L5: Bone Tissue Pt. 2 Flashcards
appears as a dark band between whiter calcified areas in the radiograph (x- ray) shown in part (a).
epiphyseal plate
allows the diaphysis of a bone to increase in length.
epiphyseal plate
Like cartilage, bone can grow in thickness (diameter) only by what type of growth?
Appositional growth
At the bone surface, what cells in the osteogenic layer of the periosteum differentiate into osteoblasts?
Osteoprogenitor cells
What do osteoblasts secrete to form bone extracellular matrix?
Collagen fibers and other organic molecules
Once osteoblasts become surrounded by extracellular matrix, what do they develop into?
Osteocytes
What does this process form on either side of a periosteal blood vessel?
Bone ridges
As the ridges enlarge, what do they create for the periosteal blood vessel?
A groove
What happens when the ridges fold together and fuse?
The groove becomes a tunnel that encloses the blood vessel.
What does the former periosteum become after the tunnel forms?
Endosteum
What cells deposit bone extracellular matrix in the endosteum?
Osteoblasts formed from the progenitor cells
What structure is formed as additional concentric bone lamellae proceed inward toward the periosteal blood vessel?
A new osteon
What do osteoblasts under the periosteum deposit as an osteon is forming?
New circumferential bone lamellae
What happens as additional periosteal blood vessels become enclosed?
The growth process continues.
What type of cells destroy the bone tissue lining the medullary cavity?
Osteoclasts
Where are osteoclasts located?
In the endosteum
What happens to the medullary cavity as the bone increases in thickness?
It enlarges.
As new bone is deposited on the outer surface of bone by osteoblasts, the bone tissue lining the medullary cavity is destroyed by ____ in the endosteum
osteoclasts
Process of bone growth in thickness
- Ridges in periosteum create groove for periosteal blood vessel.
- Periosteal ridges fuse, forming an endosteum-lined tunnel.
- Osteoblasts in endosteum build new concentric bone lamellae inward toward center of tunnel, forming a new osteon.
- Bone grows outward as osteoblasts in periosteum build new circumferential bone lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.
Like what other part of the body, bone forms before birth but continually renews itself thereafter?
Skin
What is the ongoing replacement of old bone tissue by new bone tissue called?
Bone remodeling
What does bone remodeling involve?
Bone resorption and bone deposition
What is the removal of minerals and collagen fibers from bone by osteoclasts called?
Bone resorption
What is the addition of minerals and collagen fibers to bone by osteoblasts called?
Bone deposition
What does bone resorption result in?
The destruction of bone extracellular matrix
What does bone deposition result in?
The formation of bone extracellular matrix
At any given time, what percentage of the total bone mass in the body is being remodeled?
0.05
Does remodeling take place at the same rate in different regions of the body?
No
How often is the distal portion of the femur replaced?
About every four months
In contrast, what happens to bone in certain areas of the diaphysis of the femur?
It will not be replaced completely during an individual’s life.
Even after bones have reached their adult shapes and sizes, what continually happens?
Old bone is continually destroyed and new bone is formed in its place.
What does remodeling remove and replace with new bone tissue?
Injured bone
What factors may trigger remodeling?
Exercise, sedentary lifestyle, and changes in diet
What is bone strength related to?
The degree to which it is strained
If newly formed bone is subjected to heavy loads, what happens to it?
It will grow thicker and therefore be stronger than the old bone.
What can be altered for proper support based on strain patterns experienced during remodeling?
The shape of a bone
What is more resistant to fracture: new bone or old bone?
New bone
During the process of bone resorption, what does an osteoclast attach tightly to?
The bone surface at the endosteum or periosteum
What does an osteoclast form at the edges of its ruffled border?
A leakproof seal
What does the osteoclast release into the sealed pocket?
Protein-digesting lysosomal enzymes and several acids
What do the enzymes digest?
Collagen fibers and other organic substances
What do the acids dissolve?
Bone minerals
What do several osteoclasts working together carve out?
A small tunnel in the old bone
What enters an osteoclast by endocytosis during bone resorption?
Degraded bone proteins and extracellular matrix minerals, mainly calcium and phosphorus
How do these materials cross the osteoclast?
In vesicles
What process releases them on the side opposite the ruffled border?
Exocytosis
Once in the interstitial fluid, where do the products of bone resorption diffuse?
Into nearby blood capillaries
What happens once a small area of bone has been resorbed?
