Lymphatics Flashcards
innate immune system
non-specific immunity
adaptive immune system
specific immunity
primary lymphoid organs
thymus and bone marrow
secondary lymphoid organs
spleen, lymph nodes and MALT
what are natural killer cells
they kill virus-infected cells and some tumor cells
what do B-lymphocytes do
produce antibodies (humoral immunity)
what do T-lymphocytes do
participate in cellular immunity
subsets of T-Lymphocytes
T-helper cells, Cytotoxic T cells, Suppressor T cells
supporting cells of the lymphatic system
antigen-presenting cells, epithelial cells, stromal cells, leukocytes
what do cytotoxic T cells do
kill virus-infected and some cancer cells, requiring interaction with helper cells to activate and proliferate to form clones of effector cells
what do T helper cells do
they use mediators known as interleukins to provide assistance to B cells, cytotoxic T cells and macrophages
what do suppressor T cells do
may suppress immune responsiveness to self-antigens and possibly switch off the response when antigen is removed
what do memory T cells do
provide a rapid reaction force for a subsequent encounter with the same antigen
what lymphocytes develop in the bone marrow
B lymphocytes and natural killer cells
location of the thymus
anterior mediastinum
cells of the connective tissue septa of the thymus
epithelioreticular cells
the main change of the thymus from an infant to an adult
the lymphoid tissue is replaced with adipose tissue
contents of the darkly staining cortex
large numbers of T cells, epithelioreticular cells, macrophages
contents of the lightly staining medulla
T cells (larger and less densely packed), epithelioreticular cells, Hassall’s corpuscles
life cycle of a T cell
positive selection in the cortex -> negative selection in the medulla -> enter the bloodstream
what are thymic nurse cells
form part of the blood-thymus barrier in the cortex, invested by basal lamina, with cytoplasmic processes linked by desmosomes that create a physical barrier protecting the immature lymphocytes from blood-borne antigens
contents of an epithelial reticular cell
lysosomes, electron-dense granules and tonofilaments
what are lymph vessels
thin-walled, endothelially-lined vessels that look similar to capillaries but lack a basal lamina
common locations of lymph vessels
dermis of skin, liver, beneath mucous membranes of the respiratory, genitourinary and gastrointestinal tracts
what do lymph vessels do
interstitial fluid and wandering lymphocytes are taken up by lymphatic vessels and added back to the circulation
lymphatic drainage order
lymphatic vessels -> thoracic duct -> subclavian veins
what tissue do lymph nodes derive from
mesenchyme
composition of a lymph node
capsule, cortex, para-cortex, medulla, and subcapsular sinus
structures present at the hilum of a lymph node
small artery, small vein and afferent and efferent lymphatic vessels
afferent lymphatic vessels
lymph enters the node
efferent lymphatic vessels
lymph exits the node
main functions of a lymph node
filtration, production of lymphocytes, synthesis of antibodies (mainly IgG) and recirculation of lymphocytes
contents of the cortex of lymph nodes
lymphoid nodules occupied by B cells
contents of the para-cortex of lymph nodes
T cells
primary lymphoid nodules
spherical aggregates of tightly packed B cells in a network of reticular fibres
secondary lymphoid nodules
have a germinal center containing actively dividing B cells and a mantle zone surrounding containing resting B cells
what occurs in the para-cortex
antigen-dependent T cell differentiation and proliferation
contents of the medulla of the lymph node
loosely arranged lymphoid tissue, medullary cords consisting of lymphocytes, macrophages, and plasma cells, medullary sinuses, and irregularly arranged trabeculae
flow of lymph in a lymph node
delivered to the subcapsular sinus -> trabecular sinus -> medullary sinus -> exits via efferent vessels at hilum
what cells occupy the para-cortical region of a lymph node
T cells
lining of high endothelial venules in lymph nodes
cuboidal epithelium
what are high endothelial venules
specialized venules for passage of B and T cells by selective diapedesis from the blood into perivascular areas
morphology of high endothelial venules
cuboidal endothelial cells, prominent perivascular sheath, thick basal lamina
what is homing
the movement of B and T cells across high endothelial venules into lymph nodes and other sites
what lymphoid organ lacks high endothelial venules
the spleen
evolution of B cells
naive B cell -> small centrocyte -> large centrocyte -> small centroblast -> large centroblast -> immunoblast -> memory B cell or plasma cell
divisions of MALT
GALT, NALT, BALT and VALT
what is MALT characterized by
lymphocyte infiltrations, which are not sharply delineated from surrounding CT but are supported loosely by reticular fibres
main immunoglobin formed in MALT
IgA produced by plasma cells
what type of cell is abundant in the dome of Peyer’s patches
M cells
what are palatine tonsils
organized masses of lymphoid tissue which, alongside lingual, pharyngeal, and tubal tonsils, form Waldeyer’s ring
lining of the liminal palatine tonsil
stratified squamous epithelium
what separates the base of the tonsil from the underlying muscle
dense collangenous hemicapsule
what does the tonsillar parenchyma contain
numerous lymphoid follicles with germinal centres similar to those found in lymph nodes
blood supply to the spleen
splenic artery provides the spleen with a rich blood supply
blood drainage of the spleen
splenic vein drains the blood from the spleen into the hepatic portal artery
main functions of the spleen
production of immunological responses against blood-borne antigens, removal of particulate matter or defective blood cells from circulation, and hematopoiesis in the normal fetus
what does the structure of the spleen allow
intimate contacts to be made between the blood and lymphocytes
histology of the spleen
capsule, trabeculae, white pulp and red pulp
what is white pulp
greyish-white islands of lymphoid tissue, most surrounding a central arteriole and forming a periarteriolar lymphoid sheath
where is the central arteriole in a PALS derived from
the splenic artery
where do lymphoid nodules lie in white pulp relative to the arterioles
peripherally
what is surrounding white pulp
a shell of sparsely cellular lymphoid tissue - the marginal zone - that contains macrophages and B lymphocytes
what is red pulp
it makes up a majority of the spleen and contains abundant erythrocytes
what occupy the cords of Bilroth in the spleen
reticular cells, lymphocytes, plasma cells and macrophages, alongside all formed elements of circulating blood
what is a cord of Bilroth
splenic cords which are reticular tissue rich in lymphocytes
what is a stave cell
an unusual endothelial cell with an incomplete basement membrane
