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Bones Flashcards

1
Q

What is bone?

A

a tissue & organ; and parts of the skeleton

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2
Q

How is bone a tissue?

A
  • bone is a CT w/ its cells embedded in a mineralized extracellular matrix (ECM)
  • CTs are composed of mesenchymal cells of mesodermal origin
  • the ECM of bone has an organic component (primarily collagen in the form of osteoid) & an inorganic component (primarily calcium & phosphorus in the form in hydroxyapatite)
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3
Q

What are the 2 families of bone cells?

A

those that form & maintain bone (& cartilage)
- derived from mesenchymal cells in the bone marrow

those that remove or resorb bone (& cartilage)
- derived from hematopoietic stem cells of the monocytes series that are also found in the bone marrow

stem cells are the only bone cells capable of mitosis & are, therefore, required for continuous growth & maintenance of bone

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4
Q

What are the 3 types of bone cells?

A
  1. osteoblasts (active or inactive)
  2. osteocytes
  3. osteoclasts
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5
Q

What are active osteoblasts?

A
  • plump bone forming cells
  • they line all bone-forming surfaces, produce bone matrix (osteoid), initiate mineralization of the matrix, & initiate bone resorption
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6
Q

What is osteoid?

A
  • major organic component of the ECM of bone before it is mineralized
  • about 90% of osteoid is collagen; 10% is amorphous ground substance that binds to hydroxyapatite
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7
Q

What are inactive osteoblasts?

A
  • flat cells that are sometimes referred to as bone-lining cells
  • they line bone surfaces at which neither bone formation nor bone resorption is occurring
  • they can rapidly release calcium from bone if the blood calcium concentration is low, protect bone from chemical insults, & can become active osteoblasts to form new bone
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8
Q

What are osteocytes?

A
  • differentiate from osteoblasts after becoming embedded in mineralized ECM
  • they are located in lacunae (singular: lacuna) & communicate w/ other osteocytes & bone lining cells of the endosteum & periosteum via cell processes
  • canaliculi (s. canaliculus) are the little canals w/in the mineralized ECM that contain the osteocyte processes
  • osteocytes detect forces placed on bone & signal osteoblasts to either form bone or initiate the resorption of bone
  • osteocytes also have a role in maintaining the ECM & plasma calcium
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9
Q

What are osteoclasts?

A
  • multinucleated giant cells formed from the fusion of hematopoietic stem cells of the monocyte series that reside in the bone marrow, circulate in the blood, or both
  • they are the only cells in the body capable of bone resorption
  • for osteoclasts to resorb bone they must attach to the bone surface normally lined by osteoblasts
  • osteoclasts create concavities in the bone surfaces called resorption lacunae or Howship’s lacunae
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10
Q

What is the ECM of bone?

A
  • provides strength & hardness
  • has an organic component & an inorganic component
  • organic component, osteoid, is composed of fibrous stroma & amorphous ground substance
  • fibers are type I collagen & the amorphous ground substance includes conjugated proteins (AAs attached to a non-protein chemical), proteoglycans, & lipids
  • inorganic matrix is principally a distinctive combination of minerals called hydroxyapatite (or sometimes hydroxylapatite, HAP)
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11
Q

What is hydroxyapatite?

A
  • is (Ca)10(PO4)6(OH)2; where Ca = calcium, PO4 = phosphate, & OH = hydroxide
  • apatite is any grp of minerals w/ general formula 10Ca2+ : 6PO4^3- : X^-
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11
Q

Types of gross bone (the tissue):

A
  1. compact bone
  2. cortical bone
  3. cancellous bone
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12
Q

What is compact bone?

A
  • has relatively large proportion of bone & v small proportion of interosseous space
  • compact bone is composed of lamellar bone
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13
Q

What is cortical bone?

A

is the compact bone comprising the outer layer of a bone (the cortex) of the diaphysis

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14
Q

What is cancellous (lattice-like) bone?

A
  • composed of anastomosing plates or trabeculae (‘little beams’; s. trabecula) of bone & relatively large proportion of interosseous space
  • cancellous bone is also known as trabecular bone, spongy bone, lattice bone, & reticular bone
  • cancellous bone may be composed of either woven bone or lamellar bone
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15
Q

KNOW

A
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16
Q
A
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17
Q

Types of microscopic bone (the tissue)?