Osteoclasts depart and osteoblasts move in to rebuild the bone in that area.
What is the branch of dentistry concerned with the prevention and correction of poorly aligned teeth?
Orthodontics
What does the movement of teeth by braces place a strain on?
The bone that forms the sockets that anchor the teeth
In response to this artificial strain, what cells remodel the sockets so that the teeth align properly?
Osteoclasts and osteoblasts
What exists between the actions of osteoclasts and osteoblasts?
A delicate balance
What happens if too much new tissue is formed?
The bones become abnormally thick and heavy.
What may form if too much mineral material is deposited in the bone?
Thick bumps, called spurs
What do spurs interfere with?
Movement at joints
What happens if there is excessive loss of calcium or tissue?
The bones weaken and may break.
In what condition do bones break due to excessive loss of calcium or tissue?
Osteoporosis
In what conditions do bones become too flexible due to excessive loss of calcium or tissue?
Rickets and osteomalacia
In what disease is there an excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition?
Paget’s disease or osteitis deformans
What do osteoblasts attempt to do in response to excessive bone resorption?
Compensate
Why is the new bone formed in Paget’s disease weaker?
It has a higher proportion of spongy to compact bone, mineralization is decreased, and the newly synthesized extracellular matrix contains abnormal proteins.
What happens to the newly formed bone in Paget’s disease?
It becomes enlarged, hard, and brittle and fractures easily.
Which bones are especially affected in Paget’s disease?
The pelvis, limbs, lower vertebrae, and skull.
What does normal bone metabolism—growth in the young and bone remodeling in the adult—depend on?
Several factors
What are the factors that normal bone metabolism depends on?
Adequate dietary intake of minerals and vitamins, as well as sufficient levels of several hormones.
What are the 3 factors affecting bone growth and bone remodeling?
Minerals, Vitamins, and Hormones
What are large amounts of calcium and phosphorus needed for?
While bones are growing
What smaller amounts of minerals are also necessary during bone remodeling?
Magnesium, fluoride, and manganese
What vitamin stimulates the activity of osteoblasts?
Vitamin A
What vitamin is needed for the synthesis of collagen, the main bone protein?
Vitamin C
How does vitamin D help build bone?
By increasing the absorption of calcium from foods in the digestive canal into the blood
What vitamins are also needed for the synthesis of bone proteins?
Vitamins K and B12
What hormones are most important to bone growth during childhood?
Insulin-like growth factors (IGFs)
Where are IGFs produced?
By the liver and bone tissue
What do IGFs stimulate?
Osteoblasts
What do IGFs promote?
Cell division at the epiphyseal plate and in the periosteum
What do IGFs enhance?
The synthesis of the proteins needed to build new bone
What stimulates the production of IGFs?
The secretion of growth hormone (GH) from the anterior lobe of the pituitary gland
What hormones from the thyroid gland promote bone growth?
Thyroid hormones (T3 and T4)
How do thyroid hormones promote bone growth?
By stimulating osteoblasts
What hormone from the pancreas promotes bone growth?
Insulin
How does insulin promote bone growth?
By increasing the synthesis of bone proteins
What hormones have a dramatic effect on bone growth at puberty?
Sex hormones
What are the sex hormones?
Estrogens and androgens such as testosterone
Where are estrogens produced?
In the ovaries
Where are androgens such as testosterone produced?
In the testes
Do both males and females have estrogens and androgens?
Yes, females have low levels of androgens, and males have low levels of estrogens.
What glands produce androgens in both sexes?
Suprarenal glands
What tissue can convert androgens to estrogens?
Adipose tissue
What are sex hormones responsible for?
Increased osteoblast activity, synthesis of bone extracellular matrix, and the sudden “growth spurt” during teenage years.
What skeletal change do estrogens promote in females?
Widening of the pelvis
What ultimately shuts down growth at epiphyseal plates?
Sex hormones, especially estrogens in both sexes
Why does lengthwise growth of bones end earlier in females than in males?
Because females have higher levels of estrogens
During adulthood, how do sex hormones contribute to bone remodeling?
By slowing resorption of old bone and promoting deposition of new bone
How do estrogens slow resorption of old bone?
By promoting apoptosis (programmed death) of osteoclasts
What other hormones can affect bone remodeling?
Parathyroid hormone, calcitriol (the active form of vitamin D), and calcitonin
What type of exercises help maintain sufficient strain on bones to increase and maintain their density?
