1
Q
what is bone remodeling?
A
the building of new bone tissue by osteoblasts and breaking down of old bone tissues by osteoclasts
2
Q
what kinds of tissues make up bones?
A
- bone tissue
- nervous tissue
- cartilage
- dense connective tissue
- epithelium
- adipose tissue
- blood
3
Q
what is osteology?
A
the study of bone structure and the treatment of bone disorders
4
Q
what are the basic functions of the skeletal system?
A
- support
- protection
- movement assistance
- mineral homeostasis
- hemopoiesis
- fat storage
5
Q
how does the skeletal system provide support?
A
the skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles
6
Q
how does the skeletal system provide protection?
A
the skeleton protects the most important internal organs from injury
7
Q
how does the skeletal system provide assistance in movement?
A
Most skeletal muscles attach to bones; when they contract, they pull on bones to produce movement
8
Q
how does the skeletal system perform mineral homeostasis?
A
-stores several minerals, especially calcium and phosphorus, which contribute to the strength of bone
- releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body
9
Q
how does the skeletal system perform hemopoiesis?
A
- red bone marrow produces red blood cells, white blood cells, and platelets
10
Q
how does the skeletal system perform triglyceride storage?
A
- yellow bone marrow consists of adipose cells, which store triglycerides
- potential chemical energy reserve
11
Q
what is red bone marrow?
A
highly vascularized connective tissue located in microscopic spaces between trabeculae of spongy bone tissue
12
Q
what is red bone marrow composed of?
A
- developing blood cells
- adipocytes
- fibroblasts
- macrophages
13
Q
Which bones contain red bone marrow?
A
- developing bones of fetus
- hip bones
- sternum
- vertebrae
- skull
- ends of humerus and femur
14
Q
How do red bone marrow and yellow bone marrow differ in composition and function?
A
RBM:
- hemopoiesis
- blood cells, fibroblasts
YBM:
- fat storage
- adipocytes
15
Q
what is the long bone’s diaphysis?
A
long, cylindrical, main portion of the bone
aka: shaft, body
16
Q
what are the long bone’s epiphyses?
A
the proximal and distal ends of the bone
17
Q
what are the long bone’s metaphyses?
A
the regions between the diaphysis and the epiphyses
- contains epiphyseal plate/line
18
Q
when does the epiphyseal plate turn into the epiphyseal line?
A
- epiphyseal plate is hyaline cartilage that allows diaphysis of bone to grow in length
- when bone stops growing, cartilage is ossified into epiphyseal line
- age 14-24
19
Q
what is the articular cartilage?
A
thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone
20
Q
what is the function of the articular cartilages?
A
- reduces friction
- absorbs shock at freely movable joints
21
Q
why is the repair of damage in the articular cartilages limited?
A
- cartilage is avascular, lacks perichondrium
22
Q
what is the periosteum?
A
tough connective tissue membrane and its associated blood supply that surrounds the bone surface
23
Q
what is the periosteum composed of?
A
- outer fibrous layer of dense irregular connective tissue
- inner osteogenic layer that consists of osteoprogenitor cells
24
Q
what is the function of the periosteum?
A
- protects the bone
- assists in fracture repair
- helps nourish bone tissue
- serves as an attachment point for ligaments and tendons
25
how is the periosteum attached to the underlying bone?
- attached by perforating fibers, thick bundles of collagen that extend from periosteum into the bone ECM
26
what is the medullary cavity?
hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels
27
what is the function of the medullary cavity?
- minimizes the weight of the bone by reducing the dense bony material where it is least needed
- tubular design provides maximum strength with minimum weight
28
what is the endosteum?
thin membrane that lines medullary cavity and internal spaces of spongy bone
- single layer of osteoprogenitor cells and small amt of connective tissue
29
what is the composition of the osseus extracellular matrix?
