#6 histology (epithelial tissue)

histology

study of tissues

4 major tissues in the body

1. epithelial

2. connective

3. muscle

4. nervous

three types of membrane junctions

1. tight junctions

2. desmosomes

3. gap junctions

tight junctions (what is it, what does it do)

• protein molecules in cell membrane fuse together

• serves to prevent substances from passing in between cells

• glued barrier

desmosomes (what is it, what does it do)

• loose attachments

• use linker proteins to join adjacent cells

• flexibility

gap junctions (what is it, what does it do)

• protein channels that connect adjacent cells

• allows: direct communication between cells, substances to pass between cells

• important in smooth muscle and cardiac muscle cells

• tunnels

where is epithelial tissue found?

all body surfaces and lines all the body cavities

does the epithelial tissue have blood vessels?

no.

• avascular (lacks blood vessels)

characteristics of cells that form epithelial tissue

• one free membrane

• sits on top of a basement membrane

how is epithelial tissue held together?

by tight junctions

how does epithelial tissue reproduce?

mitotic division

glands located in the epithelial tissue are formed from..

glandular epithelium

• eg. salivary glands

• major tissue of any gland is epithelial, subtype is glandular epithelium

how is epithelial tissue classified

cell layers and cell shape

simple epithelium

• single cell layer with one free surface

• sits on top of basement membrane

stratified epithelium

• several cell layers with one free surface

• basal / bottom layer sits atop a basement membrane

pseudostratified epithelium

• appears as more than one layer but all cells sit on top of basement membrane (single cell layer)

cuboidal cell shape

• cube shaped cells

• secretion and absorption

columnar cell shape

• column-shaped cells

• secretion and absorption

squamous cell shape

• irregularly shaped, scale-like

• on outer surfaces of the skin → resist abrasion (stretch)

• versatility to move

transitional cell shape

• stratified cell layer. appearance varies with stretching

• eg. cuboidal cells in the bladder appear columnar when the bladder is stretched

glandular epithelium

• epithelial tissue: glandular subtype

• adapted for secretion

• consists of exocrine and endocrine glands

exocrine glands

• secrete products onto a surface or into a cavity

• either single-celled or multi-cellular

single-celled exocrine glands

• secrete mucous (lubricant, protection) into a cavity

• in digestive, urinary, reproductive and respiratory tracts

• eg. goblet cells

multi-celular exocrine glands

• have ducts → passageways

• secretions enter ducts

• sudoriferous (sweat) glands

• sebaceous (sebum / oil) glands

• salivary glands

endocrine glands

• secretes hormones directly into blood

• ductless (fast delivery)

3 epithelial functions

1. protection

2. secretion

3. control of permeability

protection (epithelial function)

• stratified squamous epithelium

• skin provides a barrier that keeps microorganisms out of the body

secretion (epithelial function)

• glandular epithelium

• secretion of lubricants, sweat, etc

control of permeability (epithelial function)

• simple epithelium

• found at sites where exchange of material occurs

• eg. absorption of digested nutrients, kidney, intestine, capillaries