Bone Flashcards
1
Q
Cortical bone
A
- Forms the external surface
- Prominent in tubular long bone
- Provides strength
- Made of tightly packed osteons (Haversian systems)
2
Q
Trabecular bone
A
- Lies beneath the cortex
- Predominates in vertebral bodies, flat bones of the pelvis and skull
- Much less organized than cortical bone
- Consisting of interconnecting trabeculae, larger blood vessels and bone marrow
3
Q
Epiphysis
A
- Separated from the metaphysis by the physis (growth plate)
4
Q
Diaphysis
A
- Joins the two metaphysis and provides length
5
Q
Apophyses
A
- AKA tibial tuberosity are the site of new bone formation like the epiphyses but do not contribute to bone length
- They lay down new bone in response to traction
6
Q
Periosteum
A
- Covers bone except for articular surfaces
- Fibrous outer layer is site of attachment of muscles
- Inner layer contains osteoblasts that generate new bone
7
Q
Where does linear growth occur?
A
Physis
8
Q
Where does circumferential growth occur?
A
Periosteal deposition
9
Q
When does the growth of the appendicular skeleton cease?
A
Ossification of the iliac apophyses
10
Q
When does the height of the vertebral bodies cease?
A
Until the 3rd decade
11
Q
How can skeletal bone age be determined?
A
- Can be determined by secondary ossification and physeal closure (earlier in girls)
12
Q
What factors influence growth at the physis?
A
- Thyroxine
- GH
- IGF-1
(these three work together to cause peak bone mass during puberty) - Testosterone (anabolic effect)
- Estrogens suppress the growth rate by increasing the calcification of the matrix (prerequisite to epiphyseal closure)
13
Q
Biochemical composition of bone
A
- 70% minerals and 30% organic constituents
- Hydroxyapatite (mostly Ca and Phos) accounts for 95% of minerals with Mag
- Organic component is 98% matrix, mostly type I collagen and non collagenous protein ( osteocalcin, fibronectin, osteonectin, and osteopontin)
14
Q
What makes up the other 2% of the organic component?
A
Bone cells
15
Q
What do bone cells do?
A
- Responsible for formation, resorption and maintenance of the remodeling cycle
16
Q
Osteoclasts
A
- Derived from mononuclear cells and resorb bone
17
Q
Osteoblasts
A
- Form osteoid and osteoid matrix
18
Q
Osteocytes
A
- Differentiated osteoblasts and maintain the integrity of bone through a network of canaliculi
19
Q
Alkaline Phosphatase
A
- Enzyme secreted by osteoblasts, but also other cells (liver, gut, kidneys)
- In children, 50 percent from bone
- Released during osteoblastic activity
20
Q
Osteocalcin
A
- Synthesized by osteoblasts and chondrocytes and deposited in extracelullar bone matrix
- Sensitive and specific marker of bone formation
21
Q
Acid phosphatase (TRAP)
A
- Present in osteoclast and released during osteoclastic activity
- Not bone specific
22
Q
Urinary calcium to Cr ratio
A
- Marker of bone resorption
- Elevated values indicate hypercalcemia and increased bone resorption
23
Q
What is the role of parathyroid hormone?
A
- Maintains Ca concentration in the blood
- Stimulates osteoclastic activity causing bone resorption (and increased serum calcium)
- Stimulates conversion 25 (OH)D3 to 1, 25 (OH)2D3
24
Q
Calcitriol
A
- Stimulates intestinal absorption of calcium, elevating serum calcium concentration
- Receptors present on intestinal cells
25
Factors affecting bone synthesis
- Calcium intake
- Latitude
- Exposure to sunlight
- Ingestion of vitamin D
- Metabolic state
- Nutritional status
- Hormones
26
Peak bone mass
- Level of bone mass achieved at the end of skeletal maturation
- Usually reached in late adolescence during second decade
27
Intrinsic factors that effect bone mass
- Hereditary (Race, genes for vitamin D receptors, IL-6, calcitonin, TGF B, estrogen receptor A, osteocalcin etc)
- Sex
- Hormones
28
Extrinsic factors that affect skeletal bone mass
- Calcium
| - General state of health
29
How do steroids impact calcium?