15% water
30% collagen fiber
55% crystallized mineral salts
- most abundant salt is calcium phosphate
- other mineral salts include calcium hydroxide, calcium carbonate
- ions include magnesium, sulfate, potassium, fluoride
30
what is hydroxyapatite?
calcium phosphate + calcium hydroxide
31
describe the process of calcification
- mineral salts combine with other salts and ions
- mineral salts deposited in the collagen fiber framework in ECM
- mineral salts crystallize and harden on collagen fibers
32
what does a bone's hardness depend on?
the crystallized inorganic mineral salts
33
what does a bone's flexibility depend on?
the collagen fibers
34
what does the collagen fibers in a bone do?
provides tensile strength and resistance to being stretched or torn apart
35
what happens to a bone after it is soaked in an acidic soln?
- mineral salts dissolve, leaving collagen fibers
- bone becomes rubbery and flexible
36
what are the four types of cells present in bone tissue?
osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts
37
what are osteoprogenitor cells?
unspecialized bone stem cells derived from mesenchyme
- only bone cells capable of undergoing cellular division
38
where are osteoprogenitor cells found?
- along the inner osteogenic layer of the periosteum
- in the endosteum
- in the canals within bone that contain blood vessels
39
what are osteoblasts?
bone building cells
- synthesizes and secretes collagen fibers and other organic components needed to build the extracellular matrix of bone tissue
- initiates calcification
40
what is bone deposition?
the process carried out by osteoblasts of synthesizing and secreting collagen fibers and other organic components needed to build the extracellular matrix of bone tissue
41
how do osteoblasts become osteocytes?
osteoblasts become trapped in their secretions as they surround themselves with ECM
42
what are osteocytes?
mature bone cells
- the main cells in bone tissue
- maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood
43
what are osteoclasts?
huge cells derived from the fusion of as many as 50 **monocytes** and are concentrated in the endosteum
- carries out demineralization/bone resorption
44
what is the function of an osteoclast's ruffled border?
the cell's region that releases powerful lysosomal enzymes and acids which digests the protein and mineral components of the underlying extracellular bone matrix
45
what is compact bone tissue?
- strongest type of bone tissue
- no holes
- provides protection and support
- resists strains produced by weight and movement
46
what are osteons?
basic unit of structure in adult compact bone
- haversian canal
- bone lamellae
- bone canaliculi
- bone lacunae
47
what are concentric bone lamellae?
- circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the osteonic canal
48
how do neighbouring osteocytes communicate?
via gap junctions
49
how are nutrients/wastes exchanged in the bones?
- bone canaliculi connect bone lacunae with one another and osteonic canals, forming interconnected canal system, providing routes for nutrient/waste exchange with arteries and veins found in the central canals
50
why does the diaphysis of a long bone resist bending or fracturing even when considerable force is applied from either end?
- Osteons are aligned in the same direction and are parallel to the length of the diaphysis
- tissue tends to be thickest in those parts of a bone where strains are applied in few directions
51
what are interstitial bone lamellae?
areas of bone lamellae between neighbouring osteons
- fragments of older osteons that have been partially destroyed during bone rebuilding or growth
52
what are Volkmann's canals?
- transverse perforating canals
- vessels and nerves run through Volkmann's canals to penetrate compact bone, connecting with other nerves and vessels in medullary cavity, periosteum, and central canals
53
what are circumferential bone lamellae?
areas of bone lamellae arranged around outer and inner circumference of the diaphysis
- develop during initial bone formation
54
what is the external circumferential bone lamellae?
circumferential bone lamellae that is deep directly to the periosteum
- connected to periosteum by the **perforating fibers**
55
what is the internal circumferential bone lamellae?
circumferential bone lamellae that line the medullary cavity
56
what is spongy bone tissue?
- bone tissue that lacks osteons
- located in the interior of a bone
- consists of irregularly arranged bone trabeculae
- holds red bone marrow
- has great surface area
57
what are bone trabeculae?
irregular pattern of thin bone lamellae columns
- spaces between trabeculae are lined by endosteum and filled with red bone marrow and yellow bone marrow
58
how is normal bone tissue identified under a bone scanner/ gamma camera?
