Module 2
Exchange and Transport
Unit One
Cells, Exchange and Transport
AS Biology
OCR Specification
Exchange
• In groups
– discuss what is meant by the word
“exchange”
– Apply the word exchange to a biological
concept
– Exchange takes place over surfaces
• Write down features of a good exchange
surface
• Which processes are used in the exchange of
substances
Learning Outcomes
• Explain, in terms of surface area:volume
ratio, why multicellular organisms need
specialised exchange surfaces and
single-celled organisms do not.
Exchanges between organisms
and their environment
• Exchange can take place in two ways
– Passively (no energy is required)
• E.g. diffusion and osmosis
– Actively (energy is required)
• Active transport
• Pinocytosis and phagocytosis
Surface area to volume ratio
• Exchange takes place at the surface of
an organism, but the materials absorbed
are used by cells that mostly make up
its volume.
• For exchange to be effective, the
surface area of the organism must
therefore be large compared with its
volume.
Activity
• Cut out and make animals X and Y
• Compare the two animals with respect
to
–
–
–
–
–
Length
Breadth
Height
Total surface area
volume
Learning outcomes
• Explain, in terms of surface area:volume
ratio, why multicellular organisms need
specialised exchange surfaces and
single-celled organisms do not.
Evolution of organisms
• A flattened shape
• A central region that is hollow
• Specialised exchange surfaces
– Large areas to increase the surface area to
volume ratio
Why organisms need special
exchange surfaces
•
•
•
•
•
•
•
Oxygen for…
Glucose as a source of …
Proteins for … and …
Fats
Water
Minerals
To remove waste materials
Features of a specialised
exchange surface
• Good exchange surfaces have:
– A large surface area
– Thin barrier to reduce diffusion distance
– Large concentration gradient
• Fresh supply of molecules on one side
• Removal of required molecules on other side
Specialised Exchange Surfaces
•
•
•
•
•
Alveoli in the lungs
Small intestine
Liver
Root hairs in plants
Hyphae of fungi
Progress Question
• Very small organisms such as the
amoeba do not have specialised gas
exchange systems.
• Mammals are large, multicellular
organisms and have a complex gas
exchange system.
• Explain why the mammal needs such a
system when an amoeba does not.
Progress Question suggestions
• Why do we need gas exchange?
– Oxygen is needed for respiration
– Body needs to get rid of waste carbon
dioxide.
• How do simple animals take in the
oxygen they need?
– Diffusion through the surface membranes
e.g. amoeba or flatworm
Progress Question suggestions
• Why can’t multi-cellular organisms do
this?
– Cells are too far away from the oxygen in
the external environment.
– Need a specialised exchange surface.
• In humans the specialised gas exchange
surface is the alveoli.
Learning Outcomes
• Describe the features of an efficient
gas exchange surface, with reference to
diffusion of oxygen and carbon dioxide
across and alveolus.
Gas Exchange
• Gaseous exchange is the movement of
gases between an organism and its
environment.
• Gas exchange takes place by diffusion.
– The rate of diffusion depends on three
factors.
• The surface area of the gas exchange surface
• Difference in concentration
• The length of the diffusion pathway
Alveoli
• Adaptations of alveoli to gas exchange
–
–
–
–
–
Large surface area
Thin walls of alveoli and blood capillaries
Steep concentration gradient
Good blood supply
Ventilation
• Blood is constantly moving through the lungs
to maintain the concentration gradients.
• The air in the alveoli is continually refreshed
by ventilation.
Alveoli and gas exchange
• Large surface area – 70m2
• Extremely thin – lined with squamous
epithelium – allows for rapid diffusion
– 0.1μm to 0.5μm thick
• Kept moist / surfactant
• Extensive capillary network
– Capillaries 7-10μm in diameter
– Blood flow through capillaries is slowed
• Ventilation
Applying you knowledge
• Alf smoked for 40 years. He had a bad
“smoker’s cough” and easily got out of breath.