- Decrease GI calcium absorption and increase urinary excretion
30
What are the benefits of weight bearing?
- Enhance bone mineral accrual in children, esp in early puberty
31
Dual energy XR absorptiometry (DEXA)
- Gold standard
- Low radiation, high speed and accuracy
- Gives areal BMD (not true volumetric density)
- Should be interpreted with age matched controls and corrections for height, weight and geography
32
Quantitative computerized tomography
- Axial skeleton only
| - True volumetric density can be measured
33
Tendons
- Major component is Type I collagen
| - Attach muscle to bone
34
Ligament
- Function is to joint bone to bone, stabilize the joint, limit mobility
35
Entheses
- Attach tendon, ligament, fascia or capsule to bone
36
Two types of entheses
- Fibrous
| - Fibrocartilaginous
37
Fibrous
- Found at attachment of tendon to metaphysis or diaphysis composed of dense fibrous tissue, probably not important in rheum
38
Fibrocartilaginous
- Present on epiphyses of long bones and small bones of hands and feet
- Achilles, knee, foot
39
Muscle bundle (Fascicle)
- Group of muscle fibers ensheathed by a perimysium
40
What is the basic unit of muscle?
Fiber--> made of myofibrils
41
What is the basic contractile unit?
- Sarcomere
- Made of thin (actin) and thick (myosin) myofilaments
- Gives muscle striated appearance
42
Epimysium
- Surrounds a skeletal muscle
43
Perimysium
- Surrounds individual fascicles
44
Alpha motor neurons
- Cause action potential that stimulates calcium diffusion in the myoplasm and binding to thin-filament regulatory proteins
45
Type I muscle fibers
- Slow/red
- Narrower
- Poorly defined myofibrils
- Irregular in size
- Thick Z bands
- Rich in mitochondria and oxidative enzymes
- Poor in phosphorlyases
- Sustained contractions
46
Type II muscle fibers
- Fewer mitochondria and poor in oxidative enzymes
- Rich in phosphorylases and glycogen
- Acute strength
47
Z band (disk)
Helps to define the sarcomere
48
I band
- Surrounds the Z disk
| - Zone of thin filaments (actin) not superimposed by thick filaments
49
A band
- Contains the entire length of single thick filament
50
M Line
Inside the H zone of thick filaments not superimposed by thin filaments
- Formed by cross connective elements of the cytoskeleton
51
What is the arterial supply of the long bone?
- Arises from nutrient artery that penetrates the diaphysis and terminates in end arteries at epiphyseal plate
52
What is the arterial supply of the epiphyses?
Juxta-articular arteries which also supply the synovium
53
When does arterial communication between the metaphyseal and epiphyseal synovial circulations occurs?
- Not until growth has ceased
54
Components of ECM of hyaline cartilage
Collagen fibers, water, proteins and proteoglycans
55
3 compartments of ECM matrix of hyaline cartilage
Inner rim: Aggrecan rich, surrounds chondrocytes, no crosslinking
Middle rim: Aggrecan bound to hyaluronan
Outer rim: fine collagen fibrils
56
Three major classes of collagen
1. FIbril forming
2. Non fibril forming
3. Fibril associated collagens with interrupted triple helices (FACITS)
57
Type I collagen
Most connective tissues, bone, skin, tendons
58
Type II collagen
Cartilage, intervertebral disk, vitreous humor
59
Type III
Most connective tissues, particularly skin, lung, blood vessel
60
What is a proteoglycans?
Macromolecules consisting of a protein core with attached GAG
61
Keratan sulfate
Serum concentration of this reflects cartilage metabolism
62
Where can you find elastin?
- Walls of blood vessels
| - Ligaments
63
What are the properties of elastin
- Lack tensile strength of collagens but can stretch than return to original length
- Produced by fibroblasts and smooth muscle cells
64
Laminin
Major constituent of the basement together with Type IV collagen
65
Fibronectin
Dimeric glycoprotein that acts as attachment protein in ECM
