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Sometimes microorganisms are able to make it past the body's external defences (i.e. the skin) the body's immune system must defend the body.
White blood cells are really important in the immune response. They circulate in the blood along with red blood cells and other components.
There are different types of white blood cells - some are able to engulf and digest microorganisms so that they are completely destroyed. This kills microorganisms very quickly and happens they first invade the immune system.
Other white blood cells are able to generate and release special chemicals called antibodies. These are attracted to special markers on the surface of microorganisms called ANTIGENS. Each white blood cell is specific to only one type of antigen. Antibodies are released, they attach to their specific antigen on the surface of microorganisms - microorganisms can then be bunched up into clumps, making it easier for white blood cells to engulf and digest them.
Antibodies take time to generate but once they are, the body is able to recognise specific microorganisms and can react quickly to release antibodies in future attacks - this is called natural immunity.see more
The cardiac cycle is the series of events that leads to blood being pumped to the lungs and around the body.
The cycle begins with the SAN (sino-atrial node). This is the hearts 'pacemaker'. It sends out a nerve impulse which spreads over the atria and causes them to contract (atria systole), forcing blood into the ventricals. The signal is not able to spread to the ventricals as a layer of non-connective tissue blocks the signal at the base of the atria.
The signal from the SAN is recieved at the AVN (atrio-ventricular node) at the top of the ventricals. This node sends a signal down the perkyne (or purkinje) fibres which travel in the insulating Bundle of His through the inter-ventrica septum to the base of the ventricles.
At the base of the ventricals (apex) a wave of contraction passes up the ventricals causing them to contract pushing blood up and out of the ventricals.
These events can be tracked on an ECG trace.see more
In chemistry if a substance is oxidised it loses electrons in a reaction.
If a substance is reduced it gains electrons in a reaction.
A reaction that has both oxidation and reduction within it is called a REDOX reaction. We can write REDOX reactions as half equations - this can make it easier to see what is going on in the reaction.
For example, Zinc oxide can be reacted with Carbon to extract Zinc:
2ZnO + C --> 2Zn + CO2
In this reaction one of the substances is oxidised and one is reduced. If we write them as half equations:
Zn+ + e- --> Zn
C --> C2+ + 2e-
These equations show that Zn has GAINED an electron to have a neutral charge - there for it has been REDUCED.
Carbon has LOST 2 electrons to become C2+ - therefore it has been OXIDISED.see more