The Complex Field of Immunity (Coursework Sample)

Immunity
The Latin term immunis, meaning “exempt,” is the source of the English word immunity, meaning the state of protection from infectious disease.
Types of immunity:
A. Natural immunity
B. Acquired immunity/Adaptive Immunity
Natural immunity
It is also called non-specific immunity because it exists in all humans and is present from earliest time of life. It provides defense against infections by a number of chemical and mechanical barriers. These natural barriers include skin, mucous membrane, secretions, and component of blood, enzymes and often body fluids. These barriers form First line of defense against infections and diseases.
Susceptibility:
Lack of such natural resistance is called susceptibility.
Components of innate immunity :
1. Skin layer:
It provides a protective covering to all body tissues.
2. Mucous membrane:
It secretes sticky mucous, that trapped the air born particles and sweep them out by ciliary movement.
3. Acidity of stomach and vagina:
Acidic pH is toxic to most microorganisms.
4. Bile:
Bile is inhibitory to most microorganisms.
5. Lysozymes:
It is present in saliva and digest cell wall of gram positive bacteria.
6. Microbial flora:
The normal microbiota prevent pathogens from colonizing the host by competing with them for nutrients (competitive exclusion)
Second line of defense:
Once microorganism succeed in passing first line of defense, they enter the deeper tissues and are attached by specific cells of the body, which may ingest or destroy them. These cells are called phagocytes and they form second line defense.
Types:
There are two types
a. Free phagocytes.
b. Fixed phagocytes.
a)Free phagocytes:
It includes neutrophils that are present in blood stream.
b)Fixed phagocytes:
Some macrophages, called fIxed macrophages, are resident in certain tissues and organs of the body. Fixed macrophages are found in the liver (Kupffer's cells), lungs (alveolar macrophages), nervous system (microglial cells), bronchial tubes, spleen (splenic macrophages), lymph nodes, red bone marrow, and the peritoneal cavity surrounding abdominal organs (peritoneal macrophages.
Phagocytosis:
Greek words meaning eat and cell is the ingestion of a microorganism or other substances (such as debris) by a cell. It is the process by which phagocytes engulf the foreign particles in the form of phagosomes. It involves following steps.
1 Adequacy of blood flow.
2 Leukocytes adhesion to capillary walls and passing through it.