The Respiratory System

Question 1

What does the respiratory system do?

Answer 1

The respiratory system supplies the body with the oxygen (O2) it needs from the surrounding air, and removes excess amounts of carbon dioxide (CO2). The process of inspiration supplies oxygen and the process of expiration expels excess carbon dioxide.

Question 2

Describe Cells and Oxygen

Answer 2

The human body is made up of billions of individual building blocks called cells, which may be different in size, shape and function. All living cells need a constant and adequate supply of oxygen to stay alive.

Different cells have different tolerance levels to a lack of oxygen, for example:

Skin and muscle cells can last for around one hour without an oxygen supply before under-oxygenation becomes a problem.

Brain cells however, would generally die within eight minutes of oxygen deprivation.

Question 3

How much oxygen in the air around us, and what do our bodies absorb?

Answer 3

The air around us contains approximately 20-21% oxygen, and as we breathe, our bodies absorb approximately 5% of this oxygen.

Question 4

When body cells use oxygen what is produced?

Answer 4

When body cells use this oxygen, waste products are formed as a result of the intra-cellular chemical processes. Some waste products are in solid or liquid form and some are in gaseous form. As cells use up oxygen, the main waste gas produced is carbon dioxide.

Question 5

The Main parts of the respiratory system are:

Answer 5

The Nose:

The Nasopharynx:

The Pharynx:

The Larynx:

The Trachea:

The Bronchi:

The Bronchiole:

The Alveoli:

The Lungs:

The Pleura:

The Chest Wall:

The Diaphragm:

Question 6

Describe the Nose

Answer 6

The Nose:

The external nose is the visible part of the nose, formed by two nasal bones and by cartilage. It is covered and lined by skin. Inside the nose are tiny hairs which help prevent foreign material from entering further into the nasal cavity.

Question 7

Describe the Nasopharynx

Answer 7

The Nasopharynx:

This is the post-nasal space (cavity) divided by a septum and leading into the pharynx. The cavity is lined with mucus membrane which has a very good blood supply. This warms the air as it is drawn into the cavity.

Question 8

Describe the Pharynx

Answer 8

The Pharynx:
The pharynx is divided into two main areas.

The naso-pharynx is the part which lies behind the nasal cavity

and

The oro-pharynx is the part which lies behind the mouth.

Question 9

Describe the Larynx

Answer 9

The Larynx:

The larynx is continuous with the oro- pharynx above and with the trachea below. Above it lie the hyoid bone and the root of the tongue. The larynx is composed of several irregular cartilages joined together by ligaments and membranes, and it protects the vocal cords which are situated inside.

Question 10

Describe the Trachea

Answer 10

The Trachea:
The trachea begins below the larynx and runs down the front neck into the chest.

It divides into the right and left bronchi at the level of the fifth thoracic vertebra.

It is about 12cm long in the adult. The wall of the trachea consists of involuntary muscle and fibrous tissue strengthened by ‘C’ shaped rings of cartilage.

The deficiency in the cartilage rings lies at the posterior aspect where the trachea is in contact with the oesophagus.

Question 11

Describe the Bronchi

Answer 11

The Bronchi:
The two main bronchi branch off the bottom of the trachea, with one leading to each lung.

The left main bronchus is narrower, longer and more horizontal than the right main bronchus due to the position of the heart.

Each main bronchus further divides into branches, one for each lobe of each lung.

The structure of the bronchi is similar to that of the trachea but the cartilage is less regular.

Question 12

Describe the Bronchiole

Answer 12

The Bronchiole:
The finest bronchi are called bronchioles.

They have no cartilage but are composed of muscular, fibrous and elastic tissue lined with a protective membrane.

The muscular and fibrous tissue disappears as the bronchioles become smaller.

The smallest tubes are called terminal bronchioles.

Question 13

Describe the Alveoli

Answer 13

The Alveoli:
The terminal bronchioles branch repeatedly to form minute passages called alveolar ducts, from which alveolar sacs and alveoli open.

The alveoli are surrounded by an intricate network of capillaries.

De-oxygenated blood enters the capillary network from the pulmonary artery and oxygenated blood leaves it to enter the pulmonary veins.

It is in the capillary that the exchange of gasses takes place between the air in the alveoli and the blood in the vessels.

Question 14

Describe the Lungs

Answer 14

The Lungs:
The lungs are two large spongy organs lying in the thorax on either side of the heart and great vessels.

