pressure of carbon dioxide in the blood entering the alveolar capillaries is higher (45 mmHg) than in the alveoli (40 mmHg) so carbon dioxide diffuses into the alveoli from blood until the pressure is equal in both.

Question 24

How does gaseous exchange occur at the muscles?

Answer 24

The partial pressure of oxygen in the capillary membranes surrounding the muscles is 40 mmHg, and is 100 mmHg in the blood.
This lower partial pressure allows oxygen to diffuse from the blood into the muscle until equilibrium is reached.
The partial pressure of carbon dioxide in the blood 40 mmHg is lower than the tissues 46 mmHg, so diffusion occurs and the carbon dioxide moves into the blood to be transported to the lungs.

Question 25

What are the three factors involved in pulmonary ventilation regulation?

Answer 25

Neural control
Chemical control
Hormonal control

Question 26

How is breathing controlled?

Answer 26

The sympathetic nervous system prepares the body for exercise so it will increase your breathing rate, whereas the parasympathetic system will do the opposite and lower breathing rate.
The respiratory centre located in the medulla oblongata of the brain controls the rate and depth of breathing and uses both neural and chemical control.

Question 27

What does the inspiratory centre do?

Answer 27

Part of the respiratory centre.
It sends out nerve impulses via the phrenic nerve to the inspiratory muscles - diaphragm and external intercostals - to cause them to contract.
This stimulation acts for approximately 2 seconds and then the impulse stops and passive expiration occurs due to the elastic recoil of the lungs.

Question 28

How is breathing rate controlled during exercise?

Answer 28

During exercise, blood acidity increases as a result of an increase in the plasma concentration of carbon dioxide and an increase in lactic acid production.
These changes are detected by chemoreceptors, which are found in the carotid artery and the aortic arch and they send impulses to the inspiratory centre to increase ventilation until blood acidity is returned to normal.
To achieve this, the respiratory centre sends impulses down the phrenic nerve to stimulate more inspiratory muscles - the sternocleidomastoid, scalene and pectoralis minor.
The rate, depth and rhythm of breathing increase.

Question 29

What other factors affect neural control of breathing?

Answer 29

Mechanical factors
Baroreceptors
Stretch receptors

Question 30

How do mechanical factors control breathing?

Answer 30

Proprioceptors are sensory receptors located in the joints and muscles that provide feedback to the respiratory centre to increase breathing during exercise.

Question 31

How do baroreceptors control breathing?

Answer 31

A decrease in blood pressure detected by baroreceptors in the aorta and carotid arteries results in an increase in breathing rate.

Question 32

How do stretch receptors control breathing?

Answer 32

During exercise the lungs are also stretched more.
Stretch receptors prevent over-inflation of the lungs by sending impulses to the expiratory centre and then down the intercostal nerve to the expiratory muscles - abdominals and internal intercostals - so that expiration occurs.

Question 33

How does hormonal regulation of pulmonary ventilation occur during exercise?

Answer 33

Adrenaline is a natural stimulant made in the adrenal gland of the kidney.
It is transported in the blood and affects the nervous system.
Adrenaline is released in response to exercise.
Just before exercise, the brain sends impulses to the renal glands which respond and pump adrenaline into the blood in anticipation of the increased need for oxygen and carbon dioxide exchange.
Breathing rate increases.