1. Gas Exchange

2. IB Learning Objectives
Distinguish between ventilation, gas exchange and cell respiration

3. All Living things Respire.
Why living things must respire (breathe):
Cellular Respiration – controlled release of energy in the form of ATP from organic processes in the cell
C6H12O6 + O2 ---> 6CO2 + 6H20 + ATP
Gas Exchange -- Exchange of gases (Oxygen, Carbon Dioxide) between an organism and it environments
Ventilation - process of "changing" or replacing gas (Oxygen, Carbon Dioxide) in a space (ex: lungs)

5. IB Assessment Statement
Explain the need for a ventilation system

8. 6.4.2 Explain the need for a ventilation system.(3)
A ventilation system is needed to maintain concentration gradients in the alveoli 

The steep concentration gradient across the respiratory surface is maintained in two ways: by blood flow on one side and by air flow on the other side. The ventilation system replaces diffuses oxygen (keeping the concentration high) and removes carbon dioxide (keeping the concentration low).
This means oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air.

9. IB Learning Objective
Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli

10. Gas exchange in multicellular animals (i.e. Mammals)
A ventilation system is a pumping mechanism that moves air into and out of the lungs efficiently, thereby maintaining the concentration gradient for diffusion.

12. Ventilation System of Mammals
Lungs are housed in the thorax
Thorax – an airtight chamber formed by the rib cage.
The thorax is housed by ribs and its muscles called intercostal muscles.

13. Ventilation System of Mammals
Diaphragm – A sheet of muscle that separated the thorax from the abdomen
Pleural Membrane- internal surface of thorax, which secretes pleural fluid
Pleural Fluid - is a lubricating fluid from blood plasma that protects the lungs from friction during breathing movements

14. LE 42-24 Rib cage gets Rib cage Air smaller as Air expands as inhaled
rib muscles
relax
Rib cage
expands as
rib muscles
contract
Air
inhaled
Air
exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
EXHALATION
Diaphragm relaxes
(moves up)

15. Ventilation System of Mammals
LE 42-23
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
artery
(oxygen-poor
Alveoli
50 µm
Colorized SEM
SEM
Nasal
cavity
Left
lung
Heart
Larynx
Pharynx
Esophagus
Trachea
Right
Bronchus
Bronchiole
Diaphragm
Lungs connect to the mouth via the trachea
The trachea divides into 2 bronchi, on to each lung
Within the lungs the bronchi divide into even smaller bronchioles

16. Ventilation System of Mammals
The smallest bronchioles end in air sacs called alveoli.
LE 42-23
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
artery
(oxygen-poor
Alveoli
50 µm
Colorized SEM
SEM
Nasal
cavity
Left
lung
Heart
Larynx
Pharynx
Esophagus
Trachea
Right
Bronchus
Bronchiole
Diaphragm

17. The Human Respiratory System
Bronchioles subdivide into millions of tiny air sacs called alveoli.
Alveoli
Bronchiole
The respiratory system is responsible for the exchange of oxygen and carbon dioxide. After reaching the lungs, the trachea branches into smaller and smaller tubes called bronchioles, which end in alveoli, or air sacs.

18. The Human Respiratory System
Alveoli are grouped in clusters.
Alveoli have thin, moist walls
A network of capillaries surrounds each alveolus.
Pulmonary artery
Pulmonary vein
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.
Capillaries

19. Gas exchange takes place in the alveoli.
LE 42-23
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
artery
(oxygen-poor
Alveoli
50 µm
Colorized SEM
SEM
Nasal
cavity
Left
lung
Heart
Larynx
Pharynx
Esophagus
Trachea
Right
Bronchus
Bronchiole
Diaphragm
Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary.
Capillary

20. IB Learning Objective
Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli

22. IB Learning Objective
Describe the features of alveoli that adapt them to gas exchange.

23. Gas exchange takes place in the alveoli.
LE 42-23
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
artery
(oxygen-poor
Alveoli
50 µm
Colorized SEM
SEM
Nasal
cavity
Left
lung
Heart
Larynx
Pharynx
Esophagus
Trachea
Right
Bronchus
Bronchiole
Diaphragm
Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary.
Capillary

25. Cellular Respiration and Gas exchange
Diffusion:
Gas exchange between an individual cell and its environment takes place by diffusion
Gases will diffuse (move) across the cell membrane from an area of high concentration to an area of low concentration.

