epithelial

(adjective)

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport and detection of sensation

Related Terms

Examples of epithelial in the following topics:

  • Characteristics of Epithelial Tissue

    • The human body consists of four types of tissue: epithelial, connective, muscular and nervous.
    • Epithelial tissue covers the body, lines all cavities and composes the glands.
    • Epithelial tissue is composed of cells laid out in sheets with strong cell to cell attachments.
    • The epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue.
    • Cell Shapes and arrangement of layers are the basis of classifying epithelial tissues.

  • Types of Epithelial Tissue

    • Epithelial tissue is classified by cell shape and the number of cell layers.
    • Most epithelial tissue is described with twonames.
    • The thinness of the epithelial barrier facilitates these processes.
    • Simple epithelial tissues are generally classified by the shape of their cells.
    • There are three principal morphologies associated with epithelial cells.

  • Glandular Epithelia

    • Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands.
    • Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and detection of sensation.
    • Exocrine and endocrine epithelial cells are highly vascular.
    • Secretion is one major function of epithelial cells .
    • Glands are formed from the invagination / infolding of epithelial cells and subsequent growth in the underlying connective tissue.

  • Serosa

    • Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduce the friction from muscle movement.
    • Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath.
    • The epithelial layer, known as mesothelium, consists of a single layer of avascular flat nucleated cells (simple squamous epithelium) which produce the lubricating serous fluid.

  • Absorption in the Small Intestine

    • The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue.
    • The individual epithelial cells also have finger-like projections known as microvilli.
    • The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids).

  • Tubular Reabsorption

    • Passive Diffusion-passing through plasma membranes of the kidney epithelial cells by concentration gradients.
    • Active Transport-membrane bound ATPase pumps (such as NA+/K+ ATPase pumps) with carrier proteins carry substances across the plasma membranes of the kidney epithelial cells by consuming ATP.
    • These processes involve the substance passing though the luminal barrier and the basolateral membrane, two plasma membranes of the kidney epithelial cells, and into the peri-tubular capillaries on the other side.
    • Some substances can also pass through tiny spaces in between the renal epithelial cells, called tight junctions.

  • Ureters

    • The ureters are two tubes that are made out of smooth muscle and transitional epithelial tissues, which are a type of epithelial tissue that may either be columnar or squamous.
    • The ureteral valves function similarly to the semilunar valves in the veins of the body, but are structurally different, consisting of transverse mucosal epithelial folds.
    • Ureter cancer is often due to a malignant transformation of of the transitional epithelial tissue, which is more vulnerable to developing cancer cells compared to other tissues.

  • Mucous Membranes

    • Most mucosal membranes contain stratified squamous or simple columnar epithelial tissue type.
    • The epithelial tissue sheet lies directly over the layer of loose connective tissue called lamina propria.

  • Epidermal Wound Healing

    • Epithelial cells proliferate and migrate to the top layers of the wound providing a new barrier for the wounded tissue.
    • Basal keratinocytes from the wound edges and dermal appendages such as hair follicles, sweat glands, and sebacious (oil) glands are the main cells responsible for the epithelialization phase of wound healing.
    • If the basement membrane is not breached (i.e. the wound is not deep), epithelial cells are replaced within three days by division and upward migration of cells in the stratum basale in the same fashion that occurs in uninjured skin.
    • In the ensuing cellular phase, the inflammatory response develops and is followed by the synthesis of granulation tissue and the restoration of the epithelial layer.

  • Mammary Glands

    • In this stage, mammary gland development depends on systemic (and maternal) hormones, but is also under the (local) regulation of paracrine communication between neighboring epithelial and mesenchymal cells by parathyroid hormone-related protein (PTHrP).
    • This locally secreted factor gives rise to a series of outside-in and inside-out positive feedback between these two types of cells, so that mammary bud epithelial cells can get to proliferate and sprout down into the mesenchymal layer until they reach the fat pad to begin the first round of branching.
    • As one of the transcribed genes, Wnts secreted from mammary epithelial cells act paracrinely to induce more neighboring cells branching.
    • When the lactiferous duct tree is almost ready, "leaves" alveoli are differentiated from luminal epithelial cells and added at the end of each branch.
    • Laminin and collagen in myoepithelial basement membrane interacting with beta-1 integrin on epithelial surface again, is essential in this process.