The Skeletal System: Bone Tissue Flashcards
(99 cards)
1
Q
What are the 6 main functions of the skeletal system?
A
- Support; skeleton supports soft tissues and provides attachement points for tendons of most skeletal muscles.
- Protection; skeleton protects internal organs.
- Assists in body movements; skeletal muscles attach to bone which produce movement when they contract.
- Mineral homeostasis; bone tissue stores many minerals (incl. calcium and phosphorus) and releases minerals into blood to maintain mineral homeostasis and distribute minerals throughout body.
- Blood cell production; red bone marrow in certain bones produce red blood cells, white blood cells and platelets (hemopoiesis).
- Triglyceride storage; adipose cells in yellow bone marrow store triglycerides.
2
Q
What is red bone marrow made up of?
A
Developing blood cells, fibroblasts, adipocytes, and macrophages within network of reticular fibers.
3
Q
What bones have red bone marrow?
A
In developing bones of fetus and hip bones, ribs, sternum, vertebrae, skull and ends of humerus and femur in adults.
4
Q
Where does yellow bone marrow come from?
A
All bone marrow is red in newborns but changes to yellow with increasing age.
5
Q
Long bone
A
A bone that’s greater in length than width.
6
Q
diaphysis (pl. diaphyses)/body/shaft
A
Long, cylindrical, main portion of bone
7
Q
Epiphysis (pl. epiphyses)
A
Ends of bone (proximal and distal)
8
Q
Metaphysis (pl. metaphyses)
A
Regions between diaphysis and epiphyses
9
Q
Epiphyseal/growth plate
A
Epiphyseal or growth plate is a layer of hyaline cartilage that allows the bone to grow in length, it is found in the metaphyses of a growing bone.
10
Q
What is articular cartilage and it’s function
A
Thin layer of hyaline cartilage that covers joint surfaces at epiphyses. It’s reduces friction and absorbs shock.
11
Q
Why is damage repair limited in articular cartilages?
A
It lacks a perichondrium and blood vessels/a vascular
12
Q
What is an articulation?
A
Where two bones join together
13
Q
Periosteum
A
Tough connective tissue sheath and associated blood supply that covers bone where there’s no articular cartilage.
14
Q
What is the function of the periosteum and what is it composed of?
A
Composed of an inner osteogenic layer that has osteoprogenitor cells which allows appositional growth, and an outer fibrous layer of dense irregular connective tissue. Periosteum protects the bone, helps nourish the bone tissue, aids in fracture repair, and serves as attachment point for tendons and ligaments.
15
Q
Perforating fibers/Sharpey’s fibers
A
Thick bundles of collagen that extend from periosteum into bone extracellular matrix and attaches periosteum to underlying bone
16
Q
What is the medullary cavity and it’s function?
A
Hollow, cylindrical space within diaphysis that contains yellow bone marrow and blood vessels. It minimizes the weight of bone by reducing dense bony material.
17
Q
What is endosteum and what does it contain?
A
A thin membrane lining the medullary cavity and internal spaces of spongy bone containing osteoprogenitor cells and a little connective tissue.
18
Q
What is extracellular matrix consist of?
A
15% water, 30% collagen fibers, 55% crystallized mineral salts
19
Q
What is bone and what type of tissues does it contain?
A
Bone is an organ made of osseous tissue, nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells in its blood vessels
20
Q
What type of tissue is osseous tissue and what does it contain?
A
Osseous tissue is a type of connective tissue which contains widely spaced cells separated by extracellular matrix
21
Q
What contributes to bone’s hardness and tensile strength?
A
Bone hardness depends on crystallized inorganic mineral salts and tensile strength depends on collagen fibers and other organic molecules.
22
Q
How do hydroxyapatite crystals play a role in calcification (or ossification)?
A
Hydroxyapatite crystals are formed through the combination of calcium phosphate and calcium hydroxide found in the bone extracellular matrix. Hydroxyapatite will then combine with other salts (such as calcium carbonate) and ions (such as magnesium, fluoride, potassium, sulfate). Calcification/ossification occurs when these mineral salts are deposited in the framework of collagen fibers of the extracellular matrix and then crystallize which causes the tissue to harden.
23
Q
What is a requirement for calcification to occur?
A
The presence of collagen fibers
24
Q
What happens if a bone is soaked in an acidic solution and why?
A
Soaking a bone in an acidic solution will dissolve its mineral salts and causes the bone to become rubbery and flexible
25
What are the 4 types of cells present in bone tissue?
Osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts
26
Osteoprogenitor cells (what, where, why, how)
- Unspecialized bone stem cells derived from mesenchyme
- Found along inner osteogenic layer of periosteum, in the endosteum, and canals within bone that contain blood vessels
- Only bone cells that undergo cell division (develops into osteoblasts)
27
Osteoblasts (what, where, why, how)
- Performs bone deposition and initiates calcification
- Can’t divide but becomes osteocytes when cells become trapped in extracellular matrix
28
Bone deposition
The addition of minerals and collagen fibers to bone by osteoblasts to build ECM
29
“-blast”
Buds/spouts; in any connective tissue cells means cell that secrete extracellular matrix
30
Osteocytes (what, where, why, how)
- Mature bone cells that maintain daily bone metabolism (such as exchange of wastes and nutrients with blood, maintain protein and mineral content of matrix)
- Main cells in bone tissue
- Cannot divide
31
Osteoclasts (what, where, why, how)
- Huge cells formed by fusion of up to 50 monocytes
- Functions in bone resorption and helped regulate blood calcium level
- Concentrated in endosteum (one side of cell faces bone surface and plasma membrane is deeply folded into ruffled border)
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Bone resorption
The removal of minerals and collagen from ECM by osteoclasts; a part of normal development, maintenance and repair or bone
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“-cytes”
Cells; in tissue cell means cell maintains and monitors tissue
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“-clast”
Break
35
Compact (dense) bone (what, where, why, how)
- Contains few spaces
- Strongest type of bone tissue
- Makes up about 80% of skeleton
- Found beneath periosteum of all bones and makes up bulk of diaphyses in long bone
- Provides protection and supports and resists strains produced by weight and movement
36
Explain the connection between osteons (haversian systems), concentric bone lamellae, osteonic (haversian/central) canal, bone lacunae, bone canaliculi, osteocytes, blood vessels and nerves
- Compact bone tissue is made up of structural units called osteons
- Osteons are aligned parallel to each other along lines of stress (parallel to long axis in long bones)
- Osteons consist of a concentric bone lamellae (circular plates of mineralized extracellular matrix with increasing diameter) that surrounds an osteonic canal containing blood vessels and nerves
- Bone lacunae are small spaces in between the concentric bone lamellae
- Osteocytes are contained in lacunae
- Bone canaliculi are little channels filled with extracellular fluid that connect each lacuna to one another and to the osteonic canal
- Dendritic processes of osteocytes contained in canaliculi and allow communication between osteocytes via gap junctions
37
Why is the skeleton considered dynamic?
Bones are continually engaging bone remodelling throughout life
38
Skeletal system
Framework of bones and their cartilages
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Osteology
Study of bone structure and treatment of bone disorders
40
Spongy (trabecular/cancellous) bone tissue (what, where, why, how)
- Does not contain osteons
- Consists of bone trabeculae formed by bone lamellae arranged in latticework of thin columns
- Spaces in between trabeculae lined by endosteum and filled with red bone marrow (in bones that produce blood cells) or yellow bone marrow (in other bones)
- Makes up most of interior bone tissue of short, flat, sesamoid, and irregularly shaped bones, and forms core of epiphyses in long bones and narrow rim bordering medullary cavity of diaphysis
- Always protected by covering of compact bone
- Oriented along lines of stress which helps to resists stress and transfer force without breaking
- Located where bones are not heavily strained or where stresses are applied from multiple directions
- Trabeculae doesn’t achieve final arrangement until locomotion completely learned and arrangement can be lathered as lines of stress change due to poorly healed fracture or deformity
- Spongy bone tissue is light which Decreases weight of bone and allows bone to move more readily when pulled by skeletal muscle
- Trabeculae supports and protects red bone marrow
41
Bone is highly _____________.
Vascular; richly supplied with blood
42
What is a bone scan and how is it used clinically?
A bone scan works by taking a photograph of the radiation emitted from the bones after a radioactive tracer compound that’s readily absorbed by bone is injected intravenously into a person. The amount of blood flow to the bone will affect the uptake of the tracer which will result in darker or lighter areas in the image. A consistent gray colour throughout the bone indicates normal bone tissue because of its uniform uptake of the tracer. Hot spots due to increased blood flow and metabolism and therefore more absorption of the tracer may indicate bone cancer, abnormal bone growth or abnormal healing of fractures. Cold spots due to decreased blood flow and metabolism and therefore less absorption of tracer may indicate degenerative bone disease, decalcified bone, fractures, bone infections, Paget’s disease, and rheumatoid arthritis. A bone scan is useful because it can detect abnormalities 3-6 months sooner than x-rays and exposes a person to less radiation. It is the standard test for bone density screening, which is important for osteoporosis screening in females.
