An extensive network of tissues, organs, proteins, and cells make up the body’s immune system.
An immune system working correctly can distinguish healthy tissue and foreign objects. It will initiate a complex attack to defend the body from invaders if it identifies an unwanted element. Also, it detects and removes damaged and dead cells.
But, the immune system is not always reliable. For example, when a person has a medical condition or needs medications that alter how the system functions, it may be unable to fight efficiently.
In autoimmune disorders and allergies, the immune system misinterprets healthy tissue and starts an unwanted attack, resulting in painful and life-threatening symptoms.
In this article, we will examine organs of the immune system and how they function to protect the body from diseases and other outside invaders.
Table of Contents
An Overview of Immune System
The immune system functions like a police force. It wanders the entire area and alerts for assistance when it notices a disturbance. It differs from other systems in this way because it must be able to respond in any area of the body. Innate immunity and adaptive immunity are the two layers of defence offered by the immune system.
In general, exposure to many pathogens strengthens the immune system. By adulthood, most people will have been exposed to several pathogens and strengthened their immune systems.
When the body creates an antibody, it stores a copy so that it can respond more quickly the next time the same antigen surfaces.
The immune system is composed of two basic parts:
- The innate immune system: Individuals are born with this immune system.
- The adaptive immune system: Individuals develop this immunity when exposed to organisms or chemicals released by microorganisms.
The Innate Immune System
People have some immunity from birth, ready to fight against invaders immediately.
The external barriers of our body, which serve as the first line of defence against pathogens, such as the skin and gut and throat mucous membranes, are a part of our innate immunity.
This response is non-specific and generic.
Macrophages will engage in combat with infections if they can evade the innate immune system. In addition, cytokines produced by macrophages help the body respond to inflammation.
The Adaptive (Acquired) Immune System
The ability to defend against infections improves over time.
The body produces a variety of antibodies to various pathogens due to immunisations and exposure to various diseases. Immunological memory is a term used by doctors to describe this condition when the immune system recalls earlier enemies.
Active Immunity
Active immunity involves the body’s immediate reaction to a foreign antigen. The body keeps track of the infections it has already encountered in the acquired or adaptive immune system. This is a direct effect of the active immune system.
We develop active immunity when we contact the pathogen or its antigen. When a pathogen enters the body for the first time, some antibodies that combat it are stored in case the pathogen attacks again. This is referred to as natural active immunity.
Passive Immunity
Antibodies acquired from outside the body trigger an immunological response known as passive immunity. The first encounter with a disease is always a little tough on the body because the body’s initial response to it is relatively weak.
This sort of immunity is temporary and comes from a third party. For instance, a newborn acquires antibodies from their mother through the placenta before birth and breast milk after birth.
This passive immunity protects infants from several infections throughout their early years.
Also Read:Difference between Innate and Adaptive Immunity
Organs of the Immune System
The thymus and bone marrow are important primary lymphoid organs. Secondary lymphatic tissues like the spleen, lymph arteries, tonsils, lymph nodes, skin, adenoids, and liver are all important parts of the immune system.
Primary Lymphoid Organs
The primary sites of lymphocyte development, or lymphopoiesis, are known as primary lymphoid organs (PLO). Lymphocytes develop from lymphoid stem cells, multiply, and mature into useful cells known as immuno-competent cells. B-cell maturation occurs in the bone marrow of animals, whereas T-cell maturation occurs in the thymus.
Thymus
This tiny organ, located in the upper chest below the breast bone, helps to mature a particular type of white blood cell. The particular task of this cell is to recognise and memorise an intruder so that a counter-attack can be easily mounted the next time this intruder attacks.
The thymus provides an inductive environment for forming T lymphocytes from haematopoietic stem cells. Thymic stromal cells also enable the selection of a useful and self-tolerant T cell repertoire. As a result, the thymus’ induction of central tolerance is one of its most significant functions.
Bone Marrow
Red blood cells, plasma cells, several types of white blood cells, and other immune cells are all produced from stem cells found in the spongy interior of the bones. Every day, the bone marrow produces billions of new blood cells and releases them into the blood.
