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M2MUnit4 > CT - Cartilage and Bone > Flashcards

CT - Cartilage and Bone Flashcards

1
Q

Which is more dynamic: cartilage or bone?

A

Bone. It is vascularized and is constantly turned over/remodeled. Cartilage is avascular and very limited in its repair ability

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2
Q

What are the 2 main functions of cartilage?

A

(1) to provide a resilient but pliable support structure (2) to direct the formation and growth of bone

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3
Q

Which cells make cartilage matrix and tissue?

A

Chondrocytes

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4
Q

Where do chondrocytes come from?

A

Initially from primitive mesenchymal cells during fetal development. Later can also arise from an external layer of connective tissue that surrounds the cartilage called the perichondrium

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5
Q

What is the perichondrium?

A

The CT that envelops cartilage where it is not a joint

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6
Q

What is the process of cartilage formation?

A

When chondrocytes are proliferative (AKA chondroblasts) they secret components of ECM and surround themselves with matrix they become isolated from other cells. Come to reside in an isolated compartment called a lacuna.

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7
Q

What are the 3 different types of cartilage? How are they distinguished from each other?

A

Hyaline cartilage; Elastic cartilage; Fibrocartilage. Distinguished by characterstics of the matrix they contain

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8
Q

What is the general structure of hyaline cartilage?

A

Contains collagen that forms relatively thin fibrils that are generally arranged in irregular three dimensional pattern. Ground substance of hyaline cartilage is rich in proteoglycans and the free glycosaminoglycan hyaluronic acid that promotes hydration and flexibility

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9
Q

What are the structural properties of ECM of hyaline?

A

Metabolites can readily diffuse through the tissue; promotes resiliency to compression; allows growth of chondrocytes/matrix from within the matrix; during growth it can calcify and attract cells that initiate bone formation

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10
Q

What is the general structure of elastic cartilage?

A

Also contains thin collagen fibrils and proteoglycans; distinguished by abundant elastic fibers and interconnecting sheets (lamellae) of elastic material. Deisgned for elasticity and usually does not calcify (outter ear; epiglottis; etc.)

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11
Q

What is the general structure of fibrocartilage?

A

Contains large bundles of regularly arranged collagen. Very similar to/a continuation of dense regular connective tisue. Designed to resist compression and sheer forces

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12
Q

How do nutrients/metabolites get to cartilage tissue?

A

Since it is avacular; anything that is produced by chondrocytes and needs to get to cartilage must diffuse within the matrix to and from the perichondrium. Facilitated by large amounts of hydrated glycosaminoglycans.

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13
Q

What are the two main types of bone?

A

Flat (skull; mandible) and long bones

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14
Q

What are the two main parts of long bones?

A

diaphysis (shaft) and epiphysis

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15
Q

What are trabeculae?

A

Found inside spongy bone. They are thin anastomoing spicules

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16
Q

What are the main functional differences between compact and spongy bone?

A

Compact bone provides most of strength for bone support; trabeculae provide extensive surface area for metabolism.

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17
Q

What are the two types of bone marrow? Where is it found?

A

Found in between the trabeculae. There is red bone marrow (contain hematopoietic tissue) and white bone marrow (contains adipose cells)

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18
Q

What is the periosteum?

A

The outer surface covering the bone. Contains dense connective tissue containing fibroblasts; bone precursors and bone cells

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19
Q

What is the endosteum?

A

The inner surface where trabeculae contact internal soft tissue. This is where most calcium mobilization and storage occurs

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20
Q

Name 4 specialized bone cell types

A

Osteoprogenitor; osteoblasts; osteocytes; osteoclasts

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21
Q

What are osteoprogenitor cells? Where are they found?

A

Stem cells that are capable of cell division to generate the osteoblasts and osteocytes that comprise most of the cells of bone. Found in both the periosteal and endosteal surfaces and in soft CT of the channels

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22
Q

What do osteoblasts do? Where are they found?

A

Found lining the inner layers of periosteal and endosteal surfaces where bone growth/remodeling is occurring. They actively secrete the osteoid (secretory engines that make bone matrix). They also pinch off membrane-enclosed vesicles (matrix vesicles) which contain enzymes that initiate bone calcification (mineralization)

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23
Q

What is the osteoid?

