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Anatomy > Histoanatomy 2: Epithelia > Flashcards

Histoanatomy 2: Epithelia Flashcards

1
Q

Tissue

A
  • a relatively homogenous collection of structurally/ functionally similar cells/ cell products –> combine to form organs
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2
Q

LO: Where are epithelia located in body?

A
  • epithelia covers free body surfaces
  • externally = epidermis (component of skin)
  • internally lines passageways opening to exterior (GI, genitourinary, respiratory tracts); combined with underlying CT forms mucous membrane
  • endothelium: epithelium lining BVs, heart chambers, lymphatic vessels
  • mesothelium: epithelium lining internal body cavities that do NOT open exteriorly (pleural, pericardial, peritoneal cavities); combined with underlying CT forms serous membranes (pleura, pericardia, peritoneum)
  • these are all COVERING EPITHELIA: classified as either simple (1 layer of cells)/ stratified (>1)
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3
Q

LO: What are the structural characteristics of various epithelial classes?

A
  • cellularity: densely packed cells with little material between (unlike CT)
  • polarity: apical/ lateral/ basal surface specializations –> each performs specific functions
  • specialized intercellular junctions: provide stability/ allow selective movement through epithelial sheet
  • avascular: BVs do NOT cross BM (rely on diffusion for nutrients/ waste removal)
  • innervated: sensory fibres run through underlying CT
  • regeneration: by mitosis of cells lost at epithelial surface
  • attached to BM & underlying CT
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4
Q

LO: What are the functions of different epithelial classes?

A

epithelium structurally specialized to perform specific function based on location:

  • physical protection (against abrasion, dehydration, chemical/ microbial attack)
  • controlled permeability (any substance entering body must cross epithelium trans/ paracellularly)
  • provide sensation: general (touch, temp, pain), special senses (vision, hearing, balance, smell)
  • glandular epithelia produce specialized secretions: salivary, sweat, pituitary, pancreas
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5
Q

LO: What is the relationship of endocrine/ exocrine glands to epithelia?

A
  • endocrine/ exocrine glands derived from epithelia but specialized to produce/ secrete cell product
  • may be multicellular
  • may be unicellular (ie. exocrine goblet cells/ diffuse neuroendocrine cells)
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6
Q

LO: How are epithelia classified? What are the structural characteristics of the various classes of epithelia?

A
  • Covering epithelium vs glandular
  • Simple vs stratified:
    o Simple: 1 layer of cells, found at sites of molecular transfer
    o Stratified: >1 layer, at sites needing protection
  • Shape of cells at surface:
    o Squamous: flat
    o Cuboidal: height ~ width
    o Columnar: height > width
  • Specializations: microvilli, cilia, goblet cells?
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7
Q

What are the 4 tissue types?

A
  • epithelial, CT (including cartilage/ bone), muscle, neural
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8
Q

Endothelium

A
  • epithelium lining BVs, heart chambers, lymphatic vessels
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9
Q

Mesothelium

A
  • epithelium lining internal body cavities that do NOT open exteriorly (pleural, pericardial, peritoneal cavities); combined with underlying CT forms serious membranes (pleura, pericardia, peritoneum)
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10
Q

Basement membrane

A
  • acellular layer between epithelium/ CT (made of molecules produced/ secreted by cells)
    functions:
  • structurally supports epithelium
  • attachment: contacts between epithelium/ BM/ CT
  • semipermeable molecular filter: since epithelia avascular, metabolites/ wastes exchanged with CT across BM
  • scaffold for epithelial repair/ regeneration (after damage)
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11
Q

Transcellular molecular movement

A
  • occurs through/ across epithelial barrier (ie. into cell on one side, out on other)
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12
Q

Paracellular molecular movement

A
  • occurs between cells
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13
Q

Describe development of glandular epithelia

A
  • both covering/ glandular epithelia develop from simple sheets
  • covering epithelia –> simple/ stratified
  • glandular –> endocrine/ exocrine: from simple sheet, proliferating cells burrow into underlying CT
  • in endocrine glands, there is disappearance of connection to sheet surface (secrete hormones inwards into surrounding fluid –> capillaries)
  • in exocrine glands, duct forms connecting secretory portion to sheet surface (secrete outwards via duct)
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14
Q

Goblet cells

A
  • unicellular, mucous-secreting, exocrine glands amongst epithelial cells
  • secrete mucous across APICAL aspect onto exposed epithelium to protect (ie. traps particles in resp tract, lubricates GIT)
  • GCs with short, blunt microvilli in resp tract
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15
Q

Diffuse neuroendocrine cells

A
  • unicellular endocrine glands within covering epithelia
  • ie. enteroendocrine (EE) cells of GIT
  • secrete cell products across BASAL aspect into CT fluid
  • cell products may influence adjacent cells (paracrine signaling) - ie. stomach filling –> epithelial EE cells secrete gastrin –> influences adjacent cells to secrete acid
  • cell products may –> BVs –> systemic (endocrine) - ie. SI EE cells secrete cholecystokinin (CCK) –> pancreatic digestive hormone/ bile release
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16
Q

Microvilli

A
  • specialization of apical surface
  • increase SA in epithelial that function in absorption/ secretion (ie. well developed aka tall/ densely-packed in SI/ kidney –> high rate molecular transfer)
  • minimally motile, finger-like extensions of apical cell membrane
  • core: actin microfilaments cross-linked to each other/ membrane/ terminal web
  • # proportional to rate molecules move through
17
Q

