Unit 2: The continuation of life

Chapter 21:

Delivery of Oxygen to Cells

Higher Human Biology

19/04/23 1Mrs Smith Ch21 The Delivery of Oxygen to Cells.

Learning Intentions

To understand how oxygen and nutrients are delivered by the

bloodstream to every living cell in the body.

Success Criteria1. State the equation for the reversible

reaction between oxygen and haemoglobin

2. Explain the affinity of haemoglobin for oxygen in relation to:

i) changes in blood oxygen tensionii) changes in temperature

3. Use oxygen dissociation curves to explain the affinity for oxygen in relation to:

i) changes in blood oxygen tensionii) changes in temperature

19/04/23 2Mrs Smith Ch21 The Delivery of Oxygen to Cells.

• 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.

Introduction

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.

1. Haemoglobin

Instead, haemoglobin (a respiratory pigment) combines with oxygen increasing the oxygen-carrying capacity of the blood.

19/04/23 Mrs Smith Ch21 The Delivery of Oxygen to Cells.

5

Polypeptide chains

Haem group

• 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.

Structure of Haemoglobin

Haemoglobin molecule showing 4 haem groups.

19/04/23 6Mrs Smith Ch21 The Delivery of Oxygen to Cells.

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).

19/04/23 7Mrs Smith Ch21 The Delivery of Oxygen to Cells.

Image source: www.dkimages.com

Associate = to combine readily with

Oxygen

(when surrounding

O2 Concentratio

n is high)

e.g. at lungs

Affinity = tendency to combine with a substance.

Dissociate = to rapidly release Oxygen

(when surrounding

O2 Concentration

is low)

e.g. at respiring cells

Association and Dissociation

The Combining of Haemoglobin with Oxygen to give OXYHAEMOGLOBIN

This chemical reaction is reversible

19/04/23 9

Oxygen+ OxyhaemoglobinDissociation

(in tissues)

Association

(in lungs)Haemoglobin

Oxygen Tension

19/04/23 10Mrs Smith Ch21 The Delivery of Oxygen to Cells.

• 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.

Oxygen Dissociation Curve

19/04/23 11Mrs Smith Ch21 The Delivery of Oxygen to Cells.

• 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.

Oxygen Dissociation Curve

19/04/23 12Mrs Smith Ch21 The Delivery of Oxygen to Cells.

When graphed it gives an S-shaped curve this is called

the oxygen dissociation curve,

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%

Association

Dissociation

Oxygen Dissociation Curve – Extreme right

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.

Association

Dissociation

Oxygen Dissociation Curve – Moving Gradually left

Association

Dissociation

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.

Respiring cells

19/04/23 16Mrs Smith Ch21 The Delivery of Oxygen to 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.

Resting cells

19/04/23 17Mrs Smith Ch21 The Delivery of Oxygen to 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.

• 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 effectiveness of haemoglobin

e.g. respiring cells & tissues

suffering microbial infection.

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

The Effect of Temperature

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.

19/04/23 20Mrs Smith Ch21 The Delivery of Oxygen to Cells.

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.

Fetal Haemoglobin

Learning Intentions

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

Success Criteria4. Describe the features of a red blood cell:

(biconcave shape dimensions, no nucleus, flexibility).

5. Relate the features of a red blood cell to the cell’s ability to absorb oxygen.

6. Describe the life history of a red blood cell to include:

i) site of productionii) life spaniii) factors required for productioniv) sites of breakdownv) fate of the products of breakdown

19/04/23 22Mrs Smith Ch21 The Delivery of Oxygen to Cells.

• Biconcave shape so large surface area so efficient absorption of oxygen.

• Cytoplasm rich in haemoglobin

• Small size (7 μm)• No nucleus• Flexible to pass through

capillaries

STRUCTURE OF A RED BLOOD CELLS

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)

19/04/23 24Mrs Smith Ch21 The Delivery of Oxygen to 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.

RED BLOOD CELLS

19/04/23 25Mrs Smith Ch21 The Delivery of Oxygen to Cells.

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)

19/04/23 Mrs Smith Ch19 The need for transport

26

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).

19/04/23 Mrs Smith Ch19 The need for transport

27

Production of Red Blood Cells

• Red blood cells are produced in the red bone marrow.

• Red bone marrow consists of stem cells

19/04/23 28Mrs Smith Ch21 The Delivery of Oxygen to 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

Production of Red Blood Cells

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 can’t carry enough

oxygen

Iron – needed for haemoglobin formation

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

LiverBone

marrowSpleen

Macrophages destroy old

RBCs by phagocytosis

• 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.

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.

19/04/23 33Mrs Smith Ch21 The Delivery of Oxygen to Cells.

Haemoglobin is broken

down

Haem Iron

Bilirubin (excreted

as bile pigment)

Stored in liver

Task: Torrance-TYK pg163 Qu 1-3

19/04/23 35Mrs Smith Ch20: Transport Mechanisms - The Cardiac Cycle

Task: Torrance AYK pg163-4 Qu’s 1-4

19/04/23 36Mrs Smith Ch19 The need for transport