I. Blood Clotting Process
When there is a cut or open wound on the skin, a blood clot forms over the cut surface. The blood clot is over the cut surface is important to prevent excessive blood loss and to prevent entry of pathogens (disease causing bacteria).
Watch the following Youtube video to have an overview of the blood clotting process.
Video on Blood Clotting Mechanism. Click here.
Mechanism of blood clotting involves a series of inter-linked events known as a cascade of events.
(1) When the blood vessels are damaged, the damaged tissues and platelets release an enzyme known as thrombokinase.
produce
ie Damaged blood vessels ---> thrombokinase
(2) Thrombokinase convert the plasma protein prothrombin into thrombin. Calcium ions are required for this reaction. Thrombin is an enzyme that catalyses the next reaction.
thrombokinase
ie Prothrombin ---> Thrombin
(3) Thrombin catalyses the conversion of soluble fibrinogen into a mesh of insoluble fibrin threads.
thrombin
ie Soluble fibrinogen --> Insoluble Fibrin Threads
The mesh of insoluble fibrin threads entangle red blood cells that forms a clot over the cut surface.
The condition whereby the patient does not have normal blood clotting processes is known as haemophilia. Slight injuries may cause the person to bleed to death or die of internal bleeding.
II. Phagocytosis
Phagocytes engulf and digest foreign particles that enter the blood, eg bacteria that enters the wound. In the process of phagocytosis, some dead phagocytes together with the dead foreign particles eg bacteria would form the a yellowish-green liquid known as the pus. Phagocytosis is part of the innate immunity of the human body ("built-in" immunity).
III. Production of antibodies
Presence of disease-causing organisms such as bacteria and viruses stimulate lymphocytes to produce antibodies which are proteins. Antibodies help the human body to fight infections.
Antibodies help to fight infections by :
(1) Destroying the bacteria. Antibodies attach to the bacteria causing the surface membrane of the bacteria to rupture.
(2) Causing agglutination or clumping of bacteria so that it is easier for the phagocytes to engulf and ingest the clumped bacteria.
(3) Neutralising the harmful substances (eg toxins) produced by bacteria.
During a disease infection, antibodies are produced. These antibodies can stay in the blood long after the disease has been overcome. A person who has recovered thus becomes immune to the infection.
Applications
(i) Small amounts of live attenuated Varicella virus (Chickenpox virus) is injected to patients to induce the human body to produce antibodies that help to protect from full-blown infection. This process is known as immunisation.
(ii) Transplanted organ eg liver, kidney or heart may be rejected by the recipient patient. This is known as tissue rejection. To reduce the risk of tissue rejection, donor and recipient patient must be as genetically close as possible. Alternatively, immunosuppressive drugs that inhibit the responses of the recipient's immune system may be given.