Epithelia

1.Cell: the basic structure of human cell

2.Tissue: consists of cells and intercellular substance

3.Organ: consists of different tissues which have

related function 4.System: consists of different organs which have related function

Human organization

HumanTissues

Epithelia

Connective tissue

Muscle Tissue

Nervous tissue

一、 General characteristics and classification of epithelia

（一） General characteristics of epithelia

1. cells arranged intensively;small quantity of intercellular substance. 2. cells have polarity.

3. no blood vessels.

4. Function: ： Protection, secretion, and absorption,etc.

（二） Classification of Epithelia

Epithelia mainly classified into 2 sorts:

Covering epithelia ： Cells arranged like membrane

Localization: covering the outer surface of the body and the inner

surface of the cavities ,Sacs or ducts within the body.

Function: Protection.

Glandular epithelia ： Function- Secretion

二、 covering epithelia

Principles of the classification ：

Layers of the cells ： simple epithelia stratified epithelia

Shape of the cells ： Squamous epithelia Cuboidal epithelia Columnar epithelia

Simple squamous epithelia Simple cuboidal epithelia Simple columnar epithelia

Stratified squamous epithelia Transitional epitheliaPseudostratified ciliated columnar epithelia

1. simple squamous epithelia

Description: Single layer of flat cells with disc- shaped central nuclei.Top view: Polygonal, central nucleiSide view: Squamous, central nuclei

Function: Allows passage of material by diffusion & filtration and reduces friction by providing a smooth surface & secreting lubricating serous fluid.

Simple

squamous epithelia

endothelium : heart, blood vessles lymphatics

mesothelium : Pericardium, pleura peritoneum

others ： alveoli of the lungs, glomeruli in the kidney, etc

Localization

simple squamous epithelium

(1) endothelium

endothelium

(2) mesothelium

(3) others

2. simple cuboidal epithelium

Description: Single layer of cubelike cells with large, spherical central nuclei.

Function: Function in secretion and absorption.

Locations: (1) In the secretory portions of many glands : thyroid, mammary, and salivary. (2) In the kidney tubules

simple cuboidal epithelium

simple cuboidal epithelium

simple cuboidal epithelium

3. simple columnar epithelium

Description: Single layer of columnar cells with oval nuclei ; often have an apical border of microvilli; Many contain goblet cells (mucus-secreting unicellular glands).

Function: absorption of nutrients; secretion of mucus & enzymes.

Locations: digestive tract,etc.

simple columnar epithelium

simple columnar epithelium

simple columnar epithelium

4. pseudostratified ciliated columnar epithelium

Description: single layer of cells of differing heights, but some don't reach the free surface. Nuclei are seen at many different levels. They contain goblet cells and cilia.

Function: secretion & propulsion of mucus

Locations: l the trachea & most of the upper respiratory tract.

pseudostratified ciliated columnar epithelium

pseudostratified ciliated columnar epithelium

pseudostratified ciliated columnar epithelium

5. stratified squamous epithelium

Description: multiple layers of cells. Surface cells are flattened. Basal cells: cuboidal or columnar; active in mitosis and produce the cells of the more superficial layers.

Function: resists abrasion and acts as a barrier, Retards water loss through skin.

Locations: skin, mouth, vagina, esophagus ， etc.

Stratified

Squamous

epithelium

keratinized stratified squamous epithelium: skin Surface is covered with layers of compact dead cells without nuclei (and full of keratin)

nonkeratinized stratified squamous epithelium:esophagus,oral cavity

stratified squamous epithelium

keratinized stratified squamous epithelium

nonkeratinized stratified squamous epithelium

7. transitional epithelium

Description: multiple layers of cells. Surface cells are dome-shaped. Middle layers: cells are polyhedral Basal cells: cuboidal or columnar.

Locations: renal pelvis and calyces,the ureter, the urinary bladder ,etc.

transitional epithelium

transitional epithelium

transitional epithelium

6.stratified columnar

epithelium

（一） surface of epithelia

1. microvillus 2. cilium

三、 special structure of each side

1.Microvillus function ： enlarge the area of the surface

2.Cilium Function ： regularly swing

1. tight junction

2. intermediate junction

3. desmosome

4. gap junction

（二） side face of epithelia

（三 ) Underside of the

epithelia

1. basement membrane

2. plasma membrane infolding

3. hemidesmosome

1.basement membrane Function:support,connect,etc.

2.plasma membrane infolding function ： enlarge the area of the

underside

3.Hemidesmosome Function:fixing