Site author Richard Steane

The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.

THE HUMAN RESPIRATORY SYSTEM

You should be able to label a diagram showing:
mouth,
nose,
trachea (windpipe),
bronchi,
bronchioles,
alveoli (air sacs),
pleural membranes,
diaphragm,
ribs
and intercostal muscles.

Label this diagram of the "complete " human respiratory system, combining the head and thorax (chest) regions.

Many more lungs and
other anatomical models
available online
via this link

The route of air

- on its "proper " way from the outside into the lungs and out again.
Put this list together in the correct order, by writing their numbers below. Some may be used twice.
1) alveoli (air sacs) 2) bronchi 3) bronchioles 4) mouth 5) nasal passages 6) throat 7) trachea (windpipe)
(not4).5 --> . 6--> . 7--> .2 --> .3 --> . 1--> .3 --> . 2--> .7 --> . 6--> .4

The mechanism of breathing

As you roll your mouse over it, the diagram below shows the changes in the ribcage, intercostal muscles, diaphragm and lungs when we breathe in and out.

chest changes when exhaling and inhaling

NOTE: Not one of these muscles actually touches or pulls on the lungs themselves.
What force (pressure difference) actually causes the lungs to
inflate > atmospheric pressure higher than chest pressure
(and deflate)?>chest pressure higher than atmospheric pressure
In the nasal passages, air is exposed to a large surface area of moist skin which is covered with mucus, and has blood vessels near to the surface, as well as passing over nerve endings.

What do you miss out if you breathe in through your mouth instead?
>moisturising > warming >filtering/testing
First Aid for an unconscious casualty involves certain steps to be taken, after checking that it is safe to do so, and this is summed up as the ABC of resuscitation.
What do these letters stand for? Explain what needs to be done at each stage.
A> Airway - check there are no obstructions in the mouth or windpipe
B> Breathing - you can supply air to the casualty from your own breath
C> Circulation - if the heart has stopped, you may start it again by regular compressions of the chest
This reminds us that the respiratory system operates in conjunction with the circulatory system, so it is necessary to see how it fits in with the body as a whole.

Alveoli

Label the parts of the diagram above, with explanatory arrows.
What is the function of alveoli? > gas exchange
In what way can alveoli be said to offer a large surface area?
> due to their large numbers
How do the following features of alveoli help in their function?
moist surface
>oxygen must dissolve
capillary network
> blood to carry away oxygen to body

The exchange of gases

Using the letters written below, put the 12 following statements and stages into the gaps, in a logical order, to show what happens when energy is obtained from aerobic oxidation of food.
A carbon dioxide passes to the lungs, in solution
B dissolved oxygen passes through the wall of the alveoli
C dissolved carbon dioxide passes through the wall of the alveoli
D oxygen is transported in the red blood cells as oxyhaemoglobin
E oxygen is used up as food is oxidised, producing carbon dioxide
F dissolved oxygen passes out of the blood
G oxygen enters individual cells of the body, in solution
H dissolved oxygen passes into the blood through the capillaries' wall
I dissolved carbon dioxide passes out of the blood capillaries
J dissolved carbon dioxide passes into the water film
K carbon dioxide leaves solution and turns into a gas
L oxygen dissolves in a thin film of water
Clue: The first section is all about the supply of oxygen for internal respiration inside the cells of the body, and the second part is all about bringing back the product of the process, carbon dioxide.

1 oxygen gas is contained in the air breathed into the alveoli
2> L oxygen dissolves in a thin film of water
3>B dissolved oxygen passes through the wall of the alveoli
4>H dissolved oxygen passes into the blood through the capillaries' wall
5>D oxygen is transported in the red blood cells as oxyhaemoglobin
6 oxygen is released from the red blood cells leaving haemoglobin behind
7 >F dissolved oxygen passes out of the blood
8>G oxygen enters individual cells of the body, in solution
9>E oxygen is used up as food is oxidised, producing carbon dioxide

10 carbon dioxide leaves the cells, in dissolved form
11>A carbon dioxide passes to the lungs, in solution
12>I dissolved carbon dioxide passes out of the blood capillaries
13>C dissolved carbon dioxide passes through the wall of the alveoli
14>J dissolved carbon dioxide passes into the water film
15>K carbon dioxide leaves solution and turns into a gas

16 carbon dioxide gas passes out of the alveoli, into the air passages

What are the functions of the rings of cartilage along the trachea?
>prevent collapse (due to negative pressure)
>prevent bursting (due to positive pressure)
Why can you only speak when you are breathing (out?)?
> air must be passing over the vocal cords

