Isfa: (4) Epithelia

Front 1

Epithelium, epithelia

Back 1

A tissue that rests on a basement membrane, forms sheets and has polarity, i.e., an apical and a basal surface. Epithelia line internal surfaces such as ducts and tubes, cover external surfaces, and form glands.

Front 2

Epithelioid

Back 2

Cells that are arranged in such a way as to mimic epithelia. An example of an epithelioid layer is a layer of cells that surround groups of nerve fibers.

Front 3

Apical

Back 3

The face of an epithelial cell directed in a space or lumen.

Front 4

Basal

Back 4

The side of an epithelial cell that rests on a basement membrane.

Front 5

Lateral

Back 5

The cell surface in contact with adjacent epithelial cells.

Front 6

Basement Membrane

Back 6

An EXTRAcellular structure that forms a continuous sheet. It consists of two sections: the basal lamina and the reticular lamina.

Front 7

Basal Lamina

Back 7

Part of the basement membrane; immediately adjacent to the epithelial cells. It is a product of the epithelial cells.

Front 8

Reticular Lamina

Back 8

An underlying layer of reticular fibers beneath the basal lamina. This layer is secreted by connective tissue cells rather than the epithelial cells it underlies.

Front 9

Myoepithelial

Back 9

A layer of cells surrounding certain parts of glands. These cells are capable of contraction, but are located within a layer of epithelium.

Front 10

Neuroepithelial

Back 10

Two definitions: one is the embryonic cell layer that gives rise to most of the nervous system. The other is a special type of adult epithelium that actually contains neurons, such as the olfactory epithelium.

Front 11

Squamous

Back 11

These cells are flat.
The word means scale-like. When they are cut through from their apical surface to their basal surface, squamous epithelial cells look long and skinny, and if the slice goes through the nucleus, it is often seen to bulge toward the apical side.

Front 12

Stratified

Back 12

When two or more cellular layers exist.

Front 13

Pseudostratified

Back 13

In this type, all cells are attached to the underlying connective tissue, but not all cells reach the apical, or free, surface of the epithelium.

Front 14

Endothelium

Back 14

Simple squamous layer lining blood and lymphatic vessels and heart.

Front 15

Mesothelium

Back 15

Simple squamous layer covering the outside of organs so that they can slide over each other.

Front 16

Microvilli

Back 16

Surface projections of epithelial cells; an indication that the cell is involved in absorption. Always immotile, the actin filaments within are anchored at their bases to a network of microfilaments known as the terminal web.

Front 17

Cilia

Back 17

Surface projections that are capable of movement in most cases. Have a complex internal structure composed of microtubules that parallel the long axis of the cilium. The triplet microtubules at the base form the “root” of the cilium, known as the basal body.

Front 18

Junctional Complex

Back 18

Consists of, from apical to basal, a zonula occludens, a zonula adherens and a macula adherens. Found joining the lateral surfaces of epithelial cells and are located near the apical surface of the epithelium.

Front 19

Tight Junction, Zonula occludens

Back 19

Important in preventing leakage of material between epithelial cells. They have a “tongue and groove” architecture sealing the cells together.

Front 20

Zonula Adherens

Back 20

Link actin filaments of one cell with actin filaments of adjacent cells. They form belt like rings around each cell. Relatively weak and allow cells to associate and disassociate easily.

Front 21

Desmosome, Macula adherens

Back 21

Link intermediate filaments of one cell to intermediate filaments of the adjacent cell. There is an attachment plaque on the inner surface of the plasma membrane of each cell. Specific transmembrane proteins from one cell link to similar transmembrane proteins of the adjacent cell. Stronger than a zonula adherens,

Front 22

Hemidesmosomes

Back 22

Provide very strong anchoring of epithelia to underlying tissue. Important in areas where the epithelium is subject to friction, such as the epidermis. Similar to desmosomes.

Front 23

Gap Junction

Back 23

Consists of transmembrane channels or pores arranged in a tightly packed array. Gap junctions allow cells to exchange ions, regulatory molecules and other small molecules.

Front 24

Connexon

Back 24

The unit of the gap junction that spans the extracellular space between adjoining cells.