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Medical Cell Biology and Physiology
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PSL 536 Faculty
Colleges of Osteopathic Medicine and Human Medicine
unless otherwise noted, figures, tables or schematics are taken from:
AB: Abbas & Lichtman, Basic Immunology, 3/e, 2009, Elsevier
L: Langman's Medical Embryology, 11/e, 2010, Lippincott, Williams & Wilkins
M: Moore & Dalley, Clinically Oriented Anatomy, 6/e, 2010: Lippincott, Williams & Wilkins
MT: Martini & Timmon, Human Anatomy 5/e, 2006, Pearson
G: Gilroy, Atlas of Anatomy, 1/e, 2008, Theime
N: Netter, Atlas of Human Anatomy 5/e, 2011: Elsevier
R: Ross, Histology, 5/e, 2006: Lippincott, Williams & Wilkins
RB: Rhoades & Bell, Medical Physiology, 3/e, 2009: Lippincott, Williams & Wilkins
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Brief Introduction
The organs and tissues of the lymphatic system make it possible for the body to monitor and protect itself
from xenogenic (foreign, non-self) invaders and other antigenic challenges regardless of route of entry. The
THYMUS produces mature, immunocompetent, yet naive, T lymphocytes and destroys a subset of these T
lymphocytes which would otherwise maladaptively react to self antigens. LYMPH NODES monitor and filter
lymph fluid for foreign invaders, the SPLEEN monitors and filters blood, and the MUCOSAL ASSOCIATED
lymphatic TISSUE (MALT) guards against pathogens which attempt to cross the mucosal boundaries of the
digestive, respiratory, or urogenital tracts. These geographically and histologically diverse tissues and organs
actually have several structural features in common that promote monitoring and interactions among
immune system cells and foreign invaders.
Most lymphatic system organs or tissues have a reticular 'chicken-wire' ultrastructure to promote easy
movement of body fluids, cells, antigens, and hence intercellular interactions. The lymph nodes, spleen, and
MALT contain specific tissues regions in which B and T lymphocytes congregate. As you will learn in
immunology, this is ultimately related to adaptive and innate immune system responses.
Lymphocytes recirculate throughout the lymphatic tissues and organ and the method of recirculation in lymph
nodes and MALT requires specialized blood vessels called high endothelial vessels (HEVs). HEVs regulate the
egress of lymphocytes from the blood vascular network into the parenchyma of these lymphatic structures.
The bulk movement of lymphocytes in lymphatic tissues is an important aspect of immune system function
and will be discussed for each lymphatic structure.
NOTE: The taxonomy, cell biology, and intercellular communication of the numerous immune system cells
will be detailed in your immunology course this semester.
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The major stroma proteins are reticular protein fibers (Type III collagen) form a supporting fine
mesh-like scaffolding throughout the lymph node. Reticular cells synthesize reticular protein fiber
and ground substance and are indistinguishable from typical fibroblasts
Other cell types of stroma
dendritic cells
derived from red bone marrow and are the primary, 'professional', antigen presenting cells in
lymph nodes
process and present antigens to certain T lymphocytes and are usually found in T cell dense
areas of the lymph node
follicular dendritic cells
have a similar antigen presenting cell (APC) function analogous to dendritic cells but come
from a different cell lineage.
FDCs reside specifically in lymphatic follicles (a.k.a. lymphatic nodules) of lymph nodes and
are the APCs for the B lymphocytes in the lymphatic follicles
macrophages
phagocytize dysfunctional cells and cell debris after an immune battle; are also APC for T-cells
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Lymph Node Parenchyma- Cortex
outer region of lymph node consisting of a dense collection of lymphocytes (including plasma cells
derived from B lymphocytes), macrophages, dendritic cells, reticular cells, and reticular fibers
afferent lymphatic vessels bring lymph (hence potential antigenic challenges) into the cortex and
this lymph is distributed through an interconnected network of lymphatic vascular spaces called the
cortical sinuses and trabecular sinuses.
Superficial Cortex
a.k.a. Nodular Cortex; loosely referred to as the "B Cell Zone"
location of two types lymphatic follicles (Ross: lymphatic nodules): Primary and Secondary
Primary Lymphatic Follicles of the Lymph Nodes
spherical aggregates of mature-naive B lymphocytes that have yet to encounter antigen
typically there are fewer primary lymphatic follicles than secondary lymphatic follicles in a
given lymph node
terminology note: the word 'nodule' and 'follicle' are used interchangeably.
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