Connective tissues proper Flashcards
define connective tissue
tissue that connects, support, binds or separates other tissues or organs, typically having relatively few cells embedded in an amorphous matrix, often with collagen or other fibres
components of connective tissue
- cells mainly mature fibroblasts/fibrocytes, fixed adipocytes, reticular cells, melanocytes, mast cells, mesenchymal stem cells
- fibres collagens, elastin, reticular fibres
- ground substance proteoglycans, glucosaminoglycans
functions of connective tissue
- binding and supporting holding skin, gut, lungs, bones etc. together
- protection eg. bone protecting vital organs, fat as shock-absorber
- insulation eg. fat underlying skin
- storing reserve fuel and cells eg. bone marrow and fat tissue
- transporting substances within body eg. blood and interstitium
- separation of tissues eg. fascia and tendons/cartilage
what is the interstitium
space between tissues and organs of the body
types of connective tissue proper
loose connective tissue
- areolar
dense connective tissue
- regular
- irregular
structure of loose connective tissue (areolar)
contains multiple cell types
- fibroblasts, macrophages, white blood cells, mast cells, adipocytes
contains two main fibres
- collagenous
- elastic
gel-like ground substance
- proteoglycans, hyaluronic acid
functions of loose connective tissue (areolar tissue)
- holds vessels that supply fluids
- permits cell migration
- involved in inflammation pathways
- acts as packaging around organs
- generally hold everything in place
- cushions and stabilises organs
where is loose connective tissue found
- under epithelial cell layers
- around glands
- surrounds capillaries, nerves and sinusoids
- areas where bacteria/viruses that have breached the epithelial surface can be attacked and destroyed by the large number of immune cells present in the highly viscous loose connective tissue
histology of loose connective tissue
- adipocyte large white droplet
- mast cells large and darkly stained
- collagen fibres thick strands
- elastin fibres thin strands
function of fibroblasts
- synthesise and secrete the fibres lying within ground substance (extracellular matrix)
- important in wound healing process and responsible for formation of scar tissue
- myofibroblasts contain actin and myosin and responsible for wound contraction when tissue loss has occurred
function of macrophages
- derived from blood monocytes and move into loose connective tissue when there’s local inflammation
- phagocytic so degrade foreign organisms and cell debris
- professional antigen presenting cells
function of mast cells
- look like basophils
- contain abundant granules including histamine (inceases blood vessel wall permeability), heparin (anticoaguant), cytokines (attract eosinophils and neutrophils)
- found in areolar connective tissue near blood vessels
- absent from CNS to avoid damging effects of oedema
- become coated with IgE molecules that bind allergens causing contents of granules to be released from cell
what are unilocular adipocytes (white)
- single enormous lipid droplet with nucleus, cytoplasm and organelles squeezed to one side of cell
- function is padding and shock absorber, insulation and energy reserve
what are multilocular adipocytes (brown)
- multiple small lipid droplets with nucleus, cytoplasm and organelles squeezed to centre of cell
- very few in adults
- function is to provide insulation and energy reserves
- main method of generating heat in neonates through non-shivering thermogenesis
white VS brown adipose tissue
white
- single lipid droplet
- normal number of mitochondria
- single peripheral nucleus
- lipid breakdown slow in adults so heat generated by shivering reflex
white
- multiple lipid droplets
- increased number of mitochondria
- single central nucleus
- lipid breakdown accelerated in young children so oxidative phosphorylation uncoupled to generate heat
what are adipose cells generated from
- immature fibroblasts
- mesenchymal cells
fibres of connective tissue
- collagen flexible with high tenisle strength
- reticular/reticulin supporting framework/sponge
- elastic allows tissues to recoil after stretch or distension
what is extracellular matrix
complex extracellular structural network consisting of ground substance and fibres
types of collagen
type I
- most widely distributed type ~90%
- fibrils aggregate into fibres and fibre bundles eg. in tendons, skin dermis
type II
- fibrils do not form fibres
- in hyaline and elastic cartilage
type III (reticulin)
- fibrils form fibres around muscle and nerve cells and within lymphatic tissues and organs and tendons
type IV
- unique form present in basement membrane
- binds to proteoglycans
examples of loose connective tissue
- superficial fascia
- submucosa of colon
what is ground substance
- viscous, clear substance with a slippery feel
- high water content
- composed of proteoglycans, glycosaminoglycans and glycoproteins
