Glands and Secretions Flashcards
Secretions
- Mucous - protects, lubricates, and moistens; composed of mucins (heavily glycosolated proteins), inorganic salts, and water
- Enzymes - carry out digestion and other functions
- Hormones and other intercellular signals - control and coordinate functions of other cells
- Saline solutions - moisten (e.g. tears) and cool (e.g. sweat)
- Metabolic waste products (e.g. sweat)
- Bile - aids digestion of fats
Types of Glands
- Exocrine
a. Unicellular - secrete directly onto a surface; ductless
b. Multicellular - secrete into a duct - Endocrine - secrete into circulatory system; ductless
- Paracrine - secrete directly into surrounding extracellular fluid
Origin of Glands
Glands develop from epithelial sheets during embryonic development:
Exocrine Glands:
- Arise as invagination of epithelial layer
- Remain attached to epithelial layer
- Differentiate into two types of cells:
- Distal - secretory cells
- Proximal - duct cells
Endocrine Glands:
- Arise as invagination of epithelial layer
- Lose attachment with cell layer of origin
- Differentiate into secretory cells and become associated with capillaries
Unicellular Exocrine Glands
Simplest glands consisting of single cells that secrete products onto an epithelial surface
Two types:
- Goblet Cells - Mucous secreting cells found in epithelial lining of intestings and respiratory tract
- Mucous Surface Cells - mucous secreting cells that line interior surface of stomach
Mixed Endocrine-Exocrine Glands
Hepatocyte
- Secrete albumin into blood (endocrine)
- Secrete bile into bile duct (exocrine)
Pancreas
- Islet of Langerhans cells secrete insulin, glucagon, and other hormones (endocrine)
- Serous acinar cells secrete digestive enzymes (exocrine)
Structure of Endocrine Glands
Connective tissue capsule of varying thickness surrounding gland with trabeculae connective tissue partitions subdividing gland into lobes and lobules
Blood vessels enter gland via trabeculae and form branching, anastomosing capillary networks associated with secretory cells
Lightly stained, polygonal secretory cells; exhibit various forms of organization (straight/irregular cords, small clumps, follicles)
Classification of Multicellular Exocrine Glands
- Basis of Duct
- Simple gland - unbranched duct
- Compound gland - branched duct
- Morphology of Secretory Unit
- Tubular
- Alveolar/Acinar
- Mixed/Tubuloaveolar/Tubuloacinar
- Type of Secretion
- Serous
- Mucous
- Mixed/Seromucous
- Mode of Secretion
- Merocrine
- Holocrine
- Apocrine
Stroma of Multicellular Exocrine Glands
Stroma = connective tissue portion of exocrine gland
Connective tissue capsule covering gland with connective tissue partitions (septa) [interlobar and interlobular septa] that divide gland into lobes and lobules and carry blood vessels, lymphatic vessels, and nerves into gland
Secretory Units of Multicellular Exocrine Glands
Composed of secretory cells and supporting cells located in distal part of gland.
Serous, mucous or mucous with serous demilunes
Myoepithelial cell basket contains group of epithelial cells within basement membrane of secretory unit modified to contract to force secretions into duct
Ducts of Multicellular Exocrine Glands
Passageway through which secretory products pass to reach epithelial surface; composed of non-secretory cells
Types:
Intralobular - located within lobules of gland
- Intercalated duct - initial part of duct located within secretory unit; composed of simple cuboidal cells
- Intralobular duct - located within secretory unit; composed of simple cuboidal or columnar cells (striated [basal mitochondria] or non-striated)
Interlobular - located between lobes; excretory duct; composed of simple of stratified columnar epithelium
Glands/Secretion - General
Composed of epithelial cells specialized for producing secretions
Secretory products released into free space or surrounding extracellular space where they enter vessels of vascular system or diffuse through tissue fluid to nearby cells
Modes of secretion
- Constitutive - continually
- Regulated - stored until signal causes release
Mode of Secretion
- Merocrine - most common; secretory vesicles merge with plasma membrane to release products (e.g. sweat glands)
- Apocrine - secretory product released by pinching off of apical portion of cell (e.g. mammary gland cells)
- Holocrine - secretory products released when cell dies and lyses (e.g. sebaceous glands)
Morphology of Secretory Unit
- Tubular (test-tube shaped)
- Simple straight tubular (e.g. intestinal gland of colon)
- Simple coiled tubular (e.g. eccrine sweat gland)
- Simple branched tubular (e.g. fundic glands of stomach)
- Alveolar/Acinar (round-bottom flask shaped)
- Simble branched acinar (e.g. cardiac glands of stomach)
- Compound acinar (e.g. exocrine pancreas)
- Mixed/Tubuloalveolar/Tubulopacinar (e.g. submandibular)
Serous Glands
Produce watery secretions containing proteins
Basophilic cytoplasm due to large amounts of rough ER
Rounded, centrally/basally located nucleus
Apical cytoplasm may contain acidphilic secretory granules
Mucous Glands
Produce mucuous (mucins, inorganic salts, and water) which forms protective barrier, provides lubrication, and moisturizes
Cytoplasm relatively unstained in H&E, with flattened and basally located nuclei
Cytoplasm PAS positive because of mucous
e.g. labial mucous glands of lip
Mixed/Seromucous
Mucous secretory cells form central part of alveolus with serous demilune (crescent moon shaped) cap
E.g. submandibular gland