Cilia

A
  • specialization of apical surface
  • on epithelia specialized to move fluid along luminal surface
  • highly motile, synchronized, finger-like extensions of apical cell membrane
  • core: microtubules/ associated proteins (ie. dynein)
  • taller than microvilli
  • well developed in respiratory epithelia (beat mucous produced by GCs towards pharynx)/ fallopian tubes (conduct ova from ovaries –> uterus as ova incapable of autonomous movement)
  • peg cells with short, blunt microvilli, secrete nutrients to nourish egg as it travels
  • sperm tail structurally similar to cilia core –> mobility (men with ciliary dyskinesia have immotile sperm)
18
Q

Intercellular junctions

A

o Present in other tissues, most prominent in epithelia (to attach to each other/ underlying CT)
o Functional classes – different attachments, different purposes: anchoring, occluding, communicating junctions

19
Q

Anchoring junctions

A

Anchoring junctions –> mechanical strength, ability to withstand shear forces (exerted parallel to sheet – ie. Abrasion)
• Attach cytoskeletons (network of structural fibrous proteins – ie. Actin, intermediate filaments, etc) to:
o Each other across lateral membranes (ZA, desmosomes)
o Underlying BM/ CT across basal membranes (hemidesmosomes)

20
Q

Zonula Adherens (ZA)

A
  • present throughout epithelial sheet, entirely surrounding cells, binding together in all directions – ie. Six pack
    • Zonule = belt
    • Link actin microfilaments of adjacent cells – well developed in SI
    • Cadherins: transmembrane proteins that link across intercellular space
21
Q

Desmosomes

A
  • do NOT form belts, arranged more like rivets throughout epithelial sheet joining lateral surfaces
    • Link intermediate filaments of adjacent cells – well developed in skin
    • Like ZA, have cadherins
22
Q

Hemidesmosomes

A
  • present throughout epithelial sheet
    • Link intermediate filaments of epithelial cells’ to BM’s to resist separation – well developed in skin
    • Unlike ZA/ desmosomes, transmembrane proteins = integrins
23
Q

Occluding junctions

A
  • block intercellular space control paracellular movement between cells
  • ie. tight junctions
24
Q

Tight junctions

A
  • integral transmembrane glycoproteins arranged as branching, anastomosing (intertwining of distinct linear structures) strips
    o Bound to similar proteins in adjacent cell membrane
    o Aka zonula occludens (because arranged in belt-like fashion around cell)
    o Seal paracellular space around circumference of cells
    o Functional implications:
    ♣ Anatomical basis of functional tissue compartments – ie. BBB, blood-testis barrier, blood-thymus barrier
    ♣ Prevents back-diffusion of actively-transported molecules concentration gradients
    ♣ Density determines epithelial barrier properties
    • Tighter – ie. SI, BBB
    • Leakier – ie. Kidney where water follows actively transported ions
    ♣ Limits membrane protein movement from one surface to another
25
Q

Communicating junctions

A
  • control ionic/ molecular intercellular movement (between adjacent epithelial cells)
  • ie. gap junctions
26
Q

Gap junctions

A
  • complex of transmembrane proteins in lateral membranes forms pore across intercellular space
    o Connects cytoplasm of adjacent cells, permitting passage of ions/ small molecules, thus coupling metabolically/ electrically
    o Coordinates cellular function – ie. beating of cilia synchronicity
    o Open/ close with conformational change
    o Also coordinate function in bone cells, cardiac myocytes, smooth muscle cells
27
Q

Simple squamous epithelia

A
  • thinness promotes rapid/ usually passive molecular transport
    o Ie. alveoli: luminal surfaces lined with simple squamous “pneumocytes”
    o Ie. endothelium: lines luminal surface of all BVs
    o Ie. mesothelial
28
Q

Simple cuboidal epithelia

A
  • line surfaces involved in active processes of secretion/ absorption where subcellular organelles required necessitates larger volume
    o May have microvilli
    o Ie. some ducts, as in renal tubules of kidney
29
Q

Simple columnar epithelia

A
  • line surfaces involved in high rates of secretion/ absorption
    o Ie. SI – for absorption! Have microvilli, goblet cells
    o Ie. Gallbladder – to concentrate bile, actively transports water out (facilitated by microvilli/ tight junctions)
    o Ie. Fallopian tubes – cilia
30
Q

Pseudostratified epithelia

A
  • appears stratified, but all cells contact basement membrane
    o Usually ciliated - ie. in respiratory tract
31
Q

Stratified squamous keratinzed epithelia

A
  • line external surfaces requiring protection from abrasion, pathogens, chemical attack, dehydration – ie. epidermis prevents fluid loss (problem for burn victims)
32
Q

Stratified squamous nonkeratinzed epithelia

A
  • line internal surfaces requiring protection from abrasion, pathogens, chemical attack – ie. mouth, throat, esophagus, rectum, anus, vagina, cervix
    o Must be kept moist by glandular secretion
    o Desmosomes help withstand abrasion
33
Q

Transitional epithelium

A
  • stratified, lines surfaces requiring stretch/ recoil – ie. bladder, ureter
    o Surface cells dome shaped when empty flatten as organ fills/ epithelium stretches
34
Q

Keratinization

A
  • process which converts surface into sheet of dead, protein-packed cells that maintain strong connection to each other via desmosomes water-resistant properties

Anatomy (5 decks)

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