43
Where does hemopoeisis occur in adults?
Red bone marrow stored in spongy bone tissue is found in hip bones, ribs, sternum, skull, vertebrae, and proximal ends of humerus and femur, therefore site where hemopoiesis occurs in adults
44
Explain the location and roles of perforating canals, transverse canals, nutrient canal, periosteal arteries, metaphyseal arteries, epiphyseal arteries, nutrient artery, nutrient foramen.
Blood vessels enter through numerous perforating canals, which are small canals that carry small arteries from the periosteum into the bone. Examples being the periosteal arteries, metaphyseal arteries and epiphyseal arteries. The periosteal arteries and the nerves that accompany it enter diaphysis through perforating canals and into osteonic canals near the surface. Transverse canals will then transport these blood vessels from one osteonic canal to another. The metaphyseal arteries enter metaphyses through perforating canals and teams up with the nutrient artery to supply the red and yellow bone marrow and spongy bone of metaphyses. The epiphyseal arteries enter epiphyses and suplies red and yellow bone marrow and spiny bone of epiphyses. A special artery called the nutrient artery enters the compact bone at an oblique angle through the nutrient foramen. It will then pass through the nutrient canal, a small canal in compact bone of diaphysis that passes into medullary cavity, and once in medullary cavity it will divide into proximal and distal branches to supply inner part of compact bone of diaphysis and spiny bone and red and yellow bone marrow as far as the epiphyseal plates/lines.
45
What are the 3 places veins carry blood away from long bones and how?
1. 1 or 2 nutrient veins will accompany nutrient artery and exit through diaphysis
2. Many epiphyseal and metaphyseal veins accompany their respective arteries and exit through epiphyses and metaphyses
3. Many periosteal veins accompany their respective arteries and exit through periosteum
46
Nerves accompany blood vessels that supply bones. Which part of bone contains sensory nerves associated with pain? Name a situation why these nerves are important
The periosteum is rich in sensory and some carry pain sensations. Nerves are sensitive to treating or tension and are important for sensing fractures or bone tumours
47
How is a bone marrow needle biopsy performed and what conditions are diagnosed through this procedure?
In a bone marrow needle biopsy, a needle is inserted into the middle of the bone to withdraw a sample of red bone marrow. It is used to examine conditions like leukemias, metastatic neoplasms, lymphoma, Hodgkin’s disease, and aplastic anemia. Pain is felt when the needle penetrates the periosteum and only a little pain once it passes through.
48
How many nutrient arteries do most bone have and are there any exceptions?
Most bones have 1 nutrient artery while some like the femur have several
49
What are the the 2 types of ways that’s bone forms in embryo/fetus development and where in the body it occurs?
First method: intramembranous ossification where bone forms directly within the mesenchyme and this occurs in the flat bones of the skull, most of facial bones, mandible, medial part of clavicle, and the “soft spots” of fetal skull will also harden when they undergo this type of ossification.
Second method: endochrondral ossification where the bone forms within the hyaline cartilage that develops from mesenchyme and most bones including long bones are formed this way.
50
What are the 2 types of growth that occur from infancy to adolescence? How does this growth happen?
Interstitial/endogenous growth (growth from within) is when bones grow in length.
• Bone elongation happens at epiphyseal plate; cartilage grows first on epiphyseal side of epiphyseal plate and then replaced by bone through endochrondral ossification on diaphyseal side of epiphyseal plate
• Chondrocytes multiply on epiphyseal side of plate and replace old ones that were destroyed by calcification which results in cartilage being replaced by bone on diaphyseal side of plate
• Bone on diaphyseal side will increase in length while thickness of epiphyseal plate remains relatively constant
Appositional/exogenous growth (growth at outer surface) is when bone grow in thickness.
1. Osteoprogenitor cells on osteogenic layer of periosteum differentiate into osteoblasts which secrete ECM. Osteoblasts differentiate into osteocytes nice they’re surrounded by ECM. This will result in bone ridges that form on either side of periosteal blood vessels and ridges slowly enlarge and crest groove for periosteal blood vessel.
2. Ridges fold together and fuse and groove becomes a tunnel enclosing blood vessel. Periosteum becomes endosteum lining tunnel.
