Lecture 4 - Connective Tissue Flashcards
what are the characteristics of CT
-around/between other tissue types
-cells DONT form junctions
-ECM usually is the most abundant component
-ECM gives tissue its characteristic properties
-conduit for blood vessels and nerves
what are the components of CT
-fibres: proteins that polymerize into long or short fibrils and fibers. primarily fibronectin, collagen and elastin
-ground substance: hydrated space consisting of multiple proteins, glycoproteins and proteoglycans. also glycosaminoglycans
what are glycosaminoglycans
polymers of modified sugar residues
what gives CT its major functional properties
fibers and ground substance (they are in the ECM)
classification of connective tissue
fibrous CT = loose CT, dense irregular, dense regular
specialized CT = adipose tissue, cartilage, blood, bone
where is CT found
underneath the epithelium
what are the cells of CT and what do they do
-resident/fixed cells: synthesize and maintain the ECM. include fibroblasts and members of the family such as adipose cells, smooth muscle cells, chrondrocyes an osteocytes
-transient cells: cells of the immune system (leukocytes). they secondarily take up residence in the CT (macrophages) and/or traffic between CT and immune organs (lymphocytes)
what are the ECM fibers,
what proportion do they make up, how do they stain
what is their purpose
collagen: ~90% of CT fibers. they are protein polymers that make long straight fibers and meshworks. they are for tensile strength and they are very eosiniphilic
elastin: ~10% of CT fibers. their purpose is for stretch and recoil in things like ligaments, lungs, etc. they are poorly eosinophilic so they need special dyes
*most fibers we see in LM are collagen
collagen type 1 fibers - makes up what, properties
-whole procollagen molecule is all triple helix
-makes longest and largest and strongest fibers of the body
-very strong in tensile strength but not stretchy
elastin fibers - appearance and attachment, what is it produced by
-random coiled elastin molecules attached covalently together
-when fibre is stretched the coils straighten but molecules dont pull apart; recoil upon release of stretch
-produced by fibroblasts and vascular muscle cells
ground substance - what is it made up of, staining, purpose, charge, properties
-made up of ~60-90% water and CHO polymers (glycosaminoglycans and proteoglycans)
-multiple other soluble proteins and glycoproteins including fibronectin, laminin, growth factors
-generally stains poorly in H+E
-provides turgor pressure (resistance to compression) due to bound water
-PGs and GAGs carry net negative charge (bind wanter and basophilic dyes)
- can be watery to very thick gel depending on GAG concentration. gel inhibits cell movement depending on amount of GAGs. water in gels is the medium of diffusion through CT
loose (areolar) CT - ground substance vs fibres, how cellular
-abundant ground substance, few fibers
-small collagen fiber bundles
-often very cellular
reticular CT - what type of CT, what type of collagen, where is it found
type of loose CT
-collagen type 3 fibers form 3D network
-found only in lymphoid organs where it forms scaffold to support immune system cells
dense CT - types, what is abundant, what type of fibers, orientation
-abundant fibers that are mostly collagen type 1
-large prominent fiber bundles, few cells, little ground substance
-dense irregular = bundles randomly oriented
-dense regular = bundles in regular orientation
adipose tissue - what are they found as, what can they form, what do they differentiate from, how cellular are they
- adipocytes frequently found as single cells in in small groups in CT
- also forms large masses = adipose tissues
-differentiate from mesenchymal/fibroblast like precursor cells
-highly cellular
types of adipose tissue and their features, functions, extent of blood supply
-unilocular (white) = triglycerides stored as single lipid droplet, rim of cytoplasm with flattened nucleus, energy homeostasis and hormone secretion; padding and insulation when in large numbers
-multilocular (brown) = triglycerides stored in multiple droplets, round nucleus, obvious cytoplasm with lots of mitochondria, lipid metabolized in cell for heat production
-both have extensive blood supply
cartilage - function, what is the blood supply like, location
-resists mechanical stress, absorb shock and slide on surfaces
-its avascular - limits size and poor capacity for repair
-function: support soft tissue, facilitate bone movement, guides bone development
-location: on articular surfaces, ears and nose, airways and lungs, growth plates of bones
structure of cartilage - what type of cells and where are they, function and what they become
-fibroblast-like cells = edge of cartilage; form a dense CT layer called perichondrium. they proliferate to produce chondroblasts
-chondroblasts = acts as progenitors, proliferate and differentiate into chondrocytes
-chondrocytes = mature cartilage cells, produce and are trapped in the ECM, reside in matrix cavity called a lacuna
what are mature cartilage cells called
chondrocytes
what are the types of cartilage (classification)
hyaline cartilage, elastic cartilage, fibrocartilage
bone tissue - differences from cartilate, similarities, functions
-similar because CT cells are embedded in lacuna and matrix
-main differences - osteocytes instead of chondrocytes, matrix has little ground substance but extensive collagen type 1, matrix is mineralized, highly vascularized with good capacity to repair, can form very large skeletal muscles
-functions: support for body, protects vital organs, harbours bone marrow (hematopoesis), acts as mineral and ion reservoir, transforms muscle contraction into body movement
bone tissue classification - two types and where they lay in the bone
-spongy/cancellous/trabecular = bony meshwork consisting of trabeculae, forms the interior of the bone
-compact bone = dense layer that forms the outside of bone
lamellar bone tissue organization - when can you paraffin embed?