His health got worse so he went to see his
doctor. The doctor said that he had
emphysema. She explained that the coughing
had damaged a lot of the alveoli in his lungs
and reduced their surface area.
– Explain as fully as you can why Alf got out of
breath easily.
– Alf’s illness got worse. He couldn’t walk very far
and he had to breathe oxygen from a cylinder.
Explain why.
Structure of the Mammalian
Lung
Learning Outcomes
• describe the features of the mammalian
lung that adapt it to efficient gaseous
exchange;
• outline the mechanism of breathing
(inspiration and expiration) in mammals,
with reference to the function of the
rib cage, intercostal muscles and
diaphragm;
Pupil Activity
• Colour in the diagram of the lungs
– Take care to read all the information
provided as you colour in.
Think!!
• Why is the volume of oxygen that has to
be absorbed and the volume of carbon
dioxide that has to be removed in
mammals so large?
– Large organisms with large volume of living
cells
– Maintain a high body temperature
• High metabolic rate
• High respiratory rate
Mammalian Lungs
• Structure of the lungs
–
–
–
–
–
–
Trachea
Rib cage
Intercostal muscles
Bronchi
Bronchioles
Alveoli (site of gaseous exchange)
• 100μm – 300μm in diameter
• 300 million in each lung
Pupil Activity
• Design a poster using the information sheet
– 13.1 human gaseous exchange system
• Your poster should show the distribution of
tissues and highlight the functions of each of
the tissues
–
–
–
–
–
cartilage
Cilia
goblet cells
smooth muscle
elastic fibres
Learning Outcomes
• 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
• describe the functions of cartilage, cilia,
goblet cells, smooth muscle and elastic fibres
in the mammalian gaseous exchange system;
Ciliated Epithelium
Cartilage
Smooth Muscle
Squamous Epithelium
Distribution
Tissue / cell
trachea bronchus bronchioles
alveolus
Cartilage

Goblet cells




Ciliated cells




Smooth muscle






(not in the
tiniest)

Very little
Squamous epithelium




Elastic fibres




Functions of cells, tissues
and fibres
Cartilage
• Flexible supporting material
• Incomplete rings support the smooth
muscle keeping the tubes open.
• Prevents trachea and bronchi from
collapsing when air pressure lowers
during inhalation
Cilia
• Synchronised movement to transport
mucus towards the pharynx
Goblet cells
• Produce the mucus that forms a thin
layer over surface of the trachea and
bronchi
• The mucus is sticky and traps bacteria.
Pollen and dust particles, the air is
“filtered”.
Smooth muscle
• Contraction of the smooth muscle allows
the bronchioles to constrict.
• This controls the flow of air to the
alveoli.
Elastic fibres
• Elastic fibres become stretched when
the smooth muscle contracts, when the
smooth muscles relaxes the elastic
fibres recoil back into their original
positions.
• This dilates the bronchioles.
Difference in structure of
Trachea, bronchi and bronchioles
• Cartilage in trachea and bronchi keep
airways open and air resistance low.
– Trachea has c-shaped rings
– Bronchi has irregular blocks
• Bronchioles have smooth muscle which
contracts and elastic fibres to control
their diameter
Learning Outcomes
• outline the mechanism of breathing
(inspiration and expiration) in mammals,
with reference to the function of the
rib cage, intercostal muscles and
diaphragm;
Inhalation
Exhalation
Inspiration
Expiration
Diaphragm
Contracts and
flattens
Relaxes and
pushed up by
organs in abdomen
Rib cage (ribs
and intercostal
muscles)
External
intercostal
muscles contract
raising the ribs
Internal
Volume of
thorax
Pressure in
chest cavity
Air movement
Mammalian Lungs (1)
• Two reasons why mammals require a
large and constant supply of oxygen are
(1) and (2). The main organs for gaseous
exchange are the lungs, which are
connected to the outside by a tube
called the (3). This branches into two
(4), one of which enters each lung.