- consistent gray colour because of its uniform uptake of a radioactive tracer
59
what do hot spots in bone captured by a bone scanner/ gamma camera indicate?
hot spots are areas of **increased** metabolism that absorb more radioactive tracer
- bone abnormalities
- bone cancer
- abnormal healing of fractures
- abnormal bone growth
60
what do cold spots in bone captured by a bone scanner/ gamma camera indicate?
hot spots are areas of **decreased** metabolism that absorb less radioactive tracer
- degenerative bone disease
- decalcified bone
- fractures
- bone infections
- Paget's disease
- rheumatoid arthritis
61
how much sooner do bone scans detect abnormalities in bone tissue?
3 - 6 months sooner
62
where can you find spongy bone tissue?
- where bones are not heavily strained or where stresses are applied from many directions
- most of the interior bone tissue of short, flat, sesamoid, and irregularly shaped bones
- forms core of epiphyses of long bones
63
how are spongy bone trabeculae oriented?
- precisely oriented along lines of strain, a characteristic that helps bones resist strains and transfer force without breaking
64
how is spongy bone tissue different from compact bone tissue?
- light, reduces overall weight of bone
- bone trabeculae support and protect red bone marrow
- site of hemipoiesis
65
what is the nutrient artery?
- large artery that enters compact bone at an oblique angle through the **nutrient foramen** near the diaphysis center
- artery passes through nutrient canal into the medullary cavity
66
Where do periosteal arteries enter bone tissue?
through perforating/Volkmann's canals
67
which arteries supply the ends of long bones?
metaphyseal and epiphyseal arteries
68
what are the arteries that you can find on long bone?
- nutrient arteries
- periosteal arteries
- metaphyseal arteries
- epiphyseal arteries
69
what are the veins you can find on long bone?
- nutrient veins
- periosteal veins
- metaphyseal veins
- epiphyseal veins
70
How is a bone marrow needle biopsy performed?
- a needle is inserted into the middle of the bone to withdraw a sample of red bone marrow to examine it for conditions such as leukemias, metastatic neoplasms, lymphoma, Hodgkin’s disease, and aplastic anemia
- as the needle penetrates the periosteum, pain is felt
71
why are sensory neurons in bone important?
- nerves are sensitive to tearing or tension, which explains the severe pain resulting from a fracture or a bone tumor
72
Which part of a bone contains sensory nerves associated with pain?
periosteum
73
when does bone formation occur?
(1) the initial **Formation** of bones in an embryo and fetus
(2) the **Growth** of bones during infancy, childhood, and adolescence until their adult sizes are reached
(3) the **Remodeling** of bone (replacement of old bone by new bone tissue throughout life)
(4) the **Repair** of fractures (breaks in bones) throughout life
74
what is intramembranous ossification?
- bone is formed directly in mesenchyme arranged in sheetlike layers that resemble membranes
75
what is endochondral ossification?
bone forms within hyaline cartilage that develops from mesenchyme
76
what bones are formed through intramembranous ossification?
- flat bones of skull
- most of facial bones
- mandible
- medial part of clavicle/collar bone
77
what are steps of intramembranous ossification?
1. development of **ossification center**
2. **calcification**
3. formation of bone **trabeculae**
4. development of **periosteum**
78
what happens in development of ossification center in intramembranous ossification?
1. specific chemical messages cause mesenchymal cells to cluster together and differentiate into osteoprogenitor cells and then into **osteoblasts** at site where bone will develop called **ossification center**
2. osteoblasts **secrete the organic extracellular matrix** of bone until they are surrounded by it
79
what happens in calcification in intramembranous ossification?
1. secretion of extracellular matrix stops, osteocytes lie in bone lacunae and extend their cytoplasmic processes into bone canaliculi that radiate in all directions
2. **calcium and other mineral salts are deposited** and the extracellular matrix hardens or calcifies
80
what happens in development of bone trabeculae in intramembranous ossification?
1. as bone extracellular matrix forms, it **develops into bone trabeculae** that fuse with one another to form spongy bone around the network of blood vessels in the tissue
2. connective tissue associated with the blood vessels in the bone trabeculae differentiates into red bone marrow
81
what happens in development of periosteum in intramembranous ossification?