In the "breath test " for alcohol consumption, where does the alcohol come from (i.e. which parts of the body, not the bottle!), and in what physical form does it leave the body?
> blood capillaries surrounding alveoli in lungs
> as alcohol vapour
Why is it a fairly reliable test?
> there is a large surface area and efficient blood supply
In cold weather, you may warm your hands by blowing into your gloves. What (biochemical) process does the heat come from?
> (internal) respiration / oxidation of "food "
Eventually, you will notice that your gloves become damp. Where does the moisture come from, ultimately?
>oxidation of food e.g. glucose - refer to the equation for internal respiration - may also come from the moisture film inside the alveoli

Which of the following statements is correct about the oxygen content of the air you breathe in? Ring the closest alternative.
A It is pure oxygen
B It is about one-fifth oxygen/
C It is about four-fifths oxygen
D It consists of 4 parts of oxygen in 100
E It consists of 4 parts of oxygen in 1000
F It consists of 4 parts of oxygen in 10000

This should remind us that we do not breathe in pure oxygen!
Which of the following statements is correct about the carbon dioxide content of the air you breathe out? Ring the closest alternative.
A It is pure carbon dioxide
B It is about one-fifth carbon dioxide
C It is about four-fifths carbon dioxide
D It consists of 4 parts of carbon dioxide in 100 /
E It consists of 4 parts of carbon dioxide in 1000
F It consists of 4 parts of carbon dioxide in 10000

This should remind us that we do not breathe out pure carbon dioxide!
Which of the following statements is correct about the difference between the oxygen content of the air you breathe in, and what you breathe out? Ring the closest alternative.
A All the oxygen is removed
B About one-quarter of the oxygen is removed/
C About three-quarters of the oxygen is removed
D There is no change
E It changes from a little to a lot
F It stays at 79%
This should remind us that we do not use up all the oxygen we breathe in!

The Effects of Exercise

The effects of exercise on the operation of the circulatory system will be dealt with as a separate topic.

We normally breathe about 16-20 times per minute, and take in (and out) about 500 ml of air at a time.
When we exert ourselves, our bodies need to release more energy. To obtain this, we must oxidise more food in our muscles, so more oxygen must be taken in. Consequently, we increase the rate and depth of breathing, i.e. we breathe faster, and inflate the lungs more with each breath. This also assists the removal of the waste product carbon dioxide, which is being produced in greater quantities.
Although breathing is to some extent under conscious control when speaking, singing etc., part of the brain is monitoring the carbon dioxide concentration of the blood and will make automatic adjustments by sending impulses to the diaphragm and intercostal muscles.
Our body also reacts by increasing the rate of heart beat, but that is an independent action.

Breathing Problems in Unusual Circumstances

What is the percentage of oxygen on top of Mount Everest? (almost a trick question!)
>21 %
Why do Himalayan climbers often take oxygen?
>because there is less oxygen in each breath they take as the air is "thinner"
Why do divers have problems with nitrogen in compressed air causing "the bends "?
> Nitrogen dissolves in the blood, then comes out of solution
How do they get over it if they suffer the bends?
> Decompression chamber to remove the gas SLOWLY
What can be done to divers' breathing mixture, to prevent this happening?
> Add helium an inert/noble gas
For what purpose do astronauts in a space station use lithium hydroxide?
> (a light alkali) to absorb carbon dioxide

Disorders of the Respiratory System

Asthma is caused by narrowing of the fine airways (bronchioles) due to (involuntary) contraction of muscles in their walls, perhaps because of sensitivity to something in the air. This makes it difficult to breathe air into the lungs, and (paradoxically) difficult to get medicines into the airways to reduce the constriction.
Bronchitis is caused by the inflammation of the lining of the bronchioles. This may be due to infection by bacteria or viruses, or chemicals such as those found in tobacco smoke.
Lung cancer is caused by a change in the cells inside the lungs, so that they divide out of control, and produce lumps of cells (tumours) which interfere with the normal functions of lungs. A major cause of this is tobacco smoke, but other substances, including the "natural " radioactive radon gas, which may build up in some areas, may also have an effect.
Emphysema is a condition in which the structure of the alveoli is broken down (by smoke and coughing), reducing the surface area for gaseous exchange, as well as altering the elasticity of the lungs.

Many other anatomical models and charts available by following this link.

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