TOB L5 Flashcards
State functions of connective tissue
- Provide sturctural form to the body and organs
- Provide a medium for diffusion of nutrients and wastes
- Attach muscle to bone and bone to bone
- Provide a cushion between tissues and organs
- Defend against infection
- Aid in tissue repair (stem cells)
State two components making up connective tissue
- Cells
- ECM (extracellular matrix)
State the components of the ECM
- Ground substance
(hyaluronate proteoglycan aggregates) - Fibrillar proteins
(collagen fibres, elastin, fibronectin, fibrillin)
Describe the composition of ground substance / how hyaluronate
Gel-like like substance
Consists of highly glycosylated proteins (proetoglycans) attached to high molecule weight hyaluronic acid (HA) backbone
Forming long unbranched polysaccharides - glycosaminoglycans
Polysccharides form hyaluronate proteoglycan aggregates
Describe the characteristics of hyaluronate proteoglycan aggregates
- Inflexible
- Highly polar, hence attract water (90% of ECM is water)
- Resistant to compression
Describe how connective tissue is derived
From multipotent embryonic mesenchymal cells:
- Cells of mesoderm (middle embryonic germ layer) proliferate + migrate to form mesenchyme in early embryo (with ectodermal cells that form some of bones + muscles in head + neck)
How is mesenchyme found in adults?
Mescenchyme persists in adults as stromal stem cells
Diagram showing lineages derived from mesenchymal cells
This diagram is showing what mesenchymal cells can specialise into
Describe mesenchymal tissue in the developing fetus
Mesenchymal cells morphologically similar but give rise to cells that differentiate into different cell types
Describe the role of mesenchymal cells in adults
Mesenchymal cells persist in the adult
FACILITATE HEALING + RENWEAL
Describe the classification of connective tissue
Embryonic connective tissue:
- mesenchyme
-mucous connective tissue (foetal umbilical cord)
Connective tissue proper:
- loose (or areolar, meaning space) connective tissue
- dense connective tissue (irregular or regular)
Specialised connective tissue
- adipose tissue
- blood + lymphatic tissue
- cartilage (type II collagen), bone (type I collagen)
What is the most abundant human protein ?
Collagen
30% of whole body (90% of this is collagen type I)
28 types of collagen
Diagram showing triple helix structure of tropocollagen
Describe the process of collagen synthesis
RER:
1. Synthesis of pre-procollagen alpha chains (glycine every third residue allows helical conformation)
2. Vitamin C dependent hydroxylation of prolyl and lysyl residues - stabilises and strengthens collagen cross links
3. Assembly of triple helix to form procollagen
Golgi:
Packaging into secretory vesicles
Cell membrane
Constituitive exocytosis
Extracellular environment:
1. Non-helical terminal peptides cleaved
2. Collagen molecules assemle into fibrils
Describe type I collagen assembly
- We have collagen subunits
- Each fibril is composed of staggered collegen molecules with a periodic banding which repeats every 67 nm
- Fibrils assemble into fibres (visible under light microscopy), fibres assemble into larger bundles
Describe the types of collagen
Type I: 90% of all collagen. Fibrils aggregate into fibres, which assemble into large bundles (e.g. tendons , capsules of organs, dermis, organic component of bone)
Type II: Fibrils do not form fibres, so form a very fine mesh (e,g. in hyaline cartilage)
Type III: fibrils form branching fibres but not bundles. (e.g. around muscle, nerve cells) (e.g. within lymphatic tissues + organs, here it is called reticulin) (e.g. in skin, particularly papillary dermis)
Type IV: Unique (sheet) form present in basal lamina of basement membrane
Type VIII: Anchors basal lamina to underlying reticular lamina
Describe disorders related to collagen synthesis
Ehlers-Danlos (ED)
-can occur due to failures in various stages in collagen synthesis
-Faiulre in Type IV ED (vascular type),
-Failure Type III - aortic rputure
Scurvy
-lack of vit c reduces prolyl hydroxylase activity, leading to gum ulcerations + haemorrhage
Osetogenesis imperfecta (OI, brittle bone disease)
-loss of function of COL1A1, collagen 1A gene
-results in spontaneous bone fracture
Describe the structure, location and function of Elastic Fibres
- Composites of elastin deposited on a fibrillin microfibril sacffold
- Elastic fibres found in connective tissue
- Allow tissue to distend + return to original shape e.g. in dermis, artery walls, elastic cartilage
TEM of elastic fibre
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