A
  1. lamellar bone
  2. woven bone
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18
Q

What is lamellar bone?

A
  • aka mature bone or organized bone
  • collagen fibers of ECM of lamellar bone are arranged in parallel layers or concentric rings (lamellae; s. lamella)
  • most (almost all) of the adult skeleton is lamellar bone
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19
Q

What is woven bone?

A
  • aka immature bone, reactive bone, or new bone
  • collagen fibers of the ECM of immature bone appear to be haphazardly woven together
  • woven bone is temporary bone that provides short-term support during development or repair
  • it is present in fetal ossification centers, at the leading edge of growing bones, around teeth, at the points of attachment of tendons and ligaments, & in response to injury (ex: fracture), inflammation, or neoplasia
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20
Q

What is the osteon/Haversian system or osteonal canal/Haversian canal?

A
  • Haversian canals are a series of tubes around narrow channels formed by lamellae
  • Haversian canals surround blood vessels and nerve fibers throughout the bone & communicate w/ osteocytes
  • the canals + the surround lamellae are called a haversian system or an osteon
  • Haversian canals are straight & long & parallel to the length of the bone
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21
Q

What are perforating/Volkmann’s canals?

A
  • anatomic arrangements in cortical bones that allow blood vessels to enter the bones from the periosteum
  • they interconnect the Haversian canals (running inside osteons), w/ each other, & the periosteum
  • run perpendicular to the Haversian canals, & extend in random directions & at various angles
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22
Q

What is spongiosa?

A

spicules (sharp, needle-like bodies) of tissue composed partially or entirely of bone near the leading edges of ossification centers

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23
Q

What is primary spongiosa?

A
  • the temporary spongiosa formed initially during ossification
  • they are composed principally of calcified cartilage covered w/ woven bone but may contain some lamellar bone
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24
Q
A
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25
Q

What is secondary spongiosa?

A
  • thicker than primary spongiosa & is the result of remodeling
  • (replacement of calcified cartilage & woven bone w/ lamellar bone)
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26
Q

What is bone modeling?

A
  • shaping
  • refers to the CHANGE in size, shape, or contour of a bone in response to normal growth, altered mechanical use, or disease
  • in modeling, bone surfaces may undergo mostly resorption or mostly formation, depending on the stimulus
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27
Q

What is Wolff’s Law?

A
  • a bone, normal or abnormal, develops the structure most suited to resist the forces acting upon it
  • in other words, bone will undergo changes in size, shape, or contour as a response to the forces applied to it
  • BONE DEVELOPS BASED ON ITS ENVIRO
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28
Q

What is remodeling?

A
  • the normal & continuous REPLACEMENT of existing or old bone w/ new bone to allow for the repair of microscopic injury
  • in remodeling, resorption & formation are linked & occur at equal rates
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29
Q

What are the 4 major functions of bone as an organ?

A
  1. support
  2. protection
  3. mechanical advantage
  4. reservoir
    - bone is also involved in acid-base homeostasis & serves as a trap for hazardous minerals (ex: lead)
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30
Q

How does bone function as a structural support?

A

bones are arranged in a skeleton that form a frame to which the soft tissues of the body are attached

31
Q

How does bone function as protection for vital organs?

A
  • bones are hard & have developed a strategic relationship w/ vital soft tissues to provide them w/ protection
  • ex: brain & eyes w/in skull; spinal cord w/in the vertebral column; heart, lungs, & liver w/in the rib cage
  • bones are also the location of hematopoietic tissue (bone marrow)
32
Q

How does bone give us a mechanical advantage?

A

bones act as a series of levers that provide muscles w/ the mechanical advantage that enable pars of the body to move

33
Q

How does bone function as a reservoir?

A
  • bone is an important reservoir for certain minerals
  • about 99% of the body’s calcium & 85% of the body’s phosphorus are stored in the bone
34
Q

How might disease of bone affect the animal?

A
  • not protect the animal, cant move, move in a funny way, etc.
35
Q

KNOW What are the different shapes of bones?

A
  1. flat bones
  2. irregular bones
  3. tubular bones
  4. sesamoid bones
  5. short bones or cuboidal bones
36
Q

what is the axial skeleton?

