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Human Structure > Histology: Epithelium > Flashcards

Histology: Epithelium Flashcards

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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

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A
  • Visible as hair-like projections
21
Q

Cilia EM

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

Stereocilia

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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

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

Stereocilia EM

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A
  • Array of actin filaments make up projection
25
How do we classify epithelium stratified epithelium?
Classify based off of cells **at the top** of the epithelial layer.
26
**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
**Simple cuboidal epithelium** Functions: * Absorption, secretion, active transport of ions Locations: * Ducts of endocrine glands * Renal tubules * Ovary covering * Thyroid follicles
28
**Simple columnar epithelium** Functions: * Protection, lubrication, absorption, secretion Apical surface usually covered in **cilia or microvilli** Locations: * GI tract, oviduct, renal collecting ducts
29
**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
**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
**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
Stratified Cuboidal Epithelium
Functions: * protection and secretion Locations: * Ducts of sweat glands * Ovarian follicles Relatively Rare
33
Stratified Columnar Epithelium
Functions: * Protection Locations: * Conjunctiva of eye
34
Glandular Epithelium
* 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
**Goblet Cells** * **Unicellular** glands that **secrete mucous** * Nucleus and organelles in stem * Mucous in the "cup" Locations: * Intestinal and respiratory epithelium
36
Nomenclature of Glands
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
Simple Glands
*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
Compound Glands
*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
Serous Glands
* 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
Mucous Glands
* 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
Seromucous Glands
* Contains serous and mucous glands * Example: **sublingual gland**
42
Lipid Secreting Glands
* Secrete lipids * In adrenal cortex, sebaceous glands
43
Merocrine Secretion
* Secretory products released via **exocytosis**
44
Holocrine
* Secretory products accumulate in cytoplasm and are released via **cell apoptosis** * **Sebaceous Glands**
45
Apocrine Secretion
* Products accumulate in apical portion of cell & are released within membrane-enclosed vesicles (pinch off from apical plasma membrane) * **Mammary glands**
46
Mucous Membranes
Line cavities of the body that are open to the external environment.
47
Serous membranes
line the closed cavities of the body: pericardial, pleural and peritoneal.
48
Myoepithelial Cells
* Exhibit contractile properties to assist in "squeezing" secretory products out of glands * Located in basal lamina

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