1. **mesenchyme condenses** at the periphery of the bone and develops into the **periosteum**
2. a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone remains in the center
3. Much of the newly formed bone is remodeled as the bone is transformed into its adult size and shape
82
what are steps of endochondral ossification?
1. Development of the **cartilage model**
2. **Growth** of the cartilage model
3. Development of the **primary ossification center**
4. Development of the **medullary cavity**
5. Development of the **secondary ossification centers**
6. Formation of **articular cartilage** and the **epiphyseal plate**
83
what happens in development of the cartilage model in endochondral ossification?
1. At site where bone is going to form, specific chemical messages cause **mesenchymalmal cells** to crowd together in general shape of future bone, and then **develop into chondroblasts**
2. chondroblasts secrete cartilage extracellular matrix, producing a cartilage model consisting of hyaline cartilage
3. perichondrium develops around the cartilage model
84
what happens in growth of the cartilage model in endochondral ossification?
1. cartilage model grows in length by **continual cell division** of chondrocytes, accompanied by further secretion of the cartilage extracellular matrix
2. chondrocytes in midregion increase in size and surrounding cartilage extracellular matrix begins to calcify
3. chondrocytes within calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix
4. empty spaces are left behind in the extracellular matrix
85
what is interstitial cartilaginous growth?
- growth from within cartilage connective tissue
- not from perichondrium
- chondrocytes secrete ECM
- results in increase in **length**
86
what is appositional cartilaginous growth?
- growth at outer surface
- new chondroblasts at perichondrium deposit ECM on surface of cartilage
- results in increase of **thickness**
87
what happens in development of the primary ossification center in endochondral ossification?
1. Primary ossification proceeds inward from external surface of bone
2. A nutrient artery penetrates perichondrium and calcifying cartilage model through a nutrient foramen in the midregion of the cartilage model, stimulating **osteoprogenitor cells** in the perichondrium to **differentiate into osteoblasts**
3. periosteal capillaries grow into the disintegrating calcified cartilage, inducing **growth of a primary ossification center**
4. Osteoblasts begin to deposit bone extracellular matrix over the remnants of calcified cartilage, forming **spongy bone trabeculae**
88
what happens in development of the medullary cavity in endochondral ossification?
1. primary ossification grows towards bone ends
2. **osteoclasts** break down some of the newly formed spongy bone trabeculae, **leaving a cavity**
89
what happens in development of the secondary ossification centers in endochondral ossification?
1. **secondary ossification centers develop in bone epiphyses** as primary ossification center grows towards bone ends
- spongy bone remains in the interior of the epiphyses, no medullary cavity
- secondary ossification proceeds outward from the center of the epiphysis toward the outer surface of the bone
90
what happens in development of the articular cartilages and epiphyseal plates in endochondral ossification?
hyaline cartilage that covers the epiphyses becomes the articular cartilage
91
what two major events follow the growth in length of long bones?
(1) interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate
(2) replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification
92
what are the four zones that compose the epiphyseal plate?
1. zone of resting cartilage
2. zone of proliferating cartilage
3. zone of hypertrophic cartilage
4. zone of calcified cartilage
93
what is the zone of resting cartilage?
- layer nearest to the epiphysis
- consists of small, scattered chondrocytes
- cells do not function in bone growth in length
- cells anchor the epiphyseal plate to the epiphysis of the bone
94
what is the zone of proliferating cartilage?
- Slightly larger chondrocytes arranged like stacks of coins
- chondrocytes **undergo interstitial growth** as they divide and secrete extracellular matrix
- chondrocytes divide to replace those that die at the diaphyseal side of the epiphyseal plate
95
what is the zone of hypertrophic cartilage?
layer consists of large, maturing chondrocytes arranged in columns
96
what is the zone of calcified cartilage?
