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MCP Unit 1 > Tissue Organization > Flashcards

Tissue Organization Flashcards

1
Q

Features of multicellular organisms

A

cells organized into cooperative assemblies- tissues and organs. nerve, muscle, epithelium etc
-permits complex processes, compartmentalization and communication

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2
Q

two types of tissues

A

Cellular-muscle/epithelia
-composes mostly of cells
-integrity/properties derived from cell-cell and cell-ECM interactions like cell junctions
Connective Tissue- cartilage, bone, tendon
-composed to ECM with a few cells, the cells synthesize/remodel and bind the ECM
-properties of the tissue (strength and elasticity) derived from the composition of the ECM

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3
Q

Small intestine

A

Made of both tissue types, like most things in the body

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4
Q

Tight junction

A

seals neighboring cells together in and epithelial sheet to prevent leakage of molecules between them

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5
Q

adherens junction

A

joins an actin bundle in once cell to a similar bundle in a neighboring cell

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6
Q

desmosome junction

A

“spot weld” that anchors the tough IF in one cells to those in a neighbor

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7
Q

Gap Junction

A

cell-cell junction allowing passage of small water-soluble ions and molecules

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8
Q

hemidesmosome junction

A

anchors IF in a cell to the basil lamina

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9
Q

Focal adhesions

A

cell-ECM junction

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10
Q

Adhering/Anchoring junctions

A

-maintain tissue integrity when subjected to mechanical stress.
-achieved by interactions with actin of IF
-cell-cell or cell ECM (2 of each type)
cell-cell: Adherens(Zonula) and desmosome
cell-ECM: Focal adhesions and hemidesmosome

(hemi)desmosomes are IF, adherens and adhesions are actin

  • 3 basic components
    1. transmembrane glycoprotein
    2. complex of linker proteins on cytoplasmic face stabilizes link to 3rd component and regulates assembly
    3. cytoskeleton
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11
Q

Adherens Junction (Zonula adherens)

A
  • cell-cell
    1. Cadherins- homophilic interaction
    2. catenins, alpha actin
    3. actin microfilaments

stability, development of neural tube

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12
Q

Focal Adhesions/Contacts

A
  • cell-ECM- heterophilic
    1. Integrins (ca2+) sensitive- two subunits, alpha/beta heterodimers
    2. talin, vinculin
    3. actin cytoskeleton (stress fibers)

found in vascular endothelium in areas of turbulent flow and in migrating cells.
-mytendinous junction of skeletal muscle and dense plaques of smooth muscle is similar to focal adhesions

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13
Q

actin junctions

A

zonula adherens and focal adhesions

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14
Q

IF junctions

A

desmosomes and hemi-desmosomes

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15
Q

cell-cell interactions

A

zonula adherens and desmosome

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16
Q

cell-ECM interactions

A

focal adhesions and hemi-desmosomes

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17
Q

Desmosome

A
  • cell-cell
    1. cadherins
    2. desmoplakins
    3. IF (Keratin)

link IF across and epithelial sheet

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18
Q

Hemi-Desmosome

A
  • cell-ECM
    1. integrin alpha6/beta4-attaches to ECM of basil lamina *only integrin toassociate with IF
    2. desmoplakin
    3. IF

link IF across and epithelial sheet

19
Q

Skin disorders associated with anchoring/adhering junctions

A
  1. pemphigus- auto-immune- antobodies againt cadherins and disrupt cell-cell junctions
  2. epidermolysis bullosa simplex- defect in keratin assembly

both result in loss of tissue integrity and/or blistering and can be fatal

20
Q

Tight junction

A
  • provide a permeability barrier across epithelial sheets like in the small intestine.
  • allows for regulated transport of nutrients through the cells- transcellular transport (instead of things just diffusing)
  • Na2+ dependent uptake at the apical membranes and facilitated diffusion at baso-lateral membranes
  • maintain cell polarity by keeping membrane proteins in place
21
Q

proteins of tight junction

A

claudin and occludin- strings of transmembrane proteins interact with each other on adjacent cells via homophilic interactions
-permeability depends on number of strings of proteins

22
Q

Gap junctions

A
  • communication between neighboring cells

- electrical conduction in cardiac muscle and passage of small molecules aa, vitamins etc.

