There are both nonspecific and
specific defense mechanisms. The first line of defense is the skin
and mucus membranes and their secretions. The skin is the first
barrier that bacteria and viruses try to get through; this is
impossible unless there is any kind of abrasions. Also the mucus
membrane that lines the digestive, respiratory, and genitourinary
tracks prevent the entry of potentially harmful microbes. The skin
and mucus membrane act as a physical barrier as well as countering
pathogens with a chemical defense. When we secrete saliva, tears and
mucous it cleans the exposed epithelia, washing away the potential
Also, these secretions contain various antimicrobial proteins.
One of these antimicrobial proteins is lysozymes, which is an enzyme
that digest the cell wall of the bacteria and destroys the microbes
that try to enter the upper respiratory system and around the eyes.
Mucus also traps the particles it comes into contact with. When the
microbes are entering the upper respiratory system the get caught
and either swallowed or expelled. The trachea is lined with special
epithelial cells that are equipped with cilia that sweeps the out
microbes and other particles that gets trapped by the mucus.
Microbes that are present in food or caught in mucus from the upper
respiratory system has to pass through the acidic gastric juices
produced by the stomach lining.
Phagocytosis is the ingestion of invading particles by certain types
of white blood cells. This is the body main internal defense
mechanism. Phagocytic cells are called neutrophils which comprise
sixty to seventy percent of the white blood cells. These can destroy
microbes by the chemical signals, neutrophils can leave the blood
and enter infected tissue by amoeboid movement. The neurophils can
only live a few days because they are self-destructive as well as
destroying the foreign invaders.
Another five percent of the white blood
cells are made up of monocytes which provide phagocytic defense.
Once matured the monocytes circulate inside the blood for a few
hours, then they migrate into the tissue where they grow in size and
develop into macrophages. Macrophages are the largest phagocytes
cells they are especially effective and having long life as
There are also natural killer cells which do not attack the
microorganisms directly, but they destroy the bodys own infectious
cells. These killers also attack the cells that could form tumors.
There is a group of at least twenty proteins act as the
complement system, which acts in cooperation with other defense
mechanisms. These proteins act as a group in activation steps that
culminate with lysis of the invading microbes. Also there are
interferons, which are chemical messengers of the immune system,
that are produced by virus-infected cells, and capable of helping
other cells resist the virus. There are three types of
interferons-alpha, beta and gamma.
The inflammatory response is when tissue reacts to physical
injury, like a cut. When an injury occurs the small blood vessels in
the area dilate, as well as increase the blood supply to the area.
The swollen blood vessels are more preamble the fluid moves from the
blood to neighboring tissue, which causes edema. The most important
element of the inflammatory response is the phagocyte migration from
the blood to the injured tissues.