- only a few cells thick
- consists mostly of **dead chondrocytes** because the extracellular matrix around them has calcified
- Osteoclasts dissolve calcified cartilage, and osteoblasts and capillaries from diaphysis invade the area
- osteoblasts lay down bone extracellular matrix, replacing calcified cartilage by endochondral ossification
- **becomes the new diaphysis**
97
why does a bone fracture that damages the epiphyseal plate result in a shorter than normal bone?
damage to cartilage, which is avascular, **accelerates closure of the epiphyseal plate** due to the stopping of cartilage cell division, thus inhibiting lengthwise growth of the bone
98
describe how bone grows in thickness by appositional growth
1. osteoprogenitor cells of the osteogenic layer of the periosteum differentiate into osteoblasts, which secrete the collagen fibers and other organic molecules that form bone extracellular matrix
- osteoblasts become surrounded by extracellular matrix and develop into osteocytes, **forms bone ridges on either side of a periosteal blood vessel**
- ridges slowly enlarge and create a groove for a periosteal blood vessel
2. **ridges fuse**, and groove becomes a tunnel that **encloses blood vessel**
- former periosteum becomes the endosteum that lines the tunnel
3. Osteoblasts deposit bone extracellular matrix, forming new concentric bone lamellae
- formation of additional concentric bone lamellae proceeds inward toward the periosteal blood vessel, **new osteon is created**
4. As an osteon is forming, **osteoblasts under the periosteum deposit new circumferential bone lamellae**, further increasing the thickness of the bone
99
how does the medullary cavity enlarge as bone thickens?
as new bone tissue is being deposited on the outer surface of bone, the bone tissue lining the medullary cavity is destroyed by osteoclasts in the endosteum
100
what factors can trigger bone remodeling?
- exercise
- sedentary lifestyle
- changes in diet
101
why is bone remodeling beneficial?
- strength of bone is related to the degree to which it is strained, so if newly formed bone is subjected to heavy loads, it will grow thicker and stronger than old bone
- new bone is more resistant to fracture
- bone shape can be altered for proper support based on strain patterns experienced during remodeling process
102
describe the process of bone resorption
1. osteoclast attaches tightly to the bone surface at the endosteum or periosteum and forms a leakproof seal at the edges of its ruffled border
2. releases protein-digesting lysosomal enzymes and several acids into the sealed pocket, digesting collagen fibers and bone minerals
3. products of bone resorption enter an osteoclast by endocytosis, cross the cell in vesicles, and undergo exocytosis on the side opposite the ruffled border
4. products enter interstitial fluid and diffuse into nearby blood capillaries
103
what is orthodontics?
branch of dentistry concerned with the prevention and correction of poorly aligned teeth
104
what are spurs?
thick bumps on bone that interfere with movement at joints
- result of too much new tissue being formed and bones become abnormally thick and heavy
105
what is the Paget's disease?
*osteitis deformans*
- excessive proliferation of osteoclasts, bone resorption occurs faster than bone deposition
- osteoblasts attempt to compensate, but new bone is weaker because it has a higher proportion of spongy to compact bone
- mineralization is decreased
- newly synthesized extracellular matrix contains abnormal proteins.
- newly formed bone, especially that of the pelvis, limbs, lower vertebrae, and skull, becomes enlarged, hard, and brittle and fractures easily
106
what are the factors affecting bone growth and remodeling?
- minerals
- vitamins
- hormones
107
how do minerals affect bone growth and remodeling?
- Large amounts of calcium and phosphorus are needed while bones are growing, as are smaller amounts of magnesium, fluoride, and manganese
- These minerals are also necessary during bone remodeling
108
how do vitamins affect bone growth and remodeling?
- **Vitamin A** stimulates activity of osteoblasts
- **Vitamin C** is needed for synthesis of collagen
- **Vitamin D** increases the absorption of calcium from foods in the digestive canal into the blood
- **Vitamins K** and **B12** needed for synthesis of bone proteins
109
how do hormones affect bone growth and remodeling?
- **IGFs** most important in childhood, produced by liver and bone tissue, stimulate osteoblasts, promote cellular division in epiphyseal plate and periosteum, enhance synthesis of proteins needed to build new bone
- IGFs produced in response to **GH** by pituitary gland
- **T3** and **T4** from thyroid gland stimulate osteoblasts
- **insulin** increases bone protein synthesis
- **sex hormones** increase osteoblast activity, synthesis of bone ECM, shut down growth at epiphyseal plates, slows resorption of bone in adulthood
110
what is gigantism?
