Lecture 4 - Connective Tissue

Question 1

what are the characteristics of CT

Answer 1

-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

Question 2

what are the components of CT

Answer 2

-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

Question 3

what are glycosaminoglycans

Answer 3

polymers of modified sugar residues

Question 4

what gives CT its major functional properties

Answer 4

fibers and ground substance (they are in the ECM)

Question 5

classification of connective tissue

Answer 5

fibrous CT = loose CT, dense irregular, dense regular

specialized CT = adipose tissue, cartilage, blood, bone

Question 6

where is CT found

Answer 6

underneath the epithelium

Question 7

what are the cells of CT and what do they do

Answer 7

-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)

Question 8

what are the ECM fibers,
what proportion do they make up, how do they stain
what is their purpose

Answer 8

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

Question 9

collagen type 1 fibers - makes up what, properties

Answer 9

-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

Question 10

elastin fibers - appearance and attachment, what is it produced by

Answer 10

-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

Question 11

ground substance - what is it made up of, staining, purpose, charge, properties

Answer 11

-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

Question 12

loose (areolar) CT - ground substance vs fibres, how cellular

Answer 12

-abundant ground substance, few fibers
-small collagen fiber bundles
-often very cellular

Question 13

reticular CT - what type of CT, what type of collagen, where is it found

Answer 13

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

Question 14

dense CT - types, what is abundant, what type of fibers, orientation

Answer 14

-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

Question 15

adipose tissue - what are they found as, what can they form, what do they differentiate from, how cellular are they

Answer 15

• 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

Question 16

types of adipose tissue and their features, functions, extent of blood supply

Answer 16

-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

Question 17

cartilage - function, what is the blood supply like, location

Answer 17

-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

Question 18

structure of cartilage - what type of cells and where are they, function and what they become

Answer 18

-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

Question 19

what are mature cartilage cells called

Answer 19

chondrocytes

Question 20

what are the types of cartilage (classification)

Answer 20

hyaline cartilage, elastic cartilage, fibrocartilage

Question 21

bone tissue - differences from cartilate, similarities, functions

Answer 21

-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

Question 22

bone tissue classification - two types and where they lay in the bone

Answer 22

-spongy/cancellous/trabecular = bony meshwork consisting of trabeculae, forms the interior of the bone

-compact bone = dense layer that forms the outside of bone

Question 23

lamellar bone tissue organization - when can you paraffin embed?
staining? prominent fiber? what does demineralized bone show/expose?

Answer 23

-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

Question 24

what is the lacuna

Answer 24

its the space that appears white and it surrounds the cell

Question 25

parts of lamellar bone (think canals, etc) (3)

Answer 25

-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

Question 26

long bone histology - what parts are associated with this type of bone? (5)

Answer 26

-circumferential lamellae
-osteon
-osteonal canal
-interstitial lamellae
-perforating canal

Question 27

what is the difference between concentric lamellae and circumferential lamellae

Answer 27

-concentric is the lamellae that fills the individual osteons

-circumferential is what fills the rest of the space of the bone

Question 28

what are perforating canals

Answer 28

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

Question 29

woven vs lamellar bone - organization, when they appear, are they temporary or permanent

Answer 29

-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

Question 30

woven vs lamellar - how strong are they, how fast are they produced, what does the conversion involve, what plays a key role in conversion

Answer 30

-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.

Question 31

osteoclasts - what are they, how are they formed, where do they attach, what is their functions (3)

Answer 31

-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

Question 32

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?

Answer 32

-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

Question 33

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

Answer 33

-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

Question 34

can you tell the difference between bone from intramembranous ossification vs endochondral ossification

Answer 34

once mature bone is formed in endochondral, it is histologically indistinguishable from bone tissue formed by intramembranous ossificaition