staining? prominent fiber? what does demineralized bone show/expose?
-bone tissue cannot be paraffin embedded and sectioned until minerals are leached out, leaving organic material behind
-demineralized bone shows cellular artifacts but reveals arrangement of collagen layers (lamellae of osteoid)
-very eosinophilic because of collagen type 1
-mineralized bone is sliced very thin to be transparent, no cells left but see fine structure of bony spaces
what is the lacuna
its the space that appears white and it surrounds the cell
parts of lamellar bone (think canals, etc) (3)
-osteocytes are trapped in lacunae between lamellae
-central osteonal (haversian) canal runs along the length of the osteon carrying blood vessels and nerves (so runs down the center of it)
- osteonal canals lined by bone lining cells and osteoprogeniter cells (endosteum)
-fine tunnel like spaces called canaliculi cross lamellae; carry osteocyte processes
long bone histology - what parts are associated with this type of bone? (5)
-circumferential lamellae
-osteon
-osteonal canal
-interstitial lamellae
-perforating canal
what is the difference between concentric lamellae and circumferential lamellae
-concentric is the lamellae that fills the individual osteons
-circumferential is what fills the rest of the space of the bone
what are perforating canals
they are canals that run perpindicular to the osteonal canal every so often and allow for blood vessels to go in and out of the endosteum and periosteum
woven vs lamellar bone - organization, when they appear, are they temporary or permanent
-woven bone = random disposition of collagen fibers and osteocytes, 1st bone tissue to appear during development and fracture repair, temporary; its replaced by lamellar bone except for in cases like tendon insertions, alveolar sockets of teeth etc
- lamellar bone = collagen fibers organized in parallel within each lamellae of calcified matrix, collagen fibers oriented in different directions in adjacent lamellae, majority of bone tissue in adults whether its compact of cancellous
woven vs lamellar - how strong are they, how fast are they produced, what does the conversion involve, what plays a key role in conversion
-woven bone is rapidly produced but not at strong as lamellar bone
-conversion from woven to lamellar involves destruction and redisposition. osteoclasts play key role in this conversion and ongoing bone remodeling.
osteoclasts - what are they, how are they formed, where do they attach, what is their functions (3)
-they are specialized macrophages found in bone
-formed by fusion of several monocytes: multinucleated, motile an d very large
-attach to surface of bone along the outside edge of the cell, sealing off basal compartment
-functions: secrete acid into the space within the seal and mineralization dissolves to create resorption cavity, release lysosomal vescicles containing tht digest matrix proteins, released minerals etc absorbed into circulation
intramembranous ossification - what bones form by this, where does it take place, what happens in the ossification center, how do they synthesize woven bone, deposition?
-most flat bones (skull, mandible, scapula) form by this
-takes place within condensations of embryonic mesenchymal tissue
-mesenchymal cells differentiate into osteoprogenitor/osteoblast cells when they aggregate (ossification center)
-synthesize woven bone by depositing osteoid without any cartilage precursor
-additional osteoid deposition occurs on these first bony spicules and mineralizes.
-eventually, remaining mesenchymal cells give rise to periosteum and endosteum
endochondral ossification - how does depositon occur, what type of growth, how is osteoid laid down, what type of bone is it initially, is there cartilage left behind
-bone matrix deposition occurs on an existing cartilage model
-used to generatae most bones; used for growth (elongation) of long bones
-osteoid is laid down on edges of calcified cartilage matrix by osteoblasts derived from osteoprogenitor cells
-initially woven bone but remodeling leads to lamellar bone
-initially may be remnants of cartilage left but additional remodeling removes all traces of cartilage
can you tell the difference between bone from intramembranous ossification vs endochondral ossification
once mature bone is formed in endochondral, it is histologically indistinguishable from bone tissue formed by intramembranous ossificaition
