Ch.8 Bone

Question 1

what is bone?

Answer 1

• a connective tiss characterized by an extracellular matrix that’s mineralized by calcium phosphate in the form of hydroxyapatite crystals
• for support and protection
• storage site for calcium and phosphate, in homeostatic regulation of blood Ca2+ levels

Question 2

What does bone matrix contain?

Answer 2

• collagen type I, some collagen type V
• Ground substance:
  1. glycoaminoglycans (hyaluronic acid, chondroitin sulfate, keratin, sulfate)
  2. glycoproteins (osteocalcin, osteonectin, osteopontin)
  3. sialoproteins

Question 3

Lacunae spaces have:

Answer 3

-osteocyte, that extends numerous processes into canaliculi, that connect adjacent lacunae by gap junctions, forming continuous network.

Question 4

3 cell types:

1. osteoprogenitor
2. osteoblasts
3. osteoclasts

Answer 4

1. ->osteoblasts (and secrete bone matrix)
2. secrete extracell matrix, once surrounded its an osteocyte
3. bone-resorbing cells on bone surfaces where its being removed or remodeled (reorganized) or where bone has been damaged (phagocytotic cells derived from bone marrow)

Question 5

what other conn tiss is bone associated?

Answer 5

1. hemopoietic
2. fat
3. blood vessels
4. nerves

Question 6

• compact (dense)

- spongy (cancellous)

Answer 6

• outside bone

- sponge-like, inside. consist of trabeculae. occupied by marrow and blood vessels

Question 7

bones classified by shape, location of spongy and compact bone varies by shape:

1. long bones
2. short
3. flat
4. irregular
5. periosteum

Answer 7

1. shaft, 2 ends-diaphysis, epiphysis, metaphysis, medullary cavity (tiba, metacarpals)
   - almost entire shaft is compact.
2. equal length, diameter (carpals)
   - made of shell of compact bone, spongy bone, marrow space. usually forms joints w/ neighbors
3. thin, plate-like (skull, sternum)
4. complex (vertebrae)
5. fibrous connective tiss cap. covers the outer surface of bone

Question 8

Periosteum

Answer 8

• a sheath of dense fibrous conn. tiss containing osteoprogenitor cells, covering bones
• coll fibers arranged parallel to surface of bone in form of a capsule
• Sharpey’s fibers, angled in ligaments/tendons

Question 9

Periosteal cells

Answer 9

-capable of undergoing division, becoming osteoblasts under appropriate stimulus.

Question 10

Parts of long bone

Answer 10

1. diaphysis: shaft
2. epiphysis: ends
3. metaphysis: flared portion bet dia and epi
4. medullary cavity: large filled with marrow, inner portion

Question 11

articular cartilage which is exposed to joint cavity:

Answer 11

• hyaline, not covered by perichondrium

* diarthrosis: 2 parts-external fibrous layer, synovial layer that lines articular cavity except for cartilaginous area

Question 12

bone cavities lined by endosteum:

*endosteal cells

Answer 12

• layer of conn tiss that contain osteoprogenitor cells, usually one cell layer thick and can differentiate into osteoblasts
• flattened cells resemble fibroblasts

Question 13

What is bone marrow?

Answer 13

• network of reticular cells and fibers that serve as a supporting framework for developing blood cells and vessels
• doesn’t increase in proportion to bone growth, as individual grows

Question 14

what is yellow bone marrow?

Answer 14

• when rate of blood cell formation is diminished in adults, tissue consists of fat cells
• in response to stimuli (blood loss), yellow->red
• in adults, red is restricted to spaces of spongy bone in sternum and iliac crest

Question 15

mature bone is composed of:

Answer 15

-osteon (Haversain sys) structural units

Question 16

osteons

Answer 16

-consist of lamellae which are concentric bony plates surrounding a Haversian(osteonal) canal which contains vascular and nerve supply of osteon

• typically develop in preexisting compact bone
• in dev’t a tunnel is bored through compact bone by osteoclasts
• compact adult bone contains haversian systems of varying age and size

Question 17

blood supply to shaft of long bone is by:

Answer 17

• arteries that enter marrow cavity through nutrient foramina
• greatest number being in diaphysis and epiphysis

Question 18

blood supply to bone tiss is:

Answer 18

• centrifugal

- moves from marrow cavity into and through bone tiss and out via periosteal veins

Question 19

Osteoprogenitor cells found in:

Answer 19

-external and internal surfaces of bone such as periosteal cells that form innermost layer of periosteum and endosteal cells that line the marrow cav, osteonal canals, and volkman’s

Question 20

Osteoblasts

Answer 20

• retains its ability to divide since its a versatile secretory cell like the fibroblasts and chondroblasts
• secretes osteoid (initial unmineralized bone)
• calcification of the matrix
• cuboidal, polygonal, single layer of cells lying in apposition to forming bone
• basophilic cytoplasm w/ clear Golgi app, next to nucleus
• respond to mechanical stimuli to mediate changes in the bone growth and bone remodeling

