Chapter 26
The Blood
Composition of Blood
4 main parts:
a) Plasma
b) Red blood cells
c) White blood cells
d) Platelets
a) Plasma
Pale, golden liquid that makes up about 55% of blood
Plasma is made of:
90% water
7% proteins
3% dissolved materials which are being
transported
Main plasma proteins are:
•
Antibodies – produced by white blood cells to kill
foreign substances e.g. bacteria
•
Clotting proteins – Which help to form blood clots.
b) Red blood cells (erythrocytes)
• Produced in the bone marrow of bones e.g. ribs and long
bones
• Very small and round
• Biconcave shape
• No nucleus or mitochondria
• About 5 million in 1 cubic millimetre
• Contain a red protein called haemoglobin
which carries oxygen around the body.
• Broken down in the liver and spleen
• Mineral iron is needed to make
Haemoglobin
Haemoglobin + oxygen =
oxyhaemoglobin
• Function of red blood cells: Carry
oxygen gas from the lungs to all
body cells
• Iron comes from foods e.g. meat and
green veg.
• A lack of iron in the diet results in
anaemia. Symptoms include being
pale and feeling tired all the time.
Treatment would usually involve
increasing iron intake in your diet
c. White Blood Cells
(Leucocytes)
•
•
•
•
Larger than red blood cells
No definite shape
Only live for a few days
700 red blood cells: 1 white
blood cells
• Made in the bone marrow
• Some mature in the lymphatic
system
Function of white blood cells:
Defend the body against infection
and fight infection
Many different types of white blood cell
- Most white blood cells (phagocytes) attack bacteria by
surrounding them and then digesting them.
- Some white blood cells (lymphocytes) produce
antibodies which react with invading bacteria and
viruses.
Two main categories of white blood cell:
a)
•
•
•
•
•
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Lymphocytes
Made in the bone marrow
Stored in lymphatic system e.g. spleen, tonsils etc.
Make up 25% of all white blood cells
Have a large round nucleus and very little cytoplasm
Can survive from 3 months to 10 years
Main function is to make antibodies to resist infection
b) Monocytes
• Large cells that scavenge throughout the body
and digest bacteria
• Also called macrophages
• Formed in the bone marrow
• Make up 5% of white blood cells
• Survive 6-9 days
• Have kidney shaped nuclei
Leukaemia:
Form of cancer in which white blood cells
are produced too rapidly and are
immature.
They crowd out the other blood cells and
may cause anaemia, increase the risk of
infection and reduced ability to form blood
clots.
Treatment may include drugs, radiation
and bone marrow transplants.
d. Platelets (Thrombocytes)
• Made in the bone marrow from large cells called
megacytes
• Smaller than red blood cells
Function of platelets:
They reduce the loss of blood
They prevent the entry of micro-organisms
Clots do not usually form in healthy undamaged blood
vessels. If blood vessel walls are damaged a blood
vessel may form (thrombosis). A blood clot in the brain
causes a stroke and a blood vessel clot in the heart
causes a heart attack.
Functions of Blood
1. Transport of food, waste products, hormones
and plasma
2. Transport of heat to help maintain body
temperature
3. Transport of oxygen by red blood cells
4. Defence against disease using white blood
cells and platelets
Blood Groups
In 1900 Karl Landsteiner discovered that humans
have 4 main blood groups (ABO Groups)
He won the Nobel Prize for his work
He discovered that most red blood cells have a
complex carbohydrate and protein chemical on
their surface membrane
Four main blood groups are A, B, AB and O
When blood transfusions are given it is
important that to match the incoming blood
group to the group of the recipient.
Otherwise the blood may clump (stick
together) in the recipient.
Blood group O is called the universal donor
because their blood can be given safely to
any other group.
Blood group AB is the universal recipient
because they can receive blood from any
other blood group.
Rhesus Factor
• This is a factor present in some peoples
blood.
• It was first discovered in Rhesus monkeys
and is named after them.
• About 85% of Irish people have a chemical
called the rhesus factor present on the
surface of their red blood cells (called Rh+ or
rhesus positive people)
• 15% of the Irish population do not have the
factor present (called Rh- or rhesus negative
people)
People of blood group A may be A positive
(also called A+ or A Rh+ blood) or A
negative (also called A- or A Rh- blood)
Similarly for B+, B-, O+, O-, AB+, AB-
Rhesus negative blood can be given
safely to a rhesus positive person.
If rhesus positive blood is given to a
rhesus negative person it may cause a
serious reaction if the person received a
transfusion of the rhesus positive blood
before.
Rhesus factor may also lead to
complications (problems) if a rhesus
negative mother is pregnant with a rhesus
positive baby. Her first rhesus positive
baby will be safe but any further rhesus
positive babies may have their red blood
cells damaged. This may cause the baby
to be anaemic or in severe cases brain
damaged or stillborn.