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The Anatomy of Lining and Covering Tissues-Membranes!

Remember, epithelia possess tight intercellular junctions between cells!  These junctions effectively cement cells together into single layered or multilayered sheets of cells.  These tissue sheets drape body organs, line cavities, and cover external body surfaces providing protection from microbial invasion or friction.  The epithelia of these sheets can also be secretory, producing lubricating, protective, or nutritive fluids of membranes.

Membranes consist of  a lining or covering epithelium with the loose connective tissues that anchor them to underlying tissues.  For example, the epidermis of the skin is an epithelium. Epidermis with loose c.t. immediately below is considered the cutaneous membrane. In like manner, epithelia and loose connective tissue layers make up the various mucous membranes(lining respiratory, digestive, reproductive and other body tracts), serous membranes(lining the ventral body cavities), and synovial membranes(lining joint capsules).  

Serous membranes lining the ventral body cavities actually consist of two separate layers, a visceral layer and a parietal layer.  The visceral layer is the component that closely wraps or invests organs in these cavities.  The parietal layer lines the walls of the cavity.  Epithelial cells of these membrane components secrete a small quantity of slippery serous fluid that accumulates in the space between them.  This serous fluid acts as a lubricant to reduce friction between organs that shift and move as they perform bodily functions.

Let's look at membranes to see the epithelium covering and loose connective tissue immediately below!

 Loose connective tissues of membranes are important sites of inflammation due to mast cells.  Mast cells release histamine, heparin(an anticoagulant), and other vasoactive agents.  Vascular effects of histamine are important initiators of inflammation.  These include vasodilation in vessels and increased permeability in capillaries. The visible or "cardinal" signs of inflammation are explained by keeping histamine's vascular effects in mind!

Four Cardinal Signs of Inflammation

The sign:

Caused by:

1. Redness vasodilation of blood vessels
2. Edema fluid loss from more permeable capillaries
3. Sensitivity to touch pressures and chemical shifts in interstitial fluids sensitizing receptors neurons
4. Elevated temperature heat carried to site from the body core by blood

We take antihistamines to counter histamine's inflammatory effects.  Inflammation however, can be very important in body defense even though it is very uncomfortable or damaging.  Dermatitis, synovitis, peritonitis, pleuritis, and pericarditis are all terms that describe inflammation.  Notice the "itis" ending of these words.  Any medical term with this ending implies inflammation in some tissue or location.

Three of the terms mentioned above describe inflammatory events in membranes lining the ventral body cavities; the pleura, pericardia, and peritonea.  Can you pick out the term that implies inflammation in the skin?

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