3. Osteoblasts in endosteum deposit ECM to form new concentric bone lamellae. Concentric bone lamellae proceeds inward toward periosteal blood vessel and new osteon created.
4. Osteoblasts under periosteum deposit new circumferential bone lamellae which increases bone thickness.
5. Osteoclasts in endosteum destroy bone tissue lining medullary cavity which enlarges the cavity.
51
Bone tissue is dynamic and constantly being remodeled. On average 5% of total bone tissue is being remodeled at any given time and different regions of bone are remodeled at different rates. What is bone remodeling? Describe the process and what it involves.
Bone remodeling is the ongoing replacement of old bone tissue by new bone tissue. This involves bone resorption and bone deposition.
1. In bone resorption, an osteoclast attaches to bone surface at endosteum or periosteum and forms leakproof seal at edges of its ruffled border
2. It releases protein digesting lysosomal enzymes and several acids into the sealed pocket
3. The enzymes will digest collagen fibers and other organic substances and acids will dissolve bone minerals
4. Degraded bone proteins and ECM materials (mainly calcium and phosphorous) enter osteoclast by endocytosis and exit through exocytosis into interstitial fluid and these products diffuse into nearby blood capillaries
5. Osteoblasts will then move in to rebuild bone in that area
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Ossification/osteogenesis
Process of bone formation
53
In what 4 types of situations does bone formation occur?
1. Initial bone formation in embryo or fetus
2. Growth of bones from infancy to adolescent (until adult sizes are reached)
3. Remodelling of bone throughout life
4. Repair or fractures
54
The embryonic “skeleton” is initially composed of mesenchyme in the general shape of bone and is the site where cartilage formation and ossification occur during ___________________ of embryonic development.
The sixth week
55
Describe the steps of intramembranous ossification.
1. Development of ossification centre: the ossification centre which is where the mesenchymal cells will cluster together due to specific chemical messages at the site where bone will develop. The mesenchymal cells differentiate into osteoprogenitor cells then into osteoblasts. The osteoblasts will secret ECM until they’re surrounded but it, the ECM is not calcified yet.
2. Calcification: secretion of ECM stops and cells differentiate into osteocytes, which lie in lacunae with their cytoplasmic processes extending into canaliculi. After a few days, calcium and other mineral salts are deposited and the ECM calcifies.
3. Formation of trabeculae: ossification centres move towards one another and fuse to from spongy bone trabeculae around blood vessels. Connective tissue associated with blood vessels in trabeculae differentiate into red bone marrow.
4. Development of periosteum: osteoblasts and mesenchymal condenses at periphery of bone to form periosteum. Thin layer of compact bone will eventually replace surface layers of spongy bone but centre is still spongy bone.
56
Describe the steps of endochrondral ossification.
1. Development of cartilage model
• Specific chemical messages cause mesenchymal cells to crowd together into general shape of bone at site where bone is going to form
• Mesenchymal cells differentiate into chrondroblasts that secrete cartilage ECM and form cartilage model (future diaphysis) which consists of hyaline cartilage
• Perichondrium (covering) develops around cartilage models
2. Growth of cartilage model
• Chondroblasts become buried in cartilage ECM and become chondrocytes
• Interstitial/endogenous growth (increase in length) occurs by continual cell division of chrondrocytes and secretion of cartilage ECM which results in cartilage model growing in length
• Appositional/exogenous growth (growth at outer surface) occurs by chondroblasts (developed from perichondrium) depositing ECM on cartilage surface of model which results in cartilage growing in thickness
• Chondrocytes in centre hypertrophy (increase in size) and surrounding cartilage ECM calcifies
• Other chrondrocytes calcifying matrix die due to nutrients not diffusing quickly enough through ECM and space left behind by dead chrondrocytes form lacunae
3. Development of primary ossification centre
• Growth proceeds inward from external surface of bone
• Nutrient artery penetrates through a nutrient foramen in middle of cartilage model and pass perichrondrium into centre of cartilage model
• Osteoprogenitor cells in perichondrium to differentiate into osteoblasts and perichrondrium turns into periosteum once bone begins to form
• Primary ossification centre is a region where bone tissue will replace most of the cartilage, this growth is induce when periosteal capillaries grow into disintegrating calcified cartilage
• Spongy bone trabeculae forms when osteoblasts begin to deposit ECM over remnants of calcified cartilage
• Primary ossification spreads from centre toward ends of cartilage model
4. Development of medullary cavity
• Osteoclasts break down some of newly formed trabeculae and form medullary cavity
• Eventually most of wall is replaced by compact bone
5. Development of secondary ossification centre
• Growth proceeds outward from centre of epiphyses toward outer surface of bone
• Epiphyseal arteries enter epiphyses and secondary ossification centre develops usually around time of birth or after
• Bone formation similar to primary ossification centres but spongy bone at epiphyses not destroyed by osteoclasts
6. Formation of articular cartilage and epiphyseal plate
• Hyaline cartilage that cover epiphyses remains as articular cartilage and cartilage at epiphyseal plate remains for future growth
57
What is the result of a fracture at the epiphyseal plate? Why does this happen?
