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Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial (mesothelial) tissues line the outer surfaces of many internal organs, the corresponding inner surfaces of body cavities, and the inner surfaces of blood vessels.
The 4 main classes of molecules in biochemistry (often called biomolecules) are carbohydrates, lipids, proteins, and nucleic acids. [35] Many biological molecules are polymers : in this terminology, monomers are relatively small macromolecules that are linked together to create large macromolecules known as polymers.
After being formed at the base, the new cells migrate upwards and out of the crypt, maturing along the way. Eventually, they undergo apoptosis and are shed off into the intestinal lumen. [4] In this way, the lining of the intestine is constantly renewed while the number of cells making up the epithelial layer remains constant. [5]
Epithelioid cells gather around the focus of necrosis, in direct contact with the necrotic masses, forming a kind of boundary zone.. Structurally, epithelioid cells (when examined by light microscopy after stained with hematoxylin and eosin), are elongated, with finely granular, pale eosinophilic (pink) cytoplasm, and central, ovoid nuclei (oval or elongate), which are less dense than that of ...
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermal layer provides a barrier to infection from environmental pathogens [2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.
Cornification is the process of forming an epidermal barrier in stratified squamous epithelial tissue. At the cellular level, cornification is characterised by: production of keratin; production of small proline-rich (SPRR) proteins and transglutaminase which eventually form a cornified cell envelope beneath the plasma membrane; terminal ...
The basal layer fosters the epithelial stem cells in order to provide constant renewal of the epithelium. [4] These cells' cytoplasm is rich in tonofilaments and mitochondria; however, they contain few rough endoplasmic reticulum. The tonofilaments play a role in the attachment of the basal layer to the basement membrane via desmosomes. [5]
Both of these types of cells can be defined and reciprocally distinguished by their expression of cytokines, chemokines, costimulatory molecules, and transcription factors, which have an effect on thymocyte development. [4] TECs, situated in the corticomedullary junction, express two types of cytokeratin: K5 and K8.