Immune System • Features, Biology, Anatomy and Physiology

The immune system

 To protect the body, nature has created a multi-stage defence system . When invading, foreign agents encounter the subsequent components of the immune system:

• skin and mucous membranes: symbiotic bacteria living on the border of our body and therefore the environment secrete substances that have a detrimental effect on pathogenic (pathogenic) microorganisms;
• the mucous membranes of the tract , alimentary canal , urogenital system aren't only inhabited by symbiotic bacteria, but also covered with mucous secretions: foreign substances and microorganisms are faraway from the body with mucus; additionally , mucous secretions contain substances with antimicrobial, antiviral and antifungal activity (for example, lysozyme , an antibacterial agent, an enzyme that destroys murein of bacterial cell walls);
• walls of lymphatic and blood vessels: the inflammatory reaction is amid expansion of capillaries (redness - hyperemia ), a rise in temperature, a rise within the permeability of their walls for leukocytes and protein fibrinogen. Fibrinogen converts to fibrin and clogs up the lymphatic vessels. This prevents the outflow of lymph from the inflamed area and therefore the spread of infection. Edema develops. within the focus of inflammation, an outsized number of leukocytes-phagocytes accumulate, which absorb the invading microorganisms.

The immunity system system is a system of organs and tissues of vertebrates that protect the body from foreign agents: pathogens, foreign bodies, poisonous substances and degenerated cells of the organism itself.

immunity system 

The following structures belong to the system 

central organs -

• Bone marrow;
• thymus.
• Organs containing lymphatic tissue (lymphocytes of varying degrees of maturity):
• spleen;
• The lymph nodes;
• intestinal Peyer's patches;
• tonsils;
• appendix.

Rice. 1. Organs of the human system 

In terms of organization and functioning mechanisms, the system is analogous to the systema nervosum .

Both systems are represented by central and peripheral organs capable of responding to different signals, have an outsized number of receptor structures and specific memory.

Features of the immune system:

• early laying in embryogenesis;
• bone marrow and thymus are well shielded from damage;
• diffuseness: components of the system are evenly distributed throughout the body;
• circulation of cells of the system with blood and lymph flow throughout the body;
• the ability to supply antibodies - molecules that provide specific protection against certain foreign agents (antigens).

The central organs of the system include the bone marrow and thymus. within the bone marrow, B-lymphocytes are formed from its stem cells. within the thymus, differentiation of T-lymphocytes occurs, formed from the stem cells of the bone marrow that entered this organ. within the future, B- and T-lymphocytes with blood flow enter the peripheral organs of the system , which include the tonsils, lymphoid nodules located within the walls of the hollow organs of the digestive and respiratory systems, urogenital system , Peyer's lymphoid plaques within the walls of the tiny intestine, lymph nodes and therefore the spleen, also as numerous leukocytes that move freely in organs and tissues so as to look , recognize and destroy foreign substances.

The highest degree of activity of the system is that the appearance within the lymphoid nodules of the centers of reproduction - the places of formation of lymphocytes. Such centers appear with strong or prolonged antigenic influences (aggressive environment, infections, oncological processes).

Organs of the immune system	The functions of the organs of the immune system
red bone marrow	the formation of all blood cells; differentiation of B-lymphocytes
thymus	differentiation of T-lymphocytes
lymphatic system	removal of foreign substances from the body (dead cells, mutant cells, etc.) by filtering tissue fluid through the lymph nodes
tonsils (amygdala)	form a periopharyngeal lymphoid ring - protection against infection from the oral and nasal cavity
appendix	protects the lower gate of infection (from infection that penetrates through the large intestine)
spleen	lies on the path of blood flow from the arterial system to the venous system: recognition and utilization of failed erythrocytes

Thus, the system consists of the many components, but the most ones are leukocytes.

All leukocytes have a standard origin from the hematopoietic stem cells of the red bone marrow.

All these cells circulate within the blood, although they perform their functions mainly outside the vessels.

The main functions of leukocytes:

• detection and destruction of bacteria, viruses and other foreign agents by phagocytosis;
• destruction of altered cells (cancerous, etc.);
• destruction of body cells;
• participation in allergic reactions;
• participation in inflammatory reactions with tissue damage;
• the production of antibodies;
• the formation of the body's immune memory. 

Types of leukocytes

Leukocyte are divided into three main groups: granulocytes, monocytes and lymphocytes.

Granulocytes contain numerous lysosomes, secretory vesicles and granules. In accordance with the various nature of the colour of those granules, granulocytes are divided into neutrophils, basophils and eosinophils.

Eosinophils (pink granules) protect the body from parasites and contribute to the event of allergies . the extent of eosinophils increases with helminthic invasions (infections).

Basophils (blue-violet granules) secrete histamine, which is involved in inflammatory reactions. 

Neutrophils (purple-pink color of granules) are capable of phagocytosis. They capture, kill and digest microorganisms (mainly bacteria). 

Monocytes are the most important of the white blood cells. beginning of the bloodstream, they become macrophages - large blue-gray cells. Like neutrophils, they're capable of phagocytosis. Macrophages, are significantly larger and live longer than neutrophils.

Thus, phagocytes are granular neutrophils and bigger and longer-lived agranular macrophages (monocytes).

Lymphocytes are involved within the immune response:

• B lymphocytes produce antibodies;
• T lymphocytes kill cells infect with the virus and regulate the activity of other white blood cells;
• normal (natural) killer cells destroy some sorts of tumor and virus-infected cells.

B-lymphocytes form antibodies, which are altered sorts of their own surface receptors.

T-lymphocytes are classified into:

T-helpers that promote the event of an immune response;

T-suppressors that suppress the event of the immune response;

Killer T cells that destroy cells that carry antigens.

In addition to the lymphocytes of those two main classes, lymphocytes also are known that perform nonspecific reactions.

Mast cells are auxiliary cells of the system . They represent immature leukocytes that migrate from blood vessels to tissues, where they undergo final differentiation and maturation. Mast cells are found in most tissues, but they're especially abundant within the skin, near the vessels and within the mucosa of the tract and intestines.

In tissues, mast cells actively move with the assistance of pseudopodia. Their cytoplasm contains an outsized number of vesicles (vesicles). Upon contact of the mastocyte with the antigen, the vesicles fuse with the cell wall within a fraction of a second, and their contents are released. This process plays a crucial role in immediate allergic and inflammatory reactions.

Despite the very fact that mast cells are ready to destroy some antigens on their own through phagocytosis, their main role is to coordinate innate and adaptive immune responses.