Question 21

Osteocyte

Answer 21

• maintains bone matrix by synthetic and reabsorptive activities
• helps maintain homeostasis of blood Ca2+
• each occupies lacuna
• 3 functional states:
  1. Quiescent-exhibit a paucity of rER, Golgi ap,
  2. Formative-show evidence of matrix deposition and similar to osteoblast
  3. Resorptive-contain numerous ER and Golgi ap

Question 22

Osteoclast

Answer 22

• large, multi-nucleated cells found at sites where bone is being removed. As a result, a shallow bay called resorption bay (Howship’s lacuna) can be observed in bone directly under osteoclast.
• release lysosomal hydrolases, w/ collagenase, they digest organic components of bone matrix, after matrix is decalcified by acids

Question 23

Endochondral ossification:

Answer 23

• cartilage precursor (vertebrae, extremities)
• mesenchymal cells -> chondroblasts -> cartilage matrix
  1. hyaline cart model w/ the general shape of bone is formed(interstitial and app. growth)
  2. 1st sign is the appearance of cuff of bone around cart. model
• perichondrial cells in midregion do not become chondrocytes, instead osteoblasts produced.
  3. w/ the est periosteal bony collar, perichondrium becomes PERIOSTEUM (becoz of altered role), resulting in a LAYER OF BONE is formed around cart model.(can be classified at periosteal bone or intramembranous bone)
• Chondrocytes in the midregion of cart model become hypertrophic. thus surrounding matrix is resorbed forming thin irregular cart plates between hypertrophic cells.
  4. calcified cartilage matrix inhibits diffusion of nutrients, causing death of the chondrocytes in the cart
  5. periosteal cells migrate into the cavity along w/ growing blood vessels

*synthesize alkaline phosphatase

Question 24

Intramembranous ossification:

Answer 24

• w/o cart precursor (flatbones of skull, face, mandible, clavicle
• formed by differentiation of mesenchymal cells into osteoblasts. they elongate, migrate, and aggregate in specific areas where the sites of bone is destined to form.
• 8th week of gestation
• becomes more vascularized, larger, rounded
• changes from eosinophilic to basophilic w/ clear Golgi ap
• result in osteoblast
• with time, matrix becomes calcified and interconnecting cytoplasmic processes of osteocytes are contained in canaliculi
• concomitantly, more of surrounding mesenchymal cells in membrane proliferate, giving rise to a pop of osteoprogenitor cells
• through continued MITOTIC activity, the OSTEOPROGENITOR CELLS, maintain their numbers and provide a constant source of osteoblasts for growth of the bone spicules(Appositional growth). the new osteoblasts, lay down bone matrix in successive layers, giving rise to WOVEN BONE.

Question 25

*growth of endochondral bone begins 2nd trimester of fetal life and continues into early adulthood

Answer 25

1. bony collar established around cart. model in diaphyseal portion of developing bone
2. as chondrocytes enlarge, their surrounding cart. matrix is resorbed forming this irregular cart plates bet. hypertrophic cells.
3. synthesize alkaline phosphatase
4. surrounding cart matrix undergoes calcification

Question 26

• Growth of long bones depends on the presence of epiphyseal cart. throughout growth period
• Zones in the Epipyseal Cartilage

Answer 26

1. reserve cartilage-no cell proliferation or active matrix prod
2. proliferation: cells undergo division and produce matrix
3. hypertrophy: accumulate glycogen. cells become bigger
4. calcified cartilage-enlarged cells begin to degenerate and matrix becomes calcified/mineralized
5. resorption-bone has been eaten away
   - small blood vessels and accompanying connective tiss invade region occupied by dying chondrocytes. appears like a honeycomb becoz of calcified cart as spicules.

Question 27

Mineralization occurs in:

Answer 27

• extracellular matrices of bone and cartilage and in dentin, cementum, and enamel of teeth
• in enamel, mineralization occurs w/in the extracellular organic matrix secreted by the enamel organ

Question 28

Reservoir for body Ca2+

Answer 28

• delivered to blood when Ca falls below critical pt (8.9-10.1 mg/dL)
• excess blood Ca may be removed and stored in bone
• regulated by parathyroid hormone and calcitonin, secreted by parafollicular cells of thyroid
• PTH=^low blood Ca2+
• calcitonin=v elevated blood Ca2+

Question 29

Fractures and Bone repair

Answer 29

1. neutrophils then macrophage clean site
2. fibroblasts and caps proliferate and grow into site
3. new loose conn. tiss (GRANULATION TISS) is formed and as this tiss becomes denser, cart forms in parts of it, covering bone at fracture site, producing a callus (will form whether or not the fractured parts of bone are in immediate apposition to each other. helps stabilize and bind together the fractured bone
4. osteogenic buds fr new bone invade callus and deposit new bone, replacing with BONY callus. Old cartilage calcifies and is replaced by bone

*in healthy ppl, process takes 6-12 weeks depending on severity and the particular bone broken.