Moderate weight-bearing exercises
What can excessive or deficient secretion of hormones that normally control bone growth cause?
A person to be abnormally tall or short
What does oversecretion of growth hormone (GH) during childhood produce?
Gigantism (giantism)
What happens to a person with gigantism?
They become much taller (7–9 feet tall) and heavier than normal.
What is the condition of small stature in which the height of an individual is typically under 4 feet 10 inches?
Dwarfism
What is the average height of a person with dwarfism?
4 feet
What are the two types of dwarfism?
Proportionate and disproportionate
In which type of dwarfism are all parts of the body small but proportionate to each other?
Proportionate dwarfism
What is one cause of proportionate dwarfism?
Hyposecretion of GH during childhood
What is proportionate dwarfism due to hyposecretion of GH called?
Pituitary dwarfism
How can pituitary dwarfism be treated?
With administration of GH until epiphyseal plate closure
In which type of dwarfism are some parts of the body normal size or larger than normal while others are smaller than normal?
Disproportionate dwarfism
What is an example of body proportions in disproportionate dwarfism?
The trunk can be average size while the limbs are short, and the head may be large in relation to the rest of the body, with a prominent forehead and flattened nose at the bridge.
What is the most common cause of disproportionate dwarfism?
Achondroplasia
What is achondroplasia?
An inherited condition in which the conversion of hyaline cartilage to bone is abnormal and the long bones of the limbs stop growing in childhood.
Which bones are unaffected in achondroplasia?
Other bones besides the long bones of the limbs
What is the name of this type of dwarfism caused by achondroplasia?
Achondroplastic dwarfism
Is achondroplastic dwarfism treatable?
The condition is essentially untreatable.
What option do some individuals with achondroplastic dwarfism choose?
Limb-lengthening surgery
What is a fracture?
Any break in a bone
How are fractures named?
According to their severity, the shape or position of the fracture line, or even the physician who first described them.
Can a bone fracture without visibly breaking?
Yes
What is a stress fracture?
A series of microscopic fissures in bone that forms without any evidence of injury to other tissues.
What causes stress fractures in healthy adults?
Repeated, strenuous activities such as running, jumping, or aerobic dancing.
Are stress fractures painful?
Yes, they are quite painful.
What disease process can also result in stress fractures?
Osteoporosis
What percentage of stress fractures involve the tibia?
About 25%
Why do standard radiographic images often fail to reveal stress fractures?
Because the fractures are microscopic.
What imaging technique can clearly show stress fractures?
Bone scan
What does the repair of a bone fracture involve?
The following phases: reactive phase, reparative phase (fibrous cartilage callus formation and bony callus formation), and bone remodeling phase.
What is the reactive phase?
An early inflammatory phase.
What happens to blood vessels crossing the fracture line in the reactive phase?
They are broken.
What forms as blood leaks from the torn ends of the vessels?
A mass of blood (usually clotted).
What is this mass of blood called?
Fracture hematoma
How long does it take for a fracture hematoma to form after the injury?
6 to 8 hours
Why do nearby bone cells die at the site where the fracture hematoma forms?
Because the circulation of blood stops.
What occurs in response to dead bone cells in the reactive phase?
Swelling and inflammation, producing additional cellular debris.
Which cells begin to remove the dead or damaged tissue in and around the fracture hematoma?
Phagocytes (neutrophils and macrophages) and osteoclasts.
How long may the reactive phase last?
Up to several weeks.
What are the two events of the reparative phase?
The formation of a fibrous cartilage callus and a bony callus.
What grows into the fracture hematoma during the reparative phase?
Blood vessels.
What do phagocytes do during the reparative phase?
They begin to clean up dead bone cells.
What invades the fracture site and produces collagen fibers?
Fibroblasts from the periosteum.
What cells develop from the periosteum and begin to produce fibrous cartilage?
Chondroblasts.
What does the fibrous cartilage (soft) callus consist of?
Collagen fibers and cartilage.
What is the purpose of the fibrous cartilage (soft) callus?
To bridge the broken ends of the bone.
How long does the formation of the fibrous cartilage callus take?
About 3 weeks.
What do osteoprogenitor cells develop into in areas closer to well-vascularized healthy bone tissue?
Osteoblasts.
What do osteoblasts begin to produce?
Spongy bone trabeculae.
What do the spongy bone trabeculae join?
Living and dead portions of the original bone fragments.
What happens over time to the fibrous cartilage callus?
