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 glands.

What is the basic concept of epithelium?

Epithelium forms a solid tissue structure that separates a space from underlying tissue, acting 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 the epithelial layer.

What are the descriptive terms for epithelial cell surfaces?

Basolateral (adjacent to basement membrane) and apical (farthest from basement membrane).

How is epithelium classified?

Based on the number of 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 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 superficial cells in epithelial classification?

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 types cover organs or line tubular structures.

What are the two types of glands based on secretion?

Endocrine (secretes directly into the bloodstream) and exocrine (secretes into a duct).

What are the mechanisms of secretion in exocrine glands?

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

What are microvilli and their function?

Microvilli are cell surface modifications that increase surface area, primarily seen in organs like the small intestine and kidney.

What are cilia and their role?

Cilia are projections on the apical surface of epithelial cells that beat in a coordinated fashion to assist in moving material over the surface.

What are tight junctions?

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

What are desmosomes and hemidesmosomes?

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 can be continuous or discontinuous, allowing permeability for molecule passage.

What is mesothelium?

Mesothelium is the term for simple squamous epithelium that covers internal organs.

What is endothelium?

Endothelium is simple squamous epithelium lining the inside of blood vessels.

What is simple cuboidal epithelium?

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

What characterizes simple columnar epithelium?

Epithelium where length is greater than width, 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, with absorptive or secretory functions.

What is stratified squamous epithelium?

Epithelium arranged in layers, with superficial cells being squamous; suited for protection from abrasion.

What is cornification in stratified squamous epithelium?

Cornification is the process where cells in the upper layer 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 only in the urinary tract.