The term immunity derived from the Latin word immunis = exempt from tax for defining exemption or in other words resistence of the host against diseases.
Many germs survive in our environment. Germs defined as bacteria and virus are recognized as foreign to our body thanks to minute substances called antigens. Antigens play a key role in detecting germs.
The defense mechanism that protects our body against disease-making germs is called the immune system. The cells that mainly comprise the immune system are the T cells, B cells, fagocytes, natural killer (NK) cells. These cells have receptors for recognizing germs or other foreign substances. Receptors may be thought as locks that match with the keys (antigens) in germs. Cells are activated as the keys (antigens) match with locks (receptors) starting the defense mechanism against germs.
The immune system provides a three-step defense for the host against bacteria, viruses, fungi, parasites and other substances in nature:
Recognizing that it is foreign
Defending against them
Records them in memory avoiding deletion
Erythrocytes are responsible for gas transport and exchange. They dont have nuclei. They include hemoglobins.
Platelets are in charge of hemostasis. They contain coagulation factors, ADP, ATP, calcium, serotonin and katecolamines in their granules.
Neutrophils are responsible for phagocytosis of microorganisms entering the body from outside.
Basophils have dark-colored granules containing heparin, histamine and SRSA. They play role in hypersensitivity reactions relating to IgE.
Eosinophils have special granules and bilobular nuclei. They phagocytose antigen-antibody complexes and parasites.
Lymphocytes take part in viral infections, cellular and humoral immunity.
Monocytes are responsible for phagocytosis of debris and microorganisms including fungi and microbacteria, and for processing and presenting antigens.
Integrity of our skin and mucosa membranes constitute a mechanical barrier.
Sweat and sebaceous glands lower the pH level of the skin preventing survival of bacteria and fungi.
The ciliary surface cells covering respiratory system and the mucus secretions prevent dust, bacteria and viruses from entering the cells of the lungs.
Acid secretion in the stomach prevent survival of diarrhea-causing organisms.
The normal bacterial flora on the internal and external body surfaces inhibits the growth of disease-causing organisms.
Lysosymes existing in tissue and body fluids (tears) cause bacterial death.
Are in charge of protecting you against viruses and cancer
Viruses are our enemies trying to make us sick. They invade our cells forcing them to produce their harmful products once they settle inside.
Cancer, on the other hand, is the rebellion of a group of cells to our body. They proliferate so much that they dont fit their own space and invade other parts of the body. They conquer everywhere they go preventing our organs from functioning properly. We get sick unless cancer cells or virus-invaded cells are destroyed.
Every healthy cell of our body carries a flag (MHC I). Cells lose their flags once they are invaded by viruses or they are transformed into cancer cells as a result of malfunctioning of their programs. NK cells patrol around the body detecting and destroying the cells that have lost their flags. They do this by bomb-like molecules that they carry inside.
If they are not strong enough for the mission, they send signals by secretion of some substances. Other cells of our defense system come to help once they recognize these substances known as cytokines.
Phagocytes eat out germs.
Also, they call other phagocytes for help by sending messages.
Phagocytes, being one of the largest cells of the immune system are among those, who encounter the germs in the first place.
Phagocytes are the first ones that should be remembered when it comes to natural immunity. If the germ is at a distance, they travel fast to where they are called surrounding the germ with its arms, then eating-swallowing and finally digesting the germ.
They should be active, dynamic and eager to digest germs. If they are lazy, diseases would appear easily.
If the germs are too powerful and abundant in number, phagocytes call other friends, the T and B cells, for help.
Complementary system is activated quickly attacking the foreign cell and protecting us from infections.
Another cell fighting against germs in our body is the B cell. B cells are produced in the bone marrow. They look for matching antigens (keys) of their receptors (locks) by traveling around the body in the blood. They are activated with the help of other cells (T cells) once they find them. They proliferate by dividing and transformed first into memory cells and then into plasma cells.
Memory B cells wait to recognize the germ and start defense immediately if and when the same kind of germ enters the body again.
B cells produce protective proteins called immunoglobulins or antibodies.
Plasma cells produce antibodies. Antibodies are Y-shaped proteins and bind easily to antigens on the germs enabling recognition and clearance of germs by other defense cells and clear out of such germs from our body.
There are 5 types of antibodies:
A, D, E, G and M
Type G and M antibodies are the most common ones in our body but type A antibodies are more common in organs such as mouth or nose, which are relatively more susceptible to germs.
Germs enter the body causing us to get sick.
The first line of defense against germs is provided byIgM.
IgG is circulated by blood to encounter the germ.
IgA is contained in tears, saliva and mucus in our body. It is protective in regions such as the nose, lungs and intestines.
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