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Lymphatic System
LECOM Yr 1
59
Anatomy
Graduate
08/09/2011

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Term
what are lymphocytes?
Definition
the chief cellular component of lymphatic tissue; 70% (mainly T-lymphocytes) circulate from systemic circulation to lymphatics then return; 30% (immature or activated T's and B's) do not circulate and migrate to target tissues (connective tissue lining the respiratory)
Term
where do T-lymphocytes arise?
Definition
arise from bone marrow as stem cells and travel to the thymus where they differentiate
Term
what percent of lymphocytes are T-lymphocytes?
Definition
60-80%
Term
what do helper T-cells do?
Definition
interact with NK cells, macrophages, B-cells, and CD8+ T cells
Term
what do cytotoxic T-cells do?
Definition
kill target cells
Term
where are MHC-I molecules expressed?
Definition
all nucleated cells and platelets
Term
where are MHC-II molecules expressed?
Definition
on macrophages, dendritic cells and B-cells
Term
what are regulatory (suppressor) T-lymphocytes?
Definition
CD4+ or CD8+; suppress ability of T-cells to initiate immune responses
Term
where are gamma/delta T-lymphocytes located?
Definition
positioned at interfaces of the external and internal environments (epithelial cell surfaces of skin, oral mucosa, intestines, vagina) and serve as first line of defense against invading organisms
Term
Following activation, what do B-lymphocytes differentiate to?
Definition
antibody secreting plasma cells
Term
what are natural killer cells?
Definition
genetically programmed to recognize transformed cells and kill them using perforins and granzymes resulting in death by apoptosis
Term
what are the primary lymphatic organs for lymphocyte development and differentiation?
Definition
bone marrow/GALT and Thymus
Term
what are lymphocytes programmed to do?
Definition
recognize a single antigen out of an infinite number of possible antigens in a process called Antigen-Independent Proliferation and Differentiation
Term
what is the initial response to antigens?
Definition
inflammation
Term
what are the main 'players' in inflammation response?
Definition
granulocytes and macrophages
Term
what are lymphatic vessels?
Definition
network of blind capillaries in loose connective tissue beneath the epithelium of the skin and mucous membranes
Term
how permeable are the walls of lymphatic vessels?
Definition
highly permeable
Term
what passes through the lymphatic vessels and into lymph nodes?
Definition
lymph
Term
what is the function of lymph?
Definition
antigens are trapped by follicular dendritic cells and are then presented on their surface where cells known as antigen presenting cells (APC) process the antigen and present to T or B- lymphocytes
Term
True or False: lymphocytes move from blood to lymphoid tissue and back to blood during different stages of development
Definition
True
Term
what vessel allows for the entry of the lymphocytes (in lymph fluid) to enter the lymph node?
Definition
afferent lymphoid vessels
Term
what allows entry of lymphocytes (in the blood) to enter the lymph node?
Definition
the walls of postcapillary venules
Term
what does diffuse lymphatic tissue and lymphatic nodules function to do?
Definition
guard the body against pathogens and are the sites for initial immune responses
Term
what are lymphatic nodules?
Definition
localized concentrations of lymphocytes in walls of alimentary canals, respiratory passages and genitourinary tract
Term
primary lymphatic nodules are composed of?
Definition
small lymphocytes only
Term
what are some of the supporting structures of the lymph node?
Definition
capsule, trabeculae, reticular tissue
Term
what do afferent lymphatic vessels carry?
Definition
carry lymph toward the node and enter at various convex points around the lymph node
Term
what do efferent lymphatic vessels carry?
Definition
carry the lymph away from the node and exit at the hilum which serves as the entrance for blood vessels and nerves
Term
what are reticular cells?
Definition
fibroblast-like, secrete type III collagen, also attract T-cells, B-cells and macrophages
Term
what are dendritic cells?
Definition
bone marrow-derived, phagocytic, macrophage, antigen presenting cells expressing MHC-I and MHC-II
Term
which are more efficient: macrophages or dendritic cells?
Definition
dendritic cells
Term
what are follicular dendritic cells?
Definition
in germinal centers with cytoplasmic processes which interdigitate between B-cells; do not present antigen as they lack MHC molecules
Term
what are high endothelial venules?
