anatomy 25 tissue

A group of cells of similar structure that perform a common function. A community of cells working together. Between the cells is the extracellular matrix, nonliving material.

• Epithelium - covering tissue. ( skin, serous, mucous )
• Connective - supporting tissue. ( ligament )
• Muscle - movement tissue. ( muscle )
• Nervous - control tissue. ( nerves )

Epithelia are sheets of cells that cover or line body surfaces. Functions:

• Protect against physical or chemical trauma.
• Transport and or modify selected substances.
• Move materials along body surfaces.
• Defends against biological invasion.

No, epithelia are avascular, meaning they do not have blood vessels running through them, they are fed by capillaries in the connective tissues they are connected to.

The polarity has nothing to do with charge, it simply means that the two surfaces ( basal and apical ) are different from each other.

• Basal is the base of the epithelium.
• Apical is the upper layer of the epithelium, also called the "free" layer.

• Basement membrane consists of:
• Basal lamina - part of the basment membrane, layer between bottom of epithelial cell and reticular fibers, connecting the two. It is produced by the epithelial cells. It is part of the epithelium.

Reticular fibers - layer and connection between the Basal lamina and surrounding tissue. It is produced by the connective tissue. It regulates the flow of some materials between epithelium and surrounding connective tissue as well as holds the epithelium -to- the connective tissue. It is part of the connective tissue.

Simple - if there is only one layer of cells.

Stratified - if there are more than one layer of cells.

Squamous - flat, fried egg-shaped, nucleus is flattened and near the surface of the cell..

Cuboidal - cube shaped, as tall as it is wide as it is long, nucleus is round and at center of the cell.

Columnar - Tall and skinny, nucleus is elongated, stretched out and near the baseof the cell.

Stratified epithelial - Typically, stratified epithelium protect underlying connective tissues in areas where abrasion is common.

Simple squamous - Found in areas where diffusion is important, they are thin cells and material do not have as far to travel when moving through them. Capillaries and aveoli ( air sacs in lungs ) are made of simple squamous cells.

Simple cuboidal - found in tissues involved in secretion and absorbtion. They make up the smallest ducts of glands and many of the tubules in the kidneys. Also make up ovarian follicle.

Simple columnar - Functions in the active movement of molecules, especially absorbtion, secretion, and ion transport. Simple columnar epithelial line digestive tract from stomach to anus. Simple columnar make up villi for greater surface area for even greater absorbtion. Simple columnar also make up the lens of the eye and lining of the gall bladder.

Endothelium is simple squamous epithelium that lines the hollow organs of the circulatory system ( blood vessels, heart, lymphatic vessels ).

Mesothelium is the epithelium that lines the periotoneal, pleural, and periocardial cavities and covers the visceral organs ( soft squishy organs ), these are the serosa membranes.

Psuedostratified epithelium is epithelium made up of cells of different heights. They might look like they are stratified but they are all actually attached to the basal lamina.

Stratified squamous epithelium is made of many layers of squamous cells. At the base of these layers are cuboidal or columnar cells.

Transitional epithelium lines the inside of the stretchy organs of the urinary system ( bladder, gall bladder ). These cells compress and stretch from 6 to 3 layer thickness. When relaxed, the cells sort of curl in on themselves.