what are proteoglycans
- large macromolecules consisting of a core protein to which glycosaminoglycans (GAGs) are covalently bonded
- GAGs attract water and form a gel that permits diffusion but resists compression
- core proteins attached to the hyaluronate
- sugar moieties attract water but make ground substance sticky and slippery at same time
what is hyaluronic acid
unique GAG that’s bound to proteoglycans by a link protein to form giant hydrophilic macromolecules that resist compression without inhibiting flexibility so main GAG in cartilage
mucoid connective tissue
- cell: immature fibroblasts
- fibres: thin collagen III fibres
- main component: jelly-like ground substance - hyaluronic acid
where is mucoid connective tissue found
- umbilical cord
- vitreous humour of eye
how is collagen formed
- fibroblasts secrete procollagen which is converted to collagen molecules outside the cell and aggregated to from final collagen fibrils
- fibrils can group together to form collagen fibres that provide strength to the tissue eg. tendons, ligaments
what are reticular fibres
- type of fibre composed of type III collagen secreted by reticular cells
- crosslink to form reticulin which acts as supporting mesh in soft tissues
what are elastin fibres
- elastin is the primary component which enfolds and is surrounded by microfibrils called fibrillin
- occurs in most connective tissues but to varying degrees
- allows tissues to recoil after stretch or distension
- important in artery walls, dermis, lungs, elastic cartilage
structure of dense connective tissue
- few cell types - mostly fibroblasts
- many collagen fibres
- little ground substance
two types of dense connective tissue
regular
- collagen fibres arranged in parallel bundles and densely packed
- fibroblasts between bundles
- designed to withstand stress in a single direction
- tendons, ligaments, aponeuroses
irregular
- collagen fibres arranged in bundles orientated in various directions
- fibroblasts between bundles
- designed to withstand stress in multiple directions
- submucosa of intestine, deep layers of dermis
examples of dense regular connective tissue
tendon connects muscle to bone
- cylindrical mass of connective tissue at end of muscle
- collagen bundles in parallel, densely packed formation in line with tensile force exerted by muscle
- rows of elongated flattened fibroblasts between the collagen bundles so muscles can exert force onto bone and cause movement
ligament connects bone to bone
- collagen bundles densely packed in parallel arrangement
- not straight but undulate and arranged in fascicles that are separated by loose connective tissue
aponeuroses cover large areas of body and provide structural support
- flat sheet of regular connective tissue with bundles of fibres in one layer arranged at 90 degrees to those in adjacent layers
- tendon flattened into thin broad sheath
example of dense irregular connective tissue
dermis underlying epidermis of skin
- collagen bundles densely packed but irregularly arranged and orientated in multiple directions
- skin can resist forces in multiple directions to prevent tearing
- elastic fibres allow stretch and restoration to original shape after skin bent or folded
types of fascia
- superficial
- deep
- visceral/parietal
what is fascia
- made up of fibrous (dense) connective tissue containing closely packed bundles of collagen fibres oriented in a wavy pattern parallel to direction of pull
- fascia is flexible and able to resist great unidirectional tension forces until wavy pattern of fibres has been straightened out by pulling force
- collagen fibres produced by fibroblasts within fascia
why is vitamin C needed for collagen formation
vitamin C hydroxylates proline and lysine which helps form procollagen inside cell which can be oackaged, released and modified into collagen outside of cell
what is scurvy
vitamin C deficiency
- synthesis of abnormal collagen that lacks usual strength
- poor wound healing and impaired bone formation
symptoms and signs of scurvy
- gum disease and tooth loss
- bruising of skin
- hair loss
- bleeding
- poor wound healing
- weakness and fatigue
- impaired bone development in young
what is Marfan’s syndrome
- autosomal dominant disorder
- mutation in fibrillin 1 gene so elastic tissue is abnormal
signs of Marfan’s syndrome
- abnormally tall
- arachnodactyly
- frequent joint dislocation
- greater span than length
- risk of catastrophic aortic rupture
what is osteogenesis imperfecta (“brittle bone disease”)
- autosomal dominant disease
- due to mutated collagen fibres and/or not enough collagen produced
signs of osteogenesis imperfecta
- weakened bones (fractures common)
- short stature
- blue sclera
- hearing loss
- hypermobility (loose joints)
- flat or arched feet
- poor teeth development
what is Ehlers-Danlos syndrome
- collagen fibre abnormalities of dermis and tendons
- presents as joint dislocations and skin deformation