A

Initial un-mineralized extracellular matrix of bone

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24
Q

Are osteoblasts connected to each other?

A

Yes (and to nearby osteocytes) by gap junction

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25
Q

Can osteoblasts divide?

A

Yes

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26
Q

Where do osteocytes come from? How do they form?

A

Directly derived from osteoblasts. Form as they become surrounded and encased by bone matrix in a lacuna.

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27
Q

Can osteocytes divide?

A

No. They arrest in G0.

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28
Q

How are osteocytes related to gap junction?

A

They extend long processes through tiny channels (canaliculi) in the calcified matrix; these processes form gap junctions with processes from other osteocytes.

29
Q

What is the function of osteoctyes?

A

Unclear. Retain limited ability to modify bone matrix (but do not secrete much). Probably send signals to each other and to osteoblasts at the surface through their gap junctions.

30
Q

Where do osteoclasts come from? What are the closely related to?

A

Derived from monocytes in the blood (which come from hematopoietic stem cells in bone marrow); therefore are not related to any of the other bone cells. Resemble and are related to macrophages

31
Q

What is the function of osteoclasts?

A

Phagocytic cells that specifically degrade bone or cartilage matrix.

32
Q

What are the 3 reason osteoclasts will degrade bone?

A

(1) to allow inward growth of blood vessels during bone formation (2) function to resorb already made bone to promote remodeling of the bone matrix (3) resorb bone for the purpose of mobilizing Ca2+ into the bloodstream (critical for maintaining proper Ca2+ concentrations in blood).

33
Q

What is the structure of bone matrix? How is it similar/different to other types of matrix?

A

Calcified and packed with dense parallel collagen fibers. Similar: contains negatively charged proteoglycans and other glycoproteins (several of these are specific to bone). Different: the matrix is mineralized/calcified. IE the collagen and ground substance contain large amounts of hydroxyapatite [Ca10(PO4)6(OH)2]

34
Q

What are Haversian canals?

A

Channels in the long bones that traverse the long axis through compact bone.

35
Q

What is the osteon?

A

Bone lamellae tend to surround a Haversian canal in concentric rings (like the rings of a tree). These lamellae and their canal are frequently referred to as a unit called the osteon.

36
Q

What are Volkmann’s canals?

A

Other canals that link Haversian canals to each other and to the periosteum at the bone surface.

37
Q

What are the two general ways that bone as a tissue and organ is formed?

A

Intramembranous ossification and endochondral ossification

38
Q

When is intramembranou ossification used?

A

In the absence of a pre-made cartilage tissue

39
Q

What are the first steps of intramembranous ossification (from condensation to bone islands)?

A

Mesenchymal cells > osteoprogenitors > oteoblasts > secretion of osteoid > more cells become osteoblasts > bone islands joining. Within a sheet of connective tissue groups of mesenchymal cells come together (condensation); transform into osteoprogenitors; then differentiate into osteoblasts. These “islands of osteoblasts” secrete osteoid. More cells at the periphery of these islands convert into other osteoblasts (adds mass to the developing bone); eventually ?bone islands? join.

40
Q

What happens with intramembranous ossification after bone islands join?

A

Initially have trabecular network of bone. Blood vessels grow in. Woven bone gets remodeled by osteoclasts and new bone deposition by osteoblasts converts some of this bone to compact lamellar form.

41
Q

What type of bone is formed by intramembranous ossification?

A

Flat bones

42
Q

When is endochondral ossification used?

A

Within previously made cartilage tissue (a cartilage model).

43
Q

How is the cartilage model formed?

A

Mesenchymal cells undergo division and differentiate to generate a group of chondrocytes. Chondrocytes begin to secrete the hyaline cartilage matrix. Chondrocytes become encased in their lacuna. Eventually an elongate structure in the relative proportion of a long bone is formed.

44
Q

What are the 2 ways the cartilage model continues to grow?

A

Appositional growth and interstitial growth

45
Q

What is appositional growth? Where does it occur?

