Glandular Epithelium• Glandular Epithelium: epithelium of cells specialized to produce secretion. All glands are of composed of epithelium.• Secretion – Exocytotic release of products, not metabolic wastes• Molecules to be secreted may be stored in membrane bound secretory granules (vesicles)
Gland CategoriesA) Presence or absence of ducts • Exocrine – ducted • Endocrine - ductlessB) Uni- or multicellularC) Mode of secretionD) Secretion products
Gland Categories1) Exocrine - glands that exude secretions into a ductule system. Have two parts, acinous = secretory bulb and ductule.2) Endocrine - glands exuding secretions directly into body fluids, ultimately blood.3) Mixed - glands combining both the above characteristics (e.g. liver) in the same cell4) Paracrine - tissue secretions affecting own cells
Cellular Composition1) Unicellular - single cell gland, Goblet cell; mucous secreting. GI tract, respiratory ducts. Secretion process alters cell and nucleus shape.2) Multicellular - a) intra epithelial gland - gland is entirely within a layer of epithelium. Common in pseudostratified columnar epith. b) extra epithelial gland - in CT below epithelium; may have different shapes; tubular and saccular (acinar).
Modes of Secretion (how products leave the cell)1) merocrine - secretion does not affect the well-being of the cell = sweat glands.2) apocrine - small part of the cell cytoplasm is lost with the secretion; the cell is damaged but not killed = mammary glands.3) holocrine - great deal of cytoplasm is lost with the secretion; the cell dies. Sebaceous glands.
Myoepithelium• Myoepithelium - specialized squamous epithelial cells with powers of contraction;• Surround glandular acini and ducts of many glands,• Contain actin, myosin, cytotokeratin = definitely epithelial in origin, not muscle.
Diffuse Neuroendocrine System (DNES)• Paracrine secretion of norepinephrine or serotonin in non-endocrine tissue• Derived from Neural Crest Cells• About 35 types of cells in a variety of tissues such as respiratory, urinary, gastrointestinal, pituitary, thyroid• System formerly known as APUD cells – Amine Precursor Uptake Decarboxylation
Secretory Membranes• Similar names of secretion products; names based upon type of secretions; form organs (peritonea, gut tube lining, etc.) 1) Serous Membrane - thin, flat layer of squamous epithelial cells which is moistened by exudates from underlying blood vessels. 2) Mucous Membrane - moist epithelial surface, usually columnar, but may be cuboidal or squamous, that is moistened by secretions produced by glands formed by the epithelium itself.