A

head, vertebral column, ribs, sternum, & pelvis

37
Q

What is the appendicular skeleton?

A

thoracic and pelvic limbs

37
Q

KNOW which bone shapes are characteristic of the axial skeleton?

A

flat & irregular

38
Q

KNOW which bone shapes are characteristic of the appendicular skeleton?

A

tubular, sesamoid, and short bones

39
Q

What are flat bones?

A
  • provide maximal protection w/ minimal weight
  • ex: bone of the skull, scapulae, ribs, & bones of the pelvis
40
Q

What are irregular bones?

A
  • include the vertebrae & certain bones of the skull that are not flat
  • jutting processes for muscle attachment are typical of irregular bones
41
Q

What are tubular (or long) bones?

A
  • in general terms, cylindrical & conceptually, partially hollow
  • humerus, radius, ulna, femur, tibia, & the 3rd metacarpal & 3rd metatarsal bones of some spp are ex of long tubular bones
  • phalanges, metacarpal, & metatarsal bones of the paws of other spp are ex of short tubular bones
42
Q

What are sesamoid (“seed-like”) bones?

A
  • located near joints & serve to redirect the path of tendons & to protect tendons at areas where the greatest friction develops
  • the proximal sesamoid bones of the limbs, the distal sesamoid or navicular bone of the horse’s foot, the patella, & the fabellae (s. fabella) are ex of sesamoid bones
43
Q

What are short (or cuboidal) bones?

A

found in the carpal & tarsal regions

44
Q

What are the two types of fetal ossification?

A
  1. intramembranous ossification that results in membrane or membranous bones
  2. endochondral ossification that results in cartilage or cartilaginous bones
45
Q

What is intramembranous ossification?

A
  • w/in a membrane
  • begins w/ condensation (increased density) of mesenchymal cells
  • next, some of the mesenchymal cells differentiate into OSTEOBLASTS & begin to form osteoid that is quickly mineralized to form spicules of woven bone
  • spicules of woven bone increase in size & coalesce to form a continuous piece of bone
  • THE ESSENCE OF INTRAMEMBRANOUS OSSIFICATION IS THE DE NOVO FORMATION OF BONE IN MESENCHYME
  • some bones of the skull, including the maxillae, & portions of the mandibles are examples of membranous bones
46
Q

What does de novo mean?

A

of new, anew, or from the beginning

47
Q

What is endochondral (or enchondral: w/in cartilage) ossification?

A
  • begins w/ the condensation of mesenchymal cells
  • next, the mesenchymal cells differentiate into CHONDROBLASTS that form a cartilaginous model or anlage
  • all mesenchymal cells w/in the model will differentiate into chrondroblasts & mature into chondrocytes
  • therefore, the cartilaginous model is avascular & devoid of stem cells
  • w/o a blood supply, the cartilaginous model degenerates & calcifies
  • further development of the model depends on neovascularization, repopulation of the model w/ stem cells, & the production of woven bone via endochondral ossification
  • THE ESSENCE OF ENDOCHONDRAL OSSIFICATION IS THE REPLACEMENT OF CARTILAGE W/ BONE (cartilage is not converted into bone)
  • tubular bones, vertebrae, the pelvic bones, & bones of the base of the skull are examples of cartilaginous bones
48
Q
A

Intramembranous ossification

49
Q
A

endochondral ossification

50
Q

What is articular cartilage?

A

the thin layer of hyaline cartilage on the articular surfaces of bones that form synovial joints

51
Q

What is the cartilage btwn the articular cartilage & the outer surface of the epiphysis called?

A

epiphyseal cartilage

52
Q

What is subchondral bone?

A

the bone below, or deep to, the cartilage, in this case the articular cartilage

53
Q

What is the diaphysis (or shaft) ?

A
  • (dia = btwn)
  • is the elongated cylindrical portion of a tubular bone that separates, or is btwn, the 2 ends
  • it is composed of a cortex surrounding the medullar cavity
  • it is the site of the primary center for ossification
54
Q

What is the endosteum?

A
  • it is like the periosteum & lines the internal surfaces of bones, including the medullary cavity, trabecular bone, & the osteonal canals
55
Q

What is the epiphysis?