Mammalian Lungs (2)
• The actual site of gaseous exchange is
in the alveoli, which have a diameter of
(5) and have walls made of (6) which is
very thin, being only (7) in thickness.
The total number of alveoli for both
lungs is around (8) giving them a very
large surface area of about (9).
Gaseous Exchange in the
alveoli (1)
• Gaseous exchange occurs in the alveoli,
with the gas called (1) moving into the
blood and the gas called (2) moving in
the opposite direction. The diameter of
an alveolus is (3) and it is surrounded by
squamous epithelial cells that are only
(4) thick and so allow rapid (5) of gases
across them.
Gaseous exchange in the
alveoli (2)
• Each alveolus is surrounded by a
network of (6) that are around (7) in
diameter, causing (8) within them to be
flattened against their surface, thus
improving the rate of exchange of gases
between themselves and the alveoli.
Learning Outcomes
• explain the meanings of the terms tidal
volume and vital capacity;
• describe how a spirometer can be used
to measure vital capacity, tidal volume,
breathing rate and oxygen uptake;
• analyse and interpret data from a
spirometer
Breathing Rate
• Breathing refreshes the air in the
alveoli so that concentration of O2 and
CO2 remains constant
Lung Capacities
• Tidal volume
– The volume of air breathed in or out in a single
breath
• Residual volume
– The amount of air that remains in the alveoli and
airways after forced exhalation.
• Vital Capacity
– The volume of air that can be exchanged between
maximum inspiration and maximum expiration
• The effect of exercise on breathing is
measured by calculating ventilation rate,
which is the total air moved into the lungs in
one minute.
Ventilation rate = tidal volume X breathing rate
• Ventilation brings about changes in lung
volume, these changes can be ,measured by a
spirometer.
Measuring Oxygen Uptake
• If someone breathes in and out of a
spirometer for a period of time, the
carbon dioxide level increases to
dangerous levels.
• To avoid this, soda lime is used to
absorb the carbon dioxide exhaled.
• This means the total volume of gas in
the spirometer will go down.
Measuring Oxygen Uptake
• The volume of CO2 breathed out is the
same as the volume of O2 breathed in.
• This allows us to make calculations of
oxygen used under different conditions.
Spirometer trace (4 marks)
• A spirometer measures the volume of gas
breathed in and out of the lungs.
• The spirometer trace shows the results
obtained from a 17 year old male who was
sitting down while breathing in and out of a
spirometer.
• Describe this person’s breathing between
points J and K on the spirometer trace
Spirometer trace answers
Transport
Unit One
Cells, Exchange and Transport
AS Biology
OCR Specification
Learning Outcomes
• Explain the need for transport systems in
multi-cellular animals in terms of size, activity
and surface area to volume ratio
• Explain the meaning of the terms single and
double circulatory systems with reference to
the circulatory systems of fish and mammals
• explain the meaning of the terms open
circulatory system and closed circulatory
system, with reference to the circulatory
systems of insects and fish
The Mammalian Transport
System
Why do multi-cellular animals
require a transport System?
The Internal Transport
System
• Cell Metabolism – What do cells need?
– Amino acids, glucose, oxygen
– Removal of waste products
• What is important in determining whether an
organism has a transport system?
– Size
– Surface area to volume ratio
– Level of activity
Pupil Activity
• Using the table on the next slide,
determine the importance of the three
factors and give information to support
your answers?
• Size
• Surface area to volume ratio
• Level of activity
Different Transport Systems
Type of
organism
Size
range
Example
Level of
Activity
Type of
transport
system
Single celled
Microscopic
Paramecium
Move in search
of food
No special
transport sys.
Cnidarians
Microscopic 
60cm
Sea Anemone
Slow swim or
sedentary
No special
transport sys.
