1. breathe just breathe. breathing is good.
6.4 Gas Exchange
breathe just breathe. breathing is good.

2. What is gas exchange?
The process all organisms undergo in which they absorb one gas from the environment and release a different one.

3. -alveoli are tiny air sacs in our lungs where gas is exchanged
In human gas exchange…
-absorb oxygen for cell respiration and release carbon dioxide as waste
-alveoli are tiny air sacs
in our lungs where gas
is exchanged
ALVEOLI RAVIOLI

4. Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
exchange of gases occurs DIFFUSION between air in the alveoli and blood in the capillaries
concentration gradient is created by the higher oxygen concentration and lower carbon dioxide concentration in alveoli than in the blood
fresh air (oxygen) must be pumped into the lungs (alveoli) and stale air will be removed
this is VENTILATION

5. Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange.
Lungs have a lot of alveoli!!!!
This increases surface area for diffusion
Alveoli walls are a single layer of cells (type I pneumocytes), called the epithelium (flattened cells)
The wall of the adjacent capillaries also consist of a single layer of thin cells
The air in the alveoli and blood are very close to each other, so diffusion can occur quickly
Increases the rate of gas exchange

6. Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension.
the Type II pneumocytes are another type of alveolar cell but they are rounded
only occupy about 5% of surface area
secrete a fluid on to the alveolar surface
allows oxygen to dissolve and diffuse
allows carbon dioxide to evaporate and be exhaled
fluid secreted by pneumocytes contains pulmonary surfactant
structured similarly to phospholipids to reduce surface tension
prevents the sides of alveoli from sticking to themselves (prevents lung collapse)

7. Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Trachea- rings of cartilage hold it open, divides into two bronchi
Bronchioles- the two bronchi continually divide, alveoli are located at the end of the narrowest branches

8. Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them.
muscle contractions cause the pressure inside the thorax to drop below atmospheric pressure
air is drawn into lungs from the atmosphere (inspiration) until pressure inside lungs= atmospheric pressure
muscle contractions cause pressure inside the thorax to rise above atmospheric pressure= air is forced out from lungs (expiration)

9. Different muscles are required for inspiration and expiration because muscles only do work when they contract
muscles do work when they contract by exerting a pulling force (tension) that cause movement ( they become shorter when they do this)
Muscles lengthen when they relax and do not exert a pushing force (compression) so do no work at this time
inspiration and expiration involve opposite movements, so different muscles are required, working as antagonistic pairs

10. Antagonistic Muscle Action in Ventilation
Inspiration
Expiration
Diaphragm
Moves downwards and flattens
Moves upwards and becomes more domed
Ribcage
Moves upwards and outwards
moves downwards and inwards
Volume and pressure changes
the volume inside the thorax increases and consequently the pressure decreases
the volume inside the thorax decreases and consequently the pressure increase

11. Antagonistic Muscle Action in Ventilation
Movement of the diaphragm:
Inspiration
Expiration
Diaphragm
the diaphragm contracts and so it moves downwards and pushes the abdomen wall out
the diaphragm relaxes so it can be pushed upwards into a more domed shape
Abdominal wall muscles
Muscles in the abdomen wall relax allowing pressure from the diaphragm to push it out
Muscles in the abdomen wall contract pushing the abdominal organs and diaphragm upwards

12. Antagonistic Muscle Action in Ventilation
Movement of the ribcage:
Inspiration
Expiration
External intercostal muscles
the external intercostal muscles contract, pulling the ribcage upwards and outwards
the external intercostal muscles relax and are pulled back into their elongated state
Internal intercostal muscles
the internal intercostal muscles relax and are pulled back into their elongated state
the internal intercostal muscles contract, pulling the ribcage inwards and downwards

13. Lung Cancer
most common cancer in the world, both in terms of the number of cases and in the number of deaths
smoking causes 87% of lung cancer cases (tobacco smoke contains many mutagenic chemical
Passive smoking causes 3% (second hand smoke)
Air pollution causes 5%
only 15% of patients with lung cancer survive for more than 5 years

14. Emphysema
in healthy lung tissue each bronchiole leads to a small thin-walled alveoli.
in patients with emphysema these are replaced by a smaller number of larger air sacs with much thicker walls.
the total surface area for gas exchange is considerably reduced and the distance over which diffusion of gases occur is increased, and is much less effective. The lungs become less elastic, so ventilation is more difficult
damage to the alveoli is irreversible.