Chapter 2: Epithelium

Apical

The surface of a cell that faces a lumen or outside area

Basolateral

The surface of a cell that faces away from a lumen or outside area

Cilia

An organelle and cell modification that manifests as a membrane projection capable of movement

Cornification

A layer of dead cells filled with keratin that form a protective barrier over a layer of cells

What type of epithelial tissue is cornification seen with?

Stratified squamous epithelium

Desmosomes

Anchoring junction that adheres cell to cell, and prevents shearing forces to the epithelial layer

Endothelium

Type of endothelium that lines the inside of vascular structures

What type of epithelial tissue is endothelium made of?

Simple squamous epithelium

Epithelium

Basic tissue type that typically lines a surface (cavity, lumen, or outside surface) or forms glands

Hemidesmosomes

Cell modification that is responsible for the adhesion of a cell to extracellular matrix

Keratin

Structural protein and intermediate filament that provide a tough protective quality to some epithelial cell types; seen with cornified or keratinized epithelium

Microvilli

Cell modification that manifests as a membrane projection and congresses the surface area of a cell for adsorption

Pseudostratified

A type of columnar epithelium in which the nuclei are arranged in different levels in the cell layer

Tight junctions

Cell modification that is responsible for cell to cell adhesion

Urothelium

A unique type of stratified epithelium capable of stretching that lines a majority of the urinary tract

All epithelial tissue rests on a _______________ _______________

Basement membrane

Basement membrane

Layer between epithelium and underlying connective tissue; acts as a substrate that epithelium can attach to as well as grow and regenerate after injuries

Epithelial tissues have a _________ supply but they do not have a __________ supply

Nerve; blood

Three primary functions of epithelial tissue

1.) protect the tissues that lie beneath it from injury

2.) regulation and exchange of molecules between the underlying tissues and another compartment

3.) secretion of hormones into the vascular system, and secretion of sweat, mucus, enzymes ad other products that are delivered by ducts

The type of epithelium that is present in an organ system depends on the ___________ of the system

Function

Surfaces that require a water resistant surface and protection from abrasion are often composed of...

Keratinized stratified squamous epithelium

Surfaces that separate body cavities within the body are lined by....

Simple squamous, columnar, or pseudostratified cells

Endothelium

Inner lining of blood vessels; simple squamous epithelium

Mesothelium

Lines the outer surface of many organs in the abdominal and thoracic cavity; simple squamous epithelium

All epithelial cell types share five characteristics:

1.) close apposition of cells

2.) free surface of epithelial cells is adjacent to the space

3.) basal surface is adjacent to connective tissue

4.) sheets of epithelial cells may be modified into tubes forming glands

5.) absence of blood vessels within epithelial layer

Apical surface

surface of an epithelial cell that faces away from the basement membrane and associated with the lumen

Basolateral surface

includes both the base & sides of the cell that come into contact with its neighbors; continuous with the basement membrane!

Basal surface

The bottom layer of epithelial tissue that attaches to the basement membrane

Epithelium is characterized by four physical features:

1.) Number of layers of cells

2.) Shape of cells at free surface

3.) Function of the epithelium

4.) Surface modifications

Ways to classify epithelium based on number of layers of cells:

1.) simple

2.) stratified

3.) pseudostratified

simple epithelium

single layer of cells

stratified epithelium

more than one layer of cells

Pseudostratified epithelium

All cells are in contact with the basement membrane, but appears as more than one layer since nuclei are all at different levels

Pseudostratified epithelium is always what shape?

Columnar

Three shapes of epithelial cells:

1.) squamous

2.) cuboidal

3.) columnar

squamous epithelium

Wider than their height

Cuboidal epithelium

Height and width are approximately the same

columnar epithelium

Taller than they are wide

When epithelium is stratified, the shape is classified by...

The shape of the cells at the uppermost layer

Urothelium

transitional epithelium in the wall of the bladder; cells change from squamous to cuboidal, depending on the amount of tension on the epithelium

functions of simple squamous epithelium

Found in lining areas where passive diffusion of gases occur, such as walls of capillaries and alveoli of lungs

Functions of simple cuboidal

Have secretory, absorptive, or excretory functions; found in tubules of kidney, and secretory ducts of salivary glands

functions of simple columnar epithelium

Found in areas with high secretory or absorptive activity, such as the stomach or small intestine

What type of cell modification(s) does simple columnar epithelium often have?

Microvilli (small intestine) and cilia (female reproductive tract)

function of psuedostratified columnar epithelium

Found almost exclusively in the respiratory tract

Lining epithelium

Epithelium that covers free surfaces of the body and cavities

Glandular epithelium

Composed of cells that are specialized to produce and secrete substances; Invagination of epithelium that forms a solid tissue structure

Two types of glands:

1.) endocrine

2.) exocrine

Endocrine gland

Secrete a product into the extra cellular space where it is taken up by the blood

Exocrine gland

Secrete their products into a duct that then delivers the product to the lumen of an organ or onto the free surface of epithelium

Exocrine glands are further characterized by....

Method of secretion

Three types of exocrine glands based on method of secretion:

1.) Merocrine secretion

2.) Holocene secretion

3.) Apocrine secretion

Merocrine secretion

Exocytosis of secretory vesicles to the lumen of the gland

Holocrine secretion

Involves death of an entire cell within a gland which subsequently sloughs off and releases content into the lumen of the gland

Apocrine secretion

Involves release of budding vesicles off the epithelial cells themselves into the lumen of the gland

Cell junctions

contact points between the plasma membranes of tissue cells

Four types of cell junctions:

1.) tight junctions

2.) gap junctions

3.) desmosomes

4.) hemidesmosomes

Tight junctions

Transmembrane proteins that are fused on the outer plasma membrane

Gap junctions

Connect the cytoplasm of two cells and allow the passage of molecules between cells

Desmosomes

Anchoring junctions that prevent cells from being pulled apart; attach cells to other cells

Hemidesmosomes

attach the basal aspect of epithelial cells to the basement membrane rather than an adjacent cell