What is an Immune system?

What is a Cell

      Human body consists of cells, cell organells, tissues, organs, organ systems. 

  • The cell is the basic structural and functional unit of life in all living organisms. Human Cell consists of different organells. Cytoplasm, the outer bilayered phospholipid membrane.
  • Mitochondria, power house of the cell which synthesizes energy in the form of ATP.
  • Ribosomes, which involved in protein synthesis, Golgi complex, involved in processing and package of proteins.
  • Lysosomes, acting as Suicidal bags of the cell and protects the cell.
  • Endoplasmic Reticulum, both Rough and Smooth ER, involved in protein folding and transport of proteins to golgi.
  • Nucleus, which provides genetic and hereditary character to a cell.

Types of Tissues

     Group of  similar cells in structure and function constitutes a tissue. Group of similar tissues constitute Organ. Similar organs together constitutes organ systems. Tissues are  majorly 4 types. Epithelial, Connective, Muscular and Nervous tissues. 

  • Epithelial tissue constitutes the outermost layer of body like epidermis and dermis of skin etc.,
  • Connective tissue connects different parts of body like blood, bone etc., 
  • Muscular tissue which includes Skeletal muscle around bones, Smooth muscles which are present in GIT, respiratory, urinary, reproductive systems etc.,Cardiac muscle which surrounds only heart. 
  • Nervous tissues present in the parts of nervous system like brain, spinal cord  and Nerves(both spinal and cranial).

Fluid Tissues of Body

     Blood is a fluid connective tissue which gets circulated to each and every cell throughout the body.
  • It is made up of Plasma, plasma proteins like albumin, globulin, Clotting factors, Serum, different cells like Red blood cells (Erythrocytes),White blood cells (leukocytes) and blood platelets(thrombocytes). 
  • These are synthesized from the Bone marrow. The Production of blood is known as Haemopoiesis. This system is called Haemopoietic system. 
  • Apart from this, other system which flows throughout the body is Lymphatic system. it consists of lymph fluid, lymph capillaries, lymphatic vessels, lymphatic trunks. 
  • This system is called drainage system of body as the metabolic waste components of all cells drains as lymph into lympatic vessels. This lympahatic system is mainly composed of the immune cells lymphocytes, Extracellular fluid, Inorganic salts etc., Blood and Lymph plays the most prominent role in Immune response. 

Haemopoeitic system

  • RBCs are biconcave disc shaped, enucleated cells which consists of Hemoglobin(Hb). It contains non-protein part Haem and protein part called globin. This Hb transports oxygen to all the cells of the human body. 
  • Blood platelets involved in clotting of blood during an injury by a process called Haemostasis. 
  • WBCs, the leading cells of an Immune response are of two types. Granulocytes and Agranulocytes based on the presence or absense of fluid filled granules in cells.
  • Granuocytes are of four types based on the nucleur lobes. Eosinophils, basophils, Neutrophils and Mast cells. 
  • Agranulocytes are of two types Lymphocytes and Monocytes.
  • Eosinophils, basophils and Mast cells  produces Allergic Immune response, Neutrophils which are said to be microscopic policemen of body by detecting and killing the antigen. 
  • Monocytes acts as internal scavengers by cleaning the metabolic debris of the cell. Lymphocytes plays most prominent role in the Immune response.

Types of Lymphocytes

  • Lymphocytes are of two types. T- Lymphocytes, B-Lymphocytes and Natural killer cells . As the T-cells mature in thymus they were named as T- Lymphocytes. 
  • As the B-cells  mature in Bone marrow, these were named as B-Lymphocytes. T-cells are again two types, T-Cytotoxic and T-Helper cells. 
  • B-Cells on maturation yields plasma cells which synthesizes Antibodies. Dendritic cells are also a type of B-cells originated from a bone-marrow mainly involved in Presenting the Antigen to T-cells. 
  • Monocytes when leaves the blood and enters the tissues, get differentiated into Macrophages. These are also Antigen presenting cells which presents antigens to T-cells during an Immune response. 


Immune Response

  • T-Cytotoxic(Tc) cells mediate cytotoxicity, killing of an Antigen(foreign particle) that enters the body by T-Cytotoxic(Tc) cells.
  • T-Helper cells involved in activation of Tc cells by releasing Cytokines, the cell signalling molecules of Tc-Cells.
  • B-Cells matures to plama cells and memory cells. These plasma cells produces Antibodies which acts against the Antigens by Ag-Ab interactions.
  • Memory cells released after an Immune response and remains in the blood stream to detect and kill the same Antigen that invades again. 
  • Natural killer cells first responds to the signals of stressed cells and kills the Antigens(cytotoxic). Also plays an important role in host-rejection of tumor cells and viral infected cells.
  • Dendritic cells and Macrophages acts as APCs (Antigen Presenting Cells) by presenting the Antigens to Tc-cells and involves in cytotoxic immune response.
  • Signalling molecules like cytokines are released by the lymphocytes to communicate between the cells and stimulate the movement of immune cells towards the sites of infection, inflammation etc.,
  • Different types cytokines like Intleukins, Interferons, TNF(Tumor Necrosis Factor), chemokines etc., acts as signalling molecules.
  • The immunity mediated by T-cells is called Cell mediated immunity.The immunity mediated by B-cells is called Humoral mediated immunity.


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