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Flashcards in 1- Bone Deck (50):
1

What is endochondral ossification?

formation of LONG bones (any bone that grows longitudinally) from cartilage model, most common type of ossification

2

What is intramembraneous ossification?

this form does NOT use a cartilage model when forming the FLAT bones (clavicle/skull).

3

During the 6th week of bone development, the mesenchymal cells in the middle of the limb differentiate into what type of cells?

Chondroblasts

4

What is the fxn of chondoblasts?>

form the cartilage template of bone.

5

After the mesenchymal cells die, blood vessels migrate into the bone matrix bringing with them what type of cells?

osteoblasts

6

What is the fxn of osteoblasts?

which form the bone by secreting osteoid into the bone matrix

7

At what location does the matrix get calcified?

primary ossification center

8

What is the diaphysis?

the shaft of a long bone where the primary center of ossification is located

9

What is the medullary canal?

central core located w/in diaphysis that is hollowed out by resorption creating a cavity for blood vessels which bring the osteoblasts

10

What is the metaphysis?

the knobs/flared region at the ends of long bones

11

What is the epiphysis?

located across the physis just below the articular cartilage lining the joint

12

What is the periosteum?

appositional growth (bone widening) occurs under the periosteum (sleeve of connective tissue surrounding the shaft). The periosteum remains into adulthood and is a the source of cells for fracture repair and new growth. Repair of bones does not stop as scar formation like other tissue; rather it completely re-ossifies leaving little or no indication of damage

13

What is the reserve zone of the physis?

closest to epiphysis, contains cells that produce a cartilaginous matrix of type II collagen which is used for bone ossification. Smallest blood supply

14

What is the zone of proliferation of the physis?

cells stack into columns where they undergo synthesis and cell division, and excrete extracellular matrix. Largest blood supply.

15

What is the zone of hypertrophy of the physis?

zone closest to calcified bone; the chondrocytes swell and become larger and participate in mineralization of the cartilage. Broken down into 3 zones. Poor blood supply but highly metabolically active so the cells use stored glycogen.

16

What are the 3 zones of the zone of hypertrophy?

(1) Zone of Maturation: chondrocytes store Ca
(2) Zone of Degradation: chondrocytes die via apoptosis and release Ca
(3) Zone of Calcification: Ca released is used for mineralization.

17

What is the zone of ossification of the physis?

Osteoclasts and osteoblasts from the diaphyseal side break down the calcified cartilage and replace with mineralized bone tissue

18

What is woven bone?

primitive less-organized bone that is formed when calcified cartilage is replaced with bone by osteoblasts. Haphazard orientation.

19

What is lamellar bone?

occurs when woven bone is remodeled to mature bone that is well organized and is aligned for load bearing.

20

Which artery supplies the growth plate?

the epiphyseal artery, which loses it prominence when the growth plate closes.

21

What is an osteoblast?

bone forming cells. These cells make the nonmineral (organic) component of bone, primarily the osteoid which is a protein matrix of collagen type I. They also regulate the mineralization of osteoid

22

Osteoblasts make what substance which is involved in bone formation and is an important clinical marker for people forming boning (fractures)?

alkaline phosphate

23

Who do osteoblasts contain a large golgi apparatus?

they are metabolically active

24

What is an osteocyte?

osteoblasts that get trapped in established bone. They communicate with other osteocytes via processes that traverse canaliculi. This allows them to regulate the metabolic environment and respond to signals at the surface of bone.

25

What are osteoclasts?

multinucleated cells (from fusion of monocyte precursors) that break down bone. Derived from stem cells. Have a ruffled border to increase surface area in contact with bone (active osteoclast). Stimulated by signals such as PTH.

26

What are Howship's lacunae?

pits that osteoclasts sit in to resorb bone

27

What is the process of osteoclastic resorption of the bone?

osteoblasts expose part of the bone, the osteoclasts attach to this exposed bone via integrins and release proteolytic enzymes and hydrogen ions that break down the bone and release Ca via solubilizing Ca hydroxyapatite crystals (stored form of Ca in bone).

