Glandular Epithelium and Secretions Quiz

Study Notes

Objectives for the session include describing cell surface specializations, glandular epithelium classification, and its features.

Epithelial cells have modifications and specializations related to their functions.
These specializations occur on all surfaces (apical, lateral, and basal).

Microvilli: Small, finger-like projections from the cell surface into the lumen that increase the surface area for absorption.
Cilia: Long, motile, hair-like processes that propel mucus and other structures over the epithelium through rhythmic oscillations.
Flagella: Similar to cilia, but single and very long, found only in spermatozoa.
Cell coat (Glycocalyx): Glycoproteins attached to the external surface of the cell membrane, composed of carbohydrate chains attached to transmembrane proteins.

Occluding (tight) junctions: Located between adjacent plasma membranes, prevent membrane proteins and water-soluble molecules from passing between cells.
Adhering junctions: Located just below tight junctions, connect cell membranes and link cytoskeletons of both cells.
Desmosomes: Weld-like junctions that resist shearing forces. Intermediate filaments disperse shearing forces.
Gap junctions: Pores that connect adjacent cells, allowing the passage of ions, amino acids, and hormones between cells. These are present in epithelial, cardiac, and smooth muscle cells and neurons.

Glandular epithelia are specialized cells that produce secretions.
Secreted molecules are stored in small membrane-bound secretory granules.
Parenchyma includes secretory units and duct systems, while stroma is the connective tissue between the parenchyma.
Glandular epithelial cells can synthesize, store and secrete proteins (e.g., pancreas), lipids (e.g., adrenal glands), or complex carbohydrates and proteins (e.g., salivary glands). Mammary glands secrete all three substances.
Some glands have low synthesizing activity (e.g., sweat glands).

Classification can be based on the presence/absence of ducts (exocrine/endocrine/mixed), mode of secretion (holocrine, merocrine, apocrine), and number of cells (unicellular/multicellular).

Exocrine glands: Secrete substances through ducts to a particular place (e.g., salivary glands).
Endocrine glands: Secrete hormones directly into the bloodstream without ducts (e.g., thyroid gland).
Mixed glands: Possess both exocrine and endocrine functions (e.g., pancreas).

Holocrine glands: The whole cell is destroyed and detached to release secretions (e.g., sebaceous glands).
Merocrine glands: The cells remain intact and release secretions through exocytosis (e.g., salivary glands).
Apocrine glands: The apical part of the cell is detached with secretions (e.g., mammary glands).

Unicellular glands: Single-celled structures (e.g., goblet cells in respiratory and intestinal mucosa).
Multicellular glands: Multiple cells that secrete substances into a duct system (e.g., salivary glands).