chapter 7 pt 2

Question 1

The main adaptations of the alveoli for effective gaseous exchange:

Answer 1

1. Large surface area:
2. Thin layers:
3. Good blood supply:
4. Good ventilation:
5. The inner surface of the alveoli is covered in a thin layer of a solution of water, salts and lung surfactant.

Question 2

1. Large surface area:

Answer 2

there are 300-500 million alveoli per adult lung.
The alveolar surface area for gaseous exchange in the two lungs combined is around 50-75 m2
If the lungs were simple, balloon-like structures, the surface area would not be big enough for the amount of oxygen needed to diffuse into the body.
This demonstrates again the importance of the SA:V ratio

Question 3

2. Thin layers:

Answer 3

both the alveoli and the capillaries that surround them have walls that are only a single epithelial cell thick, so the diffusion distances between the air in the alveolus and the blood in the capillaries are very short.

Question 4

3. Good blood supply:

Answer 4

the millions of alveoli in each lung are supplied by a network of around 280 million capillaries.
The constant flow of blood through these capillaries brings carbon dioxide and carries off oxygen, maintaining a steep concentration gradient for both carbon dioxide and oxygen between the air in the alveoli and the blood in the capillaries.

Question 5

4. Good ventilation:

Answer 5

breathing moves air in and out of the alveoli, helping maintain steep diffusion gradients for oxygen and carbon dioxide between the blood and the air in the lungs.

Question 6

5. The inner surface of the alveoli is covered in a thin layer of a solution of water, salts and lung surfactant.

Answer 6

• It is this surfactant that makes it possible for the alveoli to remain inflated.
• Oxygen dissolves in the water before diffusing into the blood, but water can also evaporate into the air in the alveoli.
  Several of the adaptations of the human gas exchange system are to reduce this loss of water.

Question 7

diagram of alveolus

Answer 7

Question 8

Ventilating the lungs:

Answer 8

Air is moved in and out of the lungs as a result of pressure changes in the thorax (chest cavity) brought about by the breathing movements.
This movement of air is called ventilation.

Question 9

Arrangement of lungs:

Answer 9

• The rib cage provides a semi-rigid case within which pressure can be lowered with respect to the air outside it.
• The diaphragm is a broad, domed sheet of muscle, which forms the floor of the thorax.
• The external intercostal muscles and the internal intercostal muscles are found between the ribs.
• The thorax is lined by the pleural membranes, which surround the lungs.
• The space between them, the pleural cavity, is usually filled with a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe.

Question 10

Arrangement of lungs diagrams

Answer 10

Question 11

Inspiration:

Answer 11

Inspiration (taking air in or inhalation) is an energy-using process.
The dome-shaped diaphragm contracts, flattening, and lowering.
The external intercostal muscles contract, moving the ribs upwards and outwards.
The volume of the thorax increases so the pressure in the thorax is reduced.
It is now lower than the pressure of the atmospheric air, so air is drawn through the nasal passages, trachea, bronchi, and bronchioles into the lungs.
This equalises the pressures inside and outside the chest.

Question 12

Expiration:

Answer 12

Normal expiration (breathing out or exhalation) is a passive process.
The muscles of the diaphragm relax so it moves up into its resting domed shape.
The external intercostal muscles relax so the ribs move down and inwards under gravity.
The elastic fibres in the alveoli of the lungs return to their normal length.
The effect of all these changes is to decrease the volume of the thorax.
Now the pressure inside the thorax is greater than the pressure of the atmospheric air, so air moves out of the lungs until the pressure inside and out is equal again.

Question 13

how you can exhale forcibly using energy.

Answer 13

The internal intercostal muscles contract, pulling the ribs down hard and fast, and the abdominal muscles contract forcing the diaphragm up to increase the pressure in the lungs rapidly.

Question 14

diagram of Ventilating the lungs

Answer 14

Question 15

Attacking asthma

Answer 15

5.4 million people in the UK are currently being treated for asthma.
They have airways that are sensitive to everyday triggers including house dust mites, cigarette smoke, pollen, and stress.
During an asthma attack, the cells lining the bronchioles release histamines, chemicals that make the epithelial cells become inflamed and swollen.
Histamines stimulate the goblet cells to make excess mucus, and the smooth muscle in the bronchiole walls to contract.
As a result, the airways narrow and fill with mucus, making it difficult to breathe.
Asthma medicines have been developed to reduce the symptoms and even prevent attacks.
The drugs are delivered straight into the breathing system using an inhaler.

Question 16

There are two main ways of treating asthma:

Answer 16

Relievers give immediate relief from the symptoms.
They are chemicals similar to the hormone adrenaline.
They attach to active sites on the surface membranes of smooth muscle cells in the bronchioles, making them relax and dilating the airways.
Preventers are often steroids, which are taken every day to reduce the sensitivity of the lining of the airways.

Question 17

The first breath:
Newborn Breathing Challenges:

Answer 17

The first breath a newborn baby takes needs a force 15-20 times greater than any normal inhalation to inflate the lungs.
The lungs are enormously stretched as the air flows in, and the elastic tissue never returns to its original length.

Question 18

The first breath:
Surfactant Production and Solutions part 1

Answer 18

This intake of breath is only possible because of special chemicals called lung surfactants containing phospholipids and both hydrophilic and hydrophobic proteins.
The surfactant stops the alveoli collapsing and sticking together as the baby exhales.
Without it, the second breath would be as difficult as the first, and continued breathing impossible.
Babies born at full term have alveoli coated in lung surfactant all ready for breathing.

Question 19

The first breath:
Surfactant Production and Solutions part 2

Answer 19

However, the cells of the alveoli do not produce enough surfactant for the lungs to work properly until around the 30th week of pregnancy.
This is one reason why premature babies can struggle to breathe and may die.
In recent years artificial lung surfactants have been produced.
A tiny amount sprayed into the lungs of a premature baby coats the alveoli just like the natural surfactant, making breathing easier, helping to prevent lung damage and enabling many more babies to survive.

Question 20

Measuring the capacity of the lungs (volume of air that is drawn in and out of the lungs):

Answer 20

• A peak flow meter
• Vitalographs
• A spirometer

Question 21

• A peak flow meter

Answer 21

is a simple device that measures the rate at which air can be expelled from the lungs. People who have asthma often use these to monitor how well their lungs are working.

Question 22

• Vitalographs

Answer 22

are more sophisticated versions of the peak flow meter.
The patient being tested breathes out as quickly as they can through a mouthpiece, and the instrument produces a graph of the amount of air they breathe out and how quickly it is breathed out.
This volume of air is called the forced expiratory volume in 1 second.

Question 23

• A spirometer

Answer 23

is commonly used to measure different aspects of the lung volume, or to investigate breathing patterns.
There are many different forms of the spirometer but they all use the principle

Question 24

diagram of spirometer

Answer 24