Chapter 5Chapter 5

Epithelial Epithelial TissueTissue

EPITHELIAL TISSUEEPITHELIAL TISSUE

It is the basic tissue which It is the basic tissue which covers surface areas: the covers surface areas: the fill spaces, surfaces and fill spaces, surfaces and the cavities of the body.the cavities of the body.

There are three types of There are three types of epithelial tissues:epithelial tissues:

1. Covering and lining 1. Covering and lining 2. Glandular 2. Glandular 3. Sensory3. Sensory

Characterisitics of Characterisitics of epithelial cells:epithelial cells:

1. They are 1. They are contiguouscontiguous (i.e., the cells are (i.e., the cells are attached to one another or closely packed). attached to one another or closely packed).

2. The cells rest on an extracellular matrix 2. The cells rest on an extracellular matrix which they produce, called the which they produce, called the basement basement membranemembrane which acts as a semi permeable which acts as a semi permeable membrane where they get their nutrients.membrane where they get their nutrients.

3. Epithelia are 3. Epithelia are avascularavascular. This means that . This means that blood vessels do not penetrate up between blood vessels do not penetrate up between these cells, as they do in connective tissue these cells, as they do in connective tissue and muscle cells. and muscle cells.

4. A major component of epithelial tissue is 4. A major component of epithelial tissue is the intermediate filament called the intermediate filament called keratin.keratin.

Three features are important in Three features are important in the classification of epithelium:the classification of epithelium:

1. Shape1. Shape

A. squamousA. squamous - -very flat cells very flat cells

B. cuboidalB. cuboidal- - taller than taller than squamous squamous cells, all four cells, all four sides sides approximately approximately equalequal

C. columnarC. columnar- - cell length is cell length is greater than greater than cell width cell width

2. Number of Layers of cells in 2. Number of Layers of cells in the epithelium:the epithelium:

A. simpleA. simple- a single layer of cells; - a single layer of cells; all cells sit on the basement all cells sit on the basement membrane. membrane.

B. stratifiedB. stratified- several cells - several cells stacked upon one another; not stacked upon one another; not all cells touch the basement all cells touch the basement membrane. The shape of the membrane. The shape of the apical stratumapical stratum determines the determines the "shape" designation of the "shape" designation of the epithelium. epithelium.

Pseudo stratifiedPseudo stratified- a simple - a simple epithelium, but gives the epithelium, but gives the illusion of being stratified. All illusion of being stratified. All cells do sit on the basement cells do sit on the basement membrane, but not visually membrane, but not visually apparent because the nuclei are apparent because the nuclei are at various levels. at various levels.

Simple cuboidal epithelium is found in glandular tissue and in the kidney tubules.

Simple columnar epithelium lines the stomach and intestines.

Pseudostratified columnar epithelium lines portions of the respiratory tract and some of the tubes of the male reproductive tract.

Transitional epithelium can be distended or stretched. Glandular epithelium is specialized to produce and secrete substances.

Simple Squamous EpSimple Squamous Ep Flat shape characteristic Flat shape characteristic

of typical "squamous of typical "squamous cells." The cells." The nucleusnucleus (A) is (A) is centrally located, the centrally located, the cell cell membrane membrane (C) is very (C) is very thin, and the cell is filled thin, and the cell is filled with with cytoplasmcytoplasm (B). (B).

LocationsLocations:: Capillary walls, Capillary walls, alveoli of the lungs, alveoli of the lungs, covering visceral organs, covering visceral organs, lining body cavitieslining body cavities

Function:Function: diffusion and diffusion and filtrationfiltration

Simple CuboidalSimple Cuboidal In kidney tissue we find the In kidney tissue we find the

kidney's tubules cut such kidney's tubules cut such that they appear as rings of that they appear as rings of cells around empty spaces. cells around empty spaces. These cuboidal cells (A) that These cuboidal cells (A) that line these tubules are as line these tubules are as wide as they are tall as they wide as they are tall as they are deep - cuboidal. The are deep - cuboidal. The nuclei (B) are easily nuclei (B) are easily observed.observed.

Locations:Locations: lining kidney lining kidney tubules, salivary ducts, tubules, salivary ducts, pancreatic ductspancreatic ducts

Functions:Functions: secretion, secretion, excretion, and absorption excretion, and absorption

Simple ColumnarSimple Columnar The villi of the small intestine The villi of the small intestine

are lined by a single layer of are lined by a single layer of columnar cells (A) - thus the columnar cells (A) - thus the name simple columnar name simple columnar epithelium. Note these cells epithelium. Note these cells are not as wide as they are are not as wide as they are tall with the darkly stained tall with the darkly stained nuclei (B) located at the base nuclei (B) located at the base of the cells.The cell of the cells.The cell membranes (C) are very thin membranes (C) are very thin but easily identified.but easily identified.

