Chapter 7- Exchange Surfaces and Ventilation

Question 1

Definition of exchange surface

Answer 1

This is a specialised area adapted to make it easier for molecules to cross from one side of the surface to the other

Question 2

Exchange surfaces in single celled organisms and multicellular organisms

Answer 2

Single celled organisms can simply exchange material across their cell membrane to meet their requirements. They can do this by diffusion, osmosis etc. They do this by lowering the concentration of oxygen within the organism than the surroundings, so the oxygen can diffuse in, down a concentration gradient, as long as it can penetrate the organism’s surface.

Multi celled organisms need specialised structures for exchange to be fast enough

Question 3

Features of good exchange surfaces

Answer 3

Large surface area (e.g root hair cells, villi, alveoli)
Thin barrier/ exchange surface to reduce the diffusion pathway. This is possible because exchange barriers are made up of squamous epithelium cells- these are naturally flat and thin.
Maintenance of diffusion gradient by maintaining the conc gradient; by supplying molecules on one side of the membrane, and removing them on the other side- either by a good blood supply or an efficient ventilation system
Some exchange surfaces also use active transport mechanisms to increase exchange
Good blood supply- the alveoli are well supplied with capillaries which absorb the oxygen and deliver the carbon dioxide. The circulation of blood helps maintain the diffusion gradients.
The surface has to permeable
Moist surface- oxygen and carbon dioxide cannot go through the surface in gaseous state. A moist state allows these gases to dissolve and then pass through
Ventilation mechanism- this is another way to maintain the conc gradient- breathing. This constantly removes air containing carbon dioxide and reduced levels of oxygen, and replaces it with high levels of oxygen and low levels of carbon dioxide

Question 4

What are the different levels of airways

Answer 4

Trachea->two bronchi (sing. Bronchus) ->bronchioles->alveolar duct-> alveolar sac->alveoli

Question 5

Alveoli, alveoli duct and alveoli sac

Answer 5

Lung alveoli are the ends of the respiratory tree, branching from either alveolar sac or alveolar ducts, which like alveoli are sites of gas exchange.
Alveolar duct connect alveolar sacs to the bronchioles; each of which contain a collection of alveoli. These tubules divide into two or three alveolar sacs at the distal end.

Question 6

Alveoli key structural features- Capillary network

Answer 6

Mostly pulmonary capillaries
Form a dense network around each alveolus (plu. Alveoli)
Alveolar macrophages (a type of phagocytic white blood cell) digest any foreign particles that have reached that alveoli.

Question 7

Alveoli key structural feature- epithelial cells

Answer 7

Squamous epithelial cells
Referred to as Type I and Type II pneumocytes
Type I are large flattened cells and make up most of the alveolar wall.
Type II secrete surfactant

Question 8

What is a surfactant

Answer 8

This is a mixture of lipids and proteins which help reduce the surface tension of liquid lining inner surface of alveoli
Speeds up transport of gases between the air and the liquid lining the alveolus
Kills bacteria

Question 9

What is a connective tissue

Answer 9

Forms a supporting layer beneath the epithelium
Consists of fine collagen and elastin fibres together with fibroblast cells
Allows stretch and recoil of lung tissue with breathing

Question 10

Difference between recoil and contract

Answer 10

MUSCLES contract and relax
TISSUES stretch and recoil

Tissues form muscles

Question 11

What is a spirometer

Answer 11

It is a device used to measure and record the volumes of air inspired and expired over time
The paper record (trace) of the volumes is known as a spirograph or kymograph

Question 12

What is the tidal volume(TV)

Answer 12

This is the volume of air breathed in and out in one breath at rest-usually 500cm3

Question 13

What is the expiratory reserve volume (ERV)

Answer 13

This is the volume of air that you can force out after a normal tidal expiration

Question 14

What is Inspiration reserve volume (IRV)

Answer 14

This is the volume of air that can be inspired over and above a tidal inspiration

Question 15

What is the residual volume (RV)

Answer 15

Even after breathing as far put as possible some air remains in the lungs due to surfactants (residual volume). This keeps the alveoli partly inflated and allows gas exchange to continue between breaths

Question 16

What is the Vital Capacity (VC)

Answer 16

This is the greatest volume of air you can move into and out of your lungs in one breath.
VC= IRV + TV + ERV
VC is affected by age, sex, athleticism and posture

Question 17

What is important while interpreting a trace from a spirometer?

