Histology of Epithelium: Types, Features, and Functions

What are the learning objectives of studying epithelium?

Classify types of epithelia, describe common features, discuss intercellular junctions, predict intracellular components based on function, and describe types and functions of glands.

What is the basic concept of epithelium?

Epithelium forms a solid tissue structure that separates spaces from underlying tissues and acts as a cover.

What are the common features of all epithelia?

Close apposition of cells, free surface adjacent to space, basal surface adjacent to connective tissue, and absence of blood vessels within epithelial layers.

What are the descriptive terms for epithelial cell surfaces?

Basilar or basolateral (adjacent to basement membrane) and apical (farthest from basement membrane).

How is epithelium classified?

By the number of cell layers, shape of cells at the free surface, function (glandular vs non-glandular), and surface modifications.

What characterizes stratified epithelia?

Stratified epithelia have two or more cell layers, with only basal cells contacting connective tissue.

What is pseudostratified epithelium?

Pseudostratified epithelium has nuclei arranged at different levels, giving a stratified appearance, but all cells contact the basal lamina.

What defines simple epithelia?

Simple epithelia consist of only one layer of cells.

What are the shapes of epithelial cells?

Cuboidal (equal height and width), columnar (taller than wide), transitional (capable of changing shape), and squamous (flattened).

What is the difference between glandular and non-glandular epithelium?

Glandular epithelium produces and secretes extracellular products, while non-glandular epithelium typically covers or lines structures without secretion.

What are the types of glandular epithelium?

Exocrine (secretes into ducts) and endocrine (secretes directly into the bloodstream).

What mechanisms do exocrine glands use for secretion?

Merocrine (exocytosis), holocrine (cell death releases contents), and apocrine (budding vesicles release).

What are the modifications to epithelium?

Microvilli, cilia, and cellular connections (tight junctions, desmosomes, hemidesmosomes, gap junctions).

What is the function of microvilli?

Microvilli increase surface area for absorption, commonly found in the small intestine and kidneys.

What is the function of cilia?

Cilia assist in the movement of materials over the epithelial surface.

What are tight junctions?

Tight junctions hold cells together and form a barrier between compartments.

What are desmosomes?

Desmosomes bind cells to each other, while hemidesmosomes bind cells to the basement membrane.

What is simple squamous epithelium?

A single layer of flat cells that allows the passage of molecules, important in blood vessels.

What are mesothelium and endothelium?

Mesothelium is the outer membrane covering internal organs, while endothelium lines the inside of blood vessels.

What is simple cuboidal epithelium?

A single layer of cuboidal cells that provides secretory and absorptive functions.

What characterizes simple columnar epithelium?

Cells are taller than wide, with nuclei at the base, often having modifications like cilia or microvilli.

What is pseudostratified columnar epithelium?

A single layer of cells with nuclei at different levels, giving a stratified appearance, attached to the basement membrane.

What is stratified squamous epithelium?

Epithelium arranged in layers, providing protection from abrasion, with superficial cells being flattened.

What is cornification?

The process where cells in the upper layer of stratified squamous epithelium lose their nuclei and organelles, forming a tough, waterproof barrier.

What is urothelium (transitional epithelium)?

A unique type of stratified epithelium that can change shape in response to stretching, found in the urinary tract.