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CAPS 390: Histology > Adhesion > Flashcards

Adhesion Flashcards

1
Q

fuctional types of cell junctions

A
  1. anchoring: mechanical attachment to other cells or ECM
  2. occluding: seal contacts b/t neighboring cells
  3. channel-forming/communicating: form channels b/t cells and allow chemical and electrical signals to pass
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2
Q

junction structure

A

-transmembrane adhesion receptor proteins contact inside and outside environments
-extracellular region attaches to other adhesion proteins or ECM molecules
-intracellular regions attach to cytoplasmic adaptor proteins and connect to cytoskeletal linkers or cytoskeletal proteins
adapter proteins bind adhesion complex and recruit additional regulatory components

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3
Q

what increases junciton stability and strength?

A
  • they are multiprotein complexes
  • clustering of adhesion proteins inc. stregth
  • clusters link to cytoskeletal network producing a large tension bearing network through tissue
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4
Q

cell polarity

A
  • regional differences w/in cell
    1. apical domain-free, unattached PM facing open space, may be air or fluid filled
    2. lateral domain-contacts neighboring cells
    3. basal domain-attached to ECM, often faces underlying connective tissue
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5
Q

tight junctions/zonula occludens

A

zonula=belt around cell
located apically and join neighboring cells
-formed by strands of transmembrane proteins-mainly claudin and occludin (occludins required for barrier function)
-control diffusion of material b/t cells

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6
Q

adherens junctions/zonula adherens

A

form cont. belts around cell on the lateral domain just under tight junctions

  • important for sheet formation of epithelial cells
  • made of classical cadherins
    1. at low Ca levels two cadherins form a cis-homodimer
    2. Ca binding causes a confrormational change and straightens cadherins, which promotes trans-homodimer formation and facilitates binding to neighboring cells
    3. cadherins cluster and link to cytoskeleton via catenins
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7
Q

desmosomes/macula adherens

A

small, spotlike junctions that strengthen adhesion b/t epithelial cells exposed to tensile forces/mechical stress
-based on adhesions b/t cadherin-like receptors desmocollin and desmoglein which bind to intermediate keratin filaments

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8
Q

gap junctions

A
  • allow communication and sharing of small molecules b/t neighboring cells
  • connexins (6) cluster together and make connexon, which binds connexons in similar cells, which forms a channel
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9
Q

connective tissue ECM

A

composed of ground substance and fibers

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10
Q

ground substance

A

-water, electrolytes, polysaccharides and proteins, resists compression and allows diffusion
main components
1. glycosaminoglycans-chains of carbs that are negativly charged and attract Na and water
2. proteoglycan-many long GAGs linked to a protein
3. glycoproteins-proteins w/short carb chains added-1-60% carb

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11
Q

fibers

A

collagen-main ECM protein that is flexible but strong and not stretchy
-made up of units of tropocollagen (which is a helex of 3 alpha collagen protein subunits)
elastin=stretchy and distensable

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12
Q

other connective tissue components

A
  • fibroblasts: cells that synthesize ECM components

- specialized connective tissues contain osteoblasts, chondroblasts, and adipocytes

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13
Q

basement membrane

A

specialized ECM that forms carpet like mechanical barrier b/t epithelial and connective tissues and anchoring point for epithelial cells that attach via hemidesmosomes
-consists of basal lamina and reticular lamina

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14
Q

basal lamina

A
  1. lamina lucida-laminin glycoproteins and integrins-clear portion on TEM
  2. lamina densa-mostly type IV collagen, gives tensile strength, dark on TEM
    - laminin binds collagen and links two layers
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15
Q

reticular lamina

A

contains type I and III collagen and fibrillin

binds anchoring plaques, fixing basement membrane to connective tissue ECM

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16
Q

integrins

A
  • transmembrane ECM binding protein receptors
  • heterodimers of alpha and beta subunits (many combinations of different alpha and beta)
  • exist in high and low affinity states
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17
Q

intigrin activation

A
  1. outside in-binding of ECM ligands

2. inside out-integrin binds proteins that shifts their affinity state

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18
Q

focal contacts

A
  • link to actin, many cell types
  • receptor is one of many integrin heterodimers
  • dynamic, can generate traction forces–>important in cell movement
  • critical for mm attachment to tendons
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19
Q

hemidesmosomes

A
  • link to intermediate filaments, found in epithelial cells only
  • alpha6beta4 integrin heterodimer
  • bind basal surface of epithelial cells to laminin of underlying lamina lucida
20
Q

epithelium

A
  • cont layers of cells with very little ECM
  • cells adhere to basemembrane via hemisesmosomes
  • acts as protective covering
  • regulates transport by 1. paracellular transport (where tight junctions are not occluding and 2. transcellular where tight junctions are occulding
  • regulates absorbtion
  • regulates secretion
    1. exocrine from apical side onto free surfaces and ducts
    2. paracrine from basal side into underlying connective tissue
    3. endocrine from basal side into underlying connective tissue-product enters bloodstream
21
Q