The primary site of B-cell maturation and propagation in adults is the bone marrow, where all other circulating blood cells are produced. The process of producing all blood cells throughout foetal development is known as haematopoiesis. It first occurs in the blood island of the yolk sac and para-aortic mesenchyme, followed by the liver and spleen.
Secondary Lymphoid Organs
In addition to the primary lymphoid organs, there are a few other lymphoid organs known as secondary lymphoid organs. The spleen and lymph nodes are the two most significant and well-organised secondary lymphoid organs.
The secondary (or peripheral) lymphoid organs (SLO) sustain and initiate an adaptive immune response. Antigen-induced lymphocyte activation takes place in the secondary lymphoid organs. Until they come into contact with their particular antigen, mature lymphocytes travel back and forth between the blood and secondary lymphoid organs. Clonal growth and affinity maturation are produced by activation.
Lymph Nodes
The network of lymphatic channels (also known as lymphatic vessels) and lymph nodes are connected by lymphatic nodes.
Immune cells found in lymph nodes examine foreign pathogens introduced into the body. These tiny glands filter and kill them to prevent germs from spreading to other body areas. They are a component of the lymphatic system in our body. The individual lymphocytes (white blood cells) are then activated, replicated, and sent to combat that specific invader.
Numerous lymph nodes can be found throughout the body, especially in the groin, armpits, and neck. Lymph nodes that are swollen and painful are a sign that the body is fighting infections.
Spleen
The secondary lymphoid organ, the spleen, is situated high in the left abdominal area. Spleens are designed to filter blood, capture blood-borne antigens, and react to systemic infections.
The primary functions of the spleen are:
- Production of immune cells to fight antigens
- Removal of particulate matter and aged blood cells (red blood cells)
- Production of blood cells during foetal life.
The spleen has primarily efferent lymphatic channels, similar to the thymus. It receives blood from both the splenic artery and the short gastric arteries. The spleen produces antibodies in its white pulp and eliminates antibody-coated blood cells and germs through lymph nodes and blood circulation.
Mucosal-Associated Lymphoid Tissue
Along with lymph nodes, the spleen’s mucosal-associated lymphoid tissue (MALT) is also regarded as a secondary lymphoid organ. Lymphoid tissues on a thin layer surround the mucous membranes of the urogenital, respiratory, and digestive systems.
MALTs are designed to produce massive, antibody-producing plasma cells, which are essential for the body’s defence mechanism.
Lymphatic Vessels
The lymphatic vessels, also known as lymph vessels, are tubes with thin walls transporting lymph between various body parts. They consist of the tubular lymph capillary vessels, the larger collecting vessels, the right lymphatic duct, and the left lymphatic duct (thoracic duct).
Interstitial fluid in the tissues is mostly absorbed by lymph capillaries, which then move the fluid into larger collecting ducts, where it is ultimately returned to the bloodstream via a subclavian vein.
Other Lymphoid Tissues
To protect the body against infections and the growth of tumours, lymphoid tissue connected to the lymphatic system performs immunological activities. It is made up of connective tissue composed of reticular fibres (that have a variety of leukocytes or white blood cells, primarily lymphocytes) through which the lymph passes. Lymphoid follicles are areas of lymphoid tissue that are densely filled with lymphocytes.
Summary
The immune system is a complicated system that is important for survival. The body initiates an attack to eliminate infections when it encounters dangerous pathogens, such as a virus or a needle in the finger.
A certain amount of immunity is innate, although immunisations and disease exposure can also help the body’s defence mechanism.
Because of a medical condition or drug usage, some people have a compromised immune system. A physician can offer guidance on protecting one’s health when dealing with a compromised immune system.
Making healthy food and exercise choices, quitting smoking and drinking, and receiving the necessary immunisations are all ways to increase immunity.
Related Links:
- Immunology – An Overview
- MCQs on Immunology
- MCQs on Immunity
- Antibody – Role of Antibody
- Difference between Humoral and Cell-Mediated Immunity
- Difference between Active and Passive Immunity
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