Composition of the Blood
Blood contains:• Red blood cells
• White blood cells
• Plasma
• Platelets
• Oxygen is carried in the red blood cells.
• Carbon dioxide is carried in the plasma.
• The concentration of carbon dioxide carried in
the plasma is limited since it combines with
water to form an acid.
• Too much acid in the blood would lead to
problems since blood functions best between pH
7.36 and 7.44.
• Most carbon dioxide is transported in blood
plasma as bicarbonate ions. (Some CO2 is
carried in the red blood cells attached to other
molecules)
• Soluble food such as glucose and amino
acids are also transported dissolved in the
plasma.
Function of Haemoglobin
  Haemoglobin is found in red blood cells.
 In high oxygen concentrations haemoglobin
combines readily with oxygen to form oxyhaemoglobin
  This happens in the lungs
  In low oxygen concentrations, oxyhaemoglobin
releases its oxygen to the body cells.
  Blood with oxygen is bright red.
  Haemoglobin carries oxygen to the tissues of the
body.
Colour in the
blood high in
oxygen red and
the blood low
in oxygen blue.
• So:Association (in lungs)
Haemoglobin + oxygen
oxyhaemoglobin
Dissociation (in
tissues)
Associate = to combine with oxygen
Dissociate = to release oxygen
White Blood Cells
• Are less numerous than RBC’s
• They contain nuclei, can change shape and
squeeze through tiny pores in capillary walls.
• They are suited to their function of defending
the body since they can reach the site of
infection outwith the circulation.
• Two types of white blood cell are monocytes
and lymphocytes.
monocytes
lymphocytes
Phagocytosis
• Is the process by which bacteria are engulfed
and destroyed by phagocytic cells such as
monocytes and macrophages (Macrophages
are cells that come from monocytes)
• The macrophage will engulf a bacterial cell and
then digest it.
• During infection, 100’s of monocytes and
macrophages migrate to the infected area and
engulf many bacteria by phagocytosis. Dead
bacteria and these cells often accumulate at a
site of injury forming pus!
Bacterium
giving out
chemical
macrophage
Lysosome (structure
containing digestive
enzymes)
Vacuole
forming
Trapped
bacterium
Bacteria being
digested by enzymes
from lysosomes
Lysosomes move
towards and fuse
with vacuole
Immunity and Antibodies
• Immunity is an organism’s ability to resist
infectious disease.
• Phagocytosis is an example of nonspecific immune response since it
provides general protection against a
wide range of micro-organisms.
• Antibody production is an example of
specific immune response as they are
specific to a particular antigen.
ANTIGEN
A molecule that is recognised as alien to the
body by the body’s lymphocytes.
ANTIBODY
The presence of an antigen in the body stimulates the
lymphocytes to produce antibodies.
An antibody is a Y-shaped molecule. Each arm has a
receptor site whose shape is specific to a particular antigen.
When an antibody meets its complementary antigen, they combine at
their specific sites like a lock and key and the antigen is rendered
harmless. It will then be engulfed by phagocytosis.
Antibody
Receptor
sites
virus
lymphocyte
antigen
Virus gains access
to body & multiplies
inside the cell
Some viral particles
become attached to
their antigens to
lymphocytes
Lymphocytes respond to this antigen by
multiplying and producing cells that mass
produce a specific type of antibody
Antigens meet
antibodies
Antigens combine with
antibodies at receptor sites
and become a harmless
complex later engulfed by
a phagocyte.
Primary and Secondary Responses
• When a person is infected by a diseasecausing organism, the body responds by
producing antibodies.
• This is the primary response.
• Because it takes a while before the
antibodies appear, the primary response is
often unable to prevent the person from
suffering the disease.
• If the person survives and are exposed to the
same disease-causing antigen in the future, a
secondary response happens.
• This happens because the body has memory
cells which remember the antigen.
• This time the disease is usually prevented.
• During the secondary response
– Antibody production is more rapid
– The concentration of antibodies produced reaches a
higher level
– The higher concentration of antibodies is maintained
for a longer time
Increasing
concentration of
antibodies
Secondary
Response
Primary
Response
0
10
20
30
40
0
10
Time (days)
First exposure
to antigen
Second exposure
to antigen
20
30
Some later time
in a person’s life
(days)