Epithelial tissue

What are the key characteristics of epithelial tissue?

High cellularity, little extracellular material, specialized cell junctions, polarity, avascularity, ability to regenerate, and supported by connective tissue.

What is simple squamous epithelium and its function?

single flat layer; rapid passive diffusion; lines air sacs, blood vessel interiors, and ventral cavities.

Where is simple cuboidal epithelium found and what does it do?

Kidney tubules, glands; secretion and absorption.

What is simple columnar epithelium?

One tall cell layer; secretion and absorption; ciliated version lines uterine tubes.

Characteristics of pseudostratified columnar epithelium?

Appears multilayered but is single-layered; has tall + short cells; ciliated in respiratory tract.

Stratified cuboidal/columnar epithelium is found where?

Large ducts of some glands; relatively rare.

What is a gland?

One or more cells specialized to secrete a product.

How do endocrine glands secrete?

Ductless; release hormones into blood.

How do exocrine glands secrete?

Via ducts to body surfaces or cavities; includes unicellular (goblet cells) and multicellular types.

Examples of exocrine gland shapes?

Tubular, alveolar (acinar), tubuloalveolar.

What is the basal lamina?

Thin protein sheet under epithelium; acts as filter & scaffolding; part of basement membrane.

What are microvilli?

Projections that increase surface area; anchor mucus sheets.

What are cilia?

Whiplike projections that move substances; driven by microtubules.

What is the primary function of tight junctions?

To seal adjacent cells together, preventing molecules from passing between them (controls paracellular transport).

What is the function of adherens junctions (adhesive belt junctions)?

To anchor cells together using actin filaments; help resist separation during stretching.

Where are adherens junctions especially important?

n tissues subject to mechanical stress, like the intestines.

What is the main function of desmosomes?

Strong "spot weld" attachments that anchor cells and prevent tearing.

Where are tight junctions commonly found?

In epithelia that form barriers—e.g., intestines, blood–brain barrier.

Where are desmosomes found?

Skin (epidermis), heart muscle—anywhere strong mechanical stability is needed.

What is the function of gap junctions?

Allow ion and small molecule passage between cells for communication.

Where are gap junctions especially important?

Cardiac muscle & smooth muscle—for synchronous contraction.