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lymphatic system 462 lymph node
caused by microorganisms; Lymphadenopathy applies
to all other etiologies of lymph node enlargement.
Lymphadenopathies are classified as (1) reactive, (2) those
associated with clinical syndromes, (3) vascular lymphadenopathies,
(4) foreign body lymphadenopathies, and (5)
lymph node inclusions. Variability of germinal center size,
no invasion of the capsule or fat, confinement of mitotic
activity to germinal centers, and localization in the cortex
and nonhomogenous follicle distribution are observed in
benign lymphadenopathy.
lymphatic system
Network of lymphoid channels that transports lymph, a
tissue fluid derived from the blood. It collects extracellular
fluid from the periphery and channels it via the thoracic duct
to the blood circulation. Lymph nodes at the intersections of
lymphatic vessels trap and retain antigens from the lymph.
Situated at lymphatic vessel intersections are lymph nodes,
Peyer’s patches, and other organized lymphoid structures
except the spleen, which communicates directly with the
blood. The main functions of the lymphatic system include
the concentration of antigen from various body locations
into a few lymphoid organs. The circulation of lymphocytes
through lymphoid organs permits antigen to interact with
antigen-specific cells and to carry antibody and immune
effector cells to the blood circulation and tissue.
lymphatic vessels
Thinly walled channels through which lymph and cells of
the lymphatic system move through secondary lymphoid
tissues, such as lymph nodes, except for the spleen, to the
thoracic duct that joins the blood circulation.
lymphatics
Vessels that transport the interstitial fluid called lymph to
lymph nodes and away from them, directing it to the thoracic
duct, from which it reenters the blood stream.
lymph gland
More correctly referred to as lymph node.
lymph node
A relatively small (0.5 cm) secondary lymphoid organ
that serves as a major site of immune reactivity. It is
surrounded by a capsule and contains lymphocytes,
macrophages, and dendritic cells in a loose reticulum
environment. Lymph enters this organ from afferent
lymphatics at the periphery, percolates through the node
until it reaches the efferent lymphatics, exits at the hilus,
and circulates to central lymph nodes and finally to the
thoracic duct. The lymph node is divided into a cortex and
medulla. The superficial cortex contains B lymphocytes in
follicles, and the deep cortex is composed of T lymphocytes.
Differentiation of the specific cells continues in
these areas and is driven by antigen and thymic hormones.
Conversion of B cells into plasma cells occurs chiefly in
the medullary region, where enclosed lymphocytes are
protected from undesirable influences by a macrophage
sleeve. The postcapillary venules from which lymphocytes
exit the lymph node are also located in the medullary
region. Macrophages and follicular dendritic cells interact
with antigen molecules that are transported via lymph to
the lymph nodes. Reticulum cells form medullary cords
and sinuses in the central region. T lymphocytes percolate
through the lymph nodes and enter from the blood at the
postcapillary venules of the deep cortex. They then enter
the medullary sinuses and pass from the node through
Primary
follicle
Medulla
Secondary follicle
(germinal center)
Capsule
Capillary
Venule
Afferent
lymphatics
Efferent lymphatic
Lymph node.
Efferent
lymphatic
Arteriole
Lymph node.
Lymphatic vessels
Lymph node (low power).
Postcapillary
venule
Cortex
Paracortical
area
Medulla
the efferent lymphatics. T cells that interact with antigens
are detained in lymph nodes, which may be sites of major
immunologic reactivity. A lymph node is divided into B
and T lymphocyte regions. Individuals with B cell or T
cell immunodeficiencies may reveal an absence of one or
the other lymphocyte type in the areas of the lymph node
Afferent
lymphatics