Kamis, 17 Mei 2012

cell epithelium


Single-Layered Squamous Epithelium—Mesentery

Single-layered (simple) squamous epithelium consists of only one layer of cells. Simple squamous epithelium occurs in the lining of the blood and lymph vessels (endothelium), of the heart (endocardium), the pleura and the peritoneal lumen (serosa, mesothelium). Squamous epithelial cells show a polygonal pattern when viewed from the top. Mesentery tissue, as shown in this picture, consists of flat layers of connective tissue and a layer of serous membranes at each side (visceral peritoneum). The epithelial cells of the serous tissue (mesothelium, peritoneal epithelium) are flat, polygonal cells with short microvilli, which form a single-layered epithelium. In this cuticle preparation, the cells look like pieces on a puzzle board. Silver impregnation has accentuated the cell borders. The borders from underlying cells in this cuticle preparation are visible through the top layer as gray, shadowy lines.

Whole-mount preparation; stain: silver nitrate staining; magnification: × 300



Single-Layered Squamous Epithelium—Posterior

Epithelium of the Cornea The surface epithelium is a continuous layer of cells without vessels. Separated by a basal membrane, it is located on top of connective tissue. The apical border is either an inside or an outside body surface. The single-layered squamous epithelium 1 of the cornea, the posterior corneal epithelium (“corneal endothelium”), covers the surface of the cornea opposite to the anterior chamber of the eye. It is a typical single-layered squamous epithelium. A vertical section shows the flat cell profiles. This figure also allows a view of the spindle-shaped nuclei in the flat epithelial cells. Underneath the epithelium is the lamina limitans posterior, Descemet’s membrane 2 . This is the thick basal lamina between the flat epithelium and the substantia propria corneae. It is thought to arise from the corneal epithelium.
Next to it follows the wide layer of the substantia propria corneae 3. The light spaces are technical embedding artifacts.
1 Single-layered squamous epithelium, endothelium
2 Descemet’s membrane
3 Proper cornea substance
4 Fibrocytes (“cornea cells”)
Stain: hematoxylin-eosin; magnification: × 400


Single-Layered Squamous Epithelium—Posterior

Epithelium of the Cornea View of the posterior epithelium of the cornea at the border to the anterior
chamber. The cells are arranged evenly in a polygonal pattern. The cell regions containing the nuclei slightly protrude forward. The surfaces of the layer of flat cells are predominantly smooth. There are no microvilli. The ridged lines are the cell borders where the slender processes of neighboring cells tightly connect and are joined via macula adherentes (desmosomes).



Single-Layered Squamous Epithelium—Peritoneum—Serosa

The peritoneum, the serosa of the peritoneal cavity, consists of a layer of peritoneal single-layered (simple) squamous epithelium and a subepithelial layer of collagenous connective tissue—i.e., the lamina propria serosae. The free surface of the flat epithelium (mesothelium, serosa lining) is covered
with microvilli. The cells of the peritoneal epithelium are flat, polygonal cells with serrated cell borders that can be accentuated by silver impregnation. The cell borders in the figure are clearly defined and look like short bars. The nuclei have the shape of lentils. Raised plasmalemma domes indicate their location. The surface above the nuclei has fewer microvilli
Scanning electron microscopy; magnification: × 1650








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