Glandular Epithelium Overview

Study Notes

Epithelial tissue includes epithelia and glands
Epithelia line surfaces and cavities, often with secretory cells.
Glands are derived from epithelia, predominantly secretory cells.
Two types of glands: exocrine and endocrine.
Exocrine glands secrete onto external surfaces or into ducts leading to the exterior.
Endocrine glands secrete hormones or precursors into interstitial fluid, usually for distribution by bloodstream.
A gland can consist of one or more cells that make a secretion.
Secretion is the process where gland cells obtain needed substances from the blood and transform them chemically into a product discharged from the cell.
Secretions are usually water-based fluids containing proteins.
Glands are classified by where they release secretions: endocrine (internal) and exocrine (external).
Glands are also classified by number of cells: unicellular and multicellular.
Unicellular glands are scattered within epithelial sheets. An example of a unicellular gland is mucous (goblet) cells, found in intestinal linings.
Multicellular glands invaginate into the epithelial sheet and connective tissue.

Multicellular glands have a duct and a secretory portion.
The duct can either be simple or compound.
Simple ducts are undivided, compound ducts are divided.
The secretory portion's shape can be tubular (tube-shaped), alveolar or acinar (blind pockets).
The relationship between ducts and glandular areas can be branched (multiple secretory areas sharing a single duct).

Glandular epithelia include endocrine glands and exocrine glands.
Endocrine glands release hormones into interstitial fluid, no ducts.
Exocrine glands produce secretions onto epithelial surfaces or through ducts.
Exocrine glands are further classified into simple and compound.
Simple glands have a simple (undivided) duct with simple shapes for the secretory portion. Examples include simple tubular, simple coiled tubular, simple branched tubular, simple alveolar (acinar), simple branched alveolar.
Compound glands have a compound (divided) duct with more complex secretory portions. Examples include compound tubular, compound alveolar (acinar), compound tubuloalveolar.
The different types of glands have specific functions and locations in the body.

Multicellular exocrine glands are composed of an epithelium-derived duct that carries the secretion to a surface.
Secreting cells are surrounded by connective tissue which has blood and nerve fibres.
The connective tissue often forms a capsule and may divide the gland into lobes.

Simple straight tubular glands with goblet cells (colon): These create goblet (mucous) cells within the intestinal linings.
Simple branched tubular glands (stomach): Involved in mucus secretion in the stomach.
Simple coiled tubular glands (sweat glands): Produce sweat.
Simple branched acinar glands (sebaceous glands): Produce sebum (oil) for skin.
Compound tubular glands (salivary glands, mouth): Produce mucus.
Compound alveolar glands (mammary glands): Involved in milk production.
Compound tubuloalveolar glands (salivary glands, respiratory passages, pancreas): Multiple structures, complex secretions.
Pancreas (mixed gland): A mixed gland, producing both exocrine secretions and endocrine hormones. Has both acinar (exocrine) and Islets of Langerhans (endocrine).
Thyroid gland (endocrine gland): Produces hormones, has simple cuboidal epithelium with follicles, and colloid.