Secretory epithelia (exocrine) Flashcards
Compare and contrast endocrine vs exocrine glands
SIMILARITIES: (2)
-both are made of secretory ET tissue and hence are apposed
-both produce secretory products such as hormones
DIFFERENCES: (5)
-exo release products onto the surface, endo release it into the bloodstream
-exo have ducts, endo are ductless
-morphological differences: exo have a secretory unit and a duct, and endo are secretory bodies surrounded by capilaries
-exo is connected to epithelial layer whereas endo is free in the tissue
-differences in origin: exo originate from localised proliferation of ET which causes downward growth, and endo originates from stalk particle connection which is then severed.
Ways in which exocrine glands are classified (6)
- Number of cells: multicellular or unicellular
- Site (intra/extramural)
- Morphology of terminal secretory unit: acinar, tubular, alveolar
- Branching of unit or duct: simple, branched, compound
- Mode of secretion: merocrine, holocrine, apocrine
- Nature of secretion
(only for merocrine glands): serous, mucous, mixed
unicellular exocrine glands examples
ONLY goblet cells
Goblet cells morphology and function
-intercalated between lining epithelial cells
-produce mucus (which is made up of mucinogen and water) to prevent dehydration
2 regions of cell
1. Stem: containing nucleus and other organelles (very abundant golgi and RER since they produce secretory proteins)
2. Theca: contains mucinogen granules made of glycoproteins
!! located in trachea and small intestine lining
Morphology of multicellular exocrine glands:
contain 2 portions:
1. Secretory unit: cells on the lower part of the gland which produce and secrete product
- Duct: connected to secretory unit and is a passage for the secretions to pass into lumen
SITE: classifications of exocrine glands
- INTRAMURAL: located in one of the walls forming the organ.
Intraepithelial: contained in the ET of the organ
Extraepithelial: contained in the underlying CT of the organ - EXTRAMURAL: where the duct of the gland is located externally to the holow organ
MORPHOLOGY of terminal units:classifications of exocrine glands
- Acinar: rounded with a small lumen and pyramidal cells that have a rounded nucleus
- Tubular: larger lumen, circular in cross section adn tubular in longitudinal section. Nuclei are not as rounded as acinar
- Alveolar: irregular patetrn and cell shape, much larger lumen
!!! appearance depends on the plane in whcih they are cut
BRANCHING: classifications of exocrine glands
- Simple: a single secretory unit is connected to ET by a non branched duct
- Branched: multiple secretory units converse into a single duct
- Compound: duct is branched and opens up to secretory units
!! SOS: extra mural glands are always compound, and if interlobular ducts are present, the gland is automatically compound
MODE OF SECRETION: classifications of exocrine glands
- Merocrine: release via exocytosis. Vesicles fuse with plasma membrane and products are tranported in the lumen of secretory unit – cell does not undergo morphological changes
- Apocrine: cell apical cytoplasm is pinched off forming vesicles that contain the secretory product. Morphology changes depending on stage of secretion: decrease in cell size after the cytoplasmic loss, and budding shape during the formation of the vesicles
- Holocrine: dettachment of cells containing secretory product from the basement membrane, passage into duct lumen, and breakdown of cells to release it. !! needs stem cells so that cells lost can be replenished. No evident cavity/lumen because it contains cells becoming part of secretory product.
!! typical of sebaceous gland
NATURE OF SECRETION: classifications of exocrine glands
!! ONLY FOR MEROCRINE
- Serous: contains acinar secretory units, and secretion is fluid/watery.
!! evident rounded nucleus and intense stain due to granules containing SP. Lumen is not very wide because the secretion is fluid and rapid flowing - Mucous: tubular secretory units, wide lumen, secrete viscous mucous made of glycoproteins. PALE. !!! flattened nuclei bcos the cytoplasm is mainly taken up by the secretion granules that push the nucleus to the side
- Mixed: Tubuloacinar: contain both serous and mucous subunits and hence secrete both. Upper part is tubular and lower part is acinar. Acinar portion is intensely stained and is called GIANNUZZI DEMILUNE.
Myoepithelial cells location and function
-cells present externally to secretory cells
-flattened squamous epithelial cells that possess cytoskeletal mechanisms to allow for contraction (without being actual muscle cells)
-contraction of these cells helps squeeze secretory product out of the units
Morphology of extramural ducts
-usually larger, parenchymal organs
-groups of secretory units arranged in lobules which are separated by CT
-INTERLOBULAR ducts: extend into CT between the lobules, make compound glands, are surrounded by a lot of CT and have multiple layers of epithelial cells (pseudostratified columnar)
INTRALOBULAR ducts: immersed inbetween many secretory units so they are not surrounded by extensive CT, one layer of epithelial cells (simple cuboidal)
INTERCALATED ducts: connected with secretory units and lined by low cuboidal epithelium
General organisation of extramural ducts from larger to smaller
-main duct
-lobar duct
-interlobular duct
-intralobular duct
-striated duct
-intercalated duct
-acinus
Main characteristic that allows the distinction of striated ducts
-invaginations forming the basal labyrinth on the basal membrane of ducts
-appears as red/white striations under H&E
-lined by simple columnar epithelium
-contains many mitochondria
!! located in parotid and salivary glands (where they modify the contents and hence the fluidity of saliva)
Special cell type present in the pancreatic ducts
CENTROACINAR CELLS: present inside the lumen of the acinar secretory units
-help in the secretio of bicarabonate
!! pancreas has a high abundance of intercalated ducts