It is converted to spongy bone.
What is the callus referred to after it is converted to spongy bone?
Bony (hard) callus.
How long does the bony callus last?
About 3 to 4 months.
What is the final phase of fracture repair?
Bone remodeling phase.
What happens to dead portions of the original fragments of broken bone?
They are gradually resorbed by osteoclasts.
What replaces spongy bone around the periphery of the fracture?
Compact bone.
Can the fracture line become undetectable in a radiograph (X-ray)?
Yes, sometimes.
What remains as evidence of a healed fracture?
A thickened area on the surface of the bone.
Why does bone healing sometimes take months?
Because the calcium and phosphorus needed to strengthen and harden new bone are deposited only gradually, and bone cells generally grow and reproduce slowly.
What helps explain the slowness of healing in severely fractured bones?
The temporary disruption in their blood supply.
heals more rapidly than cartilage because its blood supply is more plentiful
bones
What do treatments for fractures vary according to?
Age, type of fracture, and the bone involved.
What are the ultimate goals of fracture treatment?
Realignment of the bone fragments, immobilization to maintain realignment, and restoration of function.
What must happen for bones to unite properly?
The fractured ends must be brought into alignment.
What is the process of bringing fractured ends into alignment called?
Reduction.
What is reduction commonly referred to as?
Setting a fracture.
What happens in closed reduction?
The fractured ends of a bone are brought into alignment by manual manipulation, and the skin remains intact.
What happens in 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.
What is used to keep a fractured bone immobilized following reduction?
A cast, sling, splint, elastic bandage, external fixation device, or a combination of these devices.
Type of Fracture. The broken ends of the bone protrude through the skin. Conversely, a closed (simple) fracture does not break the skin.
Open (Compound)
Type of 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
Comminuted
Type of Fracture. A partial fracture in which one side of the bone is broken and the other side bends, similar to the way a green twig breaks on one side while the other side stays whole, but bends; occurs only in children, whose bones are not fully ossified and contain more organic material than inorganic material.
Greenstick
Type of Fracture. One end of the fractured bone is forcefully driven into the interior of the other.
Impacted
Type of Fracture. Fracture of the distal end of the fibula (lateral leg bone), with serious injury of the distal tibial articulation.
pott
Type of Fracture. Fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.
Colles
Type of 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.
Vertebral compression fracture (VCF)
What are the two main ways that blood calcium level can be increased?
Release of calcium from bone matrix and retention of calcium by the kidneys
regulation of blood calcium (Ca2+) concentration is what kind of feedback system?
Negative feedback system
What percentage of total body calcium is stored in bone?
0.99
How is the level of calcium in the blood maintained?
By controlling the rates of calcium resorption from bone into blood and calcium deposition from blood into bone.
What two types of cells depend on a stable level of calcium ions (Ca2+) in extracellular fluid to function properly?
Nerve and muscle cells
What process also requires Ca2+?
Blood clotting
Why do many enzymes require Ca2+?
Because Ca2+ acts as a cofactor (an additional substance needed for an enzymatic reaction to occur).
What is the normal blood plasma level of Ca2+?
Between 9 and 11 mg/100 mL
What happens if the Ca2+ concentration goes too high?
The heart may stop (cardiac arrest).
What happens if the Ca2+ concentration falls too low?
Breathing may cease (respiratory arrest).
What is the role of bone in calcium homeostasis?
To help buffer the blood Ca2+ level by releasing Ca2+ into blood plasma when the level decreases and absorbing Ca2+ when the level rises.
What regulates Ca2+ exchange?
Hormones
What is the most important hormone in Ca2+ exchange?
Parathyroid hormone (PTH)
Where is parathyroid hormone (PTH) secreted from?
The parathyroid glands
What does parathyroid hormone (PTH) do to blood Ca2+ levels?
It increases blood Ca2+ levels.
How does PTH secretion operate?
Via a negative feedback system
What happens when the blood Ca2+ level decreases?
Parathyroid gland cells detect the change and increase their production of cyclic adenosine monophosphate (cyclic AMP).
What detects the intracellular increase in cyclic AMP?
The gene for PTH within the nucleus of a parathyroid gland cell.
What happens as a result of increased cyclic AMP?
PTH synthesis speeds up, and more PTH is released into the blood.
How does PTH increase blood Ca2+ levels?
It increases the number and activity of osteoclasts, which step up the pace of bone resorption.