28

What is the histology and microanatomy of cortical bone?

dense bark-like, with it collagen aligned in the direction of applied forces. The cortex of bone is found at the periphery and is responsible for skeletal homeostasis

29

What is an osteon?

basic unit of cortical bone that allow it to remodel, in the center is an artery, and surrounding it is rings of lamellar bone.

30

What is the histology and microanatomy of trabecullar bone?

characterized by lattices of bone spicules, which are aligned in the direction of load but with considerably more empty space than cortical bone. The extra surface to volume of trabecular bone allows for better mineral homeostasis, so it is the area of bone most affected by bone diseases.

31

What happens in bone remodeling?

in healthy pt bone resorption is coupled with new bone deoposition, resorption and removal of bone by osteoclasts shapes bones during development and continues throughout life.

32

What is the role of PTH in bone remodeling?

primary chemical signal for bone resorption, it is stimulated by lower serum Ca (works to increase serum Ca).

33

What is the role of estrogen in bone remodeling?

ensures function of osteoclasts is coupled with osteoblasts (low estrogen and osteoclasts go crazy weakening bone  osteoporosis).

34

What is the role of physical stress in bone remodeling?

stimulates bone growth

35

What does it mean when we have skeletal homeostasis?

bone resorption and deposition of new bone repairs areas of damage to maintain healthy bone

36

What does it mean when we have mineral homeostasis?

resorption of bone for minerals such as Ca to maintain serum Ca levels, this function is more important than skeletal homeostasis b/c low Ca can cause cardiac arrhythmias and sudden death.

37

What is Wolff's law?

bone deposition in areas of high load

38

How is bone deposition mediated in relation to Wolff's law?

mediated by direct stress receptors on the bone cells or by the electoral potentials created by deforming (bending) the bone under load bearing.

39

What is the crystalline storage form of Ca in the bone?

Hydroxyapetite

40

What % of the body's Ca is stored in the bone?

99%

41

How does Ca enter the body?

via the intestines and is reabsorbed through the renal tubule.

42

How much Ca should you get in your diet per day?

diet must provide 200mg of Ca a day, but the intestines have weakass absorption so you must ingest 1000mg of Ca in order for the body to absorbed 200mg of Ca.

43

What is the calcium flux?

how the body maintains serum Ca levels, most important is the ionized active Ca. If serum Ca drops the kidneys can resorb more Ca or the bone can release more Ca.

44

What are the 2 targets of PTH?

i) Bones: PTH stimulates osteoblasts (NOT osteoclasts). The PTH stimulated osteoblasts then stimulate osteoclasts to break down bone Ca
ii) Kidneys: PTH stimulates Ca resorption and conversion of inactive VitaD to its active form

45

What is the role of Vitamin D?

works to increase serum Ca, it is steroid hormone that regulates gene expression. VitaD acts on bone, intestine, and kidney.

46

What are the 2 targets of VitD?

i) Bone: vitaD stimulates release of Ca and phosphate
ii) Intestine: vitaD promotes synthesis of proteins that transport dietary Ca in circulation
iii) Kidney: vitaD increase Ca resorption

47

What is the role of calcitonin?

works to inhibit bone break down when serum Ca levels are high. Calcitonin works by inhibiting osteoclasts from resorbing bone; it is a peptide hormone from thyroid gland chief cells.

48

What is the role of PTH on phosphate resorption?

stimulates the kidney to increase Ca resorption and decrease phosphate resorption

49

Is Vitamin D fat or water soluble?

Fat

50

What is the synthesis of Vitamin D?

i) 7-dehydrocholesterol in the skin is modified by sunlight to VitaD3 (cholecalciferol).
ii) Cholecalciferol is transported to the liver and hydroxylated to 25-OH cholecalciferol
iii) 25-OH cholecalciferol travels to the kidneys where the kidneys decide to make 25-OH cholecalciferol into the active form of VitaD or the inactive storage form of VitaD.