Blood is a fluid tissue composed of cells in watery liquid called plasma.It is made up of plasma, white blood cells, platelets and red blood cells.Blood makes up 8% of body weight in a human.The primary function of blood is transport.It transports; oxygen, carbon dioxide, water, nutrients, hormones, wastes and blood cells around the body.Blood also fights infection, preventing entry of pathogens by clotting, temperature regulation, and tissue pH regulation.
Composition of blood
Plasma, the liquid portion of the blood, makes up 54% of the volume of the blood.
When blood cells are removed, plasma is left behind.
It is a straw-yellow liquid composed of 92% water, with dissolved salts, sugars, lipids and proteins (like antibodies and hormones) making up the rest.
Red Blood Cells.
Red blood cells (also known as erythrocytes), makes up 45% of the volume of the blood.
Red blood cells are made in the red bone marrow of long bones, such as the femur.
They have a disc like shape (biconcave).
Red blood cells transport oxygen around the body.
Blood that is rich in oxygen (leaving lungs) is bright red.
Blood that is low in oxygen (entering lungs) is dark red.
Red blood cells do not respire as their only function is to transport oxygen.
Haemoglobin is a red pigment, made from protein.
It gives red blood cells their colour.
It is responsible for carrying oxygen.
It is a globular protein with a haem (iron-containing) group.
The haem group is responsible for carrying oxygen.
Each haemoglobin protein can carry 4 oxygen molecules.
When haemoglobin carries oxygen, it is called oxyhaemoglobin.
It picks up the oxygen in the lungs and releases it to the tissues after travelling through the bloodstream.
Once it has released the oxygen, it is converted back to deoxyhaemoglobin.
Red blood cells have a unique affinity for oxygen.
Haemoglobin is responsible for transporting oxygen.
Red blood cells absorb it in the lungs, and release it in tissues in the body where it is less plentiful.
They are the only complete cell who don't have a nucleus, which they lose during development.
The fact that they have no nucleus and their biconcave shape enables them to be smaller than average and fit through small capillaries.
Their unique shape also gives bigger surface area for diffusion of oxygen.
They don't have a mitochondria either, which helps for squeezing through veins.
There are 30 recognised blood grouping systems in humans, of which the ABO system is the most important.
The ABO system consists of four blood types: A, B, AB, O,
The letters originate from the type of molecule present on the surface of the red blood cells.
People who are type A have a molecule on the surface of their red blood cells that stimulates anti-A antibodies if their blood is injected into people belonging to the B or O groups.
People in blood group B stimulates anti-B bodies if injected to A or O groups.
People belonging to group AB posses both molecules.
People belonging to group O have neither A or B molecules.
Inheritance of Blood Groups
Inheritance of blood groups in Mendelian in nature.This means that a person who belongs to blood group A can have one of two possible genotypes- AA or AO - since A is dominant to O.Similarly, people belonging to blood group B can be BB BO.People who belong to blood group AB have the genotype AB.People that are group O all have the genotype OO, as it is recessive to all other groups.
The Rhesus factor
For a successful blood transfusion, the blood must also match according to the Rhesus blood grouping system.
A person either has or doesn't have the Rhesus factor.
A person who is Rh+ can donate only to Rh+ people, but can receive blood from Rh+ or Rh- people..
Rh- people can donate to Rh+ or Rh- people, but can receive blood from only Rh- people.
Rhesus incompatibility can occur during pregnancy, if the mother is Rh- and the baby is Rh+.
The mother's immune system can react and produce antibodies against the baby's Rh+ blood.
White Blood Cells
White blood cells (leucocytes) and platelets make up the remainder 1% of blood volume.
They are involved in defence mechanisms in the body.
White blood cells are round with a large nucleus.
They are produced in the bone marrow and are involved in the immune response of animals.
MONOCYTES: are a large group of white blood cells that mature into more specific types of white blood cells, such as macrophages. They recognise anything that is foreign. They ingest the foreign particle through phagocytosis. Kidney shaped nucleus.
LYMPHOCYTES: are involved in more specific defences within the body and recognise individual pathogens, producing antibodies against them. This inactivates the pathogen., There are many different kinds of lymphocytes. They have a large round nucleus that takes up most of the cell.
White Blood Cells (Platelets)
Platelets (thrombocytes) are small cell fragments that have no nucleus.
Average life span in seven days.
Platelets are essential in blood clotting.
Sometimes they form an unwanted clot, especially deep in the veins of the legs.
This condition, deep vein thrombosis, occurs more frequently in older people.
It is usually brought on by sitting in one place for extended periods of time.
The clot can travel to the lungs where it causes a potentially life threatening condition, pulmonary embolism.