A

Growth at the surface. In the perichondrium at the cartilage surface mesenchymal and/or fibroblast-like cells proliferate and differentiate into more chondrocytes; which secrete more hyaline matrix.

46
Q

What is interstitial growth? Where does it occur?

A

Growth from within. Chondrocytes in a lacunae continue to proliferate and secrete the ECM; leading to internal growth of the tissue.

47
Q

What is an isogenous group? Where is this seen with interstitial growth?

A

Groups of chondroctyes within a lacuna or still close together are actually clones of cells derived from mitosis and are called isogenous groups (of clonal origin).

48
Q

Where does bone begin to replace cartilage in interstitial growth?

A

On the surface of the diaphyseal shaft of the cartilage model (i.e. within the perichondrium)

49
Q

What happens before cartilage is replaced by bone?

A

Cartilage matrix is mineralized prior to replacement by bone.

50
Q

How does cartilage matrix mineralization happen?

A

In the perichondrium mesenchymal cells develop into osteoprogenitors which become osteoblasts. Thus the perichondrium is turned into periosteum. Nearby bhondrocytes enlarge and the cartilage matrix become calcified.

51
Q

What degrades the calcified cartliage matrix?

A

Osteoclasts.

52
Q

What grows into the degraded region?

A

Blood vessels and also their sheath of connective tissue carrying more osteoprogenitors

53
Q

How is the primary/diaphysial ossification center formed?

A

The osteoclast-led blood vessels penetrate deep into the diaphysis to form a center of ossification

54
Q

What happens in the primary/diaphysial ossification centers?

A

Intense osteoclast activity and osteoblast proliferation replace the cartilage with bone; the zone of ossification continues to expand outwards and towards both ends of the model. (Later 2 new ossification centers are etablished within both epiphyseal ends)

55
Q

Where is the only region of proliferative cartilage that remains at birth?

A

The epiphyseal plate (crucial for continued growth in length of the bone)

56
Q

How/where does growth in the diameter of bone occur?

A

Occurs in the periosteum (outer surface) of the bone. Occurs by appositional growth

57
Q

Where does most resorptive activity occur?

A

At the endosteal sruface

58
Q

What is the order of activity for remodeling of bone?

A

Activated osteoclasts resorb older calcified bone. They also signal for osteoblast migration and secretion as well as stimulate osteoprogenitors to generate new osteoblasts. Osteoblast initiate mineralization of osteoid.

59
Q

What is Osteomalacia Rickets?

A

Causes abnormal increase in uncalcified osteoid by interfering with mineralization.

60
Q

How do osteoblats initiate mineralization of the osteoid?

A

By secreting matrix vesicles

61
Q

What are matrix vesicles? What is inside them?

A

Vesicles pinched off from plasma membrane. Contain high levels of calcium; phosphate that is linked to other molecules; and alkaline phosphatase enzymes.

62
Q

How do matrix vesicles get ruptured?

A

Alkaline phosphatases inside the secreted vesicles somehow become activated to generate free phosphate which forms precipitates with calcium (hydroxyapatite). These precipitates grow and rupture the vesicles

63
Q

What do the hydroxyapatite precipitates do once they are outside of the vesicles?

A

Act as nucleation sites to trigger a cascading mineralization outside in the matrix

64
Q

What are Bone Morphogenic Proteins (BMPs)?

A

Short range signals that promote specific patterns of differentiation. Some act on on connective tissue precursors to stimulate either chondrogenesis (differentiation of chondrocytes and the formation of cartilage) or osteogenesis (the differentiation of osteoblasts and formation of bone); but there are many more. Overall they control bone development and probably remodeling and turnover.

65
Q

What long-range signals act on bone and cartilage regulation?

A

Hormones. Esp. steroid hormones

66
Q

What else acts on bone and cartilage regulation?

A

Mechanical stress and neuronal stimulation

67
Q

What does parathyroid hormone do?

A

Stimulates calcium liberation (bone resorption)

68
Q

What does calcitonin hormone do?

A

Stimulates calcium uptake into bone

69
Q

What is Vit. D important for?

A

Promotes calcium uptake from the intestine.

M2MUnit4 (6 decks)

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