Histology 2 - Epithelia Exocrine Glands PDF

Glandular or secretory epithelia —> cells specialised to produce secretion Secretion —> release of substances through exocytosis —> NOT a waste product but a precious product Molecules to be secreted can be stored in vesicles and the secretion can be either continuous or regulated by a signal Exo...

Glandular or secretory epithelia —> cells specialised to produce secretion Secretion —> release of substances through exocytosis —> NOT a waste product but a precious product Molecules to be secreted can be stored in vesicles and the secretion can be either continuous or regulated by a signal Exocrine glands —> secrete their products into excretory ducts to deliver to a speci c place Endocrine glands —> the products are directly secreted in the blood (hormones) and then reach the targeted site thanks to speci c signals and receptors Origin of secretory epithelia —> exocrine and endocrine glands differentiate —> exocrine glands start developing from the upper portion of the epithelia cell and expand until the underlying connective tissue forming a duct. Endocrine glands start developing in the same way but then no excretory ducts are formed and instead the secretory portion gets surrounded by capillaries Classi cation of exocrine glands: Number of cells —> unicellular glands (goblet cells) and multicellular glands Site —> intramural cells (intraepithelia cells or close to epithelia) or extramural glands Shape of the terminal secretory unit (alveolar/acinular or tubular) Branching of the secretory unit and of the collecting ducts Mode of secretion (merocrine, apocrine and holocrine) Nature of secretion (what the product is) Unicellular exocrine gland —> goblet cell —> it is made of a tho mucous stem and of a theca and on top it might have microvilli. It can be tall. The nucleus is squeezed at the base of the cell because the cytoplasm is occupied by mucinogen droplets of the secreted product (mucus). It can be found in pseudostrati ed and simple epithelium (cuboidal or columnar). Goblet cells can be found in the small intestine and in the trachea Multicellular glands —> made of few aggregates or bigger glands —> 1. Sweat glands (in some portions of skin) and sebaceous glands (in the hair follicles), used for protection of the body 2. Intraepithelial glands in many organs (urinary tract, respiratory tract, uterus) 3. Pancreas, salivary glands and mammary glands  secretoryunit cross collectingduct SITE section Intramural glands —> within an epithelium Extramural glands —> they constitute a separate organ, they have secretory ducts too longitudinal section SHAPE Alveolar glands or acinus glands —> pretty round Tubular gland —> elongated ⬆ Both can have branching BRANCHING Shape of the secretory unit (simple or branched gland) Shape of the duct (simple or compound (more than one ducts) gland) Simple glands —> have one secretory unit connected to a non-branched secretory duct or directly to the surface Simple branched glands —> have two or more secretory glands connected to a non-branched secretory duct Compound glands —> more than one secretory unit connected to a branched secretory duct MODE OF SECRETION Merocrine —> thin granules secreted —> cell remains intact Apocrine —> big portions of the membrane are pinched off and then go out —> cell remains intact Holocrine —> whole cell disintegrates to export the content —> cells are continuously replaced so the integrity is then restored NATURE OF SECRETION Serous —> watery uids (very well visible nucleus not very squeezed, mainly water and proteins) Mucous secretion —> viscous secretion (nucleus is elongated and squeezed because of the heavy mucin)  Mixed —> some cells producing viscous product and some watery uids A serous gland has a super developed RER for protein synthesis while a mucous gland has a well developed Golgi apparatus for the production of carbohydrates Myoepithelial cells beeline Myoepithelia are specialised squamous epithelial cells with power of contraction. They are the surroundings of glandular acini and ducts —> they contract to squeeze the secretion outside of the gland. They contain actin, myosin and cytokeratin. They are NOT muscle cells, they originate from epithelial cells. They aren’t present in all glands PANCREAS —> made of an exocrine part and endocrine famine part Exocrine pancreas —> compound (several excretory gendocrine ducts) tubulo-acinar glands made of serous secretory cells (secrete proteins and digestive enzymes), produces digestive secretions that are discharged into the duodenum via a system of ducts (pancreas has a well developed network of ducts). The ducts branch extensively. Groups of acini form lobules, which are separated by connective tissues that contain blood vessels, lymphatics, nerves and excretory ducts. eggnog secretion Endocrine pancreas —> islets of Langerhans (production of hormones) lobules or these paleof areacini Gthickwau aroundowers muscle smooth autocontract Centroacinal cells —> proliferation ability, they renovate the epithelia cells in the duct, they can also differentiate in secretory cells Intercalated ducts —> collecting duct which extends from the lumen of the secretory acinus Lobule —> union of ducts and acini. Interlobular ducts pass through different ducts Lobe —> union of many lobules. Lobar ducts passes through it The intercalated duct (smallest duct) is in continuum with intralobular ducts (also called striated ducts) which are then in interlobular ducts and ultimately with the lobar duct Striated ducts —> They have basal infoldings with many mitochondria, they are ion-transporting cells and they modify the nal concentration of electrolytes Collecting ducts from the lobes join in the major pancreatic duct —> Wirsung duct —> it arrives in the duodenum (that’s why surgical operations are hard) Whitemucous coloredserous MIXED EXOCRINE GLANDS (not in the pancreas) They might have a predominance of mucous and a demilune of serous or vice versa SIMPLE GLANDS (one secretory unit and one duct) tower with immense secretary gobeetceees summonses Simple alveolar —> intraepithelial glands of the nose and urethra mucosa Simple acinus —> small sebaceous glands Simple tubular —> crypts of Lieberkühn alveolar urethra acigular (intestine), sweat glands and gastric glands  TooSmallintestinalvilli continue lamina inthe Lieberkian crypts of Of gastrin secretes amaserotonin lysozine Penethu largeintestine no villilodeeper crypts simpeecoientubveer epithelia DEEPglandin thestomachpit pyloricGLANDS stomach tubular simplebranched I s simpeebronchedacinar TO Uterus 2gearasore found endometrialstrove inthe COMPOUND GLANDS (branched ducts and more than one sacks) Compound alveolar or tubuloalveolar —> mammary gland, prostate Compound acinus for tubuloacinar —> exocrine pancreas, major salivary glands Compound tubular —> cardiac glands Compound (tubulo-) acinar gland —> serous secretion —> exocrine pancreas, parotid Compound tubuloalveolar gland —> mucous secretion —> mammary gland I alveolizinegular shape Duodenum —> rst part of small intestine epithelium Lining i cuspysogrieserkian no excollagen mynah theyproance speciiegthe daemon