1 Epithelium & Glands

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  1. H&E (Hematoxylin & Eosin)
    • • Eosin stains eosinophilic structures red: intra/extracellular proteins, cytoplasm
    • • Hematoxylin stains basophilic structures blue: DNA
    • • Melanin stains yellow & brown
    • • Hydrophobic structures (adipocytes, myelin, Golgi membranes) remain clear
  2. Glycoproteins stain poorly with _______ but stain positively with ___________
    Glycoproteins stain poorly with eosin but stain positively with the PAS reaction
  3. PAS (Periodic acid-Schiff) Stain
    • • used for structures that contain carbohydrates (glycogen, glycoprotein, proteoglycans)
    • • periodic acid breaks C-C bonds → creates aldehydes → aldehydes react with the Schiff reagent to give purple-magenta color
  4. What are the 4 primary phenotypes of mature tissues?
    • 1. Epithelium
    • 2. Connective Tissue (Soft, Hard [Cartilage, Bone] or Blood/Lymph)
    • 3. Muscle (Striated [Skeletal, Visceral, Cardiac] or Smooth)
    • 4. Nervous Tissue
  5. Epithelia
    • • all epithelia form a continuous sheet that lines a free surface; this sheet can be derived from the ectoderm, endoderm, or mesoderm
    • • the external covering of the skin is an endothelium (ectoderm-derived epidermis)
    • • endoderm-derived structures like the GI, respiratory, & genito-urinary tract are “internal” structures but they have a connection to the outside world
    • • true body cavities are derived from mesoderm (eg. pericardial, pleural, or peritoneal cavity) - this kind of epithelia are called mesothelium
  6. Endothelium
    a specialized term used for cells that line blood vessels or lymphatics

    • are derived from mesoderm NOT endoderm
  7. All epithelia are:
    POLARIZED - means they have asymmetry

    • they have a free apical surface & an attached basal surface (connected to the basal lamina [electron microscrope] or basement membrane [light microscope])
  8. What do all epithelia express?
    keratin intermediate filaments (diagnostic for all epithelia)

    • • also all epithelia are Avascular (no blood vessels present)
    • • because epithelia is seen basically everywhere in the body, they have many different functions
  9. True or False: epithelia are avascular?
    TRUE, blood vessels that nourish the epithelium are located in ADJACENT connective tissue
  10. What are the 2 general classes of epithelia?
    • 1. lining
    • 2. glandular
    • (those that line cavities or those that form glands)
  11. Epithelial Functions
    • • Protection (epidermis provides waterproofing & insulation; stomach lining protects from acid)
    • • Surface Transport (cilia = epithelia specialization; in respiratory epithelium they propel particles upward; oviduct cilia move the ovum)
    • • Absorption (microvilli in intestinal epithelium & kidney tubules absorb nutrients)
    • • Secretion (both unicellular & multicellular glands)
    • • Trans-epithelial Transport
    • - apical to basal: kidney tubules transport nutrients from the lumen to basal connective tissue
    • - basal to apical: lymph resorption into lymphatics
    • • Reproductive (seminiferous tubule epithelium generates sperm)
    • • Special Sensory (taste buds, hair cells in cochlea)
    • • Contraction (myoepithelium)
  12. What are EIGHT functions of epithelia?
    • 1) protection: e.g. epidermis of the skin provides mechanical protection, waterproofing & insulation
    • 2) absorption: eg. epithelial lining of small intestine absorbs nutrients
    • 3) reproductive: seminiferous tubule (epithelia contains sertoli cells)
    • 4) secretion: eg. mucous by goblet cells
    • 5) sensory reception: smelling, hearing, seeing
    • 6) surface transport: eg. tracheal cilia cells move mucous from lungs toward oral cavity
    • 7) trans-epithelial transport: kidney tubules transport salt & water from the lumen of collecting tubules back into bloodstream through the interstitial space
    • 8) contraction of myoepithelial cells: eg. to squeeze milk from excretory lobules of mammary glands
  13. What determines epithelial type?
    • 1. the number of layers (simple/stratified)
    • 2. cell shape at the free surface
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  14. Simple
    • • a single layer of epithelial cells
    • • typically found in tissues specialized for absorption & secretion but NOT subject to extensive wear & tear
    • • eg. endothelium, mesothelium, bowman’s capsule, distal & proximal convoluted kidney tubule, small intestine, lung alveoli
  15. Squamous
    cells that are thin, flat & scale-like
  16. Cuboidal
    cube-shaped cells
  17. Columnar
    cell that are taller than they are wide
  18. Simple Squamous Epithelia
    • a single layer of thin, flat & scale-like cells
    • the thickest part of the cell is the nucleus
    • eg. cells lining blood vessels (called endothelium, & it’s derived from the mesoderm)
    • [other examples: serosal cells lining mesentery, cells lining Bowman's capsule of kidney, cells lining lung alveoli; simple squamous endothelia are specialized for filtration, diffusion, osmosis & secretion]

