Organs of the Immune System Flashcards
The ___________ system is a collection of vessels, tissues, and organs.
Lymphatic
Lymph fluid flows through the vessels, eventually draining into the ________.
Heart
The lymphatic systems plays a major role in immunity, is part of the circulatory system, and is important for fat _________ and fluid balance.
Absorption
The vessels include the smaller, tubular vessels called lymph ___________, and the larger collecting vessels, such as the right and left (thoracic) collecting ducts.
Capillaries
As blood circulated under pressure, its fluid component seeps through the capillaries, with in excess of ____L being lost every 24 hours.
2.9
The seepage is called ________ fluid.
Intersitital
Much fluid is returned to the blood, and the remainder is absorbed in the lymph capillaries, becoming _______.
Lymph
Much fluid is returned to the blood, and the remainder is absorbed in the lymph capillaries, becoming _______.
Lymph
The cells of the lymph are mostly _____________.
Lymphocytes
The lymphatic vessels then propel lymph into the right and left (thoracic) __________ _______.
Lymphatic ducts
The________ duct drains into the left subclavian vein (75% of lymph); the right lymphatic duct drains into the right subclavian vein (25% of lymph).
Thoracic
Name two primary lymphoid organs.
Bone marrow and thymus
Which primary lymphoid organ does the following passage describe? Each lobe is arranged into lobules of a cortex and medulla. Trabeculae separates the lobules. The cortex, or outer compartment, is densely packed with thymocytes. The medulla is more scarcely populated, with mostly mature T-cells. Hassall’s corpuscles contain degenerating epithelial cells. Scattered throughout are nonlymphoid epithelial cells (nurse cells), bone marrow-derived macrophages, and interdigitating dendritic cells (located at cortico-medullary junctions).
Thymus
The thymus reaches its maximum size at _______, before atrophying with a decrease in cortical and medullary cells, and an increase in the total fat content of the organ.
Puberty
________ syndrome is a rare genetic disorder, caused by mutations of Chromosome 22, required for thymic development. It results in almost complete T-cell deficiency, and an absence of cell-mediated immunity.
DiGeorge
Outline the thymic generation of T-cells.
Early lymphoid progenitors arrive from the bone marrow, enter into the thymus, and complete their immunogenic education, before leaving as fully-functional T-cells. They learn to differentiate between self and foreign antigens, with many potentially self-reactive T-cells being destroyed along the way. Maturing thymocytes undergo a series of distinct changes in T-cell receptor genes, expression of the T-cell receptor, expression of CD4 and CD8, and others. Earliest cell population arriving in the thymus lacks T-cell markers, and is double-negative CD4-CD8-. As the T-cell moves through the thymus, it matures into double-positive T-cell CD4+CD8+, and rearranges T-cell receptor genes to give rise to a T-cell receptor. Maturing T-cells undergo positive and negative selection, and then there is loss of either CD4 or CD8. Result is the expression of mature, single positive CD4+ or CD8+ T-cells, which exit via the medulla. Positive selection occurs when T-cells mature into double-positive phenotype, bearing both CD4 and CD8 molecules in the cortex. This allows for further maturation of T-cells into single positive cells, and is based on the ability of double-positive T-cells to bind to self MHC complexes, expressed by cortical epithelial cells. Negative selection occurs in the medulla; T-cells become single positive, expressing only CD 4 or CD8. Here, T-cells bind to MHC. Negative and positive selection is mediated by avidity of T-cells to bind to MHC antigens.
Regions of the bone marrow serve as the _______ equivalent, where B-cell maturation occurs.
Bursal
__________ cells interact directly with the B-cells, and secrete various cytokines, that are required for the B-cell developmental process.
Stromal
List three secondary lymphoid organs.
Appendix, lymph node, tonsils
Mature lymphocytes initiate an _________ immune response in secondary lymphoid organs.
Adaptive
The peripheral lymphoid organs are the sites of lymphocyte activation by _________.
Antigens
Mature lymphocytes recirculate between the blood and the peripheral lymphoid organs, until they encounter their _______ antigen.
Specific
________ ________ are encapsulated, bean-shaped structures, which are specialised to trap localised antigens from regional tissues, and to allow for immune responses to occur.
Lymph nodes
__________ lymphatic vessels bring lymph into the lymph nodes.
Afferent
Efferent lymphatic vessels leave at the ________.
Hilus
Illustrate the contents of the cortex, paracortex, and medulla of a lymph node.
The cortex is the outermost area; it contains B-cells, macrophages, and follicular dendritic cells, arranged in primary follicles, with the absence of lymphocyte activation. Following antigenic challenge, the follicles become larger secondary follicles (rings of concentrically-packed B-cells), each containing a germinal centre. Germinal centres reflect proliferating B cells, memory cells, and plasma cells, interspersed with macrophages and follicular dendritic cells
The paracortex, between the cortex and the medulla, contains mostly T-cells, features high endothelial venules, where circulatory lymphocytes leave the blood stream to enter the node.
The medulla is the innermost layer; it contains large blood vessels, sinuses, and medullary cords, and is more sparsely populated with lymphocytes, many of which are plasma cells, actively secreting antibodies. Medullary cords contain antibody-secreting plasma cells, B-cells and macrophages. Medullary sinuses (sinusoids) are vessel-like spaces, that separate the medullary cords. They receive lymph from the trabecular and cortical sinuses, and contain reticular cells and histocytes, and drain the lymph into the efferent lymphatic vessels
Give one function of lymph nodes.
Filter interstitial fluid, collected from soft tissue, and returning it to the vascular system
The _______ is adapted to filtering blood and trapping blood-borne antigens during infection, together with responding to systemic infections.
Spleen
The spleen is not supplied by afferent lymphatics, but rather supplied by a single splenic ________, which divides into progressively smaller branches.
Artery
_____ pulp is a complex system of blood vessels; it facilitates the filtration and removal of old or damaged RBC and debris from circulation.
Red
_______ pulp contains immune cells (T-, B-cells, and accessory cells). Small arterioles are surrounded by T-lymphocytes (periarteriolar lymphoid sheaths (PALS)), with initial activation of T- and B-cells taking place here.
White
What does ‘MALT’ represent?
Mucosal associated lymphoid tissue
What is the function of MALT?
Protects mucosal tissues at the surface, such as gastrointestinal and respiratory surfaces
________ patches are found on the tonsils and appendix.
Peyer’s
MALT may be divided into the gut-associated (GALT), bronchial (BALT), and ________ MALT.
Diffuse
The GALT protects the _____.
GI system
Peyer’s patches have follicle-associated epithelium (FAE) on the outer layer, which has fewer goblet cells, and a thinner mucous layer, and they also have specialised ____-cells (microfold cells), which provide uptake and transport of antigens from the lumen.
M
Lymphoid and plasma cells are found in the ________ _______ of the gut.
Lamina propria
Intraepithelial ____________ are found in the epithelial layer of mucosal surfaces.
Lymphocytes
___________ lymph nodes drain from the gut tissue.
Mesenteric
Lymphocyte ______________ refers to the circulation of mature T- and B-cells via the bloodstream, and from tissue to tissue.
Trafficking
________ T-cells float around until activation.
Naïve
Effector (mature T-cell) and memory lymphocytes have _______ different recirculation pathways.
Two