Connective tissue

A
  • structural support, medium for exchange, storage of lipids
  • from mesoderm
  • consists of cells and ECM (ground substance and fibers)
  • is vascularized
22
Q

connective tissue cell types

A
  • come from mesenchymal stem cells or pleuripotent hemopoetic stem cells
  • fibroblasts make ECM
  • adipocytes-store lipid droplets in cytoplasm
  • pericytes-pleuripotent mesenchymal stem cells associated with blood vessels of CT that can become adipocytes, fibroblasts, or endothelial cells
23
Q

connective tissue proper classifications

A
  • loose/areolar-many cells, lots of ground substance, few fibers, flexible and not stress resistant
  • dense irregular-few cells/more fibers, in all orientations, resistant to stress in all directions
  • dense regular-fibers parallel and strength in one direction
  • adipose CT-high number of adipocytes grouped into lobules separated by dense CT–septae
  • reticular CT-highly cellular w/interwoven reticular fibers
24
Q

glands

A
  • secretory epithelial portion-parenchyma

- CT inductive and supportive

25
Q

types of glands

A
  • unicellular-single cells in surface, eg goblet cells
  • multicellular glands-clusters of secretory cells surrounded by stroma, secrete into duct, eg salivary glands
  • simple=unbranched, compound=branched
  • morphology: tubular=same diameter as duct, alveolar=expanded diameter
26
Q

cartilage functions

A
  • supports soft tissues
  • provides low friction sliding for joints
  • growth of long bones as reserve for new bone deposition
27
Q

cartilage cells

A

chondroblasts deposit cartilage ECM and arise from chondroprogenitor cells in perichondrium
chondrocytes in lacunae

28
Q

cartilage matrix

A

resists compression, intermediate thickness collagen type II fibers for tensile strength
avascular and relies on high diffusion and hydration

29
Q

hyaline cartiage

A

type II collagen fibers, significant amounts of proteoglycans

  • well defined perichondrium, limited regenerative potential
  • found in joints, nose, trachea
30
Q

fibrocartilage

A
  • thick, strong, collagen type I for highest tensile strength
  • no distinct perichondrium very very low regenerative potential
  • intervertebral disks, sites of tendon attachment, some joints
  • eventually degenerates and can be replaced by bone
31
Q

elastic cartilage

A
  • less matrix and more cells than hyaline
  • type II collagen and elastic fibers
  • well defined perichondrium, limited regenerative potential
  • found in flexible areas like ear, epiglottis
32
Q

osteoarthritis

A

degenerative loss of hyaline cartilage

in joints, bone contacts bone

33
Q

osteoblasts

osteocytes

A 
deposit osteoid (organic ECM)
trapped in lacunae (inorganic mineralized part), make caniliculi for communication
34
Q

osteoclasts

A

only bone cells derived from hematopoetic stem cells

-resorb/breakdown bone matrix

35
Q

periosteum

A

outer fibrous layer and inner cambium layer (osteoprogenitor cells), attached to bone via sharpys fibers

36
Q

inner spongy bone

A

small spikes/trabiculae that contact bone marrow

-remodeled by osteoclasts, lacunae filled in by osteoid deposited by osteoblasts

37
Q

outer compact/cortical bone

A

made of osteons of concentric layers that form haversian canal in middle

38
Q

bone formation

A
  • intermembranous (flat bones): forms in mesenchyme, which condeses and generates osteoprogenitor cells that differentiate and lay down bone matrix
  • endochondrial-ossification centers form where cartilage makes scaffold that is then replaced with bone
    1. central ossification center=diaphysis, outer ones are epiphyses
    2. epiphyseal plate gradually ossifies and becomes bone in response to growth hormone
39
Q

osteoporosis

A

shift toward resorption of bone ECM
-inhibit osteoclasts with bisphosphonates (which mimic hydroxyapatite and prevent the breakdown of actual hydroxyapetite)

40
Q

botox

A

prevents release of ACh from axon terminals by inhibiting fusion of vesicles to pre-synaptic membrane of NMJ

41
Q

Muscular distrophy

A
  • loss of cytoskeletal linker protein dystrophin causes ECM junction to be released from actin cytoskeleton
  • results in contraction injuries, followed by inc in connective and adipose tissue that initially causes pseudohypertrophy in the calf muscle
42
Q

cardiac myofibers

A
  • mononuclear, centrally located

- branched and connected by intercalated disks

43
Q

intercalated disks

A

adhesion junctions-anchor myofilaments (terminal sarcomeres) to actin cytoskeleton
desmosomes anchor adjacent cardiomyofibers
gap junctions (parallel to myofilaments) allow rapid info flow b/t fibers

44
Q

cardiac muscle contration

A
  • diad instead of triad (one cistern) releases small amounts of Ca, T-tubules facillatate extracellular Ca transfer to sarcoplasm
  • intercalated disks allow for quick passage of ions b/t fibers
  • cardiac muscle has sarcomeres
45
Q

smooth muscle fibers

A
  • spindle shaped, tapered, one nucleus

- no sarcomeres, actin and myosin filaments attach to dense bodies and dense plaques at PM

46
Q

contraction of smooth muscle

A

no t-tubule based contraction, instead is large number of gap junctions to allow direct electrical communication b/t fibers
contractile units consist of myosin and actin filaments

CAPS 390: Histology (3 decks)

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