The epiphyseal plate is made up of hyaline cartilage which is avascular/lacks blood vessels and repair is limited. The damage accelerates the closing of epiphyseal plate due to cartilage cell division stopping which inhibits the lengthwise growth of the bone and potentially causes the fractured bone to be shorter than normal in adult size.
58
At what ages do the epiphyseal plates close? How does this happen and what is the result?
The closing of the epiphyseal plates happen at about 18 years old in females and about 21 years in males. This happens because the epiphyseal cartilage cells stop dividing and bone replaces all remaining cartilage. This results in bone growth in length stopping and the epiphyseal plate will fade leaving a bony structure called the epiphyseal line.
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What is significance of the epiphyseal line?
It is useful in determining bone age, predicting adult height and establishing age at death in skeletal remains.
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What are the 4 zones of the epiphyseal plate? Describe what it is, what they consist of and their function.
1. Zone of testing cartilage
• Layer nearest to epiphysis
• Consists of small, scattered chondrocytes
• Cells anchor the epiphyseal plate to epiphysis of bone and do not function in lengthwise bone growth
2. Zone of proliferating cartilage
• Area of rapid chondrocyte cell division
• Consists of slightly larger chondrocytes that are arranged like stacks or coins
• Cells undergo interstitial growth as they divide and secrete ECM to replace dying chondrocytes in diaphyseal side of plates
3. Zone of hypertrophic cartilage
• Area of dying chondrocytes
• Consists of large, maturing chondrocytes arranged in columns
4. Zone of calcified cartilage
• Final zone of epiphyseal plate
• Consists mostly of dead chondrocytes and calcified ECM
• Layer is only a few cells thick
• Osteoclasts dissolve the calcified cartilage
• Osteoblasts and capillaries from diaphysis move in to create bone
• Osteoblasts lay down ECM to replace calcified cartilage through endochondral ossification
• Cartilage replaced by bone and this become the “new diaphysis”
61
What are the benefits of bone remodeling?
Bone remodeling helps bone to grow thicker and stronger as a respond to stress put on the bone. It can also alter the bone shape for better support to these stress patterns. Remodeling will remove injured bone and the new bone made during this process will be more resistant to fractures.
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What are factors that trigger bone remodeling?
Exercise and lifestyle will affect bone remodeling (active vs. sedentary lifestyle or diet)
63
There needs to be a balance between bone resorption and bone deposition. What results if bone homeostasis is not reached?
1. If too much new tissue is formed, the bones become abnormally thick and heavy
2. If too much mineral material is deposited in the bone, this could cause spurs (thick bumps) that interfere with movement at joints
3. Excessive loss of calcium or tissue weakens the bones and cause them to break like in osteoporosis. They could also become too flexible like in rickets or osteomalacia
4. If bone resorption occurs faster than bone deposition this could result in Paget’s disease (osteitis deformans)
• Caused by an excessive amount of osteoclasts
• Osteoblasts will attempt to compensate but the proportion of spongy bone is higher than compact bone and the new bone is weaker, mineralization is decreased, and new ECM contains abnormal proteins
• The bone (especially in pelvis, limbs, lower vertebrae, and skull) will be enlarged, hard, brittle, and fractures easily
64
What are the factors affecting bone growth and bone remodeling?
Nutrition or adequate dietary intake of minerals and vitamins, and sufficient levels of specific hormones are required for normal bone metabolism (growth in young and bone remodeling in adult).
1. Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride and manganese are needed while bones are growing and during bone remodeling.
