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Anatomy > Connective tissue > Flashcards

Connective tissue Flashcards

1
Q

What are the general features of connective tissue?

A
  1. Distributed throughout the body
  2. Composed of:
    - Ground substance
    - Structural proteins
    - Specialised proteins
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2
Q

What are ground substances?

A
  • Non-cellular, non-structural.
  • Has proteoglycans that extracts H20 + ions and form viscous matrix in Extra cellular space
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3
Q

What are structural proteins?

A
  • Collagen & elastin
  • Secreted by Connective Tissue cells– fibroblasts, chondrocytes, osteoblasts
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4
Q

What are specialised proteins?

A
  • Fibrillin - scaffold for deposition of Elastin
  • Fibronectin - binds integrins, & other extracellular
    matrix proteins
  • Laminin - basal lamina
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5
Q

What is the function of collagen?

A
  • Support and strengthen (tendon)
  • Intercellular binding (liver, muscles)
  • Matrix for deposition of inorganic salts (bone, teeth)
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6
Q

Outline the properties for collagen.

A

Collagen:
- Present in all tissues, most abundant
- Fibrillar collagen: long & rigid, triple helical structure
- > 20 diff types

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7
Q

Outline the distribution for collagen.

A

Collagen:
1. Fibrils: ^ tensile strength. helical structure, collagen types I, II & III.
2. Network forming: 3D mesh (basement membrane, thin + sheet like, Collagen type IV, VII)
3. Fibril associated: Links fibrils to one another & other components of ECM, collagen types IX & XII

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8
Q

Outline the structure for collagen.

A
  1. Amino acid sequence:
    - Repeating -Gly-X-Y- sequence, X = Proline, Y = hydroxyproline.
    - Proline causes bending of chain
    - Glycine fits into space made by triple helix
  2. Triple helical structure:
    - Exposed R-groups allow interactions with other collagen fibres.
  3. Post-translational modification:
    - Hydroxylation of Pro and Lys
    - Hydroxyproline maximises inter-polypeptide H-bonds (triple helix stabilised)
    - Glycosylation of hydroxylysine
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9
Q

Outline the synthesis for collagen.

A

Where:
- Fibroblasts, Osteoblasts & Chondrocytes
Go to:
- The extra cellular matrix (ECM)
Modification:
- product = mature collagen monomers aggregate & cross-link = Fibrils
How:

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10
Q

How does collagen cross-link?

A
  1. Lysyl oxidase deaminates some lys & hydroxy-lys
  2. Resulting reactive aldehydes (allylys & hydroxy-allylys)
  3. Reactive aldehydes covalently bond with lys or hydroxy-lys
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11
Q

Why is cross linking important?

A
  • Essential for tensile strength
  • Any mutations affecting cross- linking affects stability
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12
Q

Outline the degradation for collagen and elastin.

A
  • T1/2= months
    1. Collagenases: e.g. for type I cleavage at specific site 3⁄4 and 1⁄4 fragments
    2. Matrix proteinases
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13
Q

What does pro-collagen peptidase do?

A

Procollagen peptidase is an endopeptidase involved in the processing of collagen. The proteases removes the terminal peptides of the pro-collagen

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14
Q

List the different types of collagen and where they are found.

A
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15
Q

How does vitamin c deficiency affect collagen?

A
  • Vitamin c prevents auto-inactivation of lysyl and prolyl hyroxylase, two key enzymes in collagen biosynthesis.
  • Collagen fibres cannot be cross-linked
  • Decreased tensile strength
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16
Q

What is the molecular basis of the connective tissue disorder: Ehlers Danlos Syndrome

A

Defects in metabolism of fibrillar collagen:
1. Collagen processing enzyme deficiency
- Lysyl hydroxylase & Procollagen peptidase
2. Collagen sequence mutations
- Types I, III, V. III= v. serious, vascular problems.
Symptoms:
- hyper-mobile joints, hyper-elastic skin, CV complications (vessels & organs rupture), chronic pain

17
Q

What is the molecular basis of the connective tissue disorder: Osteogenesis Imperfecta

A

‘Brittle bone disease’.
- Group of diseases & range of severities, disorder of type I collagen
Types:
1. Decreased Production: mild = OI type I
2. Altered structure: severe = OI type II, III, IV
Symptoms:
- Bone bend & # easily
- Slow wound healing
- Rotated & twisted spine- humped back
- Blue sclera

18
Q

Discuss type 1 of Osteogenesis imperfecta.

A

Type 1: Osteogenesis imperfect tarda
- Most common, AD inheritance,
- Defect: Inactivation of 1 allele of a1 collagen gene,
- Result: decreased pro a1 synthesis, excess pro a2, deficiency in mature collagen (bone fragility)
- Symptoms: Blue sclera, frequent #, Conductive deafness

19
Q

Discuss type 2 of Osteogenesis imperfecta.

A

Type 2: Osteogenesis imperfecta congenita
- Defect: Mutation in a1(I) or a2 collagen genes
- Result: Defective protein in normal amounts, > 75% of Type I collagen is abnormal, abnormal collagen degraded, extreme bone fragility.
- Symptoms: telescoping of long bones, multiple congenital #, perinatal lethal

20
Q

Discuss type 3 of Osteogenesis imperfecta.

A
  • Defect: Mutation in a1(I) or a2 collagen genes
  • Result: Defective protein in normal amounts
  • Symptoms: Progressively deforming, multiple congenital #, severe bone deformity, limited growth, blue sclera, hearing loss
21
Q

Discuss type 4 of Osteogenesis imperfecta.

A

‘Norma lifespan’
- Defect: Mutation in a1(I) or a2 collagen genes
- Result: Defective protein in normal amounts
- Symptoms: #, limited growth, mild-moderate bony deformity, normal sclera*, hearing loss

22
Q

What are the properties of elastin?

A
  • Rubber like
  • Stretch to several times its length and any direction
  • Recoil to original shape
23
Q

Distribution of elastin.

A

Location: lungs, large arterial walls, ligaments

24
Q

Discuss the structure of elastin.

A
  • Linear polypeptide (700 aa)
  • Small non-polar aa e.g. Gly, Val, Ala. Rich in Pro and Lys
  • Little hydroxy-pro, NO hydroxy-lys
  • Secreted into ECM – interacts with Fibrillin
  • Lysyl oxidase oxidatively deaminates lysyl side chains to ally-lys
  • 3 allylysine & 1 lysyl cross-link tropoelastin
    **Cross-linked Tropoelastin = elastin
25
Q

Discuss elastin synthesis.

A
26
Q

Discuss elastin degradation.

A

Degraded by elastase:
- Elastase secreted by neutrophils and inhibited by a1 anti-trypsin
*a1 anti-trypsin prevents inappropriate degradation of Elastin in the lungs.

27
Q

What is the molecular basis of the connective tissue disorder: α1 anti-trypsin deficiency

A

Defect: Deficiency of a1-AT. Single allele not enough to cause disease.
Result: Premature Emphysema due to destruction of connective tissue in alveoli. Exacerbated by smoking
Treatment: a1-AT IV injections weekly

28
Q

What is the molecular basis of the connective tissue disorder: Marfan syndrome

A

Defect: Mutation of fibrillin-1 gene (FBN1), defective fibrillin, Autosomal dominant
Result: classic presentation includes aortic aneurysm or dissection, long extremities, arachnodactyly, joint hyper-mobility, and subluxation of the lens of the eye.
- No causal tx but symptoms treated.

Anatomy (18 decks)

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