Epithelial Cells

Function of Epithelial Cells (5)

protection, sensory reception, secretion, absorption, ion transport

Special Characteristics of Epithelial Cells (6)

cellularity, specialized contacts, polarity, support, avascular, regeneration

What is special about epithelial cellularity?

densly packed with little extracellular materials.

Example of epithelial specialized contact

cell junction

What is special about Epithelial Polarity?

apical and basal regions exist and differ in structure and function

What is the epithelial supported by?

underlying connective tissue

What does avascular but innovative mean?

lacks blood vessels, but has nerve endings to sense stimuli like pain or touch

How do epithelial cells regenerate?

because of high mitotic rates and presence of mesenchymal (stem) cells

What are the general surface features of epithelium tissue?

apical, lateral, basal

What are the apical surface features of epithelium?

microvilli, stereocilia, cilia

What is the function of microvilli in epithelium?

increase surface area; may anchor sheets of mucus

What are stereocilia in epithelium?

very long microvilli that cannot move.

What do Cilia do in epithelium

move fluid, usually mucus

What are the lateral surface features of epithelium?

Cell Junctions

What do cell junctions do?

form bonds with other cells or extracellular material

Examples of epithelium cell junctions

desmosomes, tight junction, gap junction

What are Basal Surface Features in Epithelium

Basal lamina, basement membrane

Basal Lamina function

sheet of proteins that acts as a filter and as a scaffolding on which regenerating epithelial cells grow.

What are basement membranes formed by?

formed by basal lamina plus some underlying reticular fibers.

Simple epithelial

one layer of cells

Stratified epithelial

2 or more layers of cells.

What is used to classify stratified cells?

The superficial or apical layer

Pseudostratified with cilia

simple epithelium that contains both short and tall cells; classification used mainly in one type (pseudostratified columnar)

Squamous cells

flattened cytoplasm and nucleus

Cuboidal cells

Cube-shaped with spherical nucleus

Columnar cells

tall, column-shaped cells with elongated nuclei placed closer to the base of the cells

transitional epithelia

stratified that stretches and changes shape due to expansion of cells lumens (open spaces)

what does Simple Squamous Epithelium form?

the endothelium of blood vessels and the mesothelium of the ventral body cavity

what does simple squamous epithelium line?

alveoli in lungs

how do molecules diffuse in simple squamous epithelium

rapidly (passive) through delicate and thin later of flat cells of this epithelium.

function of stratified squamous epithelium

protects underlying tissues in areas subjected to abrasion

what do keratinized stratified squamous types form?

epidermis of the skin

what do non keratinized stratified squamous form

moist linings of the esophagus, mouth, and vagina.

function of simple cuboidal epithelium

secretion and absorption

where do simple cuboidal epithelium occur?

in kidney tubules and in ducts and portions of small glands.

what is the function of stratified cuboidal epithelium?

protection

where do stratified cuboidal epithelium occur?

largest ducts of sweat glands, mammary glands, and salivary glands

function of simple columnar epithelium?

absorption, secretion, and ion transport

what does ciliated type simple columnar line?

small bronchi, uterine tubes, and some regions of the uterus

What does non ciliated type simple columnar line?

the stomach and intestines, gallbladder, and excretory ducts of some glands

what is the function of stratified columnar epithelium?

protection and secretion

where does stratified columnar epithelium occur?

small amnts occur in male urethra and in large ducts of some glands (rare type)

what is the function of pseudostratified (ciliated) columnar epithelium?

secretion (especially mucus) and propulsion of mucus by ciliary action

where does ciliated pseudostratified columnar epithelium line?

trachea and most of upper respiratory tract

where does non-ciliated pseudostratified columnar epithelium line?

sperm carrying ducts and ducts of large glands

what does transitional epithelium line?

ureters, bladder, and part of urethra

what does transitional epithelium do?

stretches readily and permits distension of urinary organ by contained urine

glands

many epithelial cells make and secrete a product (aqueous fluid containing proteins usually)

exocrine glands

secrete their product onto body surfaces (skin) or into body cavities

What do exocrine glands contain?

ducts that carry secreted products to epithelial surface

serous glands

produce watery solution that usually contains enzymes

mucous glands

produce viscous, sticky mucus

mixed glands

Contain both serous and mucous cell types and produce a mixture of the two types of secretions

unicellular glands (goblet cells)

individual secretory cells that occur in epithelia containing scattered gland cells

multicellular glands

composed of many cells that form a distinctive microscopic structure or macroscopic organ

How are multicellular glands classified?

ducts (simple or compound) and by the structure of their secretory units (tubular, alveolar or acinar, or tubuloalveolar)

What are the different mechanisms of secretion?

merocrine (eccorine), apocrine, holocrine

apocrine secretion

a portion of the secreting cell's body is lost during secretion

holocrine secretion

the entire cell disintegrates to secrete its substances

example of apocrine secretion

lactiferous glands in the breast

example of holocrine secretion

sebaceous glands

merocrine secretion

aka eccrine; cells secrete their substances by exocytosis

example of merocrine secretion

mucous and serous glands

endocrine glands

ductless and secrete product (typ hormones) directly into the bloodstream