Oversecretion of growth hormone (GH) during childhood leads to person becoming taller than normal
111
what is dwarfism?
condition of small stature in which the height of an individual is typically under 4 feet 10 inches
112
what is proportionate dwarfism?
all parts of the body are small but they are proportionate to each other
- one cause of proportionate dwarfism is a hyposecretion of GH during childhood
113
what is disproportionate dwarfism?
some parts of the body are normal size or larger than normal while others are smaller than normal
114
what is achondroplasia?
inherited condition in which the conversion of hyaline cartilage to bone is abnormal and the **long bones** of the limbs stop growing in childhood
- other bones unaffected
- leads to **achondroplastic dwarfism**, short stature but normal size head and trunk
115
what is a fracture?
any break in a bone
116
what is a stress fracture?
- a series of **microscopic fissures in bone** that forms without any evidence of injury to other tissues
- result from repeated, strenuous activities such as running, jumping, or aerobic dancing
- quite painful
- result from disease processes that disrupt normal bone calcification, such as osteoporosis
- show up in a bone scan
- 25% involve tibia
117
what are the phases of repairing a bone fracture?
1. Reactive phase
2A. Reparative phase: Fibrous cartilage callus formation
2B. Reparative phase: Bony callus formation
3. Bone remodeling phase
118
what happens in the reactive phase?
- early inflammatory phase
- Blood vessels crossing the fracture line are broken
- blood clot forms around fracture site
- bone cells near fracture hematoma die b/c blood circulation stops
- phagocytes and osteoclasts remove dead/damaged tissue in and around fracture hematoma
- lasts several weeks
119
what is a fracture hematoma?
a mass of blood forming around fracture site as blood leaks from torn ends of vessels
120
what happens in the reparative phase: Fibrous cartilage callus formation?
- Blood vessels grow into the fracture hematoma
- phagocytes begin to clean up dead bone cells
- Fibroblasts from periosteum invade the fracture site and **produce collagen fibers**
- cells from periosteum develop into chondroblasts and begin to produce **fibrous cartilage** in this region
- development of a fibrous cartilage callus, consisting of collagen fibers and cartilage that bridges the broken ends of the bone.
- takes about 3 weeks
121
what happens in the reparative phase: Bony callus formation?
- In areas closer to well-vascularized healthy bone tissue, osteoprogenitor cells develop into osteoblasts, which begin to produce spongy bone trabeculae
- spongy bone trabeculae join living and dead portions of the original bone fragments
- fibrous cartilage is converted to spongy bone, and the callus is then referred to as a bony callus
- lasts about 3 to 4 months
122
what happens in the bone remodeling phase?
- Dead portions of the original fragments of broken bone are gradually resorbed by osteoclasts
- Compact bone replaces spongy bone around the periphery of the fracture
- a thickened area on the surface of the bone remains as evidence of a healed fracture
123
why does bone heal more rapidly than cartilage?
bone blood supply is more plentiful
124
what is the ultimate goal for fracture treatment?
- realignment of the bone fragments
- immobilization to maintain realignment
- restoration of function
125
what is reduction?
the process of bringing fractures bone ends into alignment for them to unite properly
126
what is closed reduction?
- the fractured ends of a bone are brought into alignment by manual manipulation, and the skin remains intact
127
what is open reduction?
- the fractured ends of a bone are brought into alignment by a surgical procedure using internal fixation devices such as screws, plates, pins, rods, and wires
128
how are fractured bones immobilized following reduction?
cast, sling, splint, elastic bandage, external fixation device
129
why does bone tissue take a long time to heal even though it has plenty of blood supply?
- calcium and phosphorus needed to strengthen and harden new bone are deposited only gradually
- bone cells generally grow and reproduce slowly
- temporary disruption in bone tissue blood supply also contributed to slowness of healing of severely fractured bones
130
what is an open/compound fracture?
The broken ends of the bone protrude through the skin
131
what is a comminuted fracture?
The bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments
132
what is a greenstick fracture?
A partial fracture
- one side of the bone is broken and the other side bends
- occurs only in children, whose bones are not fully ossified and contain more organic material than inorganic material
133
what is an impacted fracture?
One end of the fractured bone is forcefully driven into the interior of the other
134
what is a pott fracture?
Fracture of the **distal end of the fibula (lateral leg bone)**, with serious injury of the distal tibial articulation
135
what is a colles fracture?
Fracture of the **distal end of the lateral forearm bone (radius)** in which the distal fragment is **displaced posteriorly**
136
what is a vertebral compression fracture?
The vertebral body of one or more vertebrae fractures and becomes compressed into a wedge-shape
- may be caused by injury, trauma, or more commonly in individuals with osteoporosis
137
what does the role bone play in mineral homeostasis?
helps “buffer” the blood Ca2+ level, releasing Ca2+ into blood plasma (using osteoclasts) when the level decreases, and absorbing Ca2+ (using osteoblasts) when the level rises
138
what are some functions of Ca2+ in the body?
- nerve and muscle cells depend on a stable level of calcium ions (Ca2+) in extracellular fluid to function properly
- blood clotting
- many enzymes need Ca2+ as cofactor
139
what happens if Ca2+ is too high?
cardiac arrest
140
what happens if Ca2+ is too low?
respiratory arrest
141
what is the blood plasma level of Ca2+?
between 9 and 11 mg/100 mL
142
what is the most important hormone that regulates Ca2+ exchange?
parathyroid hormone (PTH), secreted by parathyroid glands
143
what direction does PTH secretion's feedback system operate?
negative feedback system
144
describe the feedback system of decrease in Ca2+ blood levels
- stimulus: causes decrease in blood Ca2+ level
- receptor: parathyroid gland cells
- input: increased production of cyclic AMP
- control center: parathyroid hormone gene
- output: gene turned on, increases release of PTH
- effectors: osteoclasts increase bone resorption, kidneys retain Ca2+ in blood and produce calcitriol
- response: Increase in Ca1+ blood levels
145
what hormone works when Ca2+ levels are too high?
**calcitonin** is secreted by **parafollicular cells** in thyroid gland
- inhibits osteoclast activity
- speeds blood Ca2+ uptake by bone
- accelerates Ca2+ deposition into bone
146
what happens when bone does not experience mechanical strain?
- bone does not remodel normally because bone resorption occurs more quickly than bone formation
147
what are the main mechanical strains on the bone?
- the pull from skeletal muscles
- the pull from gravity
148
Why is it important to engage in weight-bearing exercises before the epiphyseal plates close?
to help build total mass prior to bone tissue's inevitable reduction with aging
149
Would children raised in space ever be able to return to Earth?
IDK
150
outline the loss of bone mass in females
loss usually begins after age 30 in females, accelerates greatly around age 45 as levels of estrogens decrease, and continues until as much as 30% of the calcium in bones is lost by age 70
- about 8% of bone mass is lost every 10 years
151
outline the loss of bone mass in males
calcium loss typically does not begin until after age 60, and about 3% of bone mass is lost every 10 years
152
what are the two main effects of aging on bone tissue?
- loss of bone mass through demineralization
- brittleness due to decreases protein synthesis
153
why does bone become brittle as one grows older?
- diminished production of growth hormone
- collagen fiber synthesis slows
- loss of tensile strength
154
what is osteoporosis?
condition of porous bones
155
what is osteopenia?
**low bone mass** due to a decrease in the rate of bone synthesis to a level too low to compensate for normal bone resorption; any decrease in bone mass below normal. An example is osteoporosis.
156
what is the basic problem in bone disorders?
- bone resorption (breakdown) outpaces bone deposition (formation)
- more calcium is lost in urine, feces, and sweat than is absorbed from the diet
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why do older women suffer from osteoporosis more than men?
(1) women’s bones are less massive than men’s bones
(2) production of estrogens in women declines dramatically at menopause, whereas production of the main androgen, testosterone, in older men wanes gradually and only slightly
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what are the risk factors for osteoporosis?