Insects
1mm  13cm
Locust
Move actively
(fly)
Blood system
with pump
Fish
12mm  10m
Goldfish
Move actively
Blood system
with pump
Mammals
35mm  34m
Human
Move actively
Blood system
with pump.
Determining the need for a
transport system!
Size
•Important, but not the only factor
•Small mammals and insects have a transport system
•Large cnidarians – no transport system
Determining the need for a
transport system!
Size
•Important, but not the only factor
•Small mammals and insects have a transport system
•Large cnidarians – no transport system
Surface area to volume ratio
•Small organisms have a large S.A to volume ratio, and have
no transport system
Determining the need for a
transport system!
Size
•Important, but not the only factor
•Small mammals and insects have a transport system
•Large cnidarians – no transport system
Surface area to volume ratio
•Small organisms have a large S.A to volume ratio, and have
no transport system
Level of Activity
•Fish, mammals and insects more active have a transport system
•Larger but sedentary cnidarians do not
Why transport systems?
• Diffusion only works effectively in large
surface area to volume ratios
• Small organisms. Oxygen diffuses into cells, to
mitochondria for use in respiration
• Large organisms can not rely on this
• Body surface is not large enough
• Distances from surface are too great
• Less active organisms have a smaller
requirement for glucose and oxygen.
Surface Area:Volume ratios
Length of
side (mm)
1
5
10
Volume
(mm3)
Surface
area
(mm2)
Surface
area:volume
ratio
Surface Area:Volume ratios
Length of
side (mm)
Volume
(mm3)
Surface
area
(mm2)
1
1
6
6:1
5
125
150
1.2 : 1
10
1000
600
0.6 : 1
Surface
area:volume
ratio
Surface area: volume ratio
• With a cube shape
– As it gets bigger the volume increases
faster than the surface area
– Larger multi-cellular animals need a
transport system and special gas exchange
surfaces
Open Circulation
• Insects have an open circulation
– Blood is not enclosed in vessels, and it
circulates in body spaces.
Closed circulation
• Blood flows inside
vessels
• Single circulation
e.g. Fish
– Blood flows through
heart once in every
circulation of the
body.
Closed Circulation
• Double Circulation e.g. mammals
– Blood passes through the heart twice in
every circulation of the body.
– Two circuits
• Pulmonary circuit
• Systemic circuit
Advantages of a double
circulation
• Simultaneous high pressure delivery of
oxygenated blood to all regions of the
body
• Oxygenated blood reaches respiring
cells undiluted by deoxygenated blood.
The Mammalian Heart
Structure of the Heart
Dissection
Learning Outcomes
• describe, with the aid of diagrams and
photographs, the external and internal
structure of the mammalian heart;
• explain, with the aid of diagrams, the
differences in the thickness of the
walls of the different chambers of the
heart in terms of their functions;
External Structure of the
heart
• Observe and draw the external
structure of the heart, identifying the
following parts.
–
–
–
–
–
–
Cardiac muscle
coronary arteries
Aorta
pulmonary artery
Vena cava
pulmonary vein
Internal structure of the
heart
• Observe and draw the internal structure of
the heart
• Identify and describe
– Septum
– atrium and ventricle
– Atrio-ventricular valves
• mitral/bicuspid
• tricuspid
Revision of structure of heart
• Label the diagram of the heart
–
–
–
–
Right atria / left atria
Right ventricle / left ventricle
Aorta / pulmonary artery
Vena cava / pulmonary vein
• Colour in deoxygenated blood blue /
oxygenated blood red
• Fill in the missing gaps in the summary.
• You have got 10 minutes for this activity
The Mammalian Heart
The Cardiac Cycle
Learning outcomes
• describe the cardiac cycle, with
reference to the action of the valves in
the heart;
Cardiac Cycle
• The sequence of events of a heart beat
• Alternate contractions (systole) and
relaxations (diastole)
• Between 70 and 75 bpm
Cardiac Cycle
• Blood flows through the heart
–
–
–
–
–
Muscles contract
Volume chamber decreases
Pressure increases
Blood forced to a region of lower pressure
Valves prevent backflow
Cardiac Cycle
• There are 3 main stages to the cardiac
cycle
– Atrial systole
– Ventricular systole
– Diastole
Atrial Systole
• Heart is full of blood and ventricles
relaxed
• Both atria contract
• Blood passes into ventricles
• A-V valves open due to pressure
• 70% blood flows passively atria ventricle
Atrial Systole
Ventricular Systole
• Atria relax
• Ventricles contract
• Forces blood into pulmonary artery and
aorta
• A-V valves close (lub)
• S-L valves open
• Pulse is generated
Ventricular systole
Diastole
• Ventricles relax
• Pressure in ventricle < pressure in
arteries
• High pressure blood in arteries cause SL valves to shut (dub)
• All muscles relax
• Blood from vena cava and pulmonary vein
enter atria
Diastole
Structure and function of
heart muscle
• Ventricle walls are thicker
– Need greater force when contract
• R. Ventricle –force relatively small,
pumps to lungs
• L. Ventricle – sufficient to push blood
around body
• Thickness left > right
Exam Question
• Answer the exam question
– You have got 15 minutes for this
Pressure and volume changes of
the heart
Pupil Activity
• June 2003 2803/1 question 2
Learning outcomes
• Describe how heart action is
coordinated with reference to the
sinoatrial node (SAN), the
atrioventricular node (AVN) and the
Purkyne tissue.
• Interpret and explain
electrocardiogram (ECG) traces, with
reference to normal and abnormal heart
activity.
Control of Heart Beat
• Myogenic – heart muscle contracts and
relaxes without having to receive
impulses from the nervous system
– Sino-atrial node
– Atrio-ventricular node
Sino-atrial Node
• Special cardiac muscle tissue in right
atrium
• a.k.a. SAN or Pacemaker
• Sets the rhythm at which all other
cardiac muscle cells beat
• Sends excitation wave (depolarisation)
over atrial walls
What happens next?
• Collagen fibres prevent the wave of
excitation from passing from the atria
to the ventricle walls
• Allows the ventricle to fill before they
contract
Atrio-ventricular Node
• Patch of conducting fibres in the
septum
• a.k.a AVN
• AVN picks up impulses that have passed
through atrial tissue
• Wave of excitation runs down purkyne
tissue to the base of the septum
Atrio-ventricular Node
• Wave spreads upwards and outwards
through the ventricular walls
• Blood is squeezed up and out through
arteries.
Control of cardiac cycle Summary
• Cardiac muscles is myogenic
– Wave excitation spreads out from SAN across atria,
atria contract
– septum prevents wave crossing to ventricles
– Wave excitation passes through AVN, which lies
between atria
– AVN conveys wave excitation between ventricles along
specialised muscle fibres known as bundle of His
– This conducts wave through septum to base of
ventricles, bundles branch into smaller fibres known as
Purkyne tissue
– Wave is released, ventricles contract from apex of
heart upwards
electrocardiogram
• Record of wave of electrical activity caused
by atrial systole (P), ventricular systole
(QRS), and the start of ventricular diastole
(T)
Translating ECGs
• Elevation of the ST section indicated a heart
attack
• A small or unclear P wave indicated atrial
fibrillation
• A deep S wave indicates abnormal ventricular
hypertrophy (increase in muscle thickness)
ECG of an unhealthy heart
• An abnormal ECG could indicate
– Arrhythmia
• Where the heart is beating irregularly
– Fibrillation
• Where the heart beat is not co-ordinated
– Myocardial infarction
• Heart attack
Fibrillation
• Excitation wave is chaotic
• Small sections of the cardiac muscle
contract whilst other sections relax
• Heart wall flutter
• Possible causes
– Electrical shock
– Damage to large areas of muscle in walls of
heart
Exam Question
• Answer the practice exam question
The Mammalian Transport
System
Structure and function of
Arteries, Veins and Capillaries
Learning Outcomes
• describe, with the aid of diagrams and
photographs, the structures and
functions of arteries, veins and
capillaries;
Structure of Arteries, Veins
and Capillaries
GCSE Revision
• Arteries carry blood away from the
heart
• Veins carry blood towards the heart
• Capillaries are a network of thin tubes
which link A to V, and take blood close
to cell.
Basic Structure
Lumen
Tunica externa
(hollow centre of tube)
•outer layer containing
collagen fibres.
Tunica media
•Middle layer
containing smooth
muscle and elastic
fibres
Tunica intima
•Endothelium (single
layer of cells)
Microscope Artery
Microscope Vein
Microscope Capillary
Blood Vessels
Look at the image on the
following page.
What are structures X and Y
What do parts 1 – 4 show or
represent?
X
1
2
3
Y
4
Answers
• X is an artery
• Y is a Vein
1. shows the smooth endothelial lining
cells which reduce resistance to blood
flow.
2. shows red blood cells within the lumen
of the artery
3. shows the thick muscular wall of the
artery
4. shows blood capillaries note their size
compared to arteries and veins.
Structure and Function of Arteries
Look at this cartoon.
What can you deduct
about arteries?
(answers on a postcard
please)
Structure of Arteries, Veins
and Capillaries
Arteries
Veins
Thick muscular wall
Much elastic tissue
Small lumen
Thin muscular wall
Little elastic tissue
Large lumen
Capable of
constriction
Not permeable
Valves
–(Aorta and P.A)
Not capable
constriction
Not permeable
Valves throughout
Capillaries
No muscle
No elastic tissue
Large lumen
(relative)
Not capable
constriction
Permeable
No valves
Arteries
• Function
– To transport blood, swiftly and at high pressure to
the tissues.
– The structure of the artery wall gives it strength
and resilience
– The large amounts of elastic tissue in the tunica
media allow the walls to stretch as blood pulses
through.
– As arteries move away from the heart there is a
decrease in elastic tissue and an increase in muscle
tissue.
Arteries (cont)
• Elasticity of walls – 2 functions
– “give”
– Blood at low pressure in an artery gets a
“push” as artery recoils  evens out
blood flow
• Arterioles
– More smooth muscle
– Contracts to help control the volume of
blood flowing into tissues (dilation and
constriction)
Capillaries
• Function
– To take blood as close as possible to
all cells, allowing rapid transfer of
substances between cells and blood
• Network of capillaries  capillary
bed
Veins
• Venules/veins
– Return blood to the heart
• Low venous pressure
• Semi-lunar valves
– Form from endothelium
– Allow blood to travel to the heart
– Prevents the back flow of blood
Systemic Circulation
Aorta
 artery
 arteriole
 capillary
 venule
 vein
 vena cava
Summary of function of A, V
and C
Arteries
Veins
Capillaries
Transports blood
away from heart
Oxygenated blood
(except P.A)
Blood High Pressure
Blood moves in
pulses
Blood flow rapidly
Transport blood too
heart.
Deoxygenated blood
(except P.V)
Blood low pressure
No pulses
Blood flows slowly
Links arteries to
veins
Blood changes from
oxygenated to
deoxygenated
(except in lungs)
B.P. reducing
No pulses
Blood flow slowing
Revision Questions (1)
– Suggest why arteries close to the heart
have more elastic fibres in walls than
arteries further away from the heart.
– Suggest why there are no blood capillaries
in the cornea of the eye. How might the
cornea be supplied with its requirements?
Revision Questions (2)
•
Suggest reasons for the following:
1. Normal venous pressure in the feet is about
25mm Hg. When a soldier stands at attention
the blood pressure in their feet rises very
quickly to about 90mm Hg.
2. When you breathe in (volume thorax
increases), blood moves through the veins
towards the heart.
