- Connective tissue is derived from the mesoderm
- Primitive mesenchyme forms from the mesoderm: basis for all connective tissues in the body, act as stem cells when damage to organ or connective tissue.
- Tissue found throughout body
- Provides support to rogans internally and externally
- Consists of cells surrounded by a matrix which can be watery, rigid or somewhere in between
- Matrix is often the dominating feature
- Can be further divided into
- Connective tissue proper: loos dense irregular, dens regular, adipose and reticular connective tissue
- Specialised connective tissue: bone and cartilage
- Embryological connective tissue: mesenchyme
- Structural and metabolic
- Biological packing material
- Support the skin
- Supporting body, organs and allowing movement
- Storage
- Repair
- Tissue defence
- Fibroblasts and fibrocytes
- Fibroblast is immature form of fibro cyte (blast= primitive form of cell, cyte=mature form of cell)
- Occur widely in supporting tissues that fill spaces
- Form a lot of organ capsules, tendons and ligaments
- Produce tough fibre that ables movement
- Produces collagen and elastin fibres
- Reticular cells
- Important just for forming general matrix of organs
- Dense regular tissue: fibres going everywhere
- Form scaffolding for organs
- Adipose cells
- Adipocytes
- Often occur in aggregates
- Assemble and store fat droplets
- As amount of fat grows the nucleus is displaced to one side of the cell
- Functions
- Fat storage
- Insulation
- Producing hormones that affect metabolism
- Fish net analogy- each cell has a defined border, lung= broken fishnet
- lypomas
- Chondroblasts and chondrocytes
- Found in respiratory tree, nose,ear joings, between bones, rib cage
- Template for bony skeleton during development
- Dense matrix
- Functions
- Semi-rigid supporting tissue which still provides a degree of flexibility
- Osteoblasts and osteocytes
- Found in bone
- Functions
- Support and protet
- Store calcium and other ions
- Resident and wandering cells
- Defence and immune functions
- Include:
- Mast cells (resident): contain histamine, around any tissue that has access to the outside.
- Macrophages (resident)
- Leukocytes (wandering)- white blood cell which only usually see with inflammation.
The matrix
- Connective tissue composed of
- Cells
- Extracellular matrix consisting of:
- Fibres such as collagen, elastin, reticulin
- Collagen:
- Most abundant protein in the body
- Produced by fibroblasts
- Consist of 3 types of primary proteins wrapped into a superhelix
- High tensile strength of several hundre kg/cm
- Able to stretch by 15%
- 20 diferent variants
- Type 1 most common
- Structure:
- Fibroblasts secrete tropocollage subunits
- Subunits assembled into microfibrils (overlapping subunits cause the banded appearanc in em images)
- Microfibrils are organised into fibrils which are subsequently organised into collagen fibres.
- Elastin
- Produced by smooth muscles cells in arteries and fibroblasts
- Found in structures such as lungs, arteries, veisn skin elastic cartilage etc
- Permits stetc up to 150% of original length
- Allows recoil
- Reticulin
- Secreted by reticular cells (type of fibroblast)
- Form a mesh or framework in variety of tissues
- Collagen type III
- Observed with reticulin stains
- Ground substance:
- Produced predominantly by fibroblasts
- Also secreted by chondorblasts and osteoblasts
- No definitive structure histologically
- Consists of large complexes of proteins and polysaccharides (proteoglycans ) made up of smaller molecules called glycoproteins
- Misture of proteoglycans
- Loose connective tissue
- Supports epithllial cells lining GIT , respiratory and urinary tracts
- Forms deeper layers of skin
- Loose packing for organs
- Function: provide structural support to surrounding tissues
- Provides a deformable space-occupying 'packing'
- Dense irregular connective tissue
- Connective tissue proper
- Location: dermis of the skin, sheaths surrounding nerves and tendons, organ capsules and deep fascia
- Function: provide protection and structural support, abel to withstand tension from different directions.
- Dense regular connective tissue
- Connective tissue proper
- Location: tendons and ligaments
- Function: connect muscle to bone, connect bone to bone, resist tensilve forces generated during mvoement.
