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.
    • Epithelial tissues are identified by both the number of layers and the shape of the cells in the upper layers.

  • Epithelial Tissues

    • Epithelial tissues cover the outside of organs and structures in the body.
    • Cuboidal epithelial cells are cube-shaped with a single, central nucleus .
    • Columnar epithelial cells are taller than they are wide: they resemble a stack of columns in an epithelial layer.
    • Columnar epithelial cells lining the respiratory tract appear to be stratified.
    • Simple columnar epithelial cells absorb material from the digestive tract.

  • Types of Epithelial Tissue

    • Epithelial tissue is classified by cell shape and the number of cell layers.
    • Most epithelial tissue is described with two names.
    • 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 classifications associated with epithelial cells.

  • Epithelial Membranes

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

  • 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).

  • Complex Tissue Structure

    • Animals, besides Parazoa (sponges), are characterized by specialized tissues such as muscle, nerve, connective, and epithelial tissues.
    • Epithelial tissues cover, line, protect, and secrete; these tissues include the epidermis of the integument: the lining of the digestive tract and trachea.

  • Cryptosporidiosis

    • The transmission of Cryptosporidium is based on successful ingestion of oocysts which are able to implant and infect the epithelial tissue of the intestine, hence, the gastrointestinal symptoms associated with cryptosporidiosis.
    • The trophozoites then develop into Type 1 and Type 2 merozoites which can either cause auto infection (Type 1) or undergo releasal and attach the epithelial cells (Type 2).
    • The oocysts can initiate infections by attaching to the brush border of the small intestine and attacking the epithelial cells.

  • 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.