Topic 3---A: Exchange and Transport Systems- 3. Gas exchange in humans

Question 1

What is the role of the gas exchange system?

Answer 1

• Supply your blood with oxygen
• Remove carbon dioxide from your body

Question 2

What is the structure of the gas exchange system?

Answer 2

• Trachea
• Ribcage
• Bronchi
• Bronchiole
• Alveoli
• Intercostal muscles
• Lung
• Diaphragm

Question 3

Process of where gases are exchanged

Answer 3

• As you breathe in, air enters the trachea (windpipe)
• The trachea split into two bronchi, one bronchus leading to each lung
• Each bronchus then branches off into smaller tubes called bronchioles which end in small air sacs called alveoli.
  -This is where the gases are exchanged
• Ribcage, intercostal muscles and diaphragm all work together to move air in and out.

Question 4

Intercostal muscles

Answer 4

• Found between the ribs
• There are internal and external intercostal muscles
• Internal intercostal muscles are on the inside of the external intercostal muscles

Question 5

What is ventilation?

Answer 5

• It consists of inspiration (breathing in) and expiration (breathing out).
• It’s controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.

Question 6

Inspiration- breathing in (processes)

Answer 6

1. Diaphragm contracts (flattens)
2. External intercostal muscles contract (ribcage moves upwards and outwards)
3. Increasing volume in the thoracic cavity and decreasing pressure in the lungs
4. Air moves into lungs down a pressure gradient

Question 7

Expiration- breathing out (processes)

Answer 7

1. Diaphragm relaxes (upwards)
2. External intercostal muscles relax (ribcage moves downwards and inwards)
3. Decreasing volume in the thoracic cavity and increasing pressure in the lungs
4. Air moves out of lungs down a pressure gradient

Question 8

How is expiration a passive process?

Answer 8

• It doesn’t require energy
• But if it’s forced, the external intercostal muscles relax whilst the internal intercostal muscles contract pulling the ribcage further downwards and inwards
• During this time, the movement of the two sets of intercostal muscles is said to be antagonistic

Question 9

What do lungs contain millions of and what are they surrounded by?

Answer 9

• Alveoli (air sacs) where gas exchange occurs
• They are surrounded by a network of capillaries

Question 10

Alveoli structure

Answer 10

• Wall of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium- Short diffusion distance
• Moist- gases can dissolve for diffusion
• Good blood supply from large network of capillaries- maintains concentration gradient
• Folded- large surface area

Question 11

How does the walls of the alveoli being elastic help gas exchange?

Answer 11

It helps the alveoli return to their normal shape after inhaling and exhaling air.

Question 12

Movement of oxygen and carbon dioxide through the gas exchange system

Answer 12

• Air (containing oxygen) moves down the trachea, bronchi and bronchioles into the alveoli.
• This movement happens down a pressure gradient
• Oxygen then moves into the blood where it can be transported around the body
• This happens down a diffusion gradient
• Carbon dioxide moves down it’s own diffusion and pressure gradient but in the opposite direction to oxygen so that it can be breathed out.

Question 13

Gas exchange in the alveoli

Answer 13

• Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary epothelium and into a compound called haemoglobinin the blood.
• Carbon dioxide diffuses into the alveoli from the blood.

Question 14

Factors affecting the rate of diffusion (Alveoli)

Answer 14

• Thin exchange surface- alveolar epithelium is 1 cell thick so there is a short diffusion pathway which speeds up diffusion
• Large surface area- there are millions of alveoli
• Steep concentration gradient of oxygen and carbon dioxide between the alveoli and capillary