Chapter 6- Skeletal System: Bone Tissue
Dwarfism
condition of small stature in which the height of an individual is typically under 4 feet 10 inches, usually averaging 4 feet. Generally, there are two types of dwarfism: proportionate and disproportionate
As a bone grows, chondrocytes proliferate on
epiphyseal side of the plate.
numerous epiphyseal & metaphyseal veins accompany their respective arteries & exit thru
epiphyses & metaphyses
epiphyseal line is the bordr btwn
epiphysis & metaphysis
sex hormones
estrogen(ovaries) & androgens like testerone (testes)
Bone resorption is necessary for
evelopment, maintenance, and repair of bone.
pagets disease
excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition. -osteoblasts attempt to compensate, but new bone is weaker bc it has higher proportion of spongy to compact bone, mineralization is decreased, & newly synthesized EC matrix contains abnormal proteins. The newly formed bone, especially that of the pelvis, limbs, lower vertebrae, & skull, bcms enlarged, hard, & brittle & fractures easily.
standard x-ray images often
fail to reveal the presence of stress fractures, they show up clearly in a bone scan.
Besides gender, risk factors for developing osteoporosis include
family history of disease, European or Asian ancestry, thin or small body build, an inactive lifestyle, cigarette smoking, a diet low in calcium & vitamin D, more than 2 alcoholic drinks a day, & use of certain medications.
compact bone
few spