Higher Human Biology
Unit 2: The continuation of life
Chapter 21:
Delivery of Oxygen to Cells
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
1
Success
Criteria
Learning
Intentions
To understand how
oxygen and nutrients
are delivered by the
bloodstream to every
living cell in the body.
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1.
2.
3.
State the equation for the reversible
reaction between oxygen and
haemoglobin
Explain the affinity of haemoglobin for
oxygen in relation to:
i) changes in blood oxygen tension
ii) changes in temperature
Use oxygen dissociation curves to
explain the affinity for oxygen in
relation to:
i) changes in blood oxygen tension
ii) changes in temperature
Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
2
Introduction
• Human cells are bathed in tissue fluid. Delivery of essential
materials to within DIFFUSION DISTANCE of cells is
brought about by the circulatory system.
• Since blood plasma consists of water and dissolved solutes,
it would seem reasonable to expect that materials to be
transported would need to be highly soluble in water.
THE PROBLEM IS ......
THIS IS NOT THE CASE
WITH OXYGEN.
1. Haemoglobin
As oxygen is only slightly soluble in water only a little could be
carried by blood plasma to the cells, this would be inadequate
to satisfy the needs of respiring cells. This problem is solved
by the presence of haemoglobin.
Instead, haemoglobin (a
respiratory pigment)
combines with oxygen
increasing the oxygencarrying capacity of the
blood.
Structure of Haemoglobin
• In humans, haemoglobin molecules have 4 haem (a
compound containing iron) groups and globin (a
protein made of several polypeptide chains).
• Each haem group is able to carry 1 Oxygen molecule.
Haem
group
Polypeptide
chains
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Haemoglobin molecule showing 4 haem groups.
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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2. Association and Dissociation
• To be effective a respiratory pigment must be able to
– combine easily (associate) with oxygen when the
oxygen concentration in the surroundings is high
– rapidly release (dissociate) oxygen when the
surrounding oxygen concentration is low.
• Haemoglobin has a HIGH AFFINITY for oxygen
when the oxygen concentration in the surrounding
environment is high (e.g. lungs) and a LOW
AFFINITY for oxygen when the oxygen
concentration is low (e.g. active cells).
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Association and Dissociation
Dissociate = to
rapidly release
Oxygen
Associate = to
combine readily
with Oxygen
(when
surrounding O2
Concentration is
low)
(when
surrounding O2
Concentration is
high)
e.g. at respiring
cells
e.g. at lungs
Image source: www.dkimages.com
Affinity = tendency to combine
with a substance.
The Combining of Haemoglobin with
Oxygen to give OXYHAEMOGLOBIN
Association
(in lungs)
Haemoglobin
+ Oxygen
This chemical
reaction is reversible
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Oxyhaemoglobin
Dissociation
(in tissues)
9
Oxygen Tension
• The partial pressure (tension of oxygen is a
measure of its concentration and is
expressed in kilopascals (kPa).
• The oxygen tension of inhaled alveolar air,
for example, is about 13kpa.
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Oxygen Dissociation Curve
• Percentage saturation of haemoglobin with
oxygen decreases with decreasing oxygen
tension of the surroundings.
• However the relationship between the two
in not a linear one.
• Lets
at the Oxygen Dissociation
curve.
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Oxygen Dissociation Curve
When graphed it
gives an S-shaped
curve this is called
the oxygen
dissociation curve,
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Oxygen Dissociation Curve –
Extreme right
Association
Dissociation
At the extreme
right hand
side, the
oxygen tension
of inhaled
alveolar air is
high (~12 kPa)
and
haemoglobins
level of
saturation is
close to 100%
Oxygen Dissociation Curve –
Moving Gradually left
Association
Dissociation
Moving gradually to the left along the graph, the oxygen concentration of the
surroundings is found to decreased yet haemoglobin still remains loaded up with
oxygen to levels over 85% saturation even when the oxygen tension of the
surroundings has dropped to 8kPa. This is due to the fact that haemoglobin has a
high affinity for oxygen.
Oxygen Dissociation Curve –
Extreme Left
At the extreme Left
hand side, the
oxygen tension drops
to below 6kPa and
the percentage
saturation of
haemoglobin with
oxygen drops rapidly.
This is because haemoglobin’s
affinity for oxygen decreases
rapidly in surroundings of low
oxygen concentration. As a
result it unloads its oxygen.
This process is represented by
the step part of the S-shaped
dissociation curve.
Association
Dissociation
Respiring cells
• Actively respiring cells consume much oxygen and the oxygen
tension is found to be low (2.7kPa or less. At the other extreme the
oxygen tension of alveolar air is high at about 13 Kpa.
• When haemoglobin from respiring cells returns to the lungs, it
becomes loaded up with oxygen which moves along the diffusion
gradient from alveoli to blood. This process of association continues
as before until haemoglobin is almost 100% saturated.
• When haemoglobin is transported to actively respiring cells with an
oxygen tension of 2.7kPa haemoglobins percentage saturation with
oxygen drops to a low level (about 35%). This is because
haemoglobin rapidly dissociates from oxygen and unloads it. As a
result oxygen becomes available to satisfy the demands of actively
respiring cells.
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Resting cells
• Cells at rest do not consume much oxygen as actively respiring
cells. The oxygen tension of cells at rest is therefore around
5.3kPa.
• When blood with an oxygen tension of 13kPa from the lungs
arrives at resting cells, its oxygen tension drops to 5.3kPa.
• Haemoglobin now unloads its oxygen by disassociation until its
percentage saturation is about 75%.
