1. Starter- Structure of the thorax Put them in the correct order
Nose
Terminal bronchioles
Secondary bronchi
Alveoli, alveolar ducts and alveolar air sacs.
Right and left primary bronchi
Tertiary bronchi
Trachea

2. The structure of the thorax
Nose
Trachea / Windpipe,
Right and left primary bronchi
Secondary bronchi,
Tertiary bronchi
Terminal bronchioles
Alveoli, alveolar ducts and alveolar air sacs.

3. This lesson you should be able to…
AS Biology- Module 2
The mammalian lung
This lesson you should be able to…
Grade C- Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Grade B – Outline the mechanism of ventilation.
Grade A/A* - Describe and explain the distribution and functions of the different tissues found in the lungs.

4. Total barrier to diffusion is less than 1 um
O2 from the atmospheric air entering the alveoli enters the blood by diffusion across the alveolar wall down its concentration gradient
CO2 from the blood enters the alveoli by diffusion across the alveolar wall down its concentration gradient
Total barrier to diffusion is less than 1 um

5. CO2 O2 Deoxygenated blood from Oxygenated blood to
heart via pulmonary artery
High CO2 concentration
Oxygenated blood to
heart via pulmonary vein
Low CO2 concentration
Surfactant produced by alveoli – reduces cohesive surface tension forces between H2O molecules in film of H2O
ST forces may cause collapse of alveoli during exhalation – prevented by surfactant
Capillaries
Close contact with alveolar wall
1 cell thick – short diffusion distance
Narrow – space enough for passage of single RBC – allows close contact with capillary wall
Large surface area – numerous and tubular
Alveoli – spherical and numerous (600 million); large surface area (c.70 m2)
Diffusion gradient maintained by rhythmic ventilation (replaces air in alveoli) and a rich blood supply - high [O2] on supply side (alveoli); low [O2] on demand side (capillaries) – vice versa for CO2
Film of H2O
– dissolves gases
- evaporates
Squamous (flattened)
epithelium
Alveolus wall
Capillary wall
Each 1 cell
thick
Plasma – carries 85% of CO2 as hydrogen carbonate ions, 5% dissolved in plasma, and 10% in combination with haemoglobin
RBC’s – contain haemoglobin - carries O2 as oxyhaemoglobin

6. The structure of the thorax1. 6. 3. 7. 8. 4. 5. 9.
10.

7. The structure of the thorax
C-shaped cartilage
Trachea
Right lung
Left lung
Intercostal muscle
Rib
Bronchus
Bronchiolus
Diaphragm

8. Adaptations of Respiratory System for Gas Exchange
Cleans, warms, and moistens the air entering the respiratory tract during inhalation – achieved by hairs, mucus, and blood capillaries (warm blood) in the nasal cavity and cilia in the trachea
A large number of spherical alveoli (600 million) um across – giving a large surface area of approx m2 for rapid gas exchange between the blood and atmosphere; alveolar wall is one cell thick (squamous epithelium) – short diffusion path between alveoli and blood in the pulmonary capillaries
Numerous and tubular capillaries in close contact with alveoli - wall also made of squamous epithelium and one cell thick; total diffusion distance is less than 1 um
Capillaries are narrow – red blood cells are squeezed against the capillary wall – making contact with the wall to reduce diffusion distance. The blood cells are also slowed down – increasing the time for exchange

9. Adaptations of Respiratory System for Gas Exchange
Constant ventilation - replacing the air in the alveoli to maintain a concentration gradient between the alveolar air and the blood
Alveoli are surrounded by a large number of capillaries – a rich blood supply, replaces the blood constantly, to maintain a concentration gradient between the blood and alveolar air.
Haemoglobin (Hb) in red blood cells carries oxygen and has a high affinity for oxygen – helps in maintaining a steep concentration gradient for oxygen
Moist exchange surface – allows gases to dissolve
Water in the alveoli contains a surfactant (phospholipid) – reduces surface tension – prevents collapse of alveoli
Alveoli contain phagocytic cells - for defence

10. Gases exchanged by diffusion down their concentration gradients
Respiratory Tree
Atmospheric air
Larynx (“voice box”)
Trachea
Bronchus (2)
Bronchioles
Alveoli (“air sacs”)
Site of gas exchange
Gases exchanged by diffusion down their concentration gradients
O2 from alveoli to blood in alveolar capillaries
CO2 from blood into alveoli (for excretion)
Capillaries (blood)
Red blood cells transport absorbed O2 from lungs to body tissues
CO2 transported from tissues to lungs for excretion
Direction of air flow
during inhalation
Direction of air flow
during exhalation

11. GAS EXCHANGE
...describe with the aid of diagrams and photographs, the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian gaseous exchange system
Rings of cartilage in the walls of the trachea and bronchi provide support
It is strong but flexible
It stops the trachea and bronchi collapsing when pressure drops

12. Structural components of the respiratory system
Trachea
Fill in the functions
Smooth muscle
Elastic fibres
C-shaped rings of cartilage

13. Smooth muscle and elastic fibres in the trachea
Smooth muscle is found in the walls of the trachea, bronchi and bronchioles
Elastic fibres stretch on inspiration and recoil to help push air out when exhaling
Smooth muscle relaxes during exercise, widening the lumen
Results in less resistance to airflow

14. Function/Characteristics
Describe and explain the distribution and functions of the different tissues found in the lungs.
Structure
Function/Characteristics
Cartilage

15. Structural components of the respiratory system
Inside surface of trachea – epithelial lining
Fill in function
Goblet (mucus) cells
Ciliated epithelium
Loose tissue

