Glandular Epithelium Overview

Glandular Epithelium

• 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.

Gland Structure

• 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).

Classification of Epithelia

• 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

• 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.

Specific Gland Examples

• 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.