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MSK Week 4 > ICL 5.1: Cartilage and Bone > Flashcards

ICL 5.1: Cartilage and Bone Flashcards

1
Q

what are the 3 components found in all connective tissues?

A
  1. cells
  2. extracellular fibers
  3. ground substance
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2
Q

what are the 2 supportive connective tissues in the body?

A
  1. cartilage

2. bone

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3
Q

what are the 3 types of cartilage?

A
  1. hyaline
  2. elastic
  3. fibrocartilage

the types are based on the predominant fiber present in the extracellular matrix (ECM)

it’s found where you need support but also flexibility

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4
Q

what is hyaline cartilage?

A

most abundant cartilage in the body

ex. found in the trachea and keeps the trachea open

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5
Q

what are the common characteristics of hyaline cartilage?

A
  1. large amount of ECM between cells = pale blue, semitransparent appearance
  2. avascular matrix
  3. mostly surrounded by layer of perichondrium (dense irregular CT)
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6
Q

what are the two types of cells in cartilage?

A
  1. chondroblasts

2. chondrocytes

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7
Q

what are chondroblasts?

A

chondroblasts are derived from mesenchymal
cells and chondrogenic cells in perichondrium

they are Immature cartilage cells, basophilic

elliptic shape near periphery

they secrete cartilage matrix and undergo cell division = mitosis

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8
Q

what are chondrocytes?

A

mature cartilage cells that reside in lacunae

they are more rounded deeper in the cartilage

although they’re mature, they are still capable of cell division

chondroblasts are called chondrocytes once they are embedded in ECM

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9
Q

what is an isogenous group?

A

where two or more cells are in single lacunae or are very closely associated with each other

this represents where a cell has recently undergone cell division and begun to lay down new matrix

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10
Q

what are the two methods of cartilage growth?

A
  1. interstitial growth

growth from within –> tissue is added from the inside of the tissue

  1. appositional growth

growth on outside of tissue proper –> tissue is added on the outer surface of the tissue by the perichondrium

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11
Q

what are the 2 layers of the perichondrium?

A
  1. fibrous layer

2. chondrogenic layer

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12
Q

what is the fibrous layer of the perichondrium? what is it composed of?

A

it’s an outer layer of dense irregular fibrous connective tissue containing blood vessels which supply nutrients to all of the cartilage

it’s composed of type I collagen*, vascular, and fibroblasts

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13
Q

what is the chondrogenic layer of the perichondrium? what is it composed of?

A

it’s the inner layer of the perichondrium

composed mainly of chondrogenic cells that undergo division and differentiate into chondroblasts = appositional growth

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14
Q

what is ground substance? what’s it composed of?

A

it’s one of the three components of connective tissue that’s an amorphous gel-like substance in the extracellular space that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin

it’s abundant; there’s a lot of it between cells

it consists of an amorphous gel that’s rich in proteoglycans and lots of sulfated Glycosaminoglycans (GAGs)

it’s relatively low in hyaluronic acid

two portions = territorial matrix and inter territorial matrix

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15
Q

what is the territorial matrix?

A

it’s the portion of the ground substance immediately around the cell

new chondroblastssecrete a lot of territorial matrix because it’s rich in GAGs

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16
Q

what is the interterritorial matrix?

A

it’s the portion of the ground substance between the cells

it stains lighter than the territorial matrix due to a lower sulfur content

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17
Q

what are proteoglycans?

A

it gives the matrix its characteristic structure and is more organized than connective tissue proper

this is the most important component of cartilage

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18
Q

what is the proteoglycan subunit called?

A

aggrecan

aggrecans are covalently linked to main hyaluronic acid chain forming huge proteoglycan aggregate

they are responsible for the gel-like character of the matrix

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19
Q

what are the 3 functions of proteoglycan aggregates?

A
  1. diffusion of nutrients

holds interstitial fluid important for diffusion of nutrients and oxygen from surface of cartilage to interior

all nutrients come from blood vessels in the fibrous layer of the perichondrium

  1. resists compression
  2. slippery (good for joints)
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20
Q

what are the 2 types of adhesion molecules in hyaline cartilage?

A
  1. chondronectin

adherence of cell membrane to extracellular matrix (ECM) (integrin)

  1. chondrocalcin

calcium binding in the ECM (calcify the cartilage)

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21
Q

what are the 2 types of extracellular fibers in hyaline cartilage?

A
  1. collagen type II

2. pericellular capsule

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22
Q

what is the pericellular capsule?

A

a type of extracellular fibers in hyaline cartilage

it’s immediately adjacent to cell and is a fine meshwork of other types of collagen thought to protect cells from mechanical stresses

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23
Q

where is hyaline cartilage found in the body?

