Lecture 2 Epithelial cells and Junctions

What are the 7 characteristics of Epithelial Tissue? Ce Po Su Av Re In Se

1. Cellularity: Composed almost entirely of cells.

2. Polarity: Has an apical and basal surface.

3. Supporting Connective Tissue: Basal surface attached to a basement membrane.

4. Avascularity: Lacks blood vessels.

5. Regeneration: High regenerative capacity.

6. Innervation: Contains nerve endings.

7. Secretion: Can perform secretion and absorption functions.

What is epithelial tissue?

Epithelial tissue is a type of tissue that lines the surfaces of organs and structures throughout the body. It functions mainly in protection, absorption, secretion, and sensation. (Anything you can touch)

What are the three specialized contacts of epithelial cells? T D G

Tight junctions, desmosomes, and gap junctions.

What are tight junctions?

Tight junctions are specialized connections between adjacent epithelial cells or endothelial cells that prevent the passage of materials between them, effectively sealing the spaces to maintain the integrity of the epithelial barrier. (Seal)

What are Desmosomes?

Desmosomes are anchoring junction that bind adjacent cells together and help form an internal tension-reducing network of fibers.

Desmosomes are specialized cell structures that act as strong "spot welds" between cells tissues to withstand stretching and bending.

What are gap junctions?

Gap junctions are specialized intercellular connections that allow direct communication between adjacent cells by permitting the passage of ions and small molecules from one cell to the next.

How are epithelial cells Classified?

Cell Shape and layers

What are the classifications of the cell layer? (just names)

Simple: One Layer

Stratified: 2 or more

Pseudostratified: Appears stratified (lies) due to differing height of cells (only happens to columnar)

Transitional: Stratified, multiple layers

What are the classifications of the cell shape? (just names)

Squamous: flat thing scale-like cells

Cuboidal: cube shaped

Columnar: tall rectangular cells

Where is the Simple Squamous found?

• The alveoli (air sacs) of the lungs, for gas exchange.

• The lining of blood vessels and lymphatic vessels (called endothelium).

• The lining of serous membranes in body cavities (such as the pleura in the lungs, pericardium around the heart, and peritoneum in the abdomen), which is known as mesothelium.

• The glomeruli of the kidneys, where it participates in filtration.

What is the function of the Simple Squamous?

Allows passage of Materials by diffusion and filtration in sites where protection is not important; produces lubricating fluid in serosae

What is the location of simple cuboidal epithelial cells?

Kidney tubules (tiny tubes in the kidneys that returns nutrients, fluids, and others in to the blood)

Ducts and secretory portions of small glands; ovary surfaces.

What is the function of Psuedostratified columnar epithelium.

Secretion, particularly mucus, propulsion of mucus by ciliary action (respiratory system, like the hairs in your nose catching dust particles, basically snot.)

Notice the fuzzy hair on the image, literally the hair that would be in your nose. hair=cillia

Location of Psuedostratified columnar epithelium.

Nonciliated version (non hair) in male’s sperm carrying duct (dih)

And ducts of large glands

Ciliated variety lines of trachea (windpipe), most upper respiratory tract

Function of Simple Columnar Epithelium

Absorption (for nutrients);

secretion of mucus, (goblet cells used to protect stomach inside from the digestive acids)

enzymes (in stomach), and other substances

ciliated type propels mucus (or reproductive cells dih) by ciliary action

Location of Simple Columnar Epithelium

Nonciliated type lines most of the digestive tract (stomach to rectum)

Gallbladder

Excretory ducts of some glands

;cillated variety lines

small bronchi (lung airway)

uterine tubes, and some other uterus regions

Function of transitional epithelium

• Stretching & recoiling: Surface cells change shape (dome-shaped → flat) when the organ fills.

• Barrier: Prevents urine (which is chemically harsh) from leaking into underlying tissues.

• Protection: Multiple layers of cells protect against mechanical stress from expansion.

The skin can stretch, but thats because of elastic fibers.

Things that are made to stretch alot, like an erection are made of transitional epithelium

Location of transitional epithelium

• Urinary bladder ✅ main site

• Ureters

• Proximal part of the urethra

What does stratified mean?

Multiple layers of cells (heavy armor piercing)

Function of stratified squamous epithelium is to…

Protection against:

• Mechanical abrasion (friction, scraping)

• Chemical damage

• Pathogens (microbes)

Location of stratified squamous epithelium cells

Everywhere on the surface of your skin.

Skin, oral cavity (lining of the mouth, tongue, and everything exposed)

Esophagus (lining of digestive tract) (connects throat to stomach)

Vagina

Cornea eye to keep moist

What happens when squamous epithelium cells keratinize?

Adds water proofing and extra toughness

(It’s the white part that comes when you scratch your skin)

(keratinized cells are dead cells filled with keratin)

Difference between Stratified and transitional

Stratified is made for strength (durability)

Transitional is made for mobility (stretch)

Both are layered

Stratified WILL have keratinization at the top, looks like uneven waves… if its keratinized

• Stratified squamous = stack of pancakes → always flat on top

• Transitional = balloons → dome-shaped at rest, can stretch and flatten

Function of Stratified cuboidal epithelium (rare)

protection:many layers of girth

secretion: in glands, mostly for sweat or other secretions

Location of Function of Stratified cuboidal epithelium (rare)

sweat glands (sweat)

mammary glands (breasts, used for milk)

salivary glands (produces saliva, oral)

Function of stratified columnar (rare)

Protection (anti tank)

secretion: in glands or ducts

• Its main function is to protect and potentially secrete or absorb substances. 

Location of stratified columnar (rare)

primarily found lining the larger excretory ducts of certain glands like the salivary glands and pancreas, as well as in the conjunctiva of the eye, parts of the pharynx, anus, male urethra, and vas deferens. Large ducts of some glands

• Male urethra

• Conjunctiva of the eye (partially)