They extend from the root of the neck to the diaphragm and are roughly cone shaped with the ‘apex’ above and the ‘base’ below.

Between the lungs is the mediastinum, a block of tissue which completely separates one side of the thoracic cavity from the other, stretching from the vertebrae behind to the sternum in front.

The lungs are divided into lobes.
-The left lung has 2 lobes,
-The right lung has 3 lobes.

Question 15

Describe the Pleura

Answer 15

The Pleura:
This is a membrane which surrounds each lung, and is made up of two layers:

• The visceral pleura: this is firmly attached to the lungs, covering their surfaces.
• The parietal pleura: this lines the inside of the chest wall and the superior surface of the diaphragm.

The two layers of pleura are normally in close contact with each other, separated only by a film of fluid which provides lubrication and enables them to glide over one another without friction.

The potential space between the layers is called the pleural space.

Question 16

Describe the

Answer 16

The Chest Wall:

This robust and flexible structure is mainly comprised of ribs (12 pairs), connective intercostal muscles and other soft tissue.

Question 17

Describe the Diaphragm

Answer 17

The Diaphragm: This is a large sheet of muscle forming the inferior boundary of the chest cavity and the superior boundary of the abdominal cavity. It is the main muscle of respiration, and breathing would be impossible without it. In its relaxed position it is a dome or arched shape which roughly follows the line of the lower rib margins.

Question 18

What is the Mechanism of Normal Breathing

Answer 18

The normal breathing cycle comprises three phases:
- Inspiration,
- Expiration,
- a brief Pause,
before the cycle repeats itself.

The normal speed of breathing for a healthy adult at rest is between 14 to 18 cycles per minute.

Question 19

Describe inspiration - breathing in.

Answer 19

Inspiration: - Breathing in

Requires the contraction of specific muscles around and within the chest cavity.

On inspiration the diaphragm contracts and flattens and the chest wall rises.

The intercostal muscles connect the ribs together.
- When they contract they change the shape of the chest cavity.

• The rib cage - especially the central and lower portion - is particularly flexible.

The ribs are connected to the anterior aspect of the chest at the sternum and to the posterior aspect at the spine.

In their normal resting position these curved bones slope downward.

When the intercostal muscles contract, the ribs are lifted upward and due to the curved shape the sides of the chest expand outward.

As the lungs are effectively attached to the inside of the chest wall by the pleural membranes, the outward movement of the chest wall helps the lungs to expand.

When the diaphragm contracts, it changes from a domed or arched shape, to become contracted and flattened.

This presses down on the abdominal organs but effectively increases the size of the thoracic cavity.

Negative pressure (a vacuum) builds up inside the thorax and the only way the pressure can be equalised is by drawing in air through the respiratory passages and inflating the lungs.

Question 20

Describe Expiration - Breathing out

Answer 20

Expiration: - Breathing out

On expiration, the diaphragm relaxes and rises and the chest wall falls.

This causes positive pressure to occur inside the thorax and under normal circumstances, the only way the positive pressure can be equalised is to force air out of the lungs.

This causes the lungs to deflate.

Question 21

The breathing process is severely hindered if?

Answer 21

• The chest wall is damaged or compromised.
• Movement of the chest wall is restricted.
• The airway passages are blocked.

Question 22

Normal Respiratory Rates: Adult

Answer 22

Adult:
12-20 respirations per minute

Question 23

Normal Respiratory Rates: 5-12 years

Answer 23

5-12 years:
20-25 respirations per minute

Question 24

Normal Respiratory Rates: 2-5 years

Answer 24

2-5 years:
25-30 respirations per minute

Question 25

Normal Respiratory Rates: 0-12 months

Answer 25

0-12 Months: 30-40 respirations per minute

Question 26

Describe Gaseous Exchange levels:

Answer 26

Gaseous Exchange:

The air around us is made up of approximately:

Oxygen - 21%
Carbon dioxide - 0.04%
Nitrogen & Inert Gasses - 78% Water Vapour - Variable

Every time we breathe, these quantities of gas are taken into the lungs Because we use some of the oxygen, the quantities of gas which are exhaled will be slightly different:

Oxygen - 16%
Carbon dioxide - 4%
Nitrogen & Inert Gasses - 78%
Water Vapour - Saturated

Question 27

Describe Gaseous Exchange

Answer 27

The air around us is made up
Oxygen - 21%
Carbon dioxide - 0.04%
Nitrogen & Inert Gasses - 78% Water Vapour - variable

Every time we breathe, these quantities of gas are taken into the lungs Because we use some of the oxygen, the quantities of gas which are exhaled will be slightly different:

Oxygen - 16%
Carbon dioxide - 4%
Nitrogen & Inert Gasses - 78%
Water Vapour - Saturated

Expired air has more carbon dioxide and less oxygen but the values of the nitrogen and inert gasses remain the same.

