Chapter 26 The Blood

Composition of Blood

4 main parts:

a) Plasma

b) Red blood cells

c) White blood cells

d) Platelets

a) PlasmaPale, golden liquid that makes up about 55% of blood

Plasma is made of:90% water7% proteins3% 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) 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 GroupsIn 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.