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  19. Simple Cuboidal Epithelia
    • a single layer of cube-shaped cells specialized for secretion and absorption
    • cells are not much taller than the diameter of the nucleus
    • eg. cells in renal tubules

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  20. Simple Columnar Epithelia
    • single layer of cells whose height is greater than their width
    • because they’re so tall, the nucleus occupies only a portion of the cell
    • specialized for secretion & absorption
    • these cells may or may not be ciliated (brush border)
    • eg. intestinal epithelium cells

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  21. Wandering Lymphocytes
    • have darker nuclei

    • can have them in any epithelium, especially those that face outside lumen (eg. simple columnar epithelia of the intestine)
  22. Stratified Epithelia
    • • many layers (2 or more) of epithelial cells
    • • found in tissues subjected to wear & tear
    • • eg. skin, oral cavity, esophagus, anal canal, vagina
  23. Stratified Columnar Epithelia
    • • not very common, can see in some large glandular ducts or ocular conjunctiva of the eye
    • (other egs. portions of male urethra, parts of the pharynx & anus, female's uterus, male's vas deferens)
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  24. Goblet Cells
    • • unicellular glands found in the intestinal epithelium that help keep it moist
    • • use merocrine secretion (secretory vesicles, exocytosis) to secrete mucus
  25. Stratified Squamous Epithelia
    flattened (squamous) cells on the surface of multiple layers of cells; usually protective
  26. Stratified Squamous Keratinizing Epithelia (SSKE)
    • • nuclei are NOT present in the surface layer, which is made up of dead cells (stratum corneum)
    • • differentiating cells formed by mitosis at the basal layer make a lot of keratin, lose their nuclei, & move apically to replace the outermost squamous layer of cells (eg. skin epidermis)
  27. Stratified Squamous Non-keratinizing Epithelia (SSNKE)
    • • found in the esophagus, anal canal, & vagina
    • • nuclei ARE present in the surface layer
    • • cells that produce less keratin & apical squamous cells do not lose their nuclei
  28. Pseudostratified Epithelia
    • • all cells contact basal lamina, not all reach free surface
    • • typically has cilia except in parts of male reproductive system
    • • TRUE stratified epithelia NEVER have cilia
    • • found in the trachea (respiratory tract), epididymis (male reproductive system ducts)
    • • should technically be a “simple” epithelium but because there’s a variation in nuclei level it’s called pseudostratified
    • (*when in doubt whether something is pseudostratified or stratified cuboidal or columnar, guessing pseudostratified means you will be right 99% of the time)
  29. Transitional (Urothelium)
    • • large surface cells [umbrella cells], often binucleate
    • • are unique to the urinary system
    • • appears to be stratified but is ACTUALLY pseudostratified
    • • surface cells tend to be BIGGER than those on the basal lamina & have a domed appearance
    • • appearance varies depending on whether it's contracted or expanded - specialized for distension or contraction to accommodate the changes in urine volume
  30. Glands
    • • single or groups of cells specialized for secretion
    • • glands are derived from epithelia & begin as an ingrowth “chord” of epithelial cells
    • • cells grow down into the connective tissue & remain bound to the basal lamina
    • • many different types of glands exist
  31. Exocrine Glands
    • • glands that release their secretions into ducts
    • • development: epithelial cells will differentiate into 2 types of cells: secretory (make whatever the product is) & duct (where the product is modified & secreted or just secreted)
    • • are continuous with the surface epithelium of an organ (eg. in skin or GI tract)
  32. Exocrine v. Endocrine
    • Exocrine: Maintain contact with surface epithelium, secrete products into ducts then out into lumen

