Structure And Function Of The Immune System – The immune system is a complex collection of cells and organs that destroys or neutralizes pathogens that would otherwise cause illness or death. For most people, the Lymphatic system is so closely related to the immune system that the two systems are virtually indistinguishable. The lymphatic system is a system of blood vessels, cells, and organs that carries excess fluid into the blood and filters the blood for pathogens. Swelling of lymph nodes during infection and lymphocyte trafficking through lymphatic vessels are just two examples of the many connections between these critical organ systems.
The main function of the lymphatic system is to drain body fluids and return them to the bloodstream. Blood pressure causes fluid to leak from capillaries, causing fluid to accumulate in interstitial spaces (the spaces between individual cells in tissue). In humans, 20 liters of plasma are released daily into the interstitial space by capillary filtration. Once the filtrate leaves the bloodstream and enters the interstitial spaces, it is called interstitial fluid. Of this, 17 liters are directly reabsorbed by blood vessels. But what to do with the remaining three liters? This is where the lymphatic system comes into play. It drains excess fluid and empties it back into the bloodstream through a series of blood vessels, trunks, and ducts. Lymph is the term used to describe the interstitial fluid that enters the lymphatic system. When the lymphatic system is damaged in some way, such as being blocked by cancer cells or destroyed by injury, protein-rich interstitial fluid can accumulate in the interstitial spaces (sometimes “backing up” from lymphatic vessels). This inappropriate accumulation of fluid (called lymphedema) can lead to serious medical consequences.
Structure And Function Of The Immune System
As the vertebrate immune system evolved, the lymphatic network became a convenient route for transporting immune system cells. In addition, transport of intestinally absorbed dietary lipids and fat-soluble vitamins also utilizes this system.
Anatomy Of The Lymphatic And Immune Systems
Cells of the immune system not only use lymphatic vessels to return to the circulatory system from the interstitial space, but also use lymph nodes as major transit areas for the development of critical immune responses. Lymph nodes are one of the small bean-shaped organs located throughout the lymphatic system.
Visit this website for an overview of the lymphatic system. What are the three main components of the lymphatic system?
Lymphatic vessels begin as open capillaries and flow into larger and larger lymphatic vessels, eventually emptying into the bloodstream through a series of ducts. Along the way, lymph passes through lymph nodes, which are commonly found near the groin, armpits, neck, chest, and abdomen. There are approximately 500-600 lymph nodes throughout the human body.
Figure 1. Lymphatic vessels in the arms and legs carry lymph fluid to larger lymphatic vessels in the torso.
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The main difference between the human lymphatic system and the cardiovascular system is that lymph is not actively pumped by the heart, but is forced through the blood vessels by body movement, contraction of skeletal muscles during body movement, and respiration. One-way valves (semilunar valves) in the lymphatic vessels allow lymph fluid to flow toward the heart. Lymph flows from lymph capillaries, through lymphatic vessels, and then into the circulatory system through lymphatic vessels located at the junction of the jugular and subclavian veins in the neck.
Lymphatic capillaries, also called peripheral lymphatic vessels, are blood vessels through which interstitial fluid enters the lymphatic system and becomes lymph fluid. These blood vessels are found in nearly every tissue of the body, intertwining between the arterioles and venules of the circulatory system of the body’s soft connective tissue. The exceptions are the central nervous system, bone marrow, bones, teeth, and corneas, which do not contain lymphatic vessels.
Figure 2. Lymphatic capillaries intersect with arterioles and venules of the cardiovascular system. Collagen fibers anchor lymphatic capillaries in tissue (inset). Interstitial fluid passes through the spaces between the overlapping endothelial cells that make up the lymphatic capillaries.