- gender
- family history of the disease
- European/Asian ancestry
- thin/small body build
- inactive lifestyle
- cigarette smoking
- diet low in calcium and Vit D
- alcoholism
- use of certain medications
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what are the types of medications used to treat osteoporosis?
1. **antiresorptive** drugs slow down progression of bone loss
- bisphosphonates, selective estrogen receptor modulators, estrogen replacement therapy, hormone replacement therapy
2. **bone-building** drugs promote increasing bone mass
- parathyroid hormone
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what is rickets
rickets: disease of children in which the growing bones become “soft” or rubbery and are easily deformed
- bowed legs and deformities of the skull, rib cage, and pelvis because new bone formed at the epiphyseal plates fails to ossify
- result from inadequate calcification of the extracellular bone matrix, usually caused by a vitamin D deficiency
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what is osteomalacia?
- New bone formed during remodeling fails to calcify, and the person experiences varying degrees of pain and tenderness in bones, especially the hip and legs
- Bone fractures also result from minor trauma
- result from inadequate calcification of the extracellular bone matrix, usually caused by a vitamin D deficiency
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how do you prevent/treat rickets and osteomalacia?
administration of adequate vitamin D and exposure to moderate amounts of sunlight
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what is Osteoarthritis?
The **degeneration of articular cartilage** such that the bony ends touch; the resulting friction of bone against bone worsens the condition. Usually associated with the elderly.
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what is Osteomyelitis?
An infection of bone characterized by high fever, sweating, chills, pain, nausea, pus formation, edema, and warmth over the affected bone and rigid overlying muscles. It is often caused by bacteria, usually **Staphylococcus aureus**. The bacteria may reach the bone from outside the body (through open fractures, penetrating wounds, or orthopedic surgical procedures); from other sites of infection in the body (abscessed teeth, burn infections, urinary tract infections, or upper respiratory infections) via the blood; and from adjacent soft tissue infections (as occurs in diabetes mellitus).
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what is Osteosarcoma?
**Bone cancer** that primarily affects **osteoblasts** and occurs most often in teenagers during their growth spurt; the most common sites are the metaphyses of the thigh bone (femur), shin bone (tibia), and arm bone (humerus). Metastases occur most often in lungs; treatment consists of multidrug chemotherapy and removal of the malignant growth, or amputation of the limb.
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Astronauts in space exercise as part of their daily routine, yet they still have problems with bone weakness after prolonged stays in space. Why does this happen?
Exercise causes mechanical strain on bones, but because there is effectively zero gravity in space, the pull of gravity on bones is missing. The lack of stress from gravity results in bone demineralization and weakness.
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Taryn is a high school senior who is undergoing a strenuous running regimen for several hours a day in order to qualify for her state high school track meet. Lately she has experienced intense pain in her right leg that is hindering her workouts. Her physician performs an examination of her right leg. The doctor doesn’t notice any outward evidence of injury; he then orders a bone scan. What does her doctor suspect the problem is?
Due to the strenuous, repetitive activity, Taryn has probably developed a stress fracture of her right tibia (lower leg bone). Stress fractures are due to repeated stress on a bone that causes microscopic breaks in the bone without any evidence of injury to other tissue. An x-ray would not reveal the stress fracture, but a bone scan would. Thus the bone scan would either confirm or negate the physician’s diagnosis.
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While playing basketball, nine-year-old Marcus fell and broke his left arm. The arm was placed in a cast and appeared to heal normally. As an adult, Marcus was puzzled because it seemed that his right arm was longer than his left arm. He measured both arms and he was correct—his right arm is longer! How would you explain to Marcus what happened?
When Marcus broke his arm as a child, he injured his epiphyseal (growth) plate. Damage to the cartilage in the epiphyseal plate resulted in premature closure of the plate, which interfered with the lengthwise growth of the arm bone.
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how does calcium affect bone growth?
makes bone ECM hard
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how does phosphorus affect bone growth?
makes bone ECM hard
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how does magnesium affect bone growth?
helps **form** bone ECM
