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Updated: May 25, 2025
Villus showing both the lacteal and the capillaries. 6. Small vein. 7. Layer of epithelial cells. *Work of Capillaries and Lacteals.*—The capillaries and lacteals act as receivers of material as it passes through the layer of epithelial cells covering the mucous membrane. The lacteals take up the digested fats, and the capillaries receive all the other kinds of nutrients.
It is by means of this vascular apparatus that the foetus is furnished with nourishment. The fetal and maternal placentas are made up of vascular villi and depressions that are separated only by the thin walls of capillaries, and a layer of epithelial cells. This permits a change of material between the fetal and maternal circulation.
Warren pictures a case of noli-me-tangere, a destructive type of epithelial carcinoma. The patient suffered no enlargement of the lymphatic glands. The same absence of glandular involvement was observed in another individual, in whom there was extensive ulceration.
Afterwards there are slight histological differentiations in its ectoderm, though the entoderm remains a single stratum of cells. We find the first differentiation of epithelial and stinging cells, or of muscular and neural cells, in the thick ectoderm of the hydra.
The same is to a certain extent true of the epithelial cells covering the mucous membrane of the mouth, and those lining the air passages and air cells of the lungs. Various Kinds of Epithelial Cells The second great division of the epithelial tissues consists of those whose cells are formed of highly active protoplasm, and are busily engaged in some sort of secretion.
The transverse folds in the mucous membrane, by retarding the food in its passage and by increasing the absorbing surface, also aid in the process. But of greatest importance are the minute elevations that cover the surface of the mucous membrane, known as An outer layer of epithelial cells, resting upon a connective tissue support. A network of capillaries.
The muscular coat of the pharynx is made up of a series of overlapping muscles which, by their contractions, draw the sides together and diminish the cavity. The mucous membrane lining the pharynx is smooth, like that of the mouth, being covered with a layer of flat epithelial cells. *The Esophagus*, or gullet, is a tube eight or nine inches long, connecting the pharynx with the stomach.
Of osseous tissue, hardness, stiffness, and toughness. 2. Of muscular tissue, contractility and irritability. 3. Of nervous tissue, irritability and conductivity. 4. Of cartilaginous tissue, stiffness and elasticity. 5. Of connective tissue, toughness and pliability. 6. Of epithelial tissue, ability to resist the action of external forces and power to secrete.
The varieties of cancer are distinguished according to the character and arrangement of the epithelial cells. The squamous epithelial cancer or epithelioma originates from a surface covered by squamous epithelium, such as the skin, or the mucous membrane of the mouth, gullet, or larynx.
*Observation on the Tissues.*—Examine with care the structures in the entire leg of a chicken, squirrel, rabbit, or other small animal used for food. Observe, first of all, the external covering, consisting of cuticle and hair, claws, scales, or feathers, according to the specimen. These are similar in structure, and they form the epidermis, which is one kind of epithelial tissue.
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