The reason for this is that the alveoli have an intricate network of microscopic blood vessels passing around their outside surface called capillaries.

These capillaries (and the alveoli) have very thin walls which will allow very small gas molecules to pass through them.

Individual types of gas molecule exert a particular pressure on surroundings.

If concentrations or pressures of the same gas are different, they will mix until a stable pressure balance is achieved.

A person inhales 21% oxygen into their alveoli.

The blood arriving at the alveoli from the body tissues is low in oxygen (11%).

The higher value of oxygen in the alveoli now begins to balance with the low value of oxygen in the capillary.

As the higher value drops the lower value rises until a state of balance is achieved:

O2 in Alveoli. 02 in Capillary.
21% 11%
20% 12%
19% 13%
18% 14%
17% 15%
16% 16%

This balancing or diffusion process only takes a split second. 21% oxygen arrives in the alveoli, exchange takes place and 16% oxygen is expired. 11% oxygen arrives from the body tissues, exchange takes place and 16% is returned around the body. The overall result is a higher concentration of oxygen in the blood.

The exchange of carbon dioxide happens in reverse:

CO2 in Alveoli. CO2 in Capillary.
.04% 8%
1% 7%
2% 6%
3% 5%
4% 4%

0.04% carbon dioxide arrives in the alveoli, exchange takes place and 4% carbon dioxide is expired. 8% carbon dioxide arrives from the body tissues, exchange takes place and 4% is returned to the body. The overall result is a lower concentration of carbon dioxide in the blood.

Nitrogen and inert gas molecules are much bigger than those of oxygen and carbon dioxide so when they are inhaled, they do not pass into the blood stream.

So, 78% nitrogen and inert gas is both inhaled and exhaled.

The overall result is that there is no change.

If a person normally inhales 21% oxygen and exhales 16% oxygen this means that 4/5 of the oxygen taken in with each breath is blown straight back out.

The body only absorbs about 1/5 of the inspired oxygen, so enough oxygen is exhaled to sustain life in another person.

Also, some conditions e.g. asphyxia and hyperventilation, are a direct consequence of gaseous imbalance i.e. not enough O2 is absorbed or too much CO2 is lost.

Question 28

What is External Respiration?

Answer 28

External Respiration: This is the process of gaseous exchange in the alveoli

Every time we breathe, quantities of gas are taken into the lungs.

Because we use some of the oxygen, the quantities of gas which are exhaled will be slightly different.

Expired air has more carbon dioxide and less oxygen but the values of the nitrogen and inert gasses remain the same.

The reason for this is that the alveoli have an intricate network of microscopic blood vessels passing around their outside surface called capillaries.

These capillaries (and the alveoli) have very thin walls which will allow very small gas molecules to pass through them.

Question 29

What is Internal Respiration:

Answer 29

Internal Respiration:

The oxygen which diffused into the blood is carried in the haemoglobin (now called oxyhaemoglobin) to the tissues.

The pressure of oxygen in the tissues is low, so the higher pressure of oxygen in the blood diffuses into the tissues.

At the same time, excess carbon dioxide from the tissues is diffused into the blood and carried away.

Question 30

Describe Control of Respiration

Answer 30

Control of Respiration: Respiration is controlled by the respiratory centre in the medulla oblongata of the brain.

The presence and accumulation of carbon dioxide in the blood stimulates specialised cells in the great arteries.

Impulses are then carried along by the vagus and glossopharyngeal nerves to the diaphragm and by the intercostal nerves to the intercostal muscles.

These impulses cause the muscles to contract and inspiration occurs.

The level of carbon dioxide in the blood is the primary regulator of the speed and depth of respiration.

Question 31

That is the Lung Capacity of an Average Adult

Answer 31

Lung Capacity (Average Adult):

Tidal Volume is the amount of air breathed in and out during normal respiration (about 500ml).

After a normal expiration, the amount of air taken in during a forced inspiration is called the inspiratory capacity (about 3000ml including the tidal volume).

After a normal expiration, it is possible to force another 1000ml of air from the lungs. This is called the expiratory reserve volume.