A
  • (epi = above or upon)
  • is the wide end of a tubular bone that is covered by articular cartilage &, in growing bones, is separated from the metaphysis by the physis
  • it is the site of a secondary center of ossification
  • a bone might have 2 or more epiphyses
56
Q

What is a medullary cavity (marrow cavity)?

A

the space in the diaphysis filled w/ marrow

57
Q

What is the metaphysis?

A
  • (meta = change or transition)
  • the wider part(s) of a tubular bone btwn the diaphysis & the physis
  • it’s composed of a think cortex surrounding cancellous bone
  • in growing bones, the cancellous bone is made up of both primary & secondary spongiosa
58
Q

What is the periosteum?

A
  • (peri = around or near)
  • a specialized fibrous CT that contains bone cells & covers the external surface of bones, except the articular surfaces
59
Q

What is the perichondral ring?

A

the dense layer of fibrous CT that is continuous w/ the periosteum but overlies the periphery of a physis

60
Q

what is the physis?

A
  • (physis = growth or to grow)
  • aka growth plate, metaphyseal growth plate, or epiphyseal disk
  • the plate or disk of hyaline cartilage of growing endochondral bones located btwn the metaphysis & epiphysis
61
Q

what is trabecular bone?

A
  • the less dense bone found in the metaphyses & epiphyses of tubular bones
  • it’s also called cancellous bone & spongy bone
62
Q

What is hematopoiesis?

A
  • blood cell production process
  • cells that circulate in your blood include immune cells (WBCs), RBCs, & platelets
  • your body produces an astonishing 100 billion blood cells each day
63
Q

What are the two different types of bone growth?

A
  1. growth in diameter - appositional growth
  2. growth in length of endochondral bones - endochondral ossification
64
Q

What is appositional growth?

A
  • growth in diameter (& other dimensions)
  • the diaphysis of endochondral bones & the surfaces of membranous bones grow via the apposition of bone by osteoblasts w/in the periosteum
  • while the periosteum adds new bone, the endosteum removes bone via osteoclastic activity to increase the diameter of the medullary cavity & keep the cortex in relative proportion
65
Q

What is apposition?

A

the deposition of successive layers upon those already present

66
Q
A

MD = mature diaphysis
DD = developing diaphysis

67
Q

How does growth in length of endochondral bones work?

A
  • endochondral ossification allows endochondral bones to w/stand fxnal stresses while maintaining the ability to grow in length
  • endochondral ossification at the physes is responsible for most of the growth in length while endochondral ossification w/in the EPIphyses contributes to a lesser degree
  • a physis is a temporary structure composed of hyaline cartilage
  • it is thickest when growth is most rapid & becomes thin as growth slows
  • this event is referred to as closure of the growth plate & marks skeletal maturity
  • the epiphysis contains blood vessels which provide nutrition to the physis
68
Q

What are the zones of the physis?

A

I. reserve (or resting) zone
II. proliferative zone
III. hypertrophic zone
IV. calcifying zone
- osteogenic zone

69
Q

What is the reserve (or resting) zone?

A
  • consists of typical hyaline cartilage & serves as a source of cells for the proliferative zone
70
Q

What is the proliferative zone?

A
  • clusters of cartilage cells multiply via successive mitotic divisions & form columns of chondrocytes separated by thin bands of cartilage matrix
  • this zone contributes to growth, although minimally, by adding new cells to the physis
71
Q

What is the hypertrophic zone?

A
  • chondrocytes and their lacunae become greatly enlarged & account for most of the growth in length
  • then, chondrocyte cytoplasm becomes vacuolated & the nuclear & cellular membranes fragment, consistent w/ apoptosis
72
Q

What happens within the calcifying zone?

A
  • intercellular material, which is chondrocyte ECM, becomes mineralized or calcified
  • mineralization of the intercellular material is necessary for phagocytic cells (chondroclasts) to attach & remove cartilage during remodeling
73
Q

What is the osteogenic zone?

A
  • capillary loops from the metaphysis invade btwn the columns of calcified cartilage
  • transverse septa are removed by chondroclasts that allows the lacunae to merge & form larger spaces surrounded by calcified cartilage
  • the contiguous surfaces become lined by osteoblasts which produce woven bone

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