A
  1. costal cartilage
  2. trachea, bronchi of lungs
  3. larynx, nasal cartilage
  4. articular cartilage in synovial joints (no perichondrium)
  5. fetal skeleton
  6. epiphyses (no perichondrium)
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24
Q

what is the function of hyaline cartilage?

A
  1. provides structural support

elastic firmness that is resilient yet fairly rigid; due to gel-like form of ground substance from presence of proteoglycans

  1. withstands lots of pressure and shear forces

acts as shock absorber; due to proteoglycans filled with water

  1. slippery

due to large amounts of proteoglycans containing water; 80% of wet weight is water

  1. capable of rapid growth

important to have support during development because bone grows too slowly and would be too rigid during the birth process

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25
Q

what is elastic cartilage composed of?

A

chondrocytes are principal fixed cell type – they’re widely scattered

the principal fiber type is elastic fibers; collagen type II is also present –> both fibers are secreted by the chondrocytes

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26
Q

how can you differentiate between elastic and hyaline cartilage in an H&E stain?

A

you can’t; elastic cartilage looks just like hyaline cartilage on an H&E stain

you need a special elastic stain to see the elastic fibers and type II collagen

verhoeff’s iron hematoxylin (VIH) stain is specific for the elastic fibers and stains them black and blue

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27
Q

what is the ground substance of elastic cartilage like?

A

it’s the same structure as hyaline cartilage but just not as abundant due to lots of elastic fibers

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28
Q

where is elastic cartilage found in the body?

A
  1. auricle
  2. epiglottis
  3. auditory canal
  4. larynx
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29
Q

what is the function of elastic cartilage?

A

resilient support is needed with greater flexibility & elasticity to return to original position

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30
Q

what are the characteristics of fibrocartilage?

A
  1. chrondrocytes are the principal fixed cell type and they are aligned between bundles of collagen
  2. there are densely packed type I collagen fibers in bundles
  3. not a lot of ground substance due to numerous collagen fibers
  4. NO perichondrium
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31
Q

where is fibrocartilage located in the body?

A
  1. pubic symphysis
  2. intervertebral discs
  3. junction of attachment between tendon and bone
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32
Q

what is the function of intervetebral discs?

A

cushion and absorb impact

needs to be tough and resistant to stress but not rigid

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33
Q

what are the 5 types of cells found in bones?

A
  1. osteoprogenitor cells
  2. osteoblasts
  3. osteocytes
  4. osteoclasts
  5. bone lining cells
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34
Q

what are osteoprogenitor cells?

A

they are derived from undifferentiated embryonic mesenchymal cells

they are capable of mitosis and proliferation

they differentiate into osteoblasts or chondrogenic cells (low O2)

in growing bones, they appear as flattened, elongate or ovoid nucleus

35
Q

where are osteoprogenitor cells found in the body?

A

they are found in the inner cellular layer of the periosteum, lining harversian canals and in the endosperm

36
Q

what are osteoblasts?

A

immature cells derived from osteoprogenitor cells

they are nOT capable of cell division

they are found on existing bone surfaces

37
Q

what do osteoblasts look like?

A

cuboidal in shape, closely packed together

they look like an epithelium forming a lining on the outside surface of the bone tissue

38
Q

what is the function of osteoblasts?

A

they are always actively laying down unmineralized matrix called osteoid on the editing surface and then mineralizing it

so all bone growth is appositional!! there is no interstitial growth like with cartilage

39
Q

what are osteocytes?

A

mature bone cells, derived from OBs

the osteocytes are embedded in the calcified bone matrix that is laid down by the osteoblasts

they can NOT divide

they lie in lacunae

40
Q

what is the function of osteocytes?

A

maintaining the ECM surrounding the cell

they have numerous cytoplasmic processes, which extend to adjacent cells

these processes run in small tunnels through calcified matrix called canaliculi

41
Q

how are osteocytes set up/oriented?

A

they are arranged in concentric circles around BV = bone tissue is very vascular

the blood vessel runs in a central canal/harversian canal of the osteon

the osteon is the basic structural and functional unit of compact bone

then, the cement line is the outermost limit of the osteon –> it’s deficient of collagen and lighter staining than surrounding matrix

42
Q

how does nutrient and waste material get between osteocytes?

A

gap junctions

43
Q

what are osteoclasts?

A

large, multinucleate cells that re-absorb bone tissue

they’re derived from granulocyte-macrophage progenitor cells and arise in the bone marrow –> they then fuse together to form multinucleated osteoclast

44
Q

where are osteoclasts located in the body?

A

they’re located in a depression on bone surfaces called Howship’s lacunae/Resorption Bay

45
Q

what are ruffled borders?

