1. 2-Basal domain THE BASAL DOMAIN AND ITS SPECIALIZATIONS
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2. characterized by several features: focal adhesions and hemidesmosomes.
The basal domain of epithelial cells is
characterized by several features:
The basement membrane is a specialized structure located next to the basal domain of epithelial cells and the underlying connective tissue stroma.
•Cell-to-extracellular matrix junctions anchor the cell to the extracellular matrix; they are represented by
focal adhesions and hemidesmosomes.
•Basal cell membrane infoldings increase the cell surface area and facilitate morphologic interactions between adjacent cells and extracellular matrix proteins.
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3. the urinary bladder and ureters,
Basement Membrane Structure and Function The term basement membrane
It is a dense layer of variable thickness at the basal surfaces of epithelia.
Can bee seen as a prominent structure referred to as basement membrane using hematoxylin and eosin (H&E) stain in a few locations such as the trachea and, occasionally,
the urinary bladder and ureters,
However, basement membrane requires special staining to be seen in the light microscope
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4. Stained by H&E, the basement membrane is not seen
In contrast to H&E. The periodic acid–Schiff (PAS) staining technique results in a positive reaction at the site of the basement membrane.
It appears as a thin, well-defined magenta layer between the epithelium and the connective tissue. The stain reacts with the sugar of proteoglycans, accumulating in sufficient amounts and density to make the basement membrane visible in the light microscope.
Stained by H&E, the basement membrane is not seen
Stained by the periodic acid–Schiff (PAS),
Arrows showing the basement membrane
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5. Hemidesmosomes (hemi- half) resemble desmosomes
they do not link adjacent cells
The name arises from the fact that they look like half of a desmosome
The transmembrane glycoproteins in hemidesmosomes are
Integrins rather than cadherins.
On the inside of the plasma membrane, integrins attach to intermediate filaments made of the protein keratin.
On the outside of the plasma membrane, the integrins attach to the protein laminin, which is present in the basement membrane
Thus, hemidesmosomes anchor cells not to each other but to
the basement membrane.
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6. Morphologic Modifications of the Basal Cell Surface
Many cells that transport fluid have infoldings at the basal cell surface.
They significantly increase the surface area of the basal cell domain, allowing for more transport proteins and channels to be present.
These basal surface modifications are prominent in cells that participate in active transport of molecules (e.g., in proximal and distal tubules of the kidney;
Mitochondria are typically concentrated at this basal site to provide the energy requirements for active transport.
The mitochondria are usually oriented vertically within the folds.
The orientation of the mitochondria, combined with the basal membrane infoldings, results in a striated appearance along the basal aspect of the cell when observed in the light microscope. Because of this phenomenon, the salivary gland ducts that possess these cells are referred to as striated ducts.
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•Basal infoldings. Electron micrograph of the basal portion of a kidney tubule cell showing the infolding of the plasma membrane. Note the aligned mitochondria. The infoldings of adjoining cells result in the interdigitations of cytoplasm between the two cells. 25,000.
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7. Features of Apical surface of Epithelium3
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Microvilli
Finger-like extensions of plasma membrane of apical epithelial cell.
Present mainly in absorptive cells.
Main function is the absorption of nutrients
from intestines and glomerular filtrate.
Increase surface area for absorption.
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Microvilli
Their number and size vary according to the degree of activity of the cell.
They are usually crowded on the cell apex forming the :
Striated border in the intestine.
Bruch border in the kidney.
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Striated border in the intestine.
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Cilia
Motile cytoplasmic hair like projections capable of moving fluid and particles along epithelial surfaces.
Line cells in the respiratory organs, uterine tubes, and efferent ducts in testes.
They move rhythmically and rapidly in one direction.
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Cilia
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Cilia
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Microvilli
Cilia
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Stereocilia
They are similar to microvilli except that they are longer.
Branched.
In epididimus and ductus deferens they have an absorptive function.
In the internal ear they have a sensory function.
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23. The two types of membrane are mucus membrane and serous membrane.
surface epithelium and its underlying connective tissue are regarded as a functional unit called a membrane.
The two types of membrane are mucus membrane and serous membrane.
Mucus membrane, also called mucosa, lines those cavities that connect with the outside of the body, namely, the alimentary canal, the respiratory tract, and the geni-tourinary tract. It consists of surface epithelium (with or without glands), a supporting connective tissue called the lamina propria,
Serous membrane, also called serosa, lines the peritoneal, pericardial, and pleural cavities. These cavities are usually described as closed cavities of the body, although in the female the peritoneal cavity communicates with the exterior via the genital tract. Structurally, the serosa consists of a lining epithelium, the mesothelium, a supporting connective tissue, and a basement membrane between the two. Serous membranes do not contain glands, but the fluid on their surface is watery.
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