It achieves this by importing the lymphocytes from blood and lymph.)
The thymus and the bone marrow constitute the primary lymphoid organs involved in the production and early clonal selection of lymphocyte tissues. Bone marrow is responsible for the creation of both T cells, and the production and maturation of B cells. From the bone marrow B cells immediately join the blood system and travel to secondary lymphoid organs in search of pathogens. T cells on the other hand travel from the bone marrow to the thymus where they are allowed to develop further. Mature T cells join B cells in search of pathogens. The other 95% of T cells begin a process of apoptosis (programmed cell death).
The central or primary lymphoid organs generate lymphocytes from immature progenitor cells.
Secondary or peripheral lymphoid organs which include lymph nodes and the spleen, maintain mature naive lymphocytes and initiate an adaptive immune response. The peripheral lymphoid organs are the sites of lymphocyte activation by antigen. Activation leads to clonal expansion and affinity maturation. Mature lymphocytes recirculate between the blood and the peripheral lymphoid organs until they encounter their specific antigen.
Secondary lymphoid tissue provides the environment for the foreign or altered native molecules (antigens) to interact with the lymphocytes. It is exemplified by the lymph nodes, and the lymphoid follicles in tonsils, Peyer's patches, spleen, adenoids, skin, etc. that are associated with the mucosa-associated lymphoid tissue (MALT).
Mononuclear phagocyte system. Lymphangion. Propulsion of lymph from one lymphangion to next A lymphangion is the functional unit of a lymph vessel that lies between two semilunar (half moon-shaped) valves. 
List of lymphatic vessels of the human body. Humans have approximately 500–600 lymph nodes distributed throughout the body, with clusters found in the underarms, groin, neck, chest, and abdomen.
Distribution Mononuclear phagocyte system. Glymphatic system. The glymphatic system (or glymphatic clearance pathway) is a functional waste clearance pathway for the vertebrate central nervous system (CNS).
The pathway consists of a para-arterial influx route for cerebrospinal fluid (CSF) to enter the brain parenchyma, coupled to a clearance mechanism for the removal of interstitial fluid (ISF) and extracellular solutes from the interstitial compartments of the brain and spinal cord. Exchange of solutes between the CSF and the ISF is driven by arterial pulsation and regulated during sleep by the expansion and contraction of brain extracellular space. Clearance of soluble proteins, waste products, and excess extracellular fluid is accomplished through convective bulk flow of the ISF, facilitated by/ astrocytic aquaporin 4 (AQP4) water channels. Background List of lymphatic vessels of the human body. Bone marrow. Bone marrow is the flexible tissue in the interior of bones.
In humans, red blood cells are produced by cores of bone marrow in the heads of long bones in a process known as hematopoiesis. On average, bone marrow constitutes 4% of the total body mass of humans; in an adult weighing 65 kilograms (143 lb), bone marrow typically accounts for approximately 2.6 kilograms (5.7 lb). Waldeyer's tonsillar ring. Waldeyer's tonsillar ring (also pharyngeal lymphoid ring or Waldeyer's lymphatic ring) is an anatomical term collectively describing the annular arrangement of lymphoid tissue in the pharynx.
Waldeyer's ring circumscribes the naso- and oropharynx, with some of its tonsillar tissue located above and some below the soft palate (and to the back of the oral cavity). Waldeyer's ring was named after the nineteenth century German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz. The ring consists of the (from superior to inferior): There also normally is a good amount of mucosa-associated lymphoid tissue (MALT) present between all these tonsils (intertonsillar) around the ring, and more of this lymphoid tissue can variably be found more or less throughout at least the naso- and oropharynx. Some animals, but not humans, have one or two additional tonsils: Soft palate tonsilParaepiglottic tonsil Notes Jump up ^ Some authors speak of two pharyngeal tonsils/two adenoids.
Thymus. The thymus is a specialized organ of the immune system.
Within the thymus, T cells or T lymphocytes, mature. T cells are critical to the adaptive immune system, where they adapt specifically to foreign invaders. Each T cell attacks a specific foreign substance which it identifies with its receptor. T cells have receptors which are generated by randomly shuffling gene segments. Each T cell attacks a different antigen. Spleen. The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation.
A study published in 2009 using mice found that the spleen contains, in its reserve, half of the body's monocytes within the red pulp. These monocytes, upon moving to injured tissue (such as the heart), turn into dendritic cells and macrophages while promoting tissue healing. The spleen is a center of activity of the mononuclear phagocyte system and can be considered analogous to a large lymph node, as its absence causes a predisposition to certain infections. In humans, the spleen is brownish in color and is located in the left upper quadrant of the abdomen. Structure The spleen, in healthy adult humans, is approximately 7 centimetres (2.8 in) to 14 centimetres (5.5 in) in length.
Surfaces Lymph node. Lymph nodes also have clinical significance.
They become inflamed or enlarged in various infections and diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the lymph nodes is very important in cancer staging, which decides the treatment to be used, and determines the prognosis. When swollen, inflamed or enlarged, lymph nodes can be hard, firm or tender. Structure 1) Capsule; 2) Subcapsular sinus; 3) Germinal centre; 4) Lymphoid nodule; 5) Trabeculae Lymph nodes are bean or oval shaped and range in size from a few millimeters to about 1–2 cm long. Each lymph node is surrounded by a fibrous capsule, and inside the lymph node the fibrous capsule extends to form trabeculae. Thin reticular fibers and elastin form a supporting meshwork called a reticular network (RN) inside the node.
The number and composition of follicles can change especially when challenged by an antigen, when they develop a germinal center. Other Lymphoid tissue. Lymphatic vessel. Development. Lymphatic Vessels Discovered in Central Nervous System. At a Glance Scientists discovered that the brains of mice contain functional lymphatic vessels that can carry fluid and immune cells from cerebrospinal fluid.Further work will explore whether problems in this system might play a role in neurological disorders such as Alzheimer’s disease, meningitis, and multiple sclerosis.
Fluids move throughout the body via several paths. The cardiovascular system circulates blood, nutrients, and gases throughout the body. The lymphatic system carries white blood cells and other immune cells through a network of vessels and tissues, including lymph nodes. The lymphatic system also serves as a connection between tissues and the bloodstream, performing several functions such as removing dead blood cells and other waste. The brain, part of the central nervous system, has blood vessels but has been thought to lack lymphatic vessels, as theyve never been found. These vessels may have gone undiscovered until now due to their hidden location. Scientists find the brain’s missing ‘pipes’ (iStock) “Throw out the textbooks” and “missing link” are words rarely heard anymore in science, but that’s what researchers around the world are saying about the recent discovery of microscopic lymphatic vessels connecting the brain to the immune system.
That physical link was long thought absent, confounding scientists who study neurological disorders with an immune component. The vessels were found in mice, by accident, by University of Virginia researchers who published their results in Nature. If confirmed in humans, experts say, the discovery could have profound implications for a range of conditions including chronic fatigue syndrome, autism, multiple sclerosis and Alzheimer’s disease.
Lymphatic vessels, which piggyback on blood vessels, distribute immune cells to tissues to fight infection and carry fluid away from tissues to dispose of cellular waste. This discovery, experts say, could also open new avenues of research into Alzheimer’s.