26. Gas exchange takes place in the alveoli.
LE 42-23
Branch
from
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
artery
(oxygen-poor
Alveoli
50 µm
Colorized SEM
SEM
Nasal
cavity
Left
lung
Heart
Larynx
Pharynx
Esophagus
Trachea
Right
Bronchus
Bronchiole
Diaphragm
Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary.
Capillary

27. Gas Exchange inside a cell example
Gas exchange takes place in the alveoli.
Oxygen diffuses into the blood. O2
Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary.
Capillary

28. Gas Exchange inside a cell example
Carbon dioxide in the blood diffuses into the alveolus. O2
CO2
Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary. 
Capillary

30. Features of the Alveolus that make it great for gas exchange
Large total surface area – 700 million in our lungs, providing 70m2 in total surface area times greater than the surface area of our skin
Surface Area – greater the surface area faster the rate of diffusion.

31. Features of the Alveolus that make it great for gas exchange
Walls of alveoli very thin, consisting of a single layer of flattened cells,
Thin walls decrease the length of the diffusion path. The shorter the diffusion path the greater the rate of diffusion
Thus the respiratory path must be as thin as possible.
Walls of the alveoli have elastic properties meaning they can stretch during inhalation and then shrink back to their original size during exhalation.

32. Features of the Alveolus that make it great for gas exchange
Surface of alveoli walls are covered with a film/ layer of moisture
Oxygen gas dissolves in water lining of alveoli. Oxygen diffuses into the blood when it is dissolved in solution.
Prevents the walls of the alveoli from sticking together
Surrounded by a dense network of capillaries.

33. Features of the Alveolus that make it great for gas exchange
Alveoli is surrounded by a dense network of capillaries.
Network of capillaries around each alveolus supplied deoxygenated blood from pulmonary artery and draining into pulmonary veins.
This maintains the concentration gradient of O2 and CO2.

34. Gas exchange occurs across capillaries, whose walls are one cell thick
We have 50,000 miles of them
Few human cells are > 100 μm from a capillary
Red blood cells
Capillary wall

35. 6.4.3 Describe the features of alveoli that adapt them to gas exchange.(2)
Large surface area due to the combined spherical shape (600 million alveoli = 80 m2)
Flattened epithelial cells of alveoli and close association with capillaries
Short diffusion distance from alveoli to blood ( um)
Dense capillary network
Moist surface for the solution of gases

37. Gas exchange Animations
Ventilation
Gas exchange:
Repiratory system tutorials
Lung Transplant Ted Talk
Opera Sing with a lung transplant

38. IB Learning Objective
Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal, muscles, the diaphragm and abdominal muscles

40. Breathing ventilates the lungs
The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air
LE 42-24
Rib cage
expands as
rib muscles
contract
Air
inhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Rib cage gets
smaller as
relax
exhaled
EXHALATION
Diaphragm relaxes
(moves up)

41. How a Mammal Breathes
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs
The thorax is an air tight chamber, thus as volume changes in the lungs, so does pressure.
Boyles Gas Law = P1V1=P2V2

42. How a Mammal Breathes Inhalation (inspiration) – Volume increases
Lung volume increases as the:
External rib muscles (external intercostal muscles) contract and cause the rib cage to move up.
and diaphragm contract (moves downs)
Internal rib muscles (internal intercostal muscles) relax.

43. How a Mammal Breathes Inhalation (inspiration) – Volume increases
Ribs will move upwards & outwards increasing volume
Diaphragm moves down increasing volume
Increasing Volume, Lowers Pressure (Boyles Law)
Air moves from high pressure to low pressure. Thus air will move from the atmosphere into the lungs.

44. How a Mammal Breathes Exhalation – Expiration – Decreasing Volume
Lung volume decrease as the
Internal rib muscles ( internal intercostal muscles) contract moving the rib cage up and out
and diaphragm relaxes (moves up)
Internal rib muscles (external intercostal muscles) relax.
Decrease volume/ increases the pressure in the lungs and air is forced out

45. How a Mammal Breathes Exhalation – Expiration – Decreasing Volume
The ribs move downwards and inwards, and the diaphragm moves up.
Volume is decrease
Decreasing Volume, increasing Pressure (Boyles Law)
Air moves from high pressure to low pressure. Thus, air from the lungs will be pushed towards the atmosphere.

46. LE 42-24 Rib cage gets Rib cage Air smaller as Air expands as inhaled
rib muscles
relax
Rib cage
expands as
rib muscles
contract
Air
inhaled
Air
exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
EXHALATION
Diaphragm relaxes
(moves up)

47. The respiratory system
When the diaphragm contracts, the chest cavity expands, and the lungs fill with air
Fig