What effect does PTH have on the kidneys?
It decreases loss of Ca2+ in the urine, so more is retained in the blood.
What does PTH stimulate the formation of?
Calcitriol (the active form of vitamin D).
What does calcitriol do?
It promotes absorption of calcium from foods in the gastrointestinal tract into the blood.
What hormone works to decrease blood Ca2+ levels?
Calcitonin (CT)
Where is calcitonin (CT) secreted from?
Parafollicular cells in the thyroid gland.
What effect does calcitonin (CT) have on osteoclasts?
It inhibits their activity.
How does calcitonin (CT) affect blood Ca2+ uptake by bone?
It speeds up blood Ca2+ uptake by bone.
What is the net result of calcitonin (CT)?
It promotes bone formation and decreases blood Ca2+ levels.
What is an effective drug for treating osteoporosis?
Calcitonin harvested from salmon (Miacalcin®).
How does Miacalcin® help treat osteoporosis?
It slows bone resorption.
What ability does bone tissue have within limits?
The ability to alter its strength in response to changes in mechanical strain.
What happens to bone tissue when placed under strain?
It becomes stronger through increased deposition of mineral salts and production of collagen fibers by osteoblasts.
What happens to bone tissue without mechanical strain?
It does not remodel normally because bone resorption occurs more quickly than bone formation.
What type of strain more strongly influences bone deposition?
High-impact intermittent strains.
What activities stimulate bone remodeling more dramatically than walking?
Running and jumping.
What are the main mechanical strains on bone?
The pull of skeletal muscles and the pull of gravity.
What happens to the strength of unstrained bones in a bedridden person or a person with a fractured bone in a cast?
It diminishes because of the loss of bone minerals and decreased numbers of collagen fibers.
What happens to astronauts subjected to microgravity?
They lose bone mass.
How much bone loss can occur in astronauts or immobilized individuals per month?
As much as 1-2% per month.
How do the bones of athletes compare to those of astronauts or nonathletes?
They become notably thicker and stronger.
What types of activities help build and retain bone mass?
Weight-bearing activities, such as walking or moderate weight lifting.
When should adolescents and young adults engage in regular weight-bearing exercise?
Prior to the closure of the epiphyseal plates.
Why should adolescents and young adults engage in weight-bearing exercise before the closure of the epiphyseal plates?
To help build total bone mass prior to its inevitable reduction with aging.
Who can and should strengthen their bones by engaging in weight-bearing exercise?
People of all ages.
From birth through adolescence, what happens to bone tissue during bone remodeling?
More bone tissue is produced than is lost.
In young adults, how do the rates of bone deposition and resorption compare?
They are about the same.
What happens to bone mass as the level of sex hormones diminishes during middle age?
A decrease in bone mass occurs because bone resorption by osteoclasts outpaces bone deposition by osteoblasts.
In old age, how does bone loss through resorption compare to bone gain?
Loss of bone through resorption occurs more rapidly than bone gain.
Why does bone mass loss in old age typically have a greater adverse effect in females than in males?
Because women’s bones are generally smaller and less massive than men’s bones to begin with.
What do these factors contribute to in females?
A higher incidence of osteoporosis.
What are the two principal effects of aging on bone tissue?
Loss of bone mass and brittleness.
What causes loss of bone mass?
Demineralization, the loss of calcium and other minerals from bone extracellular matrix.
At what age does loss of bone mass usually begin in females?
After age 30.
Around what age does loss of bone mass accelerate in females, and why?
Around age 45, as levels of estrogens decrease.
By what age can as much as 30% of calcium in bones be lost in females?
By age 70.
Once bone loss begins in females, how much bone mass is lost every 10 years?
About 8%.
When does calcium loss typically begin in males?
After age 60.
How much bone mass is lost in males every 10 years?
About 3%.
What is one of the problems in osteoporosis?
The loss of calcium from bones.
What is the second principal effect of aging on the skeletal system?
Brittleness.
What causes brittleness in bones?
A decreased rate of protein synthesis.
What part of the bone extracellular matrix gives bone its tensile strength?
Collagen fibers.
What does the loss of tensile strength cause in bones?
It causes bones to become very brittle and susceptible to fracture.
In some elderly people, what slows down due to diminished production of growth hormone?
Collagen fiber synthesis.
Besides increasing susceptibility to fractures, what other effects does loss of bone mass lead to?
Deformity, pain, loss of height, and loss of teeth.
