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The mesothelium is
a membrane that forms the lining of several body cavities: the pleura (thoracic
cavity), peritoneum (abdominal
cavity including the mesentery)
and pericardium (heart sac).
Mesothelial tissue also surrounds the male internal
reproductive organs (the tunica
vaginalis testis) and covers the internal
reproductive organs of women (the tunica
serosa uteri). Mesothelium that covers the internal
organs is called visceral mesothelium,
while the layer that covers the body walls is called the parietal mesothelium.
It is a form of simple
squamous epithelium.[1]
Origin
Mesothelium derives from the embryonic mesoderm cell
layer, that lines the coelom (body
cavity) in the embryo. It develops into the layer of cells
that covers and protects most of the internal organs of the
body.
[edit]Structure
The mesothelium forms a monolayer of flattened squamous-like epithelial cells
resting on a thin basement
membrane supported
by Dense
irregular connective tissue. Cuboidal mesothelial
cells may be found at areas of injury, the milky
spots of
the omentum,
and the peritonealside
of the diaphragm overlaying
the lymphatic lacunae.
The luminal surface is covered with microvilli.
The proteins and serosal fluid trapped by the microvilli
provide a frictionless surface for internal organs to slide
past one another.
[edit]Function
The mesothelium is composed of an extensive monolayer of
specialized cells (mesothelial cells) that line the body's
serous cavities and internal organs. The main purpose of these
cells is to produce a lubricating fluid that is released
between layers,[2] providing
a slippery, non-adhesive and protective surface to facilitate
intracoelomic movement.
The mesothelium is also implicated in the transport and
movement of fluid and particulate matter across the serosal
cavities, leukocyte migration
in response to inflammatory mediators, synthesis of
pro-inflammatory cytokines, growth
factors and extracellular
matrix proteins
to aid in serosal repair, and the release of factors to
promote the disposition and clearance offibrin (such
as plasminogen).
It is an antigen
presenting cell. Furthermore, the secretion of glycosaminoglycans and
lubricants may protect the body against infection and tumor
dissemination.
[edit]Role
in disease
-
Mesothelioma: (cancer of
the mesothelium) is a disease in which cells of the
mesothelium become abnormal and divide without control or
order. They can invade and damage nearby tissues and organs.
Cancer cells can also metastasize (spread) from their
original site to other parts of the body. Most cases of
mesothelioma begin in the pleura or peritoneum. More than
90% of mesothelioma cases are linked to asbestos exposure.
- Intra-abdominal
adhesions: Normally,
the mesothelium secretes plasminogen,
which removes fibrin deposits.
During surgical procedures, the mesothelium may be damaged.
Its fibrinolytic capacity becomes insufficient and fibrin
accumulates, causing fibrous adhesions between opposing
surfaces. These adhesions cause intestinal obstruction and
female infertility if it occurs in the abdomen, and may
impair cardiac and lung function in the thorax.
- Ultrafiltration
failure: The
peritoneal mesothelium is implicated in the long-term
development of ultrafiltration failure in peritoneal
dialysis patients.
The presence of supra-physiological glucose concentrations,
acidity, and glucose degradation products in peritoneal
dialysis fluids contribute to the fibrosis of
the peritoneal mesothelium, either by epithelial-mesenchymal
transition or
increased proliferation of existing fibroblasts.
A fibrosed peritoneum results in the increased passage of
solutes across the peritoneum and ultrafiltration
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