Flashcards in Connective And Adipose Tissue Deck (37):
What are the functions of connective tissue?
1. Connects cells to form tissues, connects tissues to form organs and connects organs to form the body. Some tissues provide support as well as connecting (cartilage and bone)
2. Transportation - provide a medium for diffusion of nutrients and wastes
3. Protection - provide a cushion between tissues and organs and
provides insulation (adipose tissue)
4. Storage (adipose tissue)
5. Defence against infection (blood, lymph, fixed and wandering cells)
6. Wound healing (macrophages, fibroblasts, myofibroblasts)
Which three things form general connective tissue (CT proper)?
• Ground substance
Which fibres are found in general connective tissue?
• Collagen – Flexible with high tensile strength
• Reticular – Provide a supporting framework/sponge
• Elastin – Allows tissues to recoil after stretch or distension
Describe the ground substance in general CT
- Ground substance is a viscous, clear substance with a slippery feel.
- It has a high water content.
- Composed of proteoglycans
What is a proteoglycan?
A proteoglycan is a large macromolecule consisting of a core protein to which glycosaminoglycans are covalently bound
What are Glycosaminoglycans (GAGs)?
- Glycosaminoglycans (GAGs) are long-chained polysaccharides.
- GAGs attract water to form a hydrated gel that permits rapid diffusion but also resists compression.
What is the extracellular matrix?
• A term used to describe a complex extracellular structural network that consists of ground substance and fibres
Describe the composition of loose CT
– Many cells (fibroblasts, mast cells)
– Sparse collagen fibres
- Elastin fibres
– Abundant ground substance
– Viscous, gel-like consistency
– Important role in transport (by diffusion)
Describe the composition dense CT
– Few cells, nearly all fibroblasts
– Many collagen fibres
– Little ground substance
Where can you find loose CT?
• Located beneath epithelia (to facilitate diffusion)
• Associated with epithelium of glands
• Located around small blood vessels
E.g. The superficial layer of the dermis in the skin
The submucosa of the colon
What causes swelling in the loose CT?
Loose CT located in sites where pathogens, such as bacteria that have breached an epithelial surface, can be challenged and destroyed by the cells of the immune system.
Describe the arrangement of regular dense CT
– Collagen fibres are arranged in parallel bundles and are densely packed.
- Between the bundles are fibroblasts
– Designed to withstand stress in a single direction
– Seen in tendons, ligaments and aponeuroses
Describe the arrangement of dense irregular CT
– Collagen fibres are arranged in bundles orientated in various directions.
- Between the bundles are fibroblasts
– Designed to withstand stress in multiple directions
– Examples are submucosa of intestine and deep layers of dermis
How is dense regular CT arranged in the tendons?
In tendons that connect muscles to bones the collagen bundles lie in a parallel, densely packed formation in line with the tensile force exerted by the muscle.
Describe the composition of a ligament
The collagen bundles are densely packed in parallel arrangement, but undulate and are arranged in fascicles, separated by loose connective tissue.
What is an aponeurosis?
A flat sheet of regular CT with bundles of fibres in one layer often arranged at a 90 degree angle to those in adjacent layers
What is the dermis composed of and how does this contribute to its function?
- The dermis is a dense irregular connective tissue.
- The bundles of collagen are densely packed but irregularly arranged, such that they are orientated in multiple directions.
- The skin can thus resist forces in multiple directions to prevent tearing.
- The elastic fibres allow a degree of stretch and a restoration to the original shape after the skin is bent or folded.
What fixed cells are involved in CT?
– Fibroblasts (and myofibroblasts)
– Mast cells
– Mesenchymal ‘stem cells’
Which wandering immune cells are associated with CT?
– Plasma cells
Describe the role of a fibroblast
- Fibroblasts synthesise and secrete both ground substance and the fibres that lie within the ground substance
- They are very important in wound healing and are the cells
primarily responsible for the formation of scar tissue
- Myofibroblasts are modified fibroblasts that contain actin. They
are responsible for wound contraction when tissue loss has
Explain the function of a macrophage
- Macrophages are derived from blood monocytes which move into loose connective tissue, especially when there is local inflammation
- Macrophages are phagocytic and can degrade foreign organisms and cell debris
- Macrophages are ‘professional antigen presenting cells’ (i.e. they can present foreign material to the T lymphocytes of the immune system)
Describe the structure of a mast cell
- Mast cell cytoplasm contains abundant granules
These granules contain:
• Histamine (increases blood vessel wall permeability)
• Heparin (an anticoagulant)
• Substances that attract eosinophils and neutrophils
- Mast cells become coated with Immunoglobulin E (IgE), molecules which specifically bind allergens. When an allergen cross-links these surface-bound IgE molecules, the contents of the granules are all rapidly released from the cell.
- The secretions of the granules can result in immediate hypersensitivity reactions, allergy and anaphylaxis.
What is type 1 collagen?
Type I: The most widely distributed type (90% of all collagen). Fibrils aggregate into fibres and fibre bundles (e.g. in tendons, capsules of organs and skin dermis)
Describe the structure of type 1 collagen
Each molecule is composed of a triple helix of α chains
Note, this is not the same as three alpha helices
What is reticulin?
Type III collagen
- Fibrils form fibres around muscle and nerve cells and within lymphatic tissues and organs.
How are collagen fibrils produced?
- Fibroblasts secrete procollagen that is converted to collagen
molecules outside the cell. The collagen molecules are then
aggregated to form the final collagen fibrils
- In some tissues fibrils group together to form collagen fibres
How does vitamin C deficiency lead to poor wound healing and impaired bone formation?
- Vitamin C is required for the intracellular production of
- No collagen
- No wound formation
Describe the structure of elastic fibres
• Elastin is the primary component of elastic fibres, but itself enfolds and is surrounded by microfibrils called fibrillin
• It occurs in most connective tissues but to widely varying degrees
• Amongst the sites at which elastic fibres have an important role are the dermis, artery walls, lungs and those sites bearing elastic cartilage
What is Marfan's syndrome?
Marfan’s syndrome is an autosomal dominant disorder in which expression of the fibrillin gene is abnormal such that elastic tissue is abnormal. Sufferers are abnormally tall, exhibit arachnodactyly, have frequent joint dislocation and can be at risk of catastrophic aortic rupture.
What is the role of adipose tissue?
Adipose tissue contains fat, a fuel reserve, but also has a role in thermal insulation and in shock- absorbtion.
Describe the appearance of white adipose tissue
- Most adipose tissue in the body is white fat.
- In typical H & E stained, wax-embedded preparations, the cells look empty. They are empty because the toluene and xylene, used in tissue preparation, have dissolved away the lipid.
Describe the structure of an adipose cell
- Unilocular adipose cells (fat cells) are almost completely filled by a single fat droplet.
- The cytoplasm is displaced to the rim of the cell and the nucleus to one side
How is brown fat tissue composed?
- Brown fat cells (multilocular adipose cells) each contain many lipid droplets and a central nucleus
What is the function of ghrelin?
- Appetite stimulator
- Released by stomach
- Signals hunger to brain
What is the function of leptin?
- Appetite suppressor
- Stored and secreted by fat cells
- Released when eating a meal
What is hyaluronic acid?
GAG bound to proteoglycans by a link protein to form giant hydrophilicmacromolecules. It is present in the ground substance of cartilage. The swelling pressure or turgor that occurs in cartilage ground substance allows it to resist compression without inhibiting flexibility