Epithelial Tissue 1

Epithelial TissueAbbas A. A. Shawka

ObjectivesAfter this lecture you should be able to : •Define the epithelial tissue.•Know the main characteristics of an

epithelial tissue •Know the structure, location and function

of the basement membrane.

Basic types of tissues in body•Epithelial tissue •Connective tissue •Muscle tissue •Nervous tissue

CHARACTERISTIC FEATURES Of EPITHELIAL CELLS• The e shapes and dimensions of epithelial cells

are quite variable.• The e cells’ size and morphology are generally

dictated by their function.• Nuclear shape corresponds roughly to cell shape.• the• number and shape of the stained nuclei can

indicate cell density and shape. The e nuclei also allow one to determine the number of cell layers in an epithelium, a primary morphologic criterion for classifying epithelia.

• Epithelial tissue is a vascular, so Most epithelia rest on connective tissue that contains the microvasculature bringing nutrients and Oxygen to both tissues.

• Epithelial cells generally show polarity which is difference in structure and shape between apical and basal.

• Organelles and membrane proteins distributed unevenly within the cell.

•The region of the cell contacting the connective tissue is called the basal pole and the opposite end, usually facing a space, is the apical pole.

•Regions of cuboidal or columnar cells that adjoin the neighboring cells are the lateral surfaces.

•All epithelial rest on Basement Membrane (BM) wich connect it to the connective tissue.

Basement Membrane• specialized, feltlike sheet of

extracellular material referre to as the basement membrane.

• Look at illustrate An extracellular basement membrane (red) always lies at the interface of epithelial cells and connective tissue. Nutrients for epithelial cells must diffuse across the basement membrane.

Note: Nerve fibers normally penetrate this structure, but small blood capillaries (being epithelial themselves) normally never enter epithelia.

This section of kidney shows the well-stained basement membranes (arrows) of epithelia forming structures within the large, round renal glomerulus and its surrounding tubules. In kidney glomeruli the basement membrane, besides having a supporting function, has a highly developed role as a filter that is key to renal function.

X100. Picrosiriushematoxylin(PSH).

TEM characteristics of BMThe ultrastructural components of the basement membrane are revealed by TEM. The dense basal lamina (BL) may appear with thin clear zones on each side and is anchored to a thicker, more diffuse reticular lamina (RL) containing collagen III reticular fibers. Hemi desmosomes (H) bind the basal surface of the epithelial cell (C) to the basal lamina. X54,000.

What basement membrane differ from basal lamina?

The terms “basement membrane” and “basal lamina” are often used indiscriminately, causing confusion. Most authors use “basal lamina” to denote the extracellular epithelial layer seen ultrastructurally and “basement membrane” for the entire structure below an epithelium visible with the light microscope.

The macromolecules of the basal lamina are secreted at the basal poles of the epithelial cells and form three-dimensional arrays.

Basal laminae include the following: 1- Laminin

2- Type IV collagen

3- The laminin and type IV collagen networks are held together by the adhesive glycoprotein and proteoglycan.

•These components of basal laminae are also produced by other cells besides those of epithelia, including muscle cells, adipocytes (fat-storing cells), and the cells supporting peripheral neurons.

Function of the Basement Membrane • It provide structural support and polarity to

epithelial cells.• attach epithelia to underlying connective tissue. • Proteins of the layered meshwork help filter

substances entering the epithelium from below, concentrate mitogenic growth factors, and form a scaffold for epithelial repair and regeneration.

• Basal lamina components help organize proteins in the plasma membrane of epithelial cells, affecting endocytosis, signal transduction,and other activities.

• Basement membrane proteins also mediate cell to cell interaction and migration.

QUIZ How laminin and type IV collagen networks

are held together in BM ? All epithelial cell rest on ------------------ . Shape of nuclei of the epithelial cells

corresponds to ------------------ . What is the difference between Basal

Lamina and Basement Membrane ? What we mean by “ Polarity “ of the

epithelial cell ? What if the function of the BM ?