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Loose Connective Tissue
As the name implies, loose connective tissue consists of a loosely woven
mix of fibers, cells, and ground substance. Areolar, a more technical
name used for this tissue type means "spaces". Loose connective tissue
therefore possesses randomly arranged protein fibers with abundant intercellular
spaces. Scattered within the spaces are 7 cell types worth mentioning
for their physiological roles:
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fibroblasts-elongate or tapered, flattened cells that form the protein
fibers and ground substance. Fibroblasts can often be seen
adhering to newly formed fibers.
-
macrophages or histiocytes-amoeboid or fixed phagocytic cells
derived from monocytes of the blood. Macrophages play a role in
phagocytosis(non-specific body defense) and thereafter enter the lymphatic
system to aid in activation of immune responses(specific body defense) as
antigen presenting cells or
APC's.
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leukocytes-these blood borne defensive cells leave the vascular system
during inflammatory events to patrol adjoining tissue spaces. Most
are neutrophils or
lymphocytes.
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plasma cells-are lymphatic cells derived from B-lymphocytes. Plasma
cells are highly efficient producers of antibodies. Although most are
located in lymphatic tissues like lymph nodes, they do occur in loose c.t.
areas. Plasma cells, like lymphocytes, possess a well-defined, spherical
shape with rounded nuclei .
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mast cells-This is the key cell involved in
inflammation! Mast
cells release histamine and heparin. These chemical agents induce the
vascular responses that cause inflammation. Mast cells are fragile,
granular cells that can rupture during
tissue preparation and staining.
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adipocytes-are the cells involved in the metabolism and storage of
fats or triglycerides. During tissue preparation for staining fats
are leached from these cells by alcohols. In most stained slides, they
appear as spherical, empty cells with
nuclei pushed to the periphery.
-
mesenchymal cells-these are the embryonic stem cells that divide to
form new cells of all connective tissue types. Think of the mesenchyme
cell as the precursor to fibroblasts, chondroblasts, and osteoblasts.
Areolar connective tissue is abundant and typically found in most body locales.
As the underlying connective tissue to most epithelia it is a key component
of membranes. Areolar connective
tissue also forms much of the mesentery supporting organs within the abdominal
cavity. Also, as a supportive material for blood vessels and nerves,
areolar connective tissue is found in the nooks and crannies of most tissues
where blood vessels and nerves penetrate.
Since loose connective tissue is so abundant there is variety in its appearance.
Remember, open spaces are typical of this tissue type. Protein
fibers are randomly arranged and are smaller than the fibers of dense irregular
connective tissues. In addition, where you find adipose, there will
likely be loose c.t. nearby.
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