Pupil Activity
• Bioviewer activity – slide set 68
– Read the information on the front of the card.
• how does the human circulatory system help to maintain
cell life?
• what are the three major parts of the human circulatory
system?
– Observe the following slides
•
•
•
•
Slide
Slide
Slide
Slide
1
2
3
4
–
–
–
–
human blood
Phagocyte
artery and vein
capillaries in the lung
Blood, Tissue fluid and
Lymph
Blood – the transport medium
• Plasma
– Straw coloured, alkaline liquid
– Consists mainly of water
• Functions of blood
–
–
–
–
–
Defends body against disease
Maintains diffusion gradients
Acts as a buffer
Provides pressure
Distributes heat around body
Blood plasma
• Water with dissolved substances
– Nutrients e.g. glucose
– Waste products e.g. urea
– Plasma proteins
• Buffers
• Solute potential
Red Blood Cells
Erythrocytes
• Origin
– Bone marrow
• Mature RBC transport respiratory
gases
• Life span 120 days
• No nucleus/ cell organelles
• Cytoplasm full of haemoglobin
• Biconcave disc
• Large SA: volume ratio
White Blood Cells
Leucocytes
• Protect body as part of the immune
system
• Originate in bone marrow thymus
and lymph for growth and development
• Lymphocytes
– Production of antibodies
• neutrophils, monocytes
– phagocytosis
Platelets
(cell fragments)
• Tiny packages cytoplasm containing
vesicles with thromboplastins
– Clotting factors
• Made in bone marrow
• Last 6 – 7 days
Pupil Activity
• Which of these functions could, or could
not, be carried out by a RBC.
•
•
•
•
Protein synthesis
Cell division
Lipid synthesis
Active transport
Answers SAQ
• Protein Synthesis
– NO: no DNA so no
mRNA can be
transcribed.
• Cell Division
– NO; no chromosomes,
so no mitosis; no
centrioles for spindle
formation
• Lipid Synthesis
– NO; occurs in smooth
ER
• Active Transport
– YES; occurs across
plasma membrane,
can be fuelled by ATP
from anaerobic
respiration.
Tissue Fluid
• Immediate environment of each
individual body cell.
• Homeostasis maintains composition of
tissue fluid at a constant level to
provide the optimum environment in
which cells can work.
• Contains less proteins than Blood plasma
Forces for exchange on capillaries
Blood proteins (e.g. albumins) can not escape and maintain
the water potential of the plasma, preventing excess
water loss, and help to return fluid to the capillary
Arteriole end
Venule end
Diffusion gradient
Ultrafiltration
of
water and small
molecules (O2, glucose
and amino acids) due to
hydrostatic pressure
Osmotic movement
of water
Tissue fluid
Diffusion gradient
Blood in capillary
Hydrostatic
pressure
reduced
Lymph
• Similar composition to plasma with
less proteins
• Lipids absorbed in lacteals, give lymph
milky appearance
• Tiny blind ending vessels
• Tiny valves in walls allow large
molecules to pass in.
• Drains back into blood plasma in
subclavian vein.
oedema
• If lymph does not take away proteins in
tissue fluid between cells, YOU could
die in 24 hours.
• Get a build up in tissue fluid, called
oedema.
Movement in lymph capillaries
• Contraction of muscles around vessels
• Valves
• Slow movement
– Diagram: the relationship between blood, tissue fluid
and lymph at a capillary network
» Diagram: the lymph system
Table summary
feature
Cells
Proteins
Fats
Glucose
Amino acids
Oxygen
Carbon
dioxide
Antibodies
blood
Tissue fluid
Lymph
Table summary
feature
blood
Tissue fluid
Lymph
Cells
Erythrocytes,
leucocytes,
platelets
phagocytes
Lymphocytes
Proteins
Hormones and
plasma
proteins
hormones,
proteins
secreted by
body cells
some
Fats
Transported
None
as lipoproteins
Absorbed by
lacteals
Glucose
80-120mg per
100cm3
Less
Less
Amino acids
more
less
less
Table summary
feature
blood
Tissue fluid
Lymph
Oxygen
more
less
Less
Carbon dioxide
little
Released by
body cells
More
Antibodies
yes
yes
yes
The Mammalian Transport
System
Transport of Oxygen and
Carbon Dioxide
Partial Pressure
• In a mixture of gases, each component gas
exerts a pressure that is proportional to
how much of it is present.