A

regions where collagen fibers are exposed by resorption by osteoclasts

they signify active bone resorption

46
Q

how are osteoclasts and osteoblasts related?

A

osteoclasts are ALWAYS found in associated with osteoblasts

RANK receptors on OCs are stimulated by RANKL secreted by OBs

RANK receptors can be blocked by osteoprotegerin which is a RANKL decoy receptor that leads to decreased osteoclast activity

47
Q

where are bone lining cells found in the body?

A

they are the cells that line all bone surfaces

they’re found in 3 places:

  1. all vascular channels
  2. endosteum
  3. periosteum
48
Q

what is the function of bone lining cells?

A
  1. maintains microenvironment in bone tissue
  2. forms interconnecting network with other bone lining cells, osteocytes and osteoblasts by cellular processes
  3. senses stress in bone and initiates remodeling process
49
Q

what are the 2 components of the extracellular matrix of bones?

A
  1. organic component

2. inorganic components

50
Q

what is the organic component of the ECM of bone composed of?

A

it’s made of type I collagen, non-collagenous proteins, ground substance and growth factors

  1. collagen makes up 90% of the organic matrix and gives bone its toughness and flexibility
  2. ground substance is scant and only contains small amounts of proteoglycans
51
Q

which non-collagenous glycoproteins are found in the organic component of bone ECM?

A
  1. osteocalcin that binds to Ca2+ in the matrix
  2. osteonectin binds bone mineral to collagen fibers
  3. osteopontin is also bind to hydroxyapatite
  4. bone sialoprotein has binding sites for matrix components and interns of osteoblasts and osteocytes
52
Q

what is the inorganic component of the ECM of bone?

A

consists of all mineral salts in the ECM

it’s approximately 65% of total dry bone weight is due to minerals

it provides mechanical rigidity and load bearing strength to bone tissue

53
Q

what is the inorganic component of the ECM of bone composed of?

A

ions!!!

  1. Ca2+, PO43-, CO32-, Mg2+, OH-, Fl- , citrate ions

ions are found in the form of hydroxyapatite crystals = Ca10(PO4)6(OH)2

  1. traces of Fe, Zn, Cu, Pb, Al, Sr, etc
54
Q

explain how bone is a biphasic material and how that is beneficial

A

the ECM of bone is made of an inorganic and organic matrix

the inorganic matrix has a lot of strength but it brittle

the organic matrix on the other hand is really strong from collagen fibers and is really flexible

if you remove the organic matrix, then bone is brittle like china but if you remove the inorganic matrix then the bone would be insanely flexible

so together they combine to form stronger yet flexible material that can withstand great stress yet still give without shattering

55
Q

what are the extracellular fibers found in bone?

A

type I collagen primarily that is densely packed

bone tissue is classified by the arrangement of collagen fibers

56
Q

how is bone tissue classified?

A

bone tissue is classified by the arrangement of collagen fibers

  1. woven bone = primary, immature

it’s characterized by bundles of collagen fibers running in all directions

  1. lamellar bone = secondary, mature

it’s characterized by collagen fibers in one layer running parallel to each other which makes them calcified and stronger – but the direction of fibers is different in each layer

each layer of collagen is called a lamellae

57
Q

how are bones classified by shape?

A
  1. long bones

humerus, ulna, radius, femur, tibia, fibula, phalanges

  1. short bones

carpal and tarsal bones

  1. irregular bones

vertebrae, hip, facial

  1. flat bones

skull bones

  1. sesamoid bones

patella, pisiform

58
Q

what is the gross structure terminology of the parts of a bone?

A
  1. epiphysis = enlarged area at each end
  2. diaphysis = central shaft area
  3. metaphysic = tapered cone region that connects epiphysis to diaphysis
  4. epiphyseal plate = band of cartilage
    found in metaphyseal region that function to increase length of long bones
59
Q

what is cortical bone?

A

it’s the outer layer of dense bone –> aka compact bone/dense bone

consists of osteons, interstitial lamella & circumferential lamella

has more bone tissue than space per unit volume

60
Q

what is spongy bone?

A

the small processes inside the bone

aka trabecular bone/cancellous bone

consists of thin processes of bone called trabecula or spicules with large amount of space between (Marrow Cavity)

has more space than bone tissue per unit volume

61
Q

what is the basic structural unit of compact bone?

A

an osteon = Haversian system

the central canal (Haversian canal) contains blood vessels and lies in the center of the osteon

then surrounding the blood vessels are concentric layers of collagen fibers and osteocytes

62
Q

what are Volkmann canals?

