TOPIC 1.CLASIFICATION KINGDOM FUNGI
The clotting process
Platelets at the site of an injury
produce thromboplastin which starts off the clotting process.
Thromboplastin, with the help of vitamin K and calcium neutralizes heparin,
an anticoagulant in blood.
Heparin converts prothrombin
(which is an inactive plasma protein) to thrombin (an active plasma
protein).
Thrombin
catalyzes the conversion of soluble fibrinogen to insoluble fibrin.
Fibrin forms a network of fibres that traps debris and blood cells. The result
is a clot at the site of the wound preventing further loss of blood.
Blood Groups and Blood Transfusion
Grouping of human blood is done
using the ABO system and the Rhesus factor.
The ABO system
The ABO system of grouping blood
depends on two things. First is the presence or absence of antigen A or antigen
B on the membranes of the red blood cells. Second is the presence of antibody
A or antibody B in the blood plasma.
A person cannot have a certain
antigen membrane of the red blood cell and also have the corresponding antibody
in the plasma. For example, you cannot have both antigen A antibody a. This
would cause agglutination clumping together of red blood cell. Agglutination
can cause fatal
The various blood groups and the
antigens a antibodies present in them are summarized
|
Blood group
|
Antigen on the membrane of the
blood cell
|
Antibody in the plasma
|
|
A
|
A
|
A
|
|
B
|
B
|
B
|
|
AB
|
A and B
|
(none)
|
|
O
|
(none)
|
a and b
|
Rhesus factor
This factor is named after the
Rhesus monkey in which it was first observed. When the rhesus factor is present
on the red blood cell membrane, a person is said to be rhesus positive. This is
abbreviated as Rh+. If it is absent, the person is rhesus negative this is
abbreviated as Rh-. Thus, a person’s blood is said to be A+ if it is blood
group A and has the Rhesus factor or A- if it is blood group A but lacks the
Rhesus factor. There is also B+ or B-, O+ or 0- and AB+ or AB- blood groups.
If a rhesus negative woman marries a
rhesus positive man, their children are highly likely to be rhesus positive.
During the last months of pregnancy, the rhesus antigen from the foetus passes
into the mother's blood. This causes the mother's body
to produce antibodies which destroy some of
the foetus's red blood cells. This destruction is minimal in the first child
but in the children that follow, a lot of destruction could take place, killing
the foetus. This is called haemolytic disease of the
newborn or erythroblastosisfoetalis. To prevent this, the
mother is treated with anti-rhesus globulin. This prevents her body from
forming antibodies against the rhesus antigen.
Blood transfusion
Blood transfusion is the transfer of blood from
one person (the donor) to another (the recipient). It is necessary to replace
blood when the recipient has a blood disorder or has lost a lot of blood due to
surgery or an accident