16. Ciliated epithelium Simple columnar epithelial cells
Fine hair-like outgrowths
Rapid, rhythmic, wavelike beatings
Movement of mucus
Usually found in the air passages like the nose, uterus and fallopian tubes

17. Helps to prevent lung infections
Ciliated epithelium
Cilia beat the mucus
Helps to prevent lung infections

18. Goblet cells Specialised as gland cells
Synthesising and secreting mucus

19. Mucus traps microorganisms and dust particles in inhaled air
Goblet cells
Secrete mucus
Mucus traps microorganisms and dust particles in inhaled air

20. Examples of specialised exchange surfaces
Small intestine
(absorption of nutrients)
Liver
(Sugar levels adjusted)
Examples of specialised exchange surfaces
Root hair of plants
(water and minerals absorbed)
Hyphae of fungi
(nutrients absorbed)

21. (a) Bronchiole and (b) trachea in transverse section
TASK -Look at the diagrams below.
Draw a table to describe the function and characteristics for each part.
(a) Bronchiole and (b) trachea in transverse section

22. Cross section of bronchiole
Alveolus wall
Thin - single cell thick
Squamous epithelium
Reduces diffusion distance
Bronchiole wall
Ciliated epithelium (cilia
move mucus upwards)
Goblet cells (secrete
mucus)
Blood capillary
Close to alveoli
Thin - single cell thick
Squamous epithelium
Reduces diffusion distance
Pulmonary vein
Carries oxygenated blood to heart

23. (a) Bronchiole and (b) trachea in transverse section

24. Function/Characteristics
Structure
Function/Characteristics
Cartilage
Smooth muscle
Elastic fibres
Goblet cells and glandular tissue .
Ciliated epithelium
Bronchi
Bronchioles

25. Exam Question
4. The diagram below shows the detailed structure of a small part of the mammalian lung.
(i) State the name of the structure shown between lines D and E.
[1]

26. Exam Question
List three features of the structure which you have identified in (i) which make it suitable for gas exchange.
[3]
[Total 4 marks]

27. Exam Question
5. The different parts of the gaseous exchange system, such as the bronchi, show structural adaptations to their functions. The diagram below shows a section through the wall of a bronchus as seen with a light microscope.

28. Exam Question
(a)(i)State one function for each of the following components of the bronchus wall.
goblet cell
cartilage
[2]
(ii)State two ways in which the structure of the wall of the bronchus would be different in a long-term smoker.

29. Exam Question
(b) Gaseous exchange occurs across the walls of the alveoli.
Explain why the walls of the alveoli contain elastic fibres.
[2]

30. Exam Question
(c) One feature of the disease emphysema is that the alveoli lose their elasticity.
Explain the effects of this loss of elasticity on the gaseous exchange system of a person with emphysema.
[4]
[Total 10 marks]

31. The lungs and associated structures
© Pearson Education Ltd 2008
This document may have been altered from the original

32. The lungs and associated structures2. 1. 3. 4. 5. 6. 7. 9.
10. 8.
© Pearson Education Ltd 2008
This document may have been altered from the original

33. Ventilation
The ribcage, intercostal muscles and diaphragm all work together to move air into and out of the lungs, where gas exchange occurs across the thin (single-celled) walls of the alveoli
Ventilation is a physical process, relying on the principle of Boyle’s Law – which state
“Pressure is inversely proportional to volume”
The mechanism can be illustrated using a bell jar model of the respiratory system – however, the model does not illustrate involvement of the rib cage and the intercostal muscles in ventilation
Breathing out
(expiration / exhalation)
Breathing in (inspiration / inhalation)
Internal intecostals contract in forced expiration

34. INSPIRATION EXPIRATION Diaphragm & external intercostals contract
Atmospheric pressure = 760 mmHg
Diaphragm & external intercostals contract
Rib cage raised (upwards and outwards)
Diaphragm lowered (becomes flatter)
Volume of chest cavity increases
Pressure in chest cavity drops to below
atmospheric pressure to 758 mmHg
Air moves into lungs from atmosphere
Active process
Diaphragm & external intercostals relax
Rib cage lowered
Diaphragm raised (dome shape) due to push
from abdominal organs
Volume of chest cavity decreases
Pressure in chest cavity increases to
above atmospheric pressure to763 mmHg
Air forced out of lungs into atmosphere
Aided by elastic recoil and abdominal organs Passive process

36. Inhaling (Inspiration) Exhaling (Expiration)
Volume of thorax
Diaphragm muscle
Diaphragm
Relaxes and resumes to dome shape
External intercostal muscles
Rib cage
Pressure in chest cavity
Decreases below atmospheric pressure
Movement of air

37. Inhaling (Inspiration) Exhaling (Expiration)
Volume of thorax
Increases
Decreases
Diaphragm muscle
Contracts
Relaxes
Diaphragm
Flattens and pushes digestive organs down
Relaxes and resumes to dome shape
External intercostal muscles
Contracts/expands
Rib cage
Upward and outward
Inward and downward
Pressure in chest cavity
Decreases below atmospheric pressure
Increases below atmospheric pressure
Movement of air
Into the lungs down pressure gradient
Air forced out of lungs

38. Exam question (5 marks)

40. Exam Questions - OCR
Name five tissues, cells or cell structures found in the mammalian gas exchange system and explain the function of each
[5 marks]

41. Name five tissues, cells or cell structures found in the mammalian gas exchange system and explain the function of each
[5 marks]
Goblet cells secrete mucus, the mucus traps bacteria and dust particles
Some cells are ciliated, cilia move mucus towards the throat to be removed
Elastic fibres stretch on inspiration and recoil at expiration
Smooth muscle relaxes to make air passages wider when exercising
Cartilage provides support and keeps trachea open