2. Vitamin A stimulates activity of osteoblasts.
3. Vitamin C needed for synthesis of collagen (main bone protein).
4. Vitamin D increases absorption of calcium through small intestine.
5. Vitamins K and B12 needed for bone protein synthesis.
6. Insulin-like growth factors (IGFs) stimulate osteoblasts, promote cell division at epiphyseal plate and in periosteum, and enhance synthesis of bone proteins. They are produced by liver and bone tissue in response to secretion of growth hormone (GH) from anterior lobe of pituitary gland.
7. Thyroid hormones (T3 and T4) stimulates osteoblasts. They are produced by thyroid gland.
8. Insulin increases synthesis of bone proteins. It is produced by pancreas.
9. Estrogens and testosterone at puberty increases osteoblast activity, synthesis of ECM, and results in “growth spurt” during teenage years. Estrogens cause changes to female skeleton such as widening of pelvis and contribute to closing of epiphyseal plates in both sexes. During adulthood it slows down bone resorption and promoting bone deposition due to estrogens promoting apoptosis (programmed death) of osteoclasts. The sex hormones are produced by ovaries and testes.
10. Parathyroid hormone (PTH) promotes bone resorption by osteoclasts, decreases loss of calcium from urine, promotes formation of calcitriol which promotes absorption of calcium from foods; secreted by parathyroid glands
11. Calcitonin (CT) inhibits bone resorption by osteoclasts and accelerates calcium deposition into bones; secreted by parafollicular cells in thyroid gland
12. Excercise: weight bearing activities stimulate osteoblasts that build thicker and stronger bones and delays loss of bone mass in old age
13. Aging: lower levels of sex hormones during middle ages to old age causes bone resorption to occur faster than bone deposition and leads to decrease in bone mass and increased risk of osteoporosis (especially in women after menopause)
65
How does the suprarenal glands in both sexes contribute to the production of sex hormones?
The suprarenal glands produce androgens and other tissues (like adipose tissue) in both sexes and can convert androgens to estrogens.
66
How do hormonal abnormalities affect height?
1. Oversecretion of growth hormone during childhood produces gigantism where a person becomes much taller (7-9ft)
2. Dwarfism is when a person is under 4ft10in, averaging 4ft.
• Pituitary dwarfism is the hyposecretion of GH in childhood and is one cause of proportionate dwarfism, where all parts of the body are small and proportionate to each other
• Achondroplastic dwarfism is caused by achondroplasia which is an inherited condition and causes the abnormal conversion of hyaline cartilage and results in the long bones of limbs to stop growing in childhood, while other bones are unaffected
• Achondroplasia is a common cause of disproportionate dwarfism where some parts of the body are normal sized and other parts are larger or smaller than normal
67
Which form of dwarfism is treatable and how?
Pituitary dwarfism is treatable by administration of GH until epiphyseal plate closes. Achondroplastic dwarfism is not treatable because it is caused by achondroplasia, an inherited condition.
68
How does exercise and mechanical stress affect bone tissue?
1. Stress causes bone tissue to become stronger through increased deposition of mineral salts and production of collagen fibers by osteoblasts
2. The main mechanical strains on bone are those that pull the skeletal muscles and the pull of gravity
3. Removal of mechanical stress causes bone to not remodel properly due to higher rate of bone resorption to bone deposition and weakens bone due to demineralization (loss of bone minerals) and decreased number of collagen fibers
4. High-impact intermittent strains like jumping and running is more effective at stimulating bone remodeling than lower-impact constant strains like walking
5. Moderate weight bearing exercises such as walking and moderate weightlifting helps to build and maintain bone mass
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Fracture
Any break in a bone. Named according to severity, shape, position of fracture line, or by physician who first described them.
70
Stress fracture. What causes it?
Series of microscopic fissures in bone formed without any evidence of injury to other tissues. Results from repeated, strenuous activities like running, jumping, aerobic dancing or diseases that affect normal bone calcification in adults.
71
What are the 4 phases of bone fracture repair? Describe what happens in each phase.
