All living organisms whether plants or animals or microbes are always prone to the attack of pathogenic organisms such as bacteria, fungi, viruses and other type of parasitic protozoans. There is a well-developed defense mechanism in humans and animals to fight against these parasitic and pathogenic organisms. This defense mechanism in humans and animals is known as immune system and the protective response of the body against the invading organism is called the immune response. The immune system always guards the body against the various types of microbes and parasites present in the environment. If the immune system is not responding properly, even a minor infection can become fatal.
The Immune System :
The immune system is well developed and is very complex in mammals and higher forms of vertebrates. The complexity of the immune system decreases as we go down the evolutionary scale. Organisms such as birds, reptiles, amphibians, fish, etc. have comparatively simple types of immune systems. There is no immune system in invertebrates such as starfish, hydras, earthworms, insects, etc. The immune system consists of certain specialized cells known as immune cells and certain specialized organs called lymphoid organs. The lymphoid organs in which ' the immune cells originate and mature are called the primary lymphoid organs, which include bone marrow and thymus. After maturation they migrate to other organs, the secondary lymphoid organs, where they settle down and function. These organs include the lymph nodes and the spleen.
The immune cells are distributed all over the body. Some of them reside in tissues and others circulate in the body through body fluids such as blood and lymph. The cells that carry out the immune response include phagocytic cells and natural killer cells (NK). The phagocytic cells include the white blood cells or lymphocytes and the macrophages. The macrophages engulf the invading organisms. The lymphocytes are the main immune cells and are further divided into different types. Morphologically, all lymphocytes are identical and cannot be distinguished. They can be classified based on the presence of certain specific molecules on the surface of the cell membrane and the function they perform. The most important lymphocyte groups are B-Iymphocytes or B-cells and T-Iymphocytes or T-cells.
Macrophages consist of different types of phagocytic cells. They are neutrophils, eosinophyls, and basophyls. These phagocytic cells are also called granulocytes because of the presence of granules in the cytoplasm and because they have a multi-lobed nucleus. There is another cell without any granules in the cytoplasm and without any lobes in the nucleus. These cells are called monocytes. Monocytes are the precursors of macrophages present in the tissues. The monocytes migrate into the tissues from blood and change into macrophages. Macrophages are large cells with extensive cytoplasm and have many vacuoles. The macrophages of tissues are generally called histiocytes. Those macrophages present in the liver tissues are called kupfer cells, those present in linings is known as alveolar, and those present in the peritoneal cavity are called peritoneal macrophages.
Tags: Bio Technology, Bio Genetics, Immune System
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