Epithelial tissue

• Cuboidal epithelium is a single layer of cube-shaped cells that line the kidney tubules and glands.
• Epithelium is characterized by high cellularity, avascularity, and exhibits polarity.
• Epithelia cover the external surfaces of the body: Ectoderm and Endoderm.
• Epithelia of the Digestive Tract, Liver, Pancreas, Respiratory Tract, Urinary Bladder, Urethra are part of Endoderm.
• Epithelia of the Heart, Blood, Lymph Vessels, Serous Cavities, Urinary System, Male and Female Reproductive Systems are part of Mesoderm.
• Basal Laminar limits the contact of the epithelium and other cells in the underlying tissue.
• Basal Laminar is an amorphous extracellular material, a mixture of different kinds of glycoproteins, collagens, and proteoglycans, 20-100nm thick, and is produced by the epithelial cells.
• Lamina Fibroreticularis, also known as the Basement Membrane, is a layer of extracellular material between the Basal Laminar and the underlying tissue, 200-500nm thick, and is produced by fibroblasts that form the connective tissue.
• Surface Epithelium covers the external surfaces of the body: Skin, Tongue, and Olfactory Cells for sensory, Kidney for waste excretion, Electrolyte Balance, and Testes for germ cell production.
• Jodie Ong's tissue is characterized by high cellularity, avascularity, exhibits polarity, and is derived from embryonic germ layers.
• Epithelia covers the external surfaces of the body, including the ectoderm, endoderm, and mesoderm.
• Epithelia of the digestive tract, liver, pancreas, respiratory tract, urinary bladder, and urethra are part of the endoderm.
• Epithelia of the heart, blood, lymph vessels, serous cavities, urinary system, and male and female reproductive systems are part of the mesoderm.
• Basal lamina provides structural support to the underlying epithelium, serves as a barrier that allows only water and small molecules to pass through, limits the contact of the epithelium and other cells in the underlying tissue, and is an amorphous extracellular material consisting of a mixture of different kinds of glycoproteins, collagens, and proteoglycans.
• Basal lamina and lamina fibrereticularis are collectively referred to as the basement membrane, a layer of extracellular material between the basal lamina and the underlying tissue.
• Stereocilia are like microvilli but are as long as cilia, are nonmotile, and their cores consist of actin filaments.
• Zonula occludens is the tight junction; it is most apically situated of the junction complexes, located on the lateral surface of each cell below the free surface of the cell, and allows cell membranes to stick together without intercellular substances.
• Cilia are present in the surfaces of cells specialized for the transport of fluid or mucus over the surface of the epithelium.
• The glycocalyx coats the core, which is formed by actin filaments, and its main function is to increase the surface area of the epithelium.
• Spermatozoon is the only human cell that has a flagellum (tail), and its main function is to propel the cell along the female genital tract.
• Flagella are longer cilia that beat synchronously in one direction and help in propelling substances.
• Stereocilia are also present in hair cells of the inner ear and play a role in auditory and vestibular perception.
• Zonula adherens, also known as adherens junction or adhering belt, is located below the zonula occludens, forms bands completely encircling the cell, and cell membranes are very close to each other but are separated by a narrow intercellular space that binds cell membranes.
• Cells line the epithelium with specialized junctions to communicate and attach to each other.
• Desmosomes are located below the zonula adherens.
• Secretory units in tubular glands can be blind-ending tubes (secretory tubules) or globulard/basket-like (acini/alveoli).
• Single unbranched ducts are simple glands, while glands with branches are compound glands.
• Apocrine secretions involve the release of the apical part of the cell together with the secretory product, while ceruminous glands of the external auditory meatus contain myoepithelial cells (basket cells) which are flat, stellate cells found between the epithelial cell and the basal lamina.
• Exocrine glands can be classified according to their ducts, secretory units, and nature of secretion.
• Alveolar glands are a combination of tubular and acinous glands.
• Merochine secretions are released through exocytosis and do not result in the loss of any part of the cell, while holocrine secretions involve the destruction of cells.
• Mixed alveoli are a combination of mucoous and serous secretions.
• Exocrine glands are present in the sweat glands, mammary glands, lacrimal glands, and salivary glands.
• Mucoous secretions contain mucin that when hydrated becomes mucus that protects and lubricates the epithelium, while serous secretions are thin, watery and often contain enzymes.
• These myoepithelial cells contain actin and are contractile, contracting ejects the secretions of the acini into the ducts.
• Special names for epithelium include mesothelium, which lines the serous cavities (pericardium, peritoneum, pleura), and endothelium, which lines the luminal surface of the heart, blood, and lymph vessels.
• The classification of surface epithelium includes simple squamous epithelium, simple cuboidal epithelium, simple columnar epithelium, and pseudostratified epithelium.
• Simple epithelial tissue consists of a single layer of cells.
• Stratified epithelial tissue consists of multiple layers of cells, further classified according to the shape of the cells.
• Simple cuboidal epithelium is a single layer of cells whose height approximates their width (square), with nuclei that are round and centered, and a top view that shows a polyhedral outline, lining certain parts of the salivary gland ducts, pancreas, tubules of the kidney, etc.