1. Reactive phase
• Early inflammatory phase
• Blood vessels crossing fracture line are broken
• Fracture hematoma forms 6-8 hrs after injury around fracture site due to torn vessels leaking blood and results in blood clot
• Nearby bone cells die due to lack of blood circulation causing swelling and inflammation which produces cellular debris
• Phagocytic neutrophils and macrophages and osteoclasts remove dead and damaged tissue in and around fracture hematoma
• May last up to several weeks
2. Reparative phase
a) Fibrous cartilage callus formation
• Blood vessels grow into fracture hematoma and phagocytes begin to clean up dead bone cells
• Fibroblasts from periosteum invade fracture site and produce collagen fibers
• Cells from periosteum develop into chondroblasts and produce fibrous cartilage
• Development of fibrous cartilage (soft) callus: mass of repair tissue consisting of collagen fibers and cartilage
• Fibrous cartilage callus bridges gap between broken ends of bone
• Process takes about 3 weeks
b) Bony callus formation
• Osteoprogenitor cells in well vascularized healthy bone tissue develop into osteoblasts
• Osteoblasts begin to produce spongy bone trabeculae
• Spongy bone trabeculae join living and dead portions of original bone fragments
• Fibrous cartilage converted to spongy bone
• Callus becomes known as bony (hard) callus
• Bony callus lasts ~ 3-4 months
3. Bone remodeling phase
• Dead portions of original fragments of broken bone resorbed by osteoclasts
• Compact bone places spongy bone around periphery of fracture
• Surface remodeled back to normal shape but thicker area on surface of bone remains as evidence of healed fracture
72
Why do bones heal faster than cartilage but is still a slow process?
Bones are well vascularized and therefore heal faster than cartilage. Slow healing of fractures is due to:
1. Calcium and phosphorus needed to strengthen and harden bone are deposited gradually
2. Bone cells grow and reproduce slowly
3. Blood vessel damage
73
What are the 3 goals of clinical treatments of fractures?
1. Realignment
• Reduction: process of setting a fracture
a) Closed reduction: fractured ends realigned by manual manipulation and skin is intact
b) Open reduction: fractured ends realigned through surgery using screws, plates, pins, rods, wires
2. Immobilization to maintain realignment
• Fractured bone immobilized by cast, sling, splint, elastic bandage, external fixation device, or combination of devices
3. Restore functions
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Difference between open (compound) fracture and closed (simple) fracture?
Broken ends of bone protrude through skin in open (compound) fractures while closed (simple) fractures don’t break skin.
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Comminuted fracture
Bone is splintered, crushed or broken into pieces at site of impact; smaller bone fragments lie between 2 main fragments
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Greenstick fracture
Partial fracture where one side of bone is broken and other side bends; occurs only in children because bones aren’t fully ossified and contain more organic material
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Impacted fracture
One end of fractured bone forcefully driven into interior of other
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Pott fracture
Fracture of distal end of fibula with serious injury to distal tibial articulation
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Colles fracture
Fracture of distal end of radius resulting in distal fragment moving posteriorly
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Vertebral compression fracture (VCF)
Vertebral body of one or more vertebrae fractures and becomes compressed into wedge-shape. Cause by injury, trauma and more common in people with osteoporosis.
81
What is the importance of calcium and claim homeostasis in the body?
• Nerve and muscles cells depend on stable level of calcium ions (Ca2+) in extracellular fluid
• Blood clotting requires Ca2+
• Many enzymes need Ca2+ as a cofactor (additional substance needed for enzymatic reaction to occur)
• Calcium homeostasis helps to “buffer” the blood Ca2+ level, releasing Ca2+ into blood plasma (using osteoclasts) when level decreases, and absorbing Ca2+ (using osteoblasts) when level rises
82
Why is it important to engage in weight bearing exercises before epiphyseal plates close?
It is important for adolescent and young adults to engage in weight bearing activities before the closure of the epiphyseal plates in order to build total bone mass prior to its reduction with aging.
83
What are the 2 major effects of aging on bone tissue? What does loss of bone mass lead to?
1. Demineralization: the loss of calcium and other minerals from the ECM which results in loss of bone mass and brittleness
2. Decreased rate of protein synthesis; the decreased of collagen fiber production causes loss of tensile strength and bones become brittle and susceptible to fractures
Loss of bone mass increases the susceptibility of fractures and leads to deformity, pain, and loss of height and teeth.
84
At what ages is more bone tissue produced than lost during bone remodeling?
From birth through adolescence
85
At what age group is the rates of bone deposition and resorption the same?
In young adults
86
What causes bone mass to decrease during middle and old ages? How does this happen and why is it important in women after menopause?
Decrease of sex hormones causes bone resorption to occur quicker than bone deposition. Menopause causes a decrease in estrogens which induce apoptosis in osteoclasts and works with testosterone to stimulate osteoblasts.
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Apoptosis
Programmed cell death
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At what age does demineralization begin in females and males? What percentage of calcium and bone mass is lost in both sexes?
It begins at 30 in females and accelerates around 45 as levels of estrogens decrease. As much as 30% of calcium is lost by 70. About 8% of bone mass is lost every 10 years once bone loss begins.
