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Human Structure > Histology: Epithelium > Flashcards

Histology: Epithelium Flashcards

1
Q

Define epithelial tissue.

A
  • Avascular tissue (gets oxygen/nutrient via diffusion) composed of closely aggregated cells that form sheets
    • Cover internal & external body surfaces
    • Form secretory portions of glands and ducts
    • Sensory tissues (nasal, oral cavities, eyes)
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2
Q

Functions of epithelial tissue.

A
  • Protection
  • Absorption
  • Secretion
  • Sensory reception
  • Contraction
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3
Q

Characteristics of epitheial tissues.

A
  • Close together and adhered to one another via specialized cell junctions (junctional complexes)
  • Polarized both functionally and morphologically
    • Apical domain (faces lumen)
    • Basal domain (attached to basement membrane)
    • Lateral domain
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4
Q

Basement Membrane

A
  • Attaches epithelium to connective tissue
  • Forms a semipermeable “filter” to regulate exchange between epithelium and connective tissue
  • Really thick in the trachea

2 Layers:

  • Basal lamina (secreted by epithelial cells)
  • Reticular lamina (more fibrous; secreted by CT fibroblasts)
    • Type III collagen
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5
Q

Structure of the basal lamina

A
  • Produced by epithelial cells
  • Type IV collagen (forms meshwork)

Laminins

  • Glycoproteins that bind integrin receptors in cell membrane

Nidogen (glycoprotein) & Perlecan (proteoglycan)

  • Cross-link laminin to type IV collagen
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6
Q

Basement Membrane LM

A
  • PAS stain shows BM as a line underneath epithelial cells
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7
Q

Types of Junctional Complexes

A
  1. Tight junctions (most apical)
    • ​​Also called zonula occludens (encircling entire perimeter of cell)
  2. Adherent junctions
    • Also called zonula adherens
  3. Desmosomes
    • Also called macula adherens (“macula” means spot)
  4. Gap Junctions
    • Allow cells to communicate with one another
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8
Q

Tight Junctions

A
  • Most apical
  • Form a seal between adjacent cells (form a barrier)
    • Controls passage of molecules between cells
  • Separates apical from basolateral domains
    • Cells are polarized (differning functions in different domains)

Structure:

  • Occludin & Claudin
    • ​transmembrane proteins to anchor cells together
  • Zonula Occludens Proteins
    • attach to occludin and claudin
    • attach to actin filaments in cytoskeleton
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9
Q

Transcellular Transport

A
  • Active transport system
  • Allows transport across the plasma membrane
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10
Q

Paracellular Pathway

A
  • Between cells (prevented by tight junctions)
  • Small molecules (water, electrolytes) can pass
    • Claudins form aqeuous channels
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11
Q

Adherens Junctions

A
  • Immediately below tight junctions
  • Anchors cell to adjacent cell

Structure:

  • E-cadherins
    • transmembrane protein to form junction
  • Catenins
    • binds e-cadherins and actin filaments inside plasma membrane
  • Widening between terminal bar (dots) and terminal web (line) in LM
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12
Q

Desmosomes

A
  • Localized, spot-like (macula adherens)
  • Provide structural and mechanical strength
    • Very present in skin

Structure:

  • Desmocolin & Desmoglein
    • ​Interlock with adjacent cells
  • Plakoglobins & Desmoplakins
    • ​form electron-dense plaque to attach desmocolin/desmoglein to intermediate filaments

Additional Image:

  • Spines of stratum spinosum that retain contact as cell shrinks (desmosomes)
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13
Q

Gap Junctions

A
  • Allows cell communication
    • Form channels to allow molecules to pass from one cell to another
    • Can coordinate metabolic and electrical activity

Structure:

  • Connexins
    • Transmembrane proteins that form hexameric channels (connexons)
  • Appears “zipper-like” without plaques
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14
Q

Hemidesmosomes

A
  • Basal Domain
  • ​Has electron-dense plaque to connect to basement membrane
  • Integrins proteins
  • Attach to intermediate filaments
  • Abundant in skin, oral cavity, esophagus, etc.
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15
Q

Focal Adhesions

A
  • Found in epithelial cells undergoing repair/reorganization
  • Link to actin filaments and extracellular matrix
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16
Q

Microvilli

A
  • Cytoplasmic projections that increase surface area for absorption
    • Found on intestinal epithalial cells
  • Actin filament core
    • These filament anchor into transverse actin filaments called the terminal web
  • Glycocalyx is a coat of gylcolipids and glycoprotein covering (purple-pink border in PAS stain)
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17
Q

Microvilli LM

A
  • Brush border visible
  • Will label well with PAS stain due to glycocalyx
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18
Q

Microvilli EM

A
  • Finger-like projections
  • Core of wire actin filaments
  • Covered with hazy glycocalyx
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19
Q

Cilia

A
  • Longer than microvilli and motile (move substances across epithelial surface)
    • Found in respiratory tract and reproductive tract (oviduct)
  • Axoneme core (9+2 microtubule arrangement)
    • Dynein (ATP-powered)motor protein slide microtubules past each other to produce cilia movement
  • Basal Bodies are a modified centriole that is located directly beneath cilia
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20
Q

Cilia LM

A
  • Visible as hair-like projections
21
Q

Cilia EM

A
  • Whole structure often not visible
  • Axoneme cytoskeletal structure visible (9+2 arrangment)
22
Q

Stereocilia

A
  • Long, non-motile microvilli
  • Increase surface area for absorption
    • Male Reproductive Tract (epididymis)
    • Sensory Cells of Inner Ear
  • Actin filament core
23
Q

Stereocilia LM

A
  • Individually discernable
  • Similar in appearance to cilia
24
Q

Stereocilia EM

A
  • Array of actin filaments make up projection
25
Q

How do we classify epithelium stratified epithelium?

