The Human Blood

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 centrifugation.

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 platelets.

Blood

Plasma Blood cells Blood fragments

Red blood cells

White blood cells Platelets

Plasma• 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, fibrinogens.

• Inorganic ions such as sodium, calcium, chlorides and phosphates.

Plasma

Main Functions of Plasma

a. To transport nutrients to tissues.

b. To remove waste products from tissues

c. To distribute hormones, enzymes, antibodies and other proteins

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 nucleus.• 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 oxyhaemoglobin.

• They also carry carbon dioxide from body cells to our lungs.

• 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 cells.• The lifespan of white blood cells depends on the type of white blood cells. It varies from a few hours to a few months.• 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 ingest bacteria.• 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 (Thrombocytes)• Platelets are cell fragments produced by large cells in the bone narrow.• 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.

Blood Groups• 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

O

A

B

AB

Donor’s blood

Reci

pie

nt’

s blo

od

Compatible

Incompatible

• Blood group O can safely donate blood to anyone in small quantities. People with group O are called universal donors.• 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 OBlood transfusion – donors and recipients

The importance of blood donations

• By donating blood, one could have save lives of others.

• 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 childbirth

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 recipients.• Screening tests are performed for evidence of donor infection and hepatitis, AIDS and other sexual transmitted disease.

• 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.