23
Q

protein of gap junction

A

connexin
-six connexin molecules associate in the plasma membrane to form a pole called a connexon (hemi-channel) connexons on adjacent cells associate to form a Gap junction (see picure-hemichannel as in tube cut in half down the middle, 6 make full circle and circle connects with another)

24
Q

regulation of gap junctions

A

high intracellular calcium or low pH gap junction is closed

low intracellular calcium or high pH gap junction is open

25
Q

Connective tissues

A
  • synthesized by a small number of cells dispersed within the matrix
  • secreted locally and then assembled
  • ECM is the major component of connective tissues
  • ECM provides major characteristics of tissue (tensile strength/elasticity/permeability)
  • ECM mostly produced by fibroblasts
  • some cells use specialized cells- chondroblasts and osteoblasts.
26
Q

Three major protein families of the ECM

A
  1. Fibrous- collagens and elastin
  2. Bulky-space filling proteins- proteoglycans
  3. cross-linking proteins- fibronectin/ laminin
27
Q

Fibrous proteins

A

collagen I, II, III, elastin (stabilized by fibrillin)

28
Q

Collagen I, II, III

A
  • the fibrillar collagens, type I is 90% of all collagens
  • collagen is the most abundant protein 25% of total body protein
  • collagen provides tensile strength and resists stretching (tissues require this and elasticity).
29
Q

Ehlers-Danlos Syndrome

A

hyperextensible skin and joints because of various fibrillar collagen defects

30
Q

Fibrillar collagen biosynthesis

A
  • synthesized as pro alpha chain molecule in ER
  • post translational modification (hydroxylation/glycosylation of proline and lysines) occur in the Golgi
  • three pro alpha chains associate into a triple helix (pro-collagen)
  • SECRETED FROM CELL
  • in extracellular space collagenases clip pro-peptides allowing triple helical collagen to self associate into higher order structures
  • forms FIBRILS AND FIBERS
  • cells may further re-model/order the matric by attaching it to various integrins on the cell surface and tugging on it
31
Q

Type IV collagen

A

can’t form fibrils

  • pro-peptide isn’t cleaved, blocks cross linking and thus fibril formation
  • forms a mesh and is a major component of basal lamina
32
Q

Elastin

A
  • elastic component of skin, lungs, and blood vessels.
  • 750 aa. extensive cross-linking following secretion via covalent linking of lysine residues
  • elastic features due primarily to molecule containing a large amount of random coil and turns due to high proline content
33
Q

Fibrillin

A
  • stabilizes elastin
  • glycoprotein that forms a sheath around the elastin fibers
  • mutations lead to Mafan Syndrome- aorta prone to rupture
34
Q

Bulky Filler Proteins/Molecules

A
  • space filling
  • resist compression forces
  • permit rapid diffusion ex:growth factors
  • permit cell migration-during embryogenesis, immune cell response to infection
35
Q

Proteoglycans

A
  • major component of cartilage/ loose CT
  • glycosaminoglycans (unbranched chains of repeating disaccharides)
  • Core protein backbone link to GAGs via serine
  • can complex with hyaluronic acid using linker proteins
  • range in size
36
Q

Substances on GAGs

A
  • sulfate and carboxyl groups (neg charge)
  • hydrophilic
  • hydrated gel
  • resists compression
37
Q

Cross-linker proteins

A

Fibronectin and laminin

38
Q

Fibronectin

A
  • multi-domain glycoprotein
  • homo-dimer (each chain is 225 kDa)
  • can self associate into bundles and fibrils
  • alternative space variants
39
Q

Fibronectin binding sites

A
  • integrins (cell adhesions (cell-cell)/focal adhesions (cell-ECM) (actin)) via RGDS sequence in fibronectin
  • Heparin
  • Type I, II, III collagen
  • Fibrin (platelet clotting)
  • important in loose CT/ blood clotting/ wound repair/ cell migration/development
40
Q

Laminin

A
  • three chain polypeptide
  • binds integrin on cell surface (focal adhesions and hemidesmosomes (cell-ECM))
  • Binds type IV collagen
  • binds heparoin
  • component of basal lamina (along with type IV and proteoglycans)
41
Q

Basal Lamina

A
  • specialized ECM forming a dense meshwork

- Type IV (binds integrins on cells-focal adhesions and hemi-desmosomes), laminin, proteoglycans

42
Q

Functions of basal lamina

A
  1. surrounds and supports muscle cells (DMD) also links muscle to tendon
  2. support for epithelial sheets (controls proliferation)
  3. kidney- molecular filter- blocks loss of protein from blood into kidney tubule
  4. guidance pathways- development, NCC- peripheral nervous system
43
Q

pemphigus

A
  • problem with anchoring junction and specifically cell-cell because it attacks cadherins
  • desmosome (IF) and adherens (actin)
44
Q

epidermolysis bullosa simplex

A
  • problem with anchoring junction and keratin (IF)

- desmosomes and hemidesmosomes

MCP Unit 1 (5 decks)

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