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19 Cards in this Set

  • Front
  • Back

What are the four main different types of tissue?

- Epithelial

- Muscle

- Connective

- Nerve

Connective tissue generally has two different categories in terms of shape and mechanical properties:

- pulling and stretching

- twisting and squashing

Connective tissue is broadly divided into four categories:

- Blood

- Bone (compact and spongy)

- Cartilage (hyaline, fibrocartilage, elastic)

- Connective tissue proper (loose and dense)

What are the different types of loose connective tissue proper:

- Areolar - holds organs together, underlying epithelial tissues, blood vessels, nerves

- Adipose

- Reticular - composed of reticular fibres, found in the spleen, liver and lymph nodes

What are the different types of dense connective tissue proper:

- Regular - the collagen fibres run in the same diraction, such tssue has a very high tensile strength (tendon)

- Irregular - less regularly arranged collagen fibres giving strength in all direction (dermis)

- Elastic - in this tissue, elastin is the main fibre type; an example of this is found in the vocal fold

What are the main characteristics of connective tissue?

- Abundance of extracellular matrix

- Cells are normally separated by ECM

Examples of connective tissue in other phyla:

- chitin exoskeleton in insects - main support

- connective tissue layers surrounding many organs

- CT attaching Malpighian tubules to the gut

What are the functions of connective tissues?

- Join the other tissues of the body

- Mechanical support to organs

- take the stress of movement

- maintain shape

- growth, development and repair

What is the extracellular matrix?

- A composite of insoluble fibres and soluble polymers

What are the three principle components of the ECM?

- Collagen - confer tensile strength

- Proteoglycans - confer resiliency and compressibility

- Matrix glycoproteins - elasticity, tissue cohesiveness & cell-ECM communication

What are the features of collagen?

- a family of ~29 fibrous proteins that share a common motif - trible helix

- 3 polypeptides (α chains) intertwine to form a rod-shaped super-helix

- type I collagen is the major collagen in CT

What are the features of type I collagen?

- high abundance of Glycine, Proline and Hydroxyproline

- Gly-X-Y repeating motif

- triple helix stabilised by hydrogen bonds

- denatured collagen - gelatin

What post-translational modifications does collagen go through:

1) hydroxylation of proline (ascorbate is essential co-factor = keeps enzyme in active/reduced state)

2) hydroxylation of lysine

3) glycosylation

4) lysyl oxidase - initiation of collagen cross links

What is the role of hydroxyproline residues?

- stabilize the triple helix by increasing hydrogen bonds between α chains

- more hydroxyproline = more hydrogen bonds = higher melting temperature

How do α chains fold into a triple helix?

- initiated by C-terminal propeptide - alignment

- folds from the C terminal towards the N terminal

Propeptides in the ECM are cleaved:

- Converting soluble procollagen to insoluble collagen triple helical rods

- cleavage of the C and N terminal propeptides

- The cleavage is mediated by C and N proteinases

How is type I collagen assembled (from molecules to fibrils)?

- Three precursor chains assemble into triple helix with loose ends (procollagen)

- procollagen peptidase = collagen

- assembly of collagen into fibrils - adjacent molecules are displaced approximately 1/4 of their length = striated appearance seen in electron microscope

- Collagen fibrils aggregate side-by-side in bundles into fibres

How is type I collagen assembled (image)?

How does collagen cross-linking take place and what is the purpose of it?

- initiated by oxidation of lysine or hydroxylysine residues by lysyl oxidase

- stabilizes collagen fibrils