• Concentration of gas is quoted as its partial
pressure, in kilopascals kPa.
• pO2  partial pressure of oxygen
• pCO2  partial pressure of carbon dioxide
pO2 = atmospheric pressure x % O2
100
Pupil Activity
calculation of partial pressure
• Assume the composition of air is 20% oxygen and
80% nitrogen, and is approx. the same at sea level
(atmospheric pressure = 101.3kPa) and at 5000m
above sea level (atmos. Pressure = 54.0 kPa) and at
10000m above sea level (atmos. Pressure = 26.4
kPa)
• What is the partial pressure of oxygen at these
altitudes?
Transport of Oxygen
• Haemoglobin in red blood cells (RBC)
Hb + 4O2
HbO8
Haemoglobin dissociation
curve
• A graph showing the amount of oxygen
combining with haemoglobin at different
partial pressures.
• High pO2 – haemoglobin saturated with
oxygen
• Low pO2 – oxyhaemoglobin gives up its
oxygen to respiring cells (dissociates)
Haemoglobin dissociation
curve
S-shaped curve
•
•
•
•
Each Hb molecule has 4 haem groups
1st O2 combines with first haem group
Shape of Hb distorted
Easier for other 3 O2 to bind with haem
group
Bohr Shift
• high pCO2
increases
dissociation of
oxyhaemoglobin
• Oxyhaemoglobin
releases oxygen
where it is
needed most –
actively respiring
tissues.
Fetal Haemoglobin
• Fetal Hb has a
higher
affinity for
O2 than adult
Hb.
• This allows
the fetal Hb
to “steal” O2
from mothers
Hb
Myoglobin
• Oxymyoglobin is
more stable than
oxyhaemoglobin
• Only gives up O2
at very low pO2.
• Myoglobin acts
as an oxygen
store
Carbon Dioxide Transport
• CO2 carried in three ways
– 5% in solution in plasma as CO2
– 10% combines with amino groups in Hb
molecule (carbamino haemoglobin)
– 85% hydrogen carbonate ions
Carbon dioxide transport
• Transported in blood as hydrogen
carbonate ions
• Carbonic anhydrase catalyses the
reaction
CO2 +
H2O

H2CO3
Carbon Dioxide Transport
• Carbonic acid dissociates
H2CO3  H+ + HCO3• H+ ions associate with haemoglobin
(buffer)
• Haemoglobinic acid (HHb)
• Contributes to Bohr effect
Chloride Shift
• Build up HCO3- causes them to diffuse
out of RBC
• Inside membrane positively charged
• Cl- diffuse into RBC from plasma to
balance the electrical charge
Problems with Oxygen
Transport
Carbon Monoxide
• Haemoglobin combines readily with carbon
monoxide to form carboxyhaemoglobin
(stable compound)
• Carbon monoxide has a higher affinity
with haemoglobin than oxygen does
• 0.1% CO in air can cause death by
asphyxiation.
High Altitude
• Pupil activity
– question sheet on high altitude
– Question
• Atheletes often prepare themselves for
important competitions by spending several
months training at high altitude. Explain how
this could improve their performance.
Training at high altitude
• Spending a length of time at high altitude
stimulates the body to produce more red
blood cells
• When an athlete returns to sea level, these
“extra” RBC remain in the body for sometime,
and can supply extra oxygen to muscles
enabling them to work harder and for longer
than they would otherwise.