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Lecture 44

BSC 215 Lecture Notes - Lecture 44: Lamina Propria, Reticular Connective Tissue, Reticular Fiber

Biological Sciences
Course Code
BSC 215
Jason Pienaar

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Lymphoid Cells
Lymphatic (lymphoid) tissue is a kind of connective tissue. It consists of the following types of
Lymphocytes are white blood cells ( leukocytes) that provide an immune
response that attacks specific kinds of nonself cells and foreign substances
(antigens). There are several major classes of lymphocytes:
o T cells (T lymphocytes) originate in the bone marrow but mature in the
thymus gland. T cells attack self cells that have been invaded by
pathogens, abnormal self cells (such as cancerous cells), or nonself cells
(such as those that might be introduced in an organ transplant).
o B cells (B lymphocytes) originate and mature in the bone marrow. When
B cells encounter an antigen (a toxin, virus, or bacterium), they produce
plasma cells and memory cells. Plasma cells release antibodies that bind
to the antigen and inactivate it. Memory cells circulate in the lymph and
blood with the capacity to produce additional antigens for future
encounters with the same antigen.
Macrophages are enlarged monocytes (white blood cells) that engulf microbes
and cellular debris.
Reticular cells and their reticular fibers made from collagen and glycoproteins
provide a network within which the lymphocytes and other cells reside.
Lymphatic Tissues and Organs
Lymphatic cells are organized into tissues and organs based on how tightly the lymphatic cells
are arranged and whether the tissue is encapsulated by a layer of connective tissue. Three
general categories exist:
Diffuse, unencapsulated bundles of lymphatic cells. This kind of lymphatic tissue
consists of lymphocytes and macrophages associated with a reticular fiber
network. It occurs in the lamina propria (middle layer) of the mucus membranes
(mucosae) that line the respiratory and gastrointestinal tracts.
Discrete, unencapsulated bundles of lymphatic cells, called lymphatic nodules
(follicles). These bundles have clear boundaries that separate them from
neighboring cells. Nodules occur within the lamina propria of the mucus
membranes that line the gastrointestinal, respiratory, reproductive, and urinary
tracts. They are referred to as mucosaassociated lymphoid tissue
(MALT). The nodules contain lymphocytes and macrophages that protect against
bacteria and other pathogens that may enter these passages with food, air, or
urine. Nodules occur as solitary nodules, or they cluster as patches or
aggregates. Here are the major clusters of nodules:
o Peyer's patches are clusters of lymphatic nodules that occur in the
mucosa that lines the ileum of the small intestine.
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