• Blood with an oxygen tension of 5.3kPa and haemoglobin which
is still 75% saturated with oxygen then returns to the lungs and
loads up again by association to almost 100% and so on.
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The effectiveness of haemoglobin
• The oxygen dissociation curve is especially steep
between oxygen tensions of 6 an 2pKa.
• This means that any slight drop in oxygen tension
of body cells within this range results in a rapid
release of oxygen by haemoglobin of these cells.
• So effective is haemoglobin at this loading up
(association) and unloading (dissociation) of
oxygen, that it is responsible for the transport of
97% of the oxygen carried in the bloodstream.
The Effect of Temperature
As the temperature of blood increases, haemoglobin’s affinity for
oxygen decreases, so it unloads oxygen sooner at high
temperatures
Cells in need of
more O2 rise in
temperature
triggering the
release of O2
from haemoglobin
e.g. respiring cells &
tissues suffering
microbial infection.
Significance
• Large quantities of energy is generated by
inflamed tissues suffering microbial infection.
• The rise in temperature that occurs locally in these
tissues triggers the release of extra oxygen from
haemoglobin.
• This is advantageous since these cells are exactly
where extra oxygen is required for aerobic
respiration.
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Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Fetal Haemoglobin
Foetal haemoglobin releases its O2 less readily (at a
lower range of O2 tension values) than adult
haemoglobin.
So, fetal
haemoglobin has
a higher affinity
for O2 allowing it
to draw O2 from
its mothers
bloodstream
across the
placenta.
Success
Criteria
Learning
Intentions
To understand how
oxygen and
nutrients are
delivered by the
bloodstream to
every living cell in
the body.
13/04/2015
4.
5.
6.
Describe the features of a red blood cell:
(biconcave shape dimensions, no nucleus,
flexibility).
Relate the features of a red blood cell to
the cell’s ability to absorb oxygen.
Describe the life history of a red blood
cell to include:
i) site of production
ii) life span
iii) factors required for production
iv) sites of breakdown
v) fate of the products of breakdown
Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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STRUCTURE OF A RED BLOOD CELLS
• Cytoplasm rich in
haemoglobin
• Small size (7 μm)
• No nucleus
• Flexible to pass through
capillaries
• Biconcave
shape so large
surface area so
efficient
absorption of
oxygen.
HEALTHY RED BLOOD CELLS ARE SMALL
(the actual size of a red blood cell is approx 2
micron at the rim by 7 micron in diameter)
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Mrs Smith Ch21 The Delivery of
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RED BLOOD CELLS
• THEY ARE PRODUCED IN THE BONE MARROW
FROM STEM CELLS AND LAST FOR 120 DAYS.
• THEY REQUIRE IRON FOR THEIR FORMATION.
• THEY REQUIRE VITAMIN B12 FOR THEIR
FORMATION.
• LACK OF IRON OR B12 RESULTS IN ANAEMIA.
• INTRINSIC FACTOR SECRETED BY THE STOMACH
IS REQUIRED TO AID B12 ABSORPTION.
• LACK OF INTRINSIC FACTOR RESULTS IN
PERNICIOUS ANAEMIA.
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Mrs Smith Ch21 The Delivery of
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Essay Questions:
SQA 2002 & 2007
2002
Give an account of the life
history of a red blood cell
(10)
2007
Give an account of how the
structure of a red blood cell
relates to its function. (10)
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Mrs Smith Ch19 The need for
transport
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Essay Questions:
Guide to H Grade essays pg81
Red blood cells are amongst
the most unusual and
plentiful cells in the human
body. Write an account of
these cells with reference to
the following:
(a) Relationship between
structure and function (6).
(b) Production and eventual
breakdown (9).
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Mrs Smith Ch19 The need for
transport
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Production of Red Blood Cells
• Red blood cells are
produced in the red bone
marrow.
• Red bone marrow consists
of stem cells
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Production of Red Blood Cells
• Bone marrow is distributed
throughout skeleton in children
• just in sternum, ribs, vertebrae &
long bones in adults
• Marrow contains undifferentiated
cells (stem cells), which divide by
mitosis then become specialised
.
9. Nutritional factors: Vitamins & Minerals
Vitamin B12 – needed for
production of Red Blood
Cells (RBCs) in the bone
marrow.
Iron – needed for haemoglobin
formation
Deficiency in either
prevents RBC
production so leads to
anaemia, because the
blood can’t carry
enough oxygen
Vitamin B12 –
gets absorbed
by the gut if
intrinsic factor,
a type of
chemical
secreted by the
stomach, is
present.
No intrinsic
factor leads to
pernicious
anaemia
10.Destruction of Red Blood Cells
• A red blood cell lives for about 120 days.
• Has no nucleus or ribosomes so can’t make proteins
so no growth & repair can occur.
• The red blood cells fragments (become damaged) in
the capillaries.
Macrophages
destroy old RBCs by
phagocytosis
Liver
Bone marrow
Spleen
10. Destruction of Red Blood Cells
• Worn out red blood cells are
destroyed by macrophages by
the process of phagocytosis in
the liver, bone marrow and
spleen.
• Haemoglobin molecules are
broken down and the iron stored
for future use.
• The haem group (minus the
iron) are converted to bilirubin.
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Haemoglobin
is broken down
Haem
Iron
Bilirubin Stored
(excreted as in liver
bile pigment)
Mrs Smith Ch21 The Delivery of
Oxygen to Cells.
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Task: Torrance-TYK pg163 Qu 1-3
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Mrs Smith Ch20: Transport
Mechanisms - The Cardiac Cycle
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Task: Torrance AYK
pg163-4 Qu’s 1-4
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Mrs Smith Ch19 The need for
transport
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