It begins after 60 in males and 3% of bone mass is lost every 10 years.
89
What is osteoporosis? What causes it and what does it lead to?
• Meaning porous bones; the degeneration of articular cartilage
• Bone resorption outpaces bone deposition due to more calcium being lost in urine, sweat, feces than absorbed from diet and hormonal changes
• Causes bones to fracture easily under mechanical stresses of everyday life, shrinkage of vertebrae, height loss, hunched backs, bone pain
90
Osteoporosis affects 80% of middle aged and elderly women. What are the 2 reasons older women suffer more from osteoporosis than men?
1. Women’s bones are less massive than men’s bones
2. Production of estrogens in women declines dramatically after menopause while testosterone in older men decreased gradually and only slightly
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What are the risk factors for developing osteoporosis?
Gender, family history of disease, European or Asian ancestry, thin or small body build, inactive lifestyle, cigarette smoking, diet low in calcium and vitamin D, more than 2 alcoholic drinks a day, and the use of certain medications
92
How is osteoporosis diagnosed?
It is diagnosed by taking a family history and through a bone mineral density (BMD) test. It is performed by a bone scan.
93
Bone is the body’s major calcium reservoir and stores _____% of the total body calcium.
99
94
What is the blood plasma level of Ca2+ (mg/100mL)
It is between 9-11mg/100mL
95
Which 3 hormones regulate blood Ca2+ levels? How do they do this?
1. Parathyroid hormone (PTH) increases the blood Ca2+ level and is secreted by the parathyroid glands
• operates by negative feedback system; stimulus causes blood Ca2+ level to decrease => parathyroid glands (receptors) detect change and increase production of cyclic adenosine monophosphate (cyclic AMP) => gene for PTH in nucleus of parathyroid gland cell (control centre) detects intracellular increase in cyclic AMP (input) => PTH synthesis increases and more PTH (output) released into blood => higher levels of PTH increases number and activity of osteoclasts (effectors) which increased pace of bone resorption and Ca2+ is released from bone into blood and blood Ca2+ level returns to normal
• PTH acts on kidneys (effectors) to decrease loss of Ca2+ in urine
2. Calcitriol promotes absorption of calcium from foods in GI tract into blood; PTH stimulates formation of this hormone
• active form of vitamins D
3. Calcitonin (CT) decreases blood Ca2+ level (and promotes bone formation); secreted by parafollicular cells in thyroid gland
• inhibits activity of osteoclasts
• speeds up blood Ca2+ uptake by bone
• accelerates Ca2+ deposition in bones
• calcitonin harvested from salmon is an effective drug for osteoporosis treatment because it slows bone resorption
96
Compare rickets and osteomalacia. How are they treated?
Rickets and osteomalacia are 2 forms of the same disease that results from inadequate calcification of bone ECM, usually caused by vitamin D deficiency. Prevention and treatment consists of administering adequate vitamin D and exposure to moderate amounts of sunlight.
Rickets:
• occurs in children
• new bone that’s formed at epiphyseal plates fails to ossify
• causes growing bones to become soft or rubbery and are easily deformed (bowed legs, deformities of skull, rib cage, and pelvis are common)
Osteomalacia:
• occurs in adults (sometimes called adult rickets)
• new bone formed during remodeling fails to calcify
• causes varying degrees of pain and tenderness in bones (especially y in hip and legs) and bone fractures from minor trauma
97
What is osteomyelitis? What causes it and what does it result in?
• infection of bone
• often caused by staphylococcus aureus bacteria that may reach bone from outside body (through open fractures, penetrating wounds, orthopaedic surgical procedures), from other sites of infection in body via blood (abscessed teeth, burn infections, UTI, upper respiratory infections), and from adjacent soft tissue infections (occurs in diabetes mellitus)
• characterized by high fever, sweating, chills, pain, nausea, pus formation, edema, warmth over affected bone, and rigid overlying muscles
98
Osteopenia
Reduced bone mass due to decrease in rate of bone synthesis to level too low to compensate for normal resorption; decrease in bone mass below normal (ex. osteoporosis)
99
What is osteosarcoma? Where does it often occur and in what age group? What is the treatment?
Bone cancer that affects osteoblasts and occurs often in teens during growth spurt. Common sites are metaphyses of femur, tibia, and humerus.
• metastases often in lungs
• treatment involves multidrug chemotherapy, removal of malignant growth, amputation of limb
