The Constituents of Blood
•The average human has 4 – 6 dm³ of blood
circulating in his body.
•The major constituents of blood can be separated by
The composition of human blood after centrifuge
•Blood consist of fluid called plasma which is made up
of suspended blood cells and blood fragments.
•Plasma makes up 55% of blood by volume. The other
45% consists of red blood cells, white blood cells and
Plasma Blood cells Blood fragments
•Plasma is the yellow liquid in our blood.
•90% of plasma is water. The rest are dissolved
substances which include:
•a. Nutrients such as glucose, amino acids and vitamins.
•Proteins like antibodies, hormones, enzymes, albumins,
•Inorganic ions such as sodium, calcium, chlorides and
Main Functions of Plasma
a. To transport nutrients to tissues.
b. To remove waste products from tissues
c. To distribute hormones, enzymes, antibodies and
d. To distribute heat energy from the liver and
muscles to all other parts of the body.
Red Blood Cells (Erythrocytes)
•They are biconcave, disc – shaped cells without
•The red blood cells transport oxygen from the lungs to
all parts of the body.
•They contain a red pigment called haemoglobin which
combines with oxygen molecules to form
•They also carry carbon dioxide from body cells to our
•There are about 5, 000,000 red blood cells in each
cubic millimeter of blood.
•Red blood cells are made in the bone marrow.
•The lifespan of red blood cells is about 120 days.
•When the red blood cells are worn out, they are
destroyed in the liver and spleen.
White Blood Cells (Leucocytes)
•White blood cells are much larger than red blood cells
and they have a nucleus.
•They are usually irregular in shape, colourless and do
not contain haemoglobin .
•There are several types of white blood cells.
•White blood cells are formed from bone marrow
•The lifespan of white blood cells depends on the type
of white blood cells. It varies from a few hours to a
•They play a vital role in the body’s defense against
diseases. Some white blood cells produce antibodies to
render bacteria inactive while other white blood cells
•Unlike red blood cells. White blood cells can squeeze
through the walls of the blood capillaries into the
spaces among the cells to destroy the bacteria.
•Platelets are cell fragments produced by large cells in the
•They appear as tiny oval – shaped structures without
nucleus under a high – powered microscope.
•There are between 250, 000 and 500, 000 platelets in
every cubic millimeter of blood.
•They play an important role in blood clotting. When a
blood vessel breaks, the platelets release clotting factors.
•There are many different systems by which blood is
grouped but the ABO system is the best known.
•The ABO system classifies the human blood into main
four groups called A, B, AB, and O.
•During a blood transfusion, the donor’s blood must be
compatible with the recipient’s blood.
•When an incomplete type of blood is transfused, the
red blood cells of the donated blood will clump
together (agglutinate) and cause fatal blockages in the
recipient’s blood vessels.
O A B AB
•Blood group O can safely donate blood to anyone in
small quantities. People with group O are called
•Blood group AB can safely receive blood from anyone.
Group AB people are called universal recipients.
Group Can donate to Can receive from
A A and AB A and O
B B and AB B and O
AB AB All groups
O All groups O
Blood transfusion – donors and recipients
The importance of blood donations
•By donating blood, one could have save lives of
•Blood maybe needed for treatment of accident cases,
cancer victims, haemophiliacs, surgery,
gastrointestinal bleeding and in childbirth where a
great loss of blood occurs.
•The donated blood can be used either as unfiltered
blood for one patient, or separated into components to
help several patients.
Main uses of the components of donated blood
Component Main uses
Plasma Great loss of blood in surgery and
Red blood cells Anemia
Platelets Bone marrow failure, leukemia
Blood proteins Burns
Storage and handling of donated blood
•A donor normally gives about 400 cm³ of blood from
vein in his arm.
•Blood should be collected under aseptic conditions into
a sterilised container containing anticoagulant solution
which prevents clotting.
•The donated blood is tested for ABO group and the
presence of antibodies that maybe cause problems in a
•Screening tests are performed for evidence of donor
infection and hepatitis, AIDS and other sexual
•The date of expiration should be written on the label
attached to the blood container.
•The blood can be stored at 5°C for 10 days, or longer
if glucose is added.
•The blood maybe separated into several components.
•Red blood cells can be stored under refrigeration for
42 days, or they can be frozen for up to 10 years.
•Platelets can be stored at room temperature for a
maximum of 5 days.
•Frozen plasma can be kept for up to 1 year.
•Frozen plasma and red blood cells should be thawed
in a water bath at temperature not exceeding 38°C.