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Flashcards in Bones Deck (56):
1

The structure of individual bones is designed to provide what?

maximum resistance to mechanical stress while maintaining the least body mass

2

What is bone?

specialized connective tissue consisting of cells embedded within a gel-like substance that becomes mineralized
- marked rigidity and strength while retaining a degree of elasticity
- both a tissue and an organ

3

what is an organ?

a group of tissues that perform a specific function or group of functions

4

What are the functions of bones?

-support and protection
- shape and movement
- source of calcium reserve (99%) and storage of other inorganic ions
- active participation in the maintenance of calcium homeostasis in the body

5

How do bones accommodate changes related to mechanical stresses and demands on calcium homeostasis?

by being in a dynamic state of growth and resorption throughout their life

6

What is the osteoid?

the matrix of organic extracellular material that primarily contains glycoproteins and colagen fibers

7

What happens to the osteoid in order to form bone?

rapidly undergoes mineralization by deposition of inorganic salts, mainly calcium hydroxyapatite (CHAP) crystals, to form bone

8

The variety of growth factors in the matrix probably play an important role in what?

- bone development
- modeling
- remodeling

9

What is the general consistency of substances in the bone? (%)

9% water
22% Organic matrix
69% Inorganic matrix

10

What is the primary component of the organic matrix? What feature is it responsible for?

collagen type I - responsible for the tensile strength

11

What is the inorganic matrix of bone mainly composed of?

hydroxyapatite crystals deposited within collagen fibrils to enhance tensile strength

12

What are the main minerals in bone?

Calcium phosphate (85%)
Calcium carbonate (10%)
Na, Mg, Fe (>5%)

13

What are collagen fibers produced by? What do they provide?

produced by osteoblasts and provide framework and necessary tensile strength

14

What do the proteoglycans of the bone that are embeded in collagen fibers do?

serve as a carrier for minerals

15

How does the bone matrix harden (becomes mineralized)?

by deposition mainly of hydroxyapatite

16

What are the envelopes of bone?

- Periosteum
- Endosteum

17

What is the Periosteum?

a fibrous connective tissue layer that covers outer/external surfaces of bones
- a site of insertion of muscles, tendons and ligaments

18

What is the Endosteum?

the inner delicate connective tissue surface of the bone
- lines the trabeculae of spongey bone

19

What cells are contained in both the periosteum and endosteum?

osteogenic stem cells

20

What are the functions of osteogenic stem cells?

- growth
- continuous remodeling
- repair of bone fractures

21

What are the characteristics of bone lining cells?

- flat, elongated cells
- generally inactive
- cover surfaces of inactive bone
- precursor cells to osteoblasts

22

What are the characteristics of osteoblasts?

- matrix formation
- secrete type I collagen
- regulate mineralization
- positioned external to osteoid matrix
- differentiate to become osteocytes

23

What are the characteristics of osteocytes?

- originate from osteoblasts
- maintain bone matrix
- occupy lacunae
- extend filopodia through canaliculi
- form gap junctions with neighboring cells

24

What are the characteristics of osteoclasts?

- digest bone
- large multinucleated cells
- exhibit ruffled border and clear zone
- exhibit polarity with nuclei away from bone surface
- originate from pluripotent stem cells of bone marrow

25

What are the types of bone based on maturity

woven bone and lamellar bone

26

woven bone

-immature bone present during fetal development and in early stages of bone repair
-collagen fibers make a crisscross woven pattern

27

lamellar bone

-mature bone, collagen fibers arranged in parallel pattern

28

what are the two ways in which fetal bones form

intramembranous ossification and endochondral ossificationi

29

intramembranous ossification

-occurs within condensed mesenchymal tissue; ie. flat bones of the skull
-also occurs at periosteal surfaces post-natally, and thus causes growth of width in long bones

30

endochondral ossfication

-occurs in most skeletal bones; allows length growth in long bones
-bones develop from hyaline cartilage by replacing it with ossesous tissues via ossification centers
-ossification occurs at oss. centers of immature bone and growth plates/epiphyseal plates of developing bone
-once the growth plate closes no further length can be achieved

31

Cartilage or bone: this tissue is avascular, cells are separate, and there are no nerves in the matrix

cartilage

32

cartilage or bone: poor healing potential, and appositional and interstitial growth

cartilage

33

osteoblasts originate from

osteoprogenitor cells

34

osteoblasts are found exclusively

on surface of bones

35

osteoblasts function

synthesis and secretion of collagen and osteoid: the organic components of extracellular matrix of bone
-osteoblasts are also cuboidal
-

36

osteocyte development

-an osteoblast that has had its surrounding osteoids mineralize and encase them

37

osteocytes

-mature bone cells enclosed in bone matrix within lacunae

38

how do osteocytes maintain contact with adjacent cells and transfer nutrients?

-via filipodia: cytoplasmic branching processes connecting osteocytes via canaliculi (small tunnels)
-nutrients are transfered via gap junctions

39

true or false: osteocytes undergo mitosis

false

40

osteocyte function

-synthesize and reabsorb their matrix to maintain homeostasis of Ca++

41

osteoclasts appearance

-large multinucleated cells, closely related to macrophages
-acidophilic cytoplasm

42

osteoclasts originate from

bone marrow, from monocytes

43

osteoclasts function

osteolysis, the breakdown of bone matrix to maintain Ca++ homeostasis and remodel matrix in response to growth or changes in mechanical strength
-when activated while within contact with bone surface they release enzymes to decalcify bone

44

lamellar bone is composed of

successive layers of osteocytes and bone matrix

45

lamellar bone may be formed as either

compact bone (solid) or cancellous bone (spongy mass)

46

haversian system arrangement of osteocytes

-form concentrically around blood vessels, nerves, and osteogentic/osteoclastic cells
-vessels, etc lie within harvesian canal

47

concentric lamellae contain

osteocytes surrounded by mineralized bone, each connected by canaliculi

48

harvesian canals are interconnected, and connected to endosteum and periosteum via

Volkmann's canals, which run at right angles to harversian canals

49

what is the functional unit of mature bone

osteon: concentric layers of osteocytes and mineralized bone surrounding a harvesian canal

50

2 factors that influence formation and reabsorption of bone

parathyroid hormone (PTH) and vitamin D

51

parathyroid hormone function

increases development and activity of osteoblasts and osteoclasts

52

vitamin D function

increases recruitment of osteoclasts, and mineralization of bone matrix

53

parathormone causes

increased osteoclastic activity, results in osteolysis
-serum Ca++ increases, and estrogen inhibits bone resorption

54

calcitonin

-stimulates bone formation via inhibition of osteoclastic action
-serum Ca++ decreases, and osteoblsts are stimulated to form osteoids

55

synovial joint

cavity between two movable bones
-bone surfaces are covered in Articular cartilage
-synovial membrane is highly vascularized, and lined with epitheloid cells that secrete hyaluronic acid to phagocytize debris

56

synovial fluid

-secreted by synovial cells
-made of hyaluronic acid and tissue fluid
-provides nutrition, lubrication, and protection to articular surfaces