Definition
contain receptors for antigen primed B and T cells and signal them from the blood stream to enter via a process called diapedesis; T-cells go to the deep cortex, B-cells migrate to nodular cortex
Term
what percent of the T-cells in the thymus become mature T-cells and leave the thymus?
Definition
2%
Term
MHCII is expressed in high levels in which types of cells?
Definition
dendritic cells
Term
MHCI is found in high levels in which types of cells?
Definition
macrophages
Term
what is the function of the lymph node?
Definition
phagocytosis of particulate materials (antigen) by phagocytic cells in the lymph node is an important step in initiating immune responses
Term
True or false: plasma cells migrate to medullary cords and produce antibody, which flows in and out of lymph node.
Definition
True
Term
describe the thymus and where it was developed
Definition
bilobed; developed from the 3rd and 4th oropharyngeal pouch; multipotential lymphoid stem cells move from bone marrow into thymus where they develop into immunocompetent T-cells; reduces in size by puberty and lymphatic tissue is replaced by adipose tissue
Term
where are type I epithelioreticular cells located?
Definition
boundary of cortex and capsule and separate thymic parenchyma and trabeculae
Term
where are type II epithelioreticular cells located?
Definition
in cortex and compartmentalize areas of developing T-cells and serve to educate them; express both MHC I and II
Term
where are type III epithelioreticular cells found?
Definition
boundary of cortex and medulla and serve to educate T-cells as type II. Express MHC I and II
Term
Approximately what percent of T-cells are phagocytized by macrophages since they did not meet the correct thymic education?
Definition
98%
Term
where are type IV epithelioreticular cells located?
Definition
between the cortex and medulla next to type III and help create barrier at corticomedullary junction
Term
where are type V epithelioreticular cells located?
Definition
throughout the medulla and help to compartmentalize groups of lymphocytes in the medulla
Term
where are type VI epithelioreticular cells located?
Definition
form Hassal's corpuscles which are closely packed, concentric bundles which possess keratohyalin granules, intermediate filament and lipid droplets and are joined by desmosomes; they are postulated to produce interluekins
Term
describe T-Cell education
Definition
characterized by expression and deletion of specific surface CD antigens
Term
CD1 expression in T-Cell education characterizes what stage?
Definition
the middle stage
Term
which types of cells eventually leave the thymus and "graduate" in T-Cell education?
Definition
CD4 or CD8
Term
describe the spleen and its functions
Definition
largest of lymphoid organs, contains a rich blood supply, with lymphocytes, channels, meshwork of reticular cells and fibers, macrophages and dendritic cells
Term
how much blood does the human spleen normally contain?
Definition
very little
Term
what is the spleen enclosed by?
Definition
dense connective tissue capsule from which trabeculae extend into the parenchyma of the organ
Term
what is white pulp?
Definition
lymphatic tissue, mostly lymphocytes associated with central splenic artery
Term
what is red pulp?
Definition
splenic sinuses separated by splenic cords consisting of loose meshwork of reticular cells, fibers containing large numbers of erthrocytes, macrophages, lymphocytes, dendritic cells, plasma cells and granulocytes. Splenic macrophages phagocytose damaged red blood cells, hemoglobin breakdown and iron reclamation
Term
what are the components of the spleen?
Definition
Endothelial cells line the splenic sinuses and run parallel to the direction of the vessel; Intercellular spaces allow blood cells to pass in and out of the sinuses; Strands of basal lamina loop around the outside of the sinus
Term
describe open splenic circulation
Definition
Central artery branches to the white pulp and sinuses at the perimeter (marginal sinuses) and continues into red pulp, branching to straight arterioles (penicillar arterioles). Circulation continues as arterial capillaries, some of which are surrounded by macrophages (sheathed capillaries) and then empties directly into reticular meshwork of the splenic cords.
Term
describe closed splenic circulation
Definition
In other species, the blood from the sheathed capillaries passes directly to the splenic sinuses of the red pulp.
Term
what is the immune functions of the spleen?
Definition
Ag presentation
Activation & Proliferation of B and T-cells
Antibody production
Removal of antigens from blood
Term
what is the hemopoietic function of the spleen?
Definition
Removal of old and damaged RBC & platelets
Iron removal
Formation of erythrocytes
Blood storage/reservoir (esp. RBC’s in some species)
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