What is osteoporosis?
A condition of porous bones.
How many people in the United States are affected by osteoporosis each year?
34 million.
How many people in the United States have low bone mass (osteopenia), putting them at risk for osteoporosis?
44 million.
What is the basic problem in osteoporosis?
Bone resorption (breakdown) outpaces bone deposition (formation).
What is the main cause of bone mass depletion in osteoporosis?
Depletion of calcium from the body.
Why does calcium depletion occur in osteoporosis?
More calcium is lost in urine, feces, and sweat than is absorbed from the diet.
What happens when bone mass becomes severely depleted?
Bones fracture, often spontaneously, under the mechanical strains of everyday living.
How can a hip fracture occur in someone with osteoporosis?
Simply sitting down too quickly.
How many fractures does osteoporosis cause per year in the United States?
More than 1.5 million.
Which body parts are mainly affected by osteoporosis fractures?
Hips, wrists, and vertebrae.
Besides fractures, what other effects does osteoporosis have on the skeletal system?
Shrinkage of vertebrae, height loss, hunched backs, and bone pain.
Who is primarily affected by osteoporosis?
Middle-aged and elderly people, 80% of them women.
Why do older women suffer from osteoporosis more often than men?
(1) Women’s bones are less massive than men’s bones, and (2) production of estrogens declines dramatically at menopause, whereas testosterone declines gradually and slightly.
What do estrogens and testosterone stimulate?
Osteoblast activity and synthesis of bone matrix.
What are the risk factors for developing osteoporosis?
Family history, European or Asian ancestry, thin or small body build, inactive lifestyle, cigarette smoking, low calcium and vitamin D diet, more than two alcoholic drinks a day, and certain medications.
How is osteoporosis diagnosed?
By taking a family history and undergoing a bone mineral density test (BMD test).
What do BMD tests measure?
Bone density.
What are BMD tests used for?
Confirming osteoporosis diagnosis, determining bone loss rate, and monitoring treatment effects.
What is FRAX® used for?
To estimate fracture risk by incorporating risk factors beyond bone mineral density.
What information does the FRAX® tool consider?
Age, gender, height, weight, ethnicity, prior fractures, parental history of hip fracture, glucocorticoid use, smoking, alcohol intake, and rheumatoid arthritis.
What does FRAX® estimate?
The probability of a person suffering a fracture of the hip or other major bones within 10 years.
What is an important part of osteoporosis treatment regarding nutrition?
A diet high in calcium.
Why is vitamin D necessary in osteoporosis treatment?
It helps the body utilize calcium.
What type of exercise helps maintain and build bone mass?
Weight-bearing exercises.
What are examples of weight-bearing exercises?
Walking, jogging, hiking, climbing stairs, playing tennis, and dancing.
What type of exercise builds both bone strength and muscle mass?
Resistance exercises such as weight lifting.
What are the two main types of medications for osteoporosis?
(1) Antireabsorptive drugs and (2) bone-building drugs.
What do antireabsorptive drugs do?
Slow down the progression of bone loss.
What do bone-building drugs do?
Promote increasing bone mass.
What are examples of antireabsorptive drugs?
Bisphosphonates, selective estrogen receptor modulators, estrogen replacement therapy (ERT), and hormone replacement therapy (HRT).
What do bisphosphonates do?
Inhibit osteoclasts.
What are examples of bisphosphonates?
Fosamax®, Actonel®, Boniva®, and calcitonin.
What do selective estrogen receptor modulators do?
Mimic the effects of estrogens without unwanted side effects.
What are examples of selective estrogen receptor modulators?
Raloxifene® and Evista®.
What does estrogen replacement therapy (ERT) do?
Replaces estrogens lost during and after menopause.
What is an example of an ERT medication?
Premarin®.
What does hormone replacement therapy (HRT) do?
Replaces estrogens and progesterone lost during and after menopause.
What is an example of an HRT medication?
Prempro®.
How does ERT help bone health?
It helps maintain and increase bone mass after menopause.
What increased risks do women on ERT have?
A slightly increased risk of stroke and blood clots.
What increased risks do women on HRT have?
Heart disease, breast cancer, stroke, blood clots, and dementia.
What is an example of a bone-building drug?
Parathyroid hormone (PTH).
What does parathyroid hormone (PTH) do?
Stimulates osteoblasts to produce new bone.
What is an example of a PTH medication?
Forteo®.
