Unit 2: The continuation of life

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Unit 2 The continuation of life
Higher Human Biology

• Chapter 21
• Delivery of Oxygen to Cells

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• Learning Intentions

• Success Criteria

• 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

• To understand how oxygen and nutrients are
  delivered by the bloodstream to every living cell
  in the body.

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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.

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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
oxygen-carrying capacity of the blood.
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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.

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Haemoglobin molecule showing 4 haem groups.
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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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Association and Dissociation
Affinity tendency to combine with a substance.
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The Combining of Haemoglobin with Oxygen to give
OXYHAEMOGLOBIN
Haemoglobin

• This chemical reaction is reversible

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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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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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Oxygen Dissociation Curve
When graphed it gives an S-shaped curve this is
called the oxygen dissociation curve,
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Oxygen Dissociation Curve Extreme right
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Oxygen Dissociation Curve Moving Gradually left
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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 haemoglobins 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.
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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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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.

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The Effect of Temperature
Cells in need of more O2 rise in temperature
triggering the release of O2 from haemoglobin

e.g. respiring cells tissues suffering
microbial infection.
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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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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.
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• Learning Intentions

• Success Criteria

• Describe the features of a red blood cell
  (biconcave shape dimensions, no nucleus,
  flexibility).
• Relate the features of a red blood cell to the
  cells 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

• To understand how oxygen and nutrients are
  delivered by the bloodstream to every living cell
  in the body.

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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.

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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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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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Essay QuestionsSQA 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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Essay QuestionsGuide 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
• Relationship between structure and function (6).
• Production and eventual breakdown (9).

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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

.
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9. Nutritional factors Vitamins Minerals
Vitamin B12 needed for production of Red Blood
Cells (RBCs) in the bone marrow.
Deficiency in either prevents RBC production so
leads to anaemia, because the blood cant carry
enough oxygen
Iron needed for haemoglobin formation
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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
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10.Destruction of Red Blood Cells

• A red blood cell lives for about 120 days.
• Has no nucleus or ribosomes so cant make
  proteins so no growth repair can occur.
• The red blood cells fragments (become damaged)
  in the capillaries.

Macrophages destroy old RBCs by phagocytosis
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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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Task Torrance-TYK pg163 Qu 1-3
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Task Torrance AYK pg163-4 Qus 1-4