A

they’re in the cortical bone and they contain diagonally running blood vessels

they supply blood to vessels in osteons

you can recognize them by their LACK of concentric layers of cells around them

63
Q

what are interstitial lamellae?

A

remnants of older osteons in the cortical bone layer

you can recognize them because they look like an osteon that doesn’t have its central canal

64
Q

what are the outer circumferential lamellae?

A

it’s the layers of cortical bone (osteocytes) that run all away around outside of bone

the bind bone together and help hold all the osteons in place

they’re laid down by periosteum

65
Q

what are the inner circumferential lamellae?

A

it’s the layers of cortical bone (osteocytes) that run all the way around the inner surface of the bone next to the marrow cavity

they are laid down by the endosteum

66
Q

what are Sharpey’s fibers?

A

bundles of collagen fibers extending from periosteum to be attached in the bone matrix of the cortical bone

they’re seen where muscle-tendon or ligaments attach to bone

67
Q

what is the endosteum?

A

a single layer of cells lining the inner layer of the bone adjacent to the marrow cavity

its function is to separate bone tissue from marrow cavity and it helps to maintain the proper microenvironment within bone tissue

68
Q

is bone growth interstitial or appositional?

A

ALL bone growth is appositional

69
Q

what are the 2 functions of bone?

A
  1. structural support

2. reservoir for mineral ions

70
Q

how does bone act as a structural support?

A

inorganic salts impregnated in organic matrix give bone its rigidity and great strength

bone maintains the shape and form of the body and protects major organs

it also supports soft tissues, provides attachment sites for skeletal muscles

71
Q

how does bone act as a reservoir for mineral ions?

A

bone releases and stores ions as needed –> the mechanism of ion release/storage is the process of remodeling

consists of resorption tunnels & forming osteons

bones are the storehouse for 99% of body’s calcium, 85% of Phosphorus, 65% of all the sodium and magnesium

72
Q

what is bone remodeling?

A

replacement of old bone tissue by new bone tissue

remodeling is continuous from the time bone is first formed until you die

remodeling replaces woven bone with lamellar bone in both cortical and trabecular bone

73
Q

what are the two types of bone remodeling?

A
  1. internal remodeling

2. trabecular remodeling

74
Q

what is internal remodeling?

A

aka Haversian remodeling = cortical remodeling = secondary bone formation

it occurs in response to new stress on the bone –> the process begins with bone lining cells sensing new stress

the first visible sign is the formation of osteoclasts

the end result is a new definitive Haversian system that gets formed in the compact bone

75
Q

what is the resorption cone?

A

part of internal remodeling

they’re cavities that are formed by the osteoclasts in dense bone that are tapered and look like bullets

OCs are actively removing bone matrix resulting the
release of Ca2+ and other ions into blood

a resorption cavity is characterized by large lumen in the bone matrix with osteoclasts lining it

76
Q

what is the reversal zone?

A

part of internal remodeling

it’s when there is no longer any bone resorption but bone deposition has not yet begun

macropages scavenge the debris and smooth out the surface

77
Q

what is the closing cone?

A

aka forming the osteon

a blood vessel follows down behind the formation of the respiration tunnel

it carries osteoprogenitor cellsthat migrate across the gap between the BV and the outer limit of the resorption cavity –> the OPs attach to the surface of resorption tunnel and differentiate into OBs

then the osteoblasts lay down a layer of bone osteoid

78
Q

how long does one remodeling cycle take to complete?

A

4 months

79
Q

internal remodeling is under the control of which 2 hormones?

A
  1. parathyroid hormone (PTH)

2. calcitonin

80
Q

how does parathyroid hormone control internal remodeling?

A

it’s secreted where there is low peripheral blood Ca2+ level

PTH stimulates the osteoclasts to increase their resorption activity –> increased bone resorption which in turn increases release of Ca2+

this decreases osteoblastic activity and bone matrix isn’t being laid down as rapidly

the net effect is an increase in the blood Ca+2 level!

81
Q

how does calcitonin control internal remodeling?

A

it decreases osteoclastic activity

this increases osteoblastic activity and pulls more Ca2+ from blood

the net effect is to lower blood Ca2+ level

82
Q

what is trabecular remodeling?

A
  1. osteoclasts scoop out a cavity of bone where the new packet will form
  2. osteoprogenitor cells migrate in and differentiate into osteoblasts
  3. osteoblasts fill in the cavity one layer at a time to create lamellar bone

trabecular remodeling is faster than cortical remodeling!

83
Q

how often do you get a new skeleton via the remodeling process?

A

about 3% of all cortical bone is turned over each year

about 26% of all trabecular bone is remodeled each year

new skeleton every 12-15 years!!

MSK Week 4 (11 decks)

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