    • Endocrine: Lose contact with surface epithelium, secrete products into interstitial space which then go into capillaries/the blood stream
  33. Endocrine Glands
    • • glands that secrete products into the bloodstream through the interstitial space
    • • development: cord of epithelial cells grow into connective tissue but then those cells are lost; end up with an island of cells that NO LONGER have a connection to the surface
    • • they are connected to blood vessels
    • • they do NOT have ducts & are not ALL derived from epithelia
  34. How are exocrine cells classified?
    • • the number of cells in the gland: unicellular or multicellular
    • • the duct system: simple or compound
    • • mode of secretion: merocrine, apocrine, holocrine
    • • nature of secretion: mucous or serous
    • • architecture of terminal branches: tubular or acinar
  35. Unicellular Glands (Exocrine)
    • • eg. goblet cells
    • • often found in tracheal pseudostratified epithelia, intestinal simple columnar epithelia

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    • • because goblet cells contain a lipid rich substance, & lipids don’t stain well, usually they look white
    • • when stained with PAS (targets carbohydrates), mucin granules in goblet cells appear magenta

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  36. Multicellular Glands (Exocrine)
    • Simple: either do not branch or branch only once (eg. dermal sebaceous glands)

    • Compound: branch repeatedly to form a branched tree (eg. pancreas)
  37. Merocrine Secretion
    • • secretion by exocytosis: cell makes a product & only that particular product is released
    • • eg. mechanism for the secretion of mucus by goblet cells; mucus or serous by salivary glands
    • • type of secretion done by exocrine glands
    • • (subcategory of merocrine secretion is ECCRINE, which refers only to sweat secretion from eccrine sweat glands in the skin)
  38. What are typical secretions from merocrine glands?
    • 1. zymogens
    • 2. sweat
    • 3. mucus
    • 4. lysozyme (antibacterial type products)
  39. Apocrine Secretion
    • • secretion by decapitation of cells’ apical region
    • • cells make a product & release part of their apical cytoplasm + plasma membrane with the release of said product
    • • mechanism for the production of milk in mammary gland
    • • type of secretion done by exocrine glands

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  40. Holocrine Secretion
    • • the entire cell & it’s contents become the secretory product following apoptosis
    • • mechanisms for the production of sebum (mixture of lipids) by the sebaceous gland in the skin
    • • type of secretion done by exocrine glands

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  41. Describe the phenotypic progression of cells from base to duct during Holocrine secretion:
    • • cell borders disappear
    • • nucleus degenerates
    • • cytoplasmic droplets coalesce
  42. Mucous Secretion
    • • mucus is very hygroscopic, it has a lot of charged molecules in it
    • • during fixation it causes the cells to SWELL, which flattens the nuclei toward the base of the cell
    • • cells look empty (white) because mucus doesn’t stain well

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    • Mucus Acinus Picture
  43. Serous Secretion
    • • quite watery
    • • cells will have a cytoplasm that contains a bunch of rough endoplasmic reticulum making the product (eg. enzyme)
    • • nuclei are pushed toward the periphery but maintain their rounded shape

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  44. Myoepithelial (Basket) Cells
    • • epithelial cells that are contractile
    • • eg. skin sweat glands - see cells that have nuclei running along the same axis of the cell (look columnar), but then in contrast there are nuclei that run PARALLEL to the basal lamina
    • • these are the myoepithelial cells
    • • when these contract, they force the product (eg. sweat) into the lumen, where it can then be conveyed by the ducts
    • • these cells tend to be more eiosinophilic than cells closer to the lumen because they contain contractile proteins

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Card Set Information

1 Epithelium & Glands
2016-09-17 14:52:55
MedFoundationsI Histology Exam2
Histology Exam 2
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