Answer 17

Always carefully read whether the gas volume refers to the volume in the spirometer tank or in the lungs. Check the units it is measured in.
The trace on the kymograph gets lower as an experiment progresses as the oxygen is consumed by the body.

Question 18

How are the exchange surfaces adapted specifically for organisms that have evolved to colonise land

Answer 18

The surfaces are waterproof to avoid excessive water loss, and such surfaces are impermeable to oxygen and carbon dioxide

Question 19

What is the thoracic cavity

Answer 19

This is the division of the body cavity that lies above the diaphragm. It contains the lungs and heart

Question 20

What are intercostal muscles

Answer 20

These are several groups of muscles that run between the ribs and help form the chest wall. These move the ribs in and out during deeper breathing.

Question 21

What are pleural membranes and what is a pleura cavity

Answer 21

The lungs are surrounded by double membranes called pleural membranes; between which, in the pleural cavity, is a fluid.

Question 22

What does the fluid in the pleural cavity do

Answer 22

This fluid acts as a lubricant between the lungs and the rib cage.

Question 23

What is a diaphragm

Answer 23

This is a sheet of muscle at the base of the thoracic cavity

Question 24

Where is the lung situated

Answer 24

Within the rib cage, which protects them, in the thoracic cavity.

Question 25

Different tissues of gas exchange

Answer 25

Cartilage
Ciliated epithelium
Goblet

Question 26

What is a cartilage

Answer 26

A form of connective tissue that provides strengthening and support.
It is composed of cells surrounded by material consisting of mucopolysaccharides. These are complex polysaccharides containing amino acids.
This tissue is resistant to both tension and compression however it is not as rigid or strong as a bone
This tissue is more flexible
In gas exchange system, the function of cartilage is to keep the larger tubes open (the trachea, the bronchi and the larger bronchioles). These tubes have a relatively large diameter and thin walls, and without the strengthening of cartilage, they would collapse.

Question 27

Ciliated epithelium

Answer 27

Epithelium is the name given to any layer of cells that form a covering or lining. Ciliated epithelium consists of cilia on the lining. This moves the mucus ( which traps dust and bacteria that enter with the air) to the top of the trachea, which is close to the opening of the oesophagus. The mucus can then be swallowed and is eventually eliminated through the digestive tract.
This is how mucus is safely disposed.

Question 28

Goblet cell

Answer 28

These produce the mucus that lines the trachea, bronchi and larger bronchioles. These are found between the ciliated cells in the epithelium. Their goblet-like shape has a ‘bowl’ containing mucus, ready to be secreted.

Question 29

Smooth muscle and elastic fibres

Answer 29

Smooth muscles is found in the trachea, bronchi and the large bronchioles. It maintains the tone in the airways and also allows expansion in conditions where extra oxygen is needed (e.g during exercise).

Elastic fibres are found in all lung tissues, including the alveoli. The elasticity of the lungs is vital, because expiration is a passive process due to the recoil of the lungs.

Question 30

Trachea

Answer 30

Biggest tube
Has no particular function apart from allowing air to reach the lungs
Isn’t very thick because of this
Isn’t very thin either; gas exchange does not occur here
Essential that the trachea is open at all times for constant air flow; because thin walls are more likely to collapse than an evenly thick wall(which would need plenty of cells and therefore a lot of resources), trachea has evolved rings of cartilage that provide a form of ‘scaffolding’ to keep the tube open. These rings are distributed at intervals along the trachea; so the softer tissue in between retains flexibility.
The rings of cartilage are also C-shaped to prevent being rubbed against the oesophagus when food goes down through it. The ends of the cartilaginous rings are joined by tissue containing smooth muscle and elastic fibres.
The trachea is lined by ciliated epithelium that contain goblet cells- which secrete mucus.
Below the epithelium, there are mucous glands. These along, with goblet cells produce adequate mucus that trap dust particles and bacteria.