A

Classify based off of cells at the top of the epithelial layer.

26
Q
A

Simple squamous epithelium

​Functions

  • Selective barrier (endothelium of blood vessels)
  • Lubrication of internal body cavities
    • ​Serous lining of body cavities: Mesothelium

Locations:

  • Walls of alveoli
  • Visceral pleura covering of the lung
  • Kidney (Bowman’s Capsule)
  • Endothelium of blood vessels
27
Q
A

Simple cuboidal epithelium

Functions:

  • Absorption, secretion, active transport of ions

Locations:

  • Ducts of endocrine glands
  • Renal tubules
  • Ovary covering
  • Thyroid follicles
28
Q
A

Simple columnar epithelium

Functions:

  • Protection, lubrication, absorption, secretion

Apical surface usually covered in cilia or microvilli

Locations:

  • GI tract, oviduct, renal collecting ducts
29
Q
A

Stratified squamous epithelium

Function:

  • Protection

Keratinized:

  • surface cells accumulate keratin protein and lose nuclei
  • This prevents water loss
    • Skin epidermis, hair, nails

Non-Keratinized:

  • Surface cells retain nuclei (oral cavity, esophagus, vagina)
30
Q
A

Pseudostratified columnar epithelium

  • Tall, irregular cells. Every cell contacts basement membrane
  • Often ciliated

Functions:

  • Protection, secretion and movement of substances

Locations:

  • Respiratory tract: pseudostratified ciliated columnar epithelium (PCCE)
31
Q
A

Transitional Epithelium (Urothelium)

  • Variability in cell shape and numbers of layers
  • Superficial layer of larged, domed cells (umbrella cells)
  • Has keratin intermediate filaments

Functions:

  • Protection
  • Distensibility

Location:

  • Urinary Tract
32
Q

Stratified Cuboidal Epithelium

A

Functions:

  • protection and secretion

Locations:

  • Ducts of sweat glands
  • Ovarian follicles

Relatively Rare

33
Q

Stratified Columnar Epithelium

A

Functions:

  • Protection

Locations:

  • Conjunctiva of eye
34
Q

Glandular Epithelium

A
  • Glands develop from surface epithelium

Exocrine Glands:

  • Maintain connection to surface epithelium via ducts

Endocrine Glands:

  • Lose connection with surface epithelium
  • Secrete products into blood vessels
35
Q
A

Goblet Cells

  • Unicellular glands that secrete mucous
  • Nucleus and organelles in stem
  • Mucous in the “cup”

Locations:

  • Intestinal and respiratory epithelium
36
Q

Nomenclature of Glands

A
  1. How many ducts?
    • One = simple glands
    • Many = compound glands
  2. In simple glands, is there more than one secretory portion?
    • Yes = “branched” is added
  3. What is the shape of the secretory portion?
    • Tubular
    • Acinar
37
Q

Simple Glands

A

Ducts do not branch

  • Tubular: secretory part is long tube
    • Simple Tubular
    • Branched Tubular (stomach)
    • Coiled Tubular (sweat glands in skin)
  • Acinar: secretory portion is sac-like
    • Branched
38
Q

Compound Glands

A

Ducts branch

  • Tubular: secretory part is long tube
    • Duodenum
    • Testis
  • Acinar: secretory part is sac-like
    • Pancreas
  • Tubuloacinar: some secretory parts are tubular, some acinar
39
Q

Serous Glands

A
  • Produced thin, watery secretions (e.g. enzymes)
  • Usually acinar shaped
  • Typically stain intensely with H&E
    • Secretory vesicles are eosinophilic and apical
    • Nucleus and organelles are basal
40
Q

Mucous Glands

A
  • Viscous, carbohydrate-rich secretion (mucins)
  • Paler H&E stain (mucins don’t stain well)
  • Usually tubular
    • ​Appear round-tube
    • Nuclei in basal portion of cell

Examples: goblet cells; submandibular glands

41
Q

Seromucous Glands

A
  • Contains serous and mucous glands
  • Example: sublingual gland
42
Q

Lipid Secreting Glands

A
  • Secrete lipids
  • In adrenal cortex, sebaceous glands
43
Q

Merocrine Secretion

A
  • Secretory products released via exocytosis
44
Q

Holocrine

A
  • Secretory products accumulate in cytoplasm and are released via cell apoptosis
  • Sebaceous Glands
45
Q

Apocrine Secretion

A
  • Products accumulate in apical portion of cell & are released within membrane-enclosed vesicles (pinch off from apical plasma membrane)
  • Mammary glands
46
Q

Mucous Membranes

A

Line cavities of the body that are open to the external environment.

47
Q

Serous membranes

A

line the closed cavities of the body: pericardial, pleural and peritoneal.

48
Q

Myoepithelial Cells

A
  • Exhibit contractile properties to assist in “squeezing” secretory products out of glands
  • Located in basal lamina

Human Structure (30 decks)

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