Lecture 4 - Epithelial Tissue

What is the overall function of epithelial tissue?

to cover and protect body surfaces/cavities and form boundaries between different environments

• covering and lining epithelia: located on external and internal surfaces

  • ex: skin

• glandular epithelia located in secretory tissue in glands

  • ex: salivary glands

Polarity of epithelial tissue

• epithelial cells have a “distinct” top & bottom meaning they have opposite charges

• Top Surface - Apical (faces the surface/outward) **have cilia or microvilli

• Bottom Surface - Basal (faces inward/touches what is being protected)

  • attaches to basal lamina

What specialized contact points join epithelial cells?

Tight junctions and desmosomes

What is the relationship between epithelial tissue and connective tissue?

Connective tissue called the basement membrane sits below epithelial tissue and supports it

*think of as double sided tape that makes sure the epithelial tissue sticks to what it is protecting

• is made up of basal and reticular lamina

• resists stretching & tearing

• defines epithelial boundary

Does epithelial tissue have blood vessels?

No

How does epithelial tissue get nourishment of minerals if it is avascular?

Diffusion from blood vessels in the underlying connective tissues

Regenerative Property of Epithelial Tissue

top cells that undergo damage are replaced very quickly due to the high regenerative capacity of epithelial cells

Simple epithelial tissue

One layer

Function of ALL forms: absorption, secretion, filtration

Stratified epithelial tissue

multiple layers (2+)

named according to the shape of the top (apical) layer

Function: protection (they’re very durable, think skin)

Squamous epithelial tissue

flattened, scale like

“squashed” = squamous

Cuboidal epithelial tissue

box-like, cube shaped

“cube” = cuboidal

Columnar epithelial tissue

tall, column-like

Where is simple squamous epithelium located?

Lining of lymphatic vessels, blood vessels, and the heart (Endothelium)

Serous membranes in the ventral body cavity (Mesothelium)

• the lining of all internal organs

• secretes a substance that is very slippery so holes don’t form when organs rub against one another

Where is simple cuboidal epithelium located?

Walls of smallest ducts of glands and kidney tubules

Where is simple columnar epithelium located?

In respiratory tract (specifically bronchi) = have cilia

In GI tract (specifically small intestine) = microvilli

• think gut = microbiome = microvilli

Some layers contain interspersed goblet cells that secrete mucus

What is Pseudo-Stratified columnar epithelium?

• column shaped cells that LOOK like multiple layers but are really only one (name means fake-stratified)

  • can tell bc nuclei are all in different positions

• are ciliated —> helps move mucus up the respiratory tract

Where is stratified squamous epithelium located?

skin (and other areas with high wear and tear)

most widespread type of stratified epithelia

What is transitional stratified epithelium?

Epithelium cells that have the ability to change shape when stretched

• found in the bladder, uterus, and urethra

  • stretch for increased flow of urine (urethra)/more storage space (bladder)

What is Glandular epithelia?

cells that make and secrete aqueous fluid

• can be unicellular (goblet) or formed by multiple cells (salivary)

What do endocrine glands release and where?

hormones into the bloodstream/lymph

• via exocytosis (active transport!!)

• don’t have ducts

Where do exocrine glands release?

onto the surface of an organ

• secrete products into ducts which then push it outwards onto body surface

• ex: sweat onto skin’s surface

• ex: cells in pancreas secrete pancreatic juices containing enzymes that enter a duct

• Unicellular: goblet cells and mucous cells (respiratory and GI tracts)

• Multicellular: picture attached

Merocrine mode of secretion of exocrine glands

products secreted by exocytosis as they are produced

• sweat, pancreas, salivary

Holocrine mode of secretion of exocrine glands

products build up within the cell and then it ruptures

• sebaceous oil glands