Lymphatic capillaries are formed by a single cell-thick layer of endothelial cells and represent the open end of the system, allowing interstitial fluid to flow into it through overlapping cells. When interstitial pressure is low, the endothelial flap closes to prevent “backflow.” As interstitial pressure increases, the spaces between cells open, allowing fluid to enter. Collagen filaments that anchor capillaries to surrounding structures also enable fluid to enter lymphatic capillaries. As interstitial pressure increases, the filaments pull on the endothelial cell flaps, opening them further to allow fluid to enter easily.
Immune System Structure And Function
In the small intestine, lymphatic capillaries called chyloducts are critical for transporting dietary lipids and fat-soluble vitamins into the bloodstream. In the small intestine, dietary triglycerides combine with other lipids and proteins and pass into the chylous ducts to form a milky fluid called chyle. The chyle then travels through the lymphatic system and eventually into the liver and then into the bloodstream.
Lymphatic capillaries flow into larger lymphatic vessels, which are similar to veins in their three-layered structure and presence of valves. These one-way valves are quite close to each other, and each one causes the lymphatic vessels to bulge, giving the vessels a beady appearance.
Superficial and deep lymphatic vessels eventually merge to form larger lymphatic vessels called lymphatic trunks. On the right side of the body, the right side of the head, chest, and right upper limb drain lymph through the right lymphatic vessels into the right subclavian vein. On the left side of the body, the rest of the body drains into the larger thoracic duct, which drains into the left subclavian vein. The thoracic duct itself begins below the diaphragm in the cisterna chyli, a sac-like chamber that receives lymph from the lower abdomen, pelvis, and lower extremities via the left and right lumbar trunks and intestinal trunks.
Figure 3. The thoracic duct drains a larger portion of the body than the right lymphatic vessels.
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The overall drainage system of the body is asymmetrical. The right lymphatic vessel receives lymph fluid only from the upper right side of the body. Lymph from other parts of the body passes through all remaining lymphatic trunks into the bloodstream through the thoracic duct. Generally speaking, the lymphatic vessels in the subcutaneous tissue of the skin, that is, the superficial lymphatic vessels, follow the same route as veins, while the deep lymphatic vessels in the internal organs generally follow the arterial route.
The immune system is a collection of barriers, cells, and soluble proteins that interact and communicate in extremely complex ways. Modern models of immune function are divided into three stages based on their duration of action. The three time phases consist of the following components:
Blood cells, including all cells involved in the immune response, are generated in the bone marrow through various differentiation pathways of hematopoietic stem cells. In contrast to embryonic stem cells, hematopoietic stem cells exist throughout adulthood and allow blood cells to continue to differentiate to replace those lost due to age or function. These cells can be divided into three categories based on their functions:
Figure 4. All immune response cells and blood cells are differentiated from hematopoietic stem cells. Platelets are cellular fragments involved in blood clotting.
The Lymphatic System 2: Structure And Function Of The Lymphoid Organs
As mentioned above, lymphocytes are the primary cells of the adaptive immune response (see Table 1 for more details). The two basic types of lymphocytes, B cells and T cells, are morphologically identical, having a large central nucleus surrounded by a thin layer of cytoplasm. They are distinguished by surface protein markers as well as the molecules they secrete. B cells mature in the red bone marrow and T cells mature in the thymus, but both initially develop from the bone marrow. T cells migrate from the bone marrow to the thymus, where they mature further. B cells and T cells are found in many parts of the body, circulating in the blood and lymph and residing in secondary lymphoid organs, including the spleen and lymph nodes, which are described later in this section. The human body contains approximately 10
B cells are immune cells that function primarily by producing antibodies. An antibody is any protein that specifically binds to a pathogen-related molecule called an antigen. Antigens are chemical structures on the surface of pathogens that bind to T or B lymphocyte antigen receptors. Once activated by binding to antigen, B cells differentiate into cells that secrete soluble forms of surface antibodies. These activated B cells are called plasma cells.
T cells, on the other hand, do not secrete antibodies but perform multiple functions in the adaptive immune response. Different types of T cells can secrete soluble factors to communicate
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