Locations:Locations: lining most of the lining most of the digestive tractdigestive tract

Function:Function: protection, protection, secretion and absorptionsecretion and absorption

3. Surface Specializations: 3. Surface Specializations:

MicrovilliMicrovilli – finger like – finger like projectionsprojections

CiliaCilia

CiliaCilia – Hair-like – Hair-like structurestructure

GobletGoblet – flask like – flask like structurestructure

Neuro-epithiliumNeuro-epithilium

Psuedostratified Ciliated Psuedostratified Ciliated Columnar Ep.Columnar Ep.

Locations:Locations: This is a This is a respiratory epithelium respiratory epithelium being found in such being found in such places as the nasal places as the nasal septum, trachea, and septum, trachea, and bronchi.bronchi.

Function:Function: trap and trap and move "pollutants" to move "pollutants" to the mouth where they the mouth where they are swallowed are swallowed

Stratified SquamousStratified Squamous

The bracket labeled A The bracket labeled A marks the stratified marks the stratified squamous epithelium.The squamous epithelium.The many layers of cells that many layers of cells that make up this tissue are make up this tissue are easily seen with higher easily seen with higher magnification (right). magnification (right). Observe that the surface Observe that the surface cells (at B) are flattened cells (at B) are flattened (are squamous). (are squamous).

LocationLocation: mouth, vagina, : mouth, vagina, esophagus, anal canalesophagus, anal canal

Function:Function: protection protection

Stratified Cuboidal or Stratified Cuboidal or ColumnarColumnar

relatively rare. relatively rare. Examples are found in larger Examples are found in larger

excretory ducts of salivary glands excretory ducts of salivary glands and portions of the urethra and portions of the urethra (stratified (stratified columnar)columnar) and and

the ducts of sweat glands the ducts of sweat glands (stratified (stratified cuboidal)cuboidal)

Transitional EpTransitional Ep

At the left observe the At the left observe the ureter is lined by ureter is lined by transitional epithelium (A). transitional epithelium (A). At the left the epithelium is At the left the epithelium is more highly magnified. more highly magnified. Note that the cells at the Note that the cells at the exposed surface (A) are exposed surface (A) are large and rounded. They large and rounded. They are also larger than the are also larger than the cells at the attached cells at the attached surface (B). surface (B).

LocationsLocations: ureter, urinary : ureter, urinary bladderbladder

Function:Function: distention distention

GLANDULAR EPITHELIAGLANDULAR EPITHELIA

There are two types of glandular tissue in There are two types of glandular tissue in the body: the body: exocrine and endocrineexocrine and endocrine. .

ExocrineExocrine glands secrete through glands secrete through ducts or directly onto an epithelial surface. ducts or directly onto an epithelial surface.

EndocrineEndocrine glands do not secrete into glands do not secrete into ducts, but rather secrete into the ducts, but rather secrete into the bloodstream. bloodstream.

Mechanisms of Mechanisms of Secretion:Secretion:

Merocrine- Merocrine- Secretory Secretory granules granules released by released by exocytosis. exocytosis.

Apocrine- Apocrine- Secretion Secretion "pinched off." "pinched off."

Holocrine- Holocrine- Cells released Cells released as part of as part of secretion.secretion.

Merocrine Merocrine This is the most This is the most

common type of common type of secretion mechanism. secretion mechanism. Secretory granules Secretory granules form in the cells and form in the cells and accumulate in the accumulate in the apex. The granules apex. The granules fuse with the plasma fuse with the plasma membrane and are membrane and are secreted into the secreted into the lumen of the gland by lumen of the gland by exocytosisexocytosis

ApocrineApocrine

There are few examples There are few examples of this type of gland in of this type of gland in the body. Secretions in the body. Secretions in the apex of the cell and a the apex of the cell and a portion of the cell itself portion of the cell itself (including the plasma (including the plasma membrane) is pinched off membrane) is pinched off for secretion. Some for secretion. Some cytoplasm may be cytoplasm may be discharged with the discharged with the secretion. An example is secretion. An example is the lactating mammary the lactating mammary gland gland

Holocrine Holocrine

In these glands the In these glands the cell fills with its cell fills with its secretory product secretory product while the nucleus while the nucleus becomes smaller. becomes smaller. The cell dies and the The cell dies and the entire cell is entire cell is released and released and disintegrates, disintegrates, releasing its product. releasing its product.

End of PresentationEnd of Presentation Next Meeting Next Meeting

EXAM!EXAM!

SerousSerous

These secrete These secrete enzyme-rich enzyme-rich products as in the products as in the pancreas or pancreas or salivary glands. salivary glands. Usually the Usually the secretion is watery. secretion is watery.

These cells secrete These cells secrete a carbohydrate-a carbohydrate-rich, viscous rich, viscous secretion.secretion.

Glands found in the Glands found in the soft palate and soft palate and esophagus are esophagus are examples.examples.