- Very little vascularisation- slow healing process in damaged tendons and ligaments
- Reticular connnective tissue
- Type III collagen
- Adipose connective tissue: looks like a fish net
- Special connective tissue:
- cartilage
- Bone
- blood
Cartilage
- Special type of connective tissue
- Stronger than other tissues, more flexible and lighter than bone
- 3 components
- Cells
- Fibres
- Ground substance
- Extracellular Matrix (ECM)
- Abundant in cartilage
- Produced by condrocytes and consists of collagen fibrils which aggregating proteoglycans are embeded
- Cartilage lacks nerves blood vessels and lymphatic vessels
- Surrouned by perchondrium except in case of articular cartilage
- Makes repair difficult
- Perichondrium for repair
- Cartilage gains nutrients via diffusion
- Cartilage cell types:
- Chondroblasts (stem cells)
- Location: derived from mesenchymal cells in perchondrium
- Function: secrete Ecm of cartilage and become chondrocytes
- Chondrocytes
- Chondroblasts (stem cells)
Patterns of growth
- Interstitial
- Existing chondrocytes divide and make more matrix
- Isogenous groups formed by interstitial growth
- Appositional growth
- Happens in perichondrium, stem cells into chondroblasts then condrocytes
Perichondrium
- Cartilaginous tissues surrounded by it except articulate cartilage
- Cells within perichondrium are condrogenic
- Dense irregular connective tissue.
- Hyaline
- Most common and contains many chondrocytes (trachea)
- ECM contains 40% type I I collagen fibres and 60% clycosaminoglycans
- High water content-good at resisting compressive forces
- Found in larynx, articular surfaces, sternal end of ribs
- Elastic
- Contains some type II collagen but mostly elastin fibres
- Found in external ear, nose, larynx
- Fibro
- Least common type
- ECM consists of type I collage oriented in direction of tensile stress (collagen fibres)
- Found in intervetebral disc, public symphysis, menisci
- All contain chondrocytes, difference occur wtihin ECM
Cartilage repair
- Cartilage is avascular gets nutrients via diffusion, if chondrocytes live then some repair through interstitial growth
- If chondrocytes die then some limited regeneration due to differentiation of cells from perichondreum
- Injury to articular cartilage bad as it lacks perichondreum so lack of repair if death of chondrocytes
- Usual repair by fibrosis and collagen formation: diminishes structural integrity of articular cartilage, when cartilage damaged can get calcification and spurs on articular surface.
- Injury to articular cartilage bad as it lacks perichondreum so lack of repair if death of chondrocytes
- Specialised connective tissue
- 3 components: fibres, cells, ground substance
- ECM is mineralised for rigidity and strength
- Involved in calcium homeostasis
- Woven bone (immature)
- Lamellar bone (mature)
- Bone cells
- Osteoprogenitor (stem cells) located in periosteum and endosteum which mature into osteoblasts
- Osteoblasts (bone forming cells) located beneath periosteum
- Osteocytes: trapped within lacunae and maintain the ECM
- Osteoclasts (bone resorbing cells) of macrophage origin located in endosteum. Often have multiple nuclei
- Osteoid
- type I collagen GAG
- Mineralisation occurs due to deposition of calcium hydrocyapatite
- Function: provides bone with its rigidity and strength
- Mesenchymal cells have great array of differentiation so tumour containing more than 1 type of cell
Periosteum
- Difficult to dettach from bone due to fibres penetrating
Bone types
- Woven
- Random organisation of collagen fibres
- Overtime becomes remodelled to produce mature lamellar bone
- Lamellar
- Cancellous forms a spongy mass and less organised than compact bone
- Surrounded by adipose tissue (the more adipose tissue the older the animal is)
- Compact
- Dense and organised into layerslamellae
- In long bone, osteons are formed to enable bone to bear weight
- If bone solid, osteocytes wouldn't get any nutrients
- Mature bone has lamellar organisation that can be concentric or parallel in orientation collage type I fibres are laid in precise array for each lamella
- Analogy : 'reinforced concrete'
- Volkman canal
Blood supply
- Arteries penetrate through foramina via periosteium
- Blood in spongy bone itself-bone marrow
- Vines follow return rought
Learn More
Cliffs Notes: Connective Tissue Quiz
Proprofs: connective tissue quiz
Crash Course Histology: Connective Tissue
Crash Course Histology: Connective Tissue Types