Immune System

The immune system is biological structures and processes within an organism that protects against disease. To function properly, an immune system has agents known as pathogens. It distinguishes the healthy tissues of any organism from viruses or parasitic worms.

There are two main subsystems of the immune system in most of the species, first is the innate immune system and second is the adaptive immune system. In humans, the blood-brain barrier, fluid–brain barriers, and blood-cerebrospinal fluid barrier separate the peripheral immune system from the neuroimmune system, which helps to protect the brain.

Pathogens can rapidly evolve and adapt, and thus avoid detection and neutralization by the immune system.

Disorders of the immune system can result in diseases like inflammatory diseases and cancer. when the immune system is less active than normal Immunodeficiency occurs, which results in recurring and life-threatening infections.

In humans, immunodeficiency can either be the result of a genetic disease or critical conditions such as HIV/AIDS.


Lymphatic System

The lymphatic system is an organ system which is the part of the immune system and the circulatory system. which is made up of a bulky network of lymphatic vessels, organs, and lymphatic tissues. These vessels carry a clear fluid called lymph.

The lymphatic system is not a closed system, Unlike the circulatory system. Through capillary filtration, the human circulatory system processes an average of 20 liters of blood per day, which removes plasma from the blood, 17 liters of the filtered plasma is reabsorbed into the blood vessels while the remaining liters remain in the interstitial fluid. To provide an accessory return route to the blood for the surplus three liters is the main function of the lymphatic system.

Other function is that of immune defence. Lymph contains waste products and cellular debris like blood plasma, together with bacteria and proteins. These include the lymph nodes (where the maximum lymphocyte concentration is found), the thymus, the spleen, and the tonsils. Lymphocytes are primarily generated in the bone marrow. for support, the lymphoid organs also contain other types of cells such as stromal cells. Lymphoid tissue is also connected with mucosa such as mucosa-associated lymphoid tissue. Fluid from circulating blood leaks into the tissues by capillary action carrying nutrients to the cells. The fluid cleans the tissues as interstitial fluid collecting waste products, damaged cells and bacteria, and then drains into the lymphatic capillaries and vessels.

These vessels carry the lymph and passing through several lymph nodes which filter out waste materials such as bacteria and damaged cells, lymph then passes into lymph ducts, the right lymphatic duct drains the right side of the region.

And the left lymphatic duct, known as the thoracic duct, which drains the left side of the body. To return to the blood circulation these ducts empty into the subclavian veins.

Lymph is moved by muscle contractions through the body but in some vertebrates, a lymph heart is present that pumps the lymph to the veins.

Primary lymphoid organs

The primary lymphoid organs from immature progenitor cells produce lymphocytes.

Bone marrow

Bone marrow is responsible for both the formation of T and B cells, which are significant cells of the immune system. From the bone marrow, B cells directly join the circulatory system and move to secondary lymphoid organs to search pathogens. On the other hand, T cells move from the bone marrow to the thymus, 95% of T cells start apoptosis process, which is the form of programmed cell death.

Thymus

At the age of puberty, the thymus with adipose tissue start replacing the thymic stroma. In many species, the thymus consists of lobules divided by septa which are made up of epithelium, considered an epithelial organ.

Secondary lymphoid organs

The secondary lymphoid organs, which contain spleen and the lymph nodes. Mature lymphocytes circulate in the blood until they encounter their specific antigen.

Spleen

Spleen perform functions:
Like produce immune cells to fight with antigens and remove aged blood cells, mostly red blood cells. It produces blood cells during fetal life.

Lymph nodes

A lymph node is an arranged collection of lymphoid tissue, through which the lymph passes to the blood. Human body contains 800 lymph nodes about 300 of which are placed in the head and neck. Lymph sustain pathogen contamination from injuries.

Lymphatic vessels

Thin-walled vessels called lymph vessels that conduct lymph between different parts of the body. Absorption of interstitial fluid from the tissues is the main function of the lymph capillaries.