Blood is the fluid of life, without blood the
human body would stop working. As the heart pumps it forces blood
through a network of tube-like blood vessels which branch out throughout
every part of the body. There are three main types of blood vessels:
The heart pumps
blood through the arteries, capillaries and veins, carrying nutrients
from digested food and oxygen to every cell in the body. The blood
also removes carbon dioxide and waste products.
The adult human body contains
approximately 5 litres of blood and accounts for approximately 7-8%
of our total body weight.
Blood cells are produced in the bone marrow,
which is a soft spongy material that fills up the cavities of the
bones. All of the different types of blood cells are made in the bone marrow. In a healthy individual millions of
red and white cells are produced and formed daily in the bone marrow.
Everyones blood is
made up of a fluid called plasma and three types of blood cells,
red, white and platelets. Nearly half the blood, approximately 45%
is made up of the various blood cells the remaining 55% is plasma.
Carry on reading to learn more about each of these.
Plasma is the liquid portion of the blood, it
is a clear, yellowish (straw colour) fluid and is mostly made up
of water(90%) and salts. Blood cells travel through the body in
plasma. In addition to carrying blood cells throughout the body,
plasma also carries hormones, nutrients, proteins and chemicals
such as iron.
Red blood cells
Red blood cells are also known as erythrocytes,
their primary function is to carry oxygen from the lungs to the
cells all around the body. They do this through haemoglobin, an
iron containing protein that actually carries the oxygen and gives
blood its red colour.
The blood contains more red blood cells than
any other type of cell. In a single drop of blood there are millions
of red blood cells.
Besides carrying oxygen, red blood cells help
to remove carbon dioxide from the body.
White blood cells
White blood cells are also know as leukocytes
and their main function is to help our body fight infection. They
circulate around the body so that they can be transported to an
area where an infection develops. A drop of blood can contain anywhere
from 7,000 to 25,000 white blood cells at a time. When the number
of white blood cells in the blood increase, this is a sign of infection
somewhere in your body, for example a person with leukaemia could have as many as 50,000 white blood cells in a drop of blood.
There are 5 different types of white blood cells
produced by the bone marrow, the main two are called, neutrophils,
the most numerous of the white blood cells and one of the body's
main defences against bacteria and lymphocytes,
the second most numerous of the white blood cells, lymphocytes are
involved in making antibodies as part of the immune response.
Platelets also known as thrombocytes are the
smallest of the blood cells. Platelets are irregularly shaped, colourless
bodies that are present in blood, it is their sticky surface, along
with other substances that forms clots to stop bleeding. Without
them we would bleed to death. When bleeding from a wound suddenly
occurs, the platelets gather at the wound and attempt to block the
blood flow. A clot begins to form when the blood is exposed to air.
When we get a scab over a cut that is an external blood clot, when
we have a bruise that is the result of an internal blood clot. Both
scabs and bruises are clots that lead to healing. However,
some clots can be dangerous, as in deep
vein thrombosis (DVT) or if a blood clot forms inside
a blood vessel it can block the flow of blood and so cut off supply
of oxygen. A stroke is the result of a clot in an artery of the brain.
What are the different blood groups?
In 1901, scientist Karl Landsteiner reported that
blood could be classified into blood 'types'.
There are 4 main blood groups A, B, AB and O, of which
group O is the most common (47% of population). The blood type is
determined by proteins called antigens found on the surface of red
blood cells. If you have the antigen A on the red blood cells then
you have got type A blood. When B antigen is present, you have type
B blood, when both A and B are present, you have type AB blood.
When neither are present you have type O blood.
Another blood group system involves Rhesus factors.
The name Rhesus comes from the Rhesus monkeys in which the protein
was first discovered. Rhesus factor D, the most important, is found
in the blood of 85% of people, they are known as Rhesus positive.
The remaining 15% are Rhesus negative. So people can be classified
according to both systems, for example AB positive or O negative.
The Rhesus factor is important during pregnancy, a
baby's life can be endangered if it inherits a Rhesus positive blood
type from its father while the mother is Rhesus negative. This is
because the mother can form antibodies against the baby's blood.
Here is a list of the blood types and their frequency
in the UK population :
|O Rh (D) Positive
|O Rh (D) Negative
|A Rh (D) Positive
| A Rh (D) Negative
|B Rh (D) Positive
|B Rh (D) Negative
|AB Rh (D) Positive
|AB Rh (D) Negative
We sell a test on this website which helps identify
what blood group you are, for more information or to buy click
Blood donations and transfusions
Blood grouping is essential for safe blood transfusions.
A patient must receive a blood type that is compatible with their
own blood type. If the blood types are not compatible, red blood
cells will clump together, making clots that can block vessels and
In general a person with type A blood can donate to
a person with type A or AB. A person with type B blood can donate
to a person with type B or AB. A person with type AB blood can only
donate to a person with AB only and someone with O type blood can
donate to anyone. This is because type O blood has no antigen on
its surface and is often called a universal donor. Blood type AB
is the universal recipient as they can receive red blood cells of
any ABO type. In an emergency if there is no time for blood grouping
the person in need of a transfusion would be given type O blood.
In general anyone aged between 17 and 70 who weighs
at least 7 stone 12lbs and is in good health can give blood. Here
are a few examples of people who are unable to give blood :
- If you are pregnant
- If you have a chesty cough, sore
throat or active cold sore.
- If you have already given blood in the last
- If you are taking antibiotics or have just
- Those with HIV, hepatitis
B or hepatitis
Please visit the UK blood service website for more
information on who can and can't give blood : www.blooddonor.org.uk
What can go wrong with blood?
Disorders can affect any of the blood's components,
here are a few of the ones you would have heard of:
- Anaemia is the most common disorder of the blood.
is another condition that affects the blood.
- HIV is a virus that attacks
the white blood cells called lymphocytes.
There is also a rare group of disorders where abnormally
prolonged or excessive bleeding may occur anywhere in the body after
injury or even without injury. One well known, but luckily rare
example of this is haemophilia, an inherited condition in which
even the smallest injury can cause fatal internal or external bleeding.
How do I maintain healthy blood?
Blood like every part of the body needs good nutrition
so a healthy
balanced diet with plenty of fruit and vegetables will
help to maintain healthy blood.
vein thrombosis (DVT)