Connective tissue Flashcards
What is connective tissue?
A term given for a diverse and abundant supporting tissue.
What are the functions of connective tissue?
Support other tissues:
Structural support e.g. bone
Strong fibrous connective tissues - tensile strength
Scaffold - support and bind tissues
What are the less rigid functions of connective tissue?
Elasticity - allows flexibility and recoil
Fat - cushioning, metabolism and energy storage
Blood - immune defence
What is basic connective tissue?
Loose and dense connective tissue, non-specialised
Connective tissue proper
What are the components of connective tissue?
Cells
Extracellular matrix: Ground substance and fibres
What are the types of fibres in extracellular matrix?
Elastin, collagen and reticular fibres
Fibres provide strength and durability to tissue.
Embedded in ground substance.
What is ground substance?
Clear viscous substance that fills space between cells and fibres
Contains glycosaminoglycan, proteoglycans, water.
How does ground substance change?
Properties depends on the balance between cells and ECM fibres
Cells needing mechanical strength have lots of ECM fibres - ligaments, tendons, bones.
Needing protection or metabolism - more cells present - blood and adipose tissue.
What are fibroblasts?
The main cell type in connective tissue proper.
Produce and maintain ECM and ground substance.
Spindle shaped cell, and cigar shaped nucleus.
What is the function of fibroblasts?
Inactive form is fibrocyte
Activated myofibroblasts are involved in wound healing - fibrosis.
But can become chronically activated.
What are adipocytes?
Fat cells, can be white or brown.
White adipocytes have a large hole in middle of cell, cytoplasm and nucleus pushed to periphery.
Has a cygnet ring appearance.
What are the fixed connective tissue cells?
Fibroblasts
Adipocytes
Fibrocytes
Macrophages
What are macrophages?
Phagocytotic - immune function - engulf foregin material like bacteria and dead cells.
Derived from monocytes.
What cells are found in specialised connective tissue?
E.g. in cartilage, bone, dentine:
Chondroblasts
Osteoblasts
Odontoblasts
What are wandering connective tissue cells?
Migrate into connective tissue when needed - mostly immune cells:
Plasma cells
Eosinophils
Neutrophils
Lymphocytes
Mast cells
What are plasma cells?
Oval clock face
Nucleus
Actively produces antibodies.
What are eosinophils?
2 lobe nuclei
Involved in inflammatory reactions
Eosin stains mainly granules in this.
What are neutrophils?
Mutlilobed nuclei
Phagocytic functions
What are lymphocytes?
Round nucleus - plasma cells are mature lymphocytes, have a smaller cytoplasm.
Antibody production.
Specialised lympocytes are involved in protection against viruses.
What are mast cells?
Produce histamine and heparin and bioactive substances which mediate inflammation.
Basophilic granules - stains purple not red.
What is the structure of ground substance?
Transparent semi solid gel.
Amorphous - no clear shape, fills space between cells and fibres.
Fibres are embedded in ground substance.
Hyaluronic acid backbone.
What does the hyaluronic acid backbone in ground substance contain?
Glycoproteins and complex carbohydrates - glycosaminoglycans (GAGs).
GAGs have negative side chains so are highly hydrophilic, binds water in ECM - has hydrated gel-like structure.
Water provides volume to the connective tissue and allows vessels to pass through.
What does ground substance look like?
see image
The blue is ground substance
What does elastin look like?
see image
What is elastin?
Secreted as precursor tropoelastin.
Polymerises to become elastin
Requires glycoprotein fibrillin scaffold.
Can be made into fenestrated sheet called elastin lamella.
What is the function of elastin?
Allows stretch and recoil to maintain shape.
Where is elastin found?
Skin
Ears
Arteries
Lung
Bladder
What is the function of collagen?
Main fibre type
Provides tensile strength
Can resist pulling and stretch to an extent but can break.
How is collagen produced?
Secreted by fibroblasts as collagen, made into tropocollagen.
Triple helix structure
Aggregate into fibrils, can form collagen fibres.
How does collagen differ from elastin?
Collagen is thicker than elastin and does not branch
What does collagen look like?
see image
Collagen usually stained pink in H&E.
In Masson’s trichrome, elastin is red/pink, collagen is blue.
What are the types of collagen?
Type 1 - Bone, skin, tendons, ligaments
Type 2 - Cartilage
Type 3 - Reticular fibres
Type 4 - Basement membrane
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What are reticular fibres?
Type 3 collagen
Delicate and thin
Form the framework of organs, glands and blood vessels.
What do reticular fibres look like?
see image
What is collagen type 4?
Found in basement membrane
Acts as a filter allowing only small molecules to pass
Not stained with H&E, but is stained with PAS.
Usually underlies epithelial cells but can surround muscle fibres and separate 2 sheets of cells.
What is loose connective tissue?
Loosely and randomly arranged
Mostly ground substance and many cells present.
What is the function of loose connective tissue?
Binds tissues
Allows diffusion
Allows nerve and blood vessels to pass freely through the tissue
E.g lamina propria
What is lamina propria?
Immediately underlies certain epithelia - digestive, reproductive and respiratory tract (exposed to external environment).
Good for diffusion
But the extra space allows a good breeding ground for microbes so has many immune cells.
What is dense irregular connective tissue?
Fewer cells and less ground substance.
More ECM fibres, randomly arranged.
What is the function of dense irregular connective tissue?
Strong, withstands pressure from different directions.
E.g. the dermis
What is dense regular connective tissue?
Fewer cells and less ground substance
Lots of ECM fibres, highly organised in parallel.
Allows for good tensile strength, resists force in one direction.
e.g. tendons and ligaments.
What is the function of white adipose tissue?
Uniocular - looks like an eye
Specialised for storing energy
Stores and mobilises triglycerides
Structural - padding and shock absorbing, thermal insulator.
What is brown adipose tissue?
Mutliocular - several lipid depositions within a cell.
Most common in newborn, but found in adults around kidney and adrenal gland.
Rich in mitochondria and capillaries.
Specialised for thermogenesis.
What are genetic mutations in connective tissue?
Type 1 collagen - osteogenesis imperfecta
Type 2 - chondrodysplasia
Type 1, 3, 5 - Elhers Danlos syndrome
Fibrillin - Marfan’s syndrome