Question 31

Bronchi

Answer 31

Smaller diameter and thinner walls compared to the trachea. Bronchi have complete rings of cartilage rather than C-shaped ones. This is because it does not lie against the oesophagus.

Question 32

Bronchioles

Answer 32

Vary in size and structure as they get smaller towards the alveoli. Although the walls of the bronchioles are thin. Narrow tubes tend to be self-supporting. Therefore they do not need rings of cartilage. There are no mucous glands in bronchioles- the larger bronchioles have goblet cells though. The small ones don’t these or cilia on their epithelium cells. This is because there would have plenty of opportunity to collect dust and bacteria before this.
The walls of larger bronchioles contain elastic fibres and smooth muscle, and the muscles can adjust the diameter of the airways to increase or reduce air flow.
However smaller bronchioles just have elastic fibres

Question 33

Alveoli

Answer 33

Wall of an alveolus consists of a single layer of epithelium, but there is an extracellular matrix that contains elastic fibres, which allow the alveoli to expand during inspiration and recoil during expiration

Many capillaries surround the alveoli for gas exchange and to also produce surface tension

Question 34

How does breathing work

Answer 34

Results from the action of the intercostal muscles between the ribs and the diaphgram. The elasticity of the lungs also play a key role by simply just responding to the events around it.

Question 35

What happens during inspiration

Answer 35

The rib cage moves up and out and the diaphgram move down; by doing so the volume of the thoracic cavity is increased. Due to this the pressure inside the lungs has decreased below atmospheric pressure. This causes air to move in from the outside. As a result, the lungs expand.

Question 36

What happens during expiration

Answer 36

Volume of thoracic cavity decreases because the diaphgram moves up and the rib cage moves in. The increases the pressure in the lungs- higher than atmospheric pressure. Air moves out as the lungs recoil- this is only possible due to their natural elasticity.

Question 37

Internal intercostal muscles

Answer 37

When these muscles contract, they pull the rib cage down and in. These muscles are only used when there is forced expiration (e.g blowing) and during strenuous exercise, where extra pressure on lung is needed.
These are controlled by an expiratory centre in the brain.

Question 38

External intercostal muscles

Answer 38

The elasticity of the lungs and the relaxing of these muscles is enough for normal expiration

Question 39

The inspiration system

Answer 39

The inspiration centre in the medulla oblongata of the brain sends out a nerve impulse
This causes the external intercostal muscles to contract, raising the rib cage. Simultaneously, the diaphragm contracts and flattens
This then causes the volume of the thoracic cavity to increase and the pressure to decrease to a level below the atmospheric level in the lungs.
As a result, air is drawn into the gas exchange system
This then causes the lungs to expand due to reduced pressure on them
This then activates the stretch receptors in the lungs

Question 40

The expiration system

Answer 40

The activation of the stretch receptors in the lungs caused by its expansion, triggers the inspiratory centre in the brain to stop sending an impulse.
This then causes the external intercostal muscles to relax, lowering the rib cage. Simultaneously, the diaphragm relaxes too, and moves upwards.
This then causes the volume in the thoracic cavity to decrease and the pressure to increase to the level above the atmospheric pressure in the lungs.
the lungs then recoil due to their elasticity and the increased pressure on them.
Because of this, the air is pushed out of the gas exchange system
This deactivates the stretch receptors in the lungs
Due to this the inhibition of the respiratory centre stops

Question 41

How does the spirometer work

Answer 41

The subject breathes in and out through the spirometer. The carbon dioxide is absorbed from the re-breathed air by soda lime to prevent respiratory distress, which may be caused if air containing high levels of carbon dioxide is breathed in.
Using the volume of carbon dioxide absorbed, this machine produces a trace on a revolving drum or a screen.