Factors that affect Bone Growth
Minerals, Vitamins, Hormones, Exercise, and Aging
Make bone extracellular matrix hard.
Calcium and phosphorus
Helps form bone extracellular matrix.
Magnesium
Helps strengthen bone extracellular matrix.
Fluoride
Activates enzymes involved in synthesis of bone extracellular matrix.
Manganese
Needed for the activity of osteoblasts during remodeling of bone; deficiency stunts bone growth; toxic in high doses.
Vitamin a
Needed for synthesis of collagen, the main bone protein; deficiency leads to decreased collagen production, which slows down bone growth and delays repair of broken bones.
Vitamin C
Active form (calcitriol) is produced by the kidneys; helps build bone by increasing absorption of calcium from digestive canal into blood; deficiency causes faulty calcification and slows down bone growth; may reduce the risk of osteoporosis but is toxic if taken in high doses. People who have minimal exposure to ultraviolet rays or do not take vitamin D supplements may not have sufficient vitamin D to absorb calcium. This interferes with calcium metabolism.
Vitamin D
Needed for synthesis of bone proteins; deficiency leads to abnormal protein production in bone extracellular matrix and decreased bone density.
Vitamins K and B12
Secreted by the anterior lobe of the pituitary gland; promotes general growth of all body tissues, including bone, mainly by stimulating production of insulin- like growth factors.
Growth hormone (Gh)
Secreted by the liver, bones, and other tissues on stimulation by growth hormone; promotes normal bone growth by stimulating osteoblasts and by increasing the synthesis of proteins needed to build new bone.
Insulin like growth factors (IGFs)
Secreted by thyroid gland; promote normal bone growth by stimulating osteoblasts
thyroid hormones (t3 and t4)
Secreted by the pancreas; promotes normal bone growth by increasing the synthesis of bone proteins.
Insulin
Secreted by the ovaries in women (estrogens) and by the testes in men (testosterone); stimulate osteoblasts and promote the sudden “growth spurt” that occurs during the teenage years; shut down growth at the epiphyseal plates around age 18–21, causing lengthwise growth of bone to end; contribute to bone remodeling during adulthood by slowing bone resorption by osteoclasts and promoting bone deposition by osteoblasts.
Sex hormones (estrogens and testosterone)
Secreted by the parathyroid glands; promotes bone resorption by osteoclasts; enhances recovery of calcium ions from urine; promotes formation of the active form of vitamin D (calcitriol).
parathyroid hormone (pth)
Secreted by the thyroid gland; inhibits bone resorption by osteoclasts.
Calcitonin (Ct)
Weight- bearing activities stimulate osteoblasts and, consequently, help build thicker, stronger bones and retard loss of bone mass that occurs as people age
exercise
As the level of sex hormones diminishes during middle age to older adulthood, especially in women after menopause, bone resorption by osteoclasts outpaces bone deposition by osteoblasts, which leads to a decrease in bone mass and an increased risk of osteoporosis.
aging
In ___, bone resorption outpaces bone formation, so bone mass decreases.
osteoporosis
What are rickets and osteomalacia?
Two forms of the same disease that result from inadequate calcification of the extracellular bone matrix.
What is the usual cause of rickets and osteomalacia?
Vitamin D deficiency.
What is rickets?
A disease of children in which the growing bones become “soft” or rubbery and are easily deformed.
Why do bones become soft or rubbery in rickets?
New bone formed at the epiphyseal plates fails to ossify.
What are common deformities caused by rickets?
Bowed legs, deformities of the skull, rib cage, and pelvis.
What is osteomalacia?
The adult counterpart of rickets, sometimes called adult rickets.
What happens to new bone formed during osteomalacia?
It fails to calcify.
What symptoms do people with osteomalacia experience?
Varying degrees of pain and tenderness in bones, especially the hip and legs.
What can result from minor trauma in osteomalacia?
Bone fractures.
What is the prevention and treatment for rickets and osteomalacia?
Administration of adequate vitamin D and exposure to moderate amounts of sunlight.
The degenera tion of articular cartilage such that the bony ends touch; the result ing friction of bone against bone worsens the condition. Usually associated with the elderly.
Osteoarthritis
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).
Osteomyelitis
Reduced 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.
Osteopenia
Bone cancer that primarily affects osteoblasts and occurs most often in teenagers during their growth spurt; the most com mon 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 chemo therapy and removal of the malignant growth, or amputation of the limb.
Osteosarcoma
