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AQA AS Biology
Unit Biol 1
Biology and Disease
Part B
The Lungs and Lung Disease
The Heart and Heart Disease
The Defensive Role of Blood
Phil Simpson
© ZigZag Education, 2010
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Introduction
 The first part of this unit resource examined some
general aspects of infectious and lifestyle disease;
the digestive system and how enzyme hydrolysis
produces smaller molecules that can be absorbed
and assimilated; cell structure and function.
 This second part will cover aspects of lung structure,
function and dysfunction; functioning of the heart and
the biological basis of heart disease; the defensive
roles of blood.
Introduction
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The need for lungs and circulatory system
The lungs and lung disease
The heart and heart disease
The defensive role of blood
(Red links are disabled)
Need for transport system in animals
 All animals must:
 maintain a supply of materials they need:
 nutrients
 oxygen
 required for respiration and growth
 remove the waste products of metabolism
 carbon dioxide
 ammonium
 urea
… need for transport system in animals…
 In small organisms such needs can easily be met by
diffusion
 distances are short (less than 0.5 mm)
 surface area is relatively large
 exchange can take place across their body/cell
surface
… need for transport system in animals…
 Large active organisms cannot rely upon diffusion
 distances are too great
 surface area relative to volume is insufficient for
exchange
 they need:
transport system
specialist exchange
surfaces
deliver materials to/from
exchange surfaces
satisfy the demands created
by high activity levels.
Imagine an animal composed of a ball of cells. What is the
relationship between size, surface area, volume and s.a.:volume
ratio?
Side
/ mm
Surface
area / mm2
Volume
/ mm3
s.a. :
volume ratio
1
2
3
4
5
Side
/ mm
1
2
3
4
5
Surface
area / mm2
6
24
54
96
150
Volume
/ mm3
1
8
27
64
125
s.a. :
volume ratio
6
3
2
1.5
1.2
In small groups, discuss the answers to the following
questions…
 How do each of the following change as the length of
the side increases?
 Surface area
 Volume
 Surface area:volume ratio
 For each cube, how far away from the surface of the
cube is its centre?
 Use the data on the effect of size on surface area,
volume, and surface area:volume ratio to explain why
larger animals need specialist exchange surfaces.
How do surface area, volume, and surface area:volume
ratio change as the cube size increases?
 Surface area increases
 Volume increases also, but at a faster rate
 The ratio decreases!
For each cube, how far away from the surface of the
cube is its centre?
 Sorry about this, but the maximum will be 0.5 of the
diagonal (which is √3 x length of side)
 0.87, 1.73, 2.59, 3.46 and 4.33 mm for the 1, 2, 3, 4
and 5 mm sided cubes respectively.
 Remember, diffusion is not efficient over distances
greater than 0.5 mm. Consequently cells at the
centre of any cube-shaped animal bigger than 1 mm
would have a problem supplying nutrients and
removing wastes using diffusion alone.
Use the data on the effect of size on surface area,
volume and surface area:volume ratio to explain why
larger animals need specialist exchange surfaces
 Increase in size increases the distance that materials
need to be transported over
 If distance is > 0.5 mm, diffusion is too slow to supply
cell needs
 As size increases, volume increases
disproportionately compared to volume
 Demands of cells for nutrients and waste removal
also increase disproportionately
 Problem is made worse in an active organism!
The lungs and lung disease
The lungs allow exchange of respiratory gases. Their
function might be affected by pathogens and lifestyle
factors.
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 Lung structure and function
 Lung disease
 Data interpretation
 Summary
(Red links are disabled)
Lung structure
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 Gross structure of the lung
 Histology of the airways
 Exchange of gases in the lungs
 Mechanism of breathing
 Lung volumes and their measurement
(Red links are disabled)
Structure and function of gas exchange system
 Mammalian gas exchange or respiratory system
consists of the airways and lung tissue
 It is usual to breathe in via the nose
 air is
 warmed, moistened and filtered
 air then travels through the trachea, bronchi,
bronchioles
 ultimately ends up in the air sacs or alveoli
 large surface area
 squamous epithelium (thin so short diffusion path)
 vascularised (helps maintain diffusion gradients)
 Lungs are situated in the thorax
 surrounded by the ribcage
 each lung is covered by pleural membrane
 secretes a lubricating fluid
 allows lung to inflate/deflate without rubbing up against
the inner walls of the ribcage
 Intercostal muscles are present between the ribs
 external set raise the ribcage
 internal set lower the ribcage
 Lungs are separated from the abdomen by a
muscular diaphragm
 normally domed
 muscular contraction flattens it
Gas Exchange System
Trachea with
strengthening rings of
cartilage
Cut end of rib
Intercostal muscle
Left lung
Bronchiole –
respiratory bronchioles
lack cartilage
Bronchus
Position of heart
Grape-like clusters
of air sacs or alveoli
Pleural membranes
secrete lubricating
fluid into the pleural
cavity
Domed diaphragm
Muscle of diaphragm
Structure of airways
 The trachea and bronchi are similar in structure
 essentially different in size
 Inner surface is covered with ciliated epithelium
 ciliated cells
 cilia 3–4 µm long
 rhythmic wave-like movement moves mucus to top of
trachea where it is swallowed
 microbes destroyed by stomach acid
 goblet cells
 secrete sticky mucus containing glycoprotein
 protects from dehydration and traps microbes and dust
 lysozyme is also present which causes bacterial lysis
 Cartilage
 strong and flexible
 holds airways open during inhalation
 trachea has incomplete or C-shaped rings
 allow food to pass down the oesophagus
 bronchi cartilage is in irregular blocks
 To the inside of the cartilage is ‘loose tissue’
 Smooth muscle
 contract or relax to alter diameter
 note asthma causes constriction and so narrows airways
 Elastic fibres recoil during exhalation
 Glandular tissue
 makes mucus secretion
 Blood vessels
Extension: Histology of the Trachea (low power)
Ciliated epithelium.
Note the cellular
debris
Lumen or
airway
Cartilage block. Cartilage
cells (chondrocytes) clearly
visible in the matrix
Loose layer containing blood
vessels, smooth muscle, elastic
tissue and glandular tissue
Extension: Histology of the Trachea
Ciliated epithelium
Cilia
Elastic tissue
Goblet cell
Blood vessel with
numerous blood cells
clearly visible
Smooth muscle
Cartilage – chondrocytes
clearly visible
Extension: Histology of the Bronchiole and alveolar tissue
Alveolar space
Lumen or
airway
Alveolar wall cell
Smooth muscle
Block of cartilage
Capillary – blood vessels
have been injected with dye
Epithelium – ciliated in
bronchiole but not
respiratory bronchiole
Extension: Histology of the Bronchiole and alveolar tissue
Alveolar space
Lumen or
airway
Alveolar wall cell
(nucleus purplish stain)
Smooth muscle
Capillary – blood vessels
have been injected with dye
Epithelium – ciliated in
bronchiole but not
respiratory bronchiole
Structure of alveoli
 The air spaces are divided up by the alveolar walls




single layer of squamous epithelium
flattened cells, 0.5 µm thick
adjacent blood capillaries are also squamous epithelium
combined thickness 1 µm, so the diffusion path is short
 Elastic fibres present
 stretch during inhalation
 recoil during exhalation
 White blood cells are present
 despite ciliated epithelium, microbes may still get through
 Moist film into which gases dissolve before diffusion
 surfactant (detergent) present reduces cohesion of water
molecules and so prevents collapse of alveoli
Alveolar tissue
Blood capillary –
injected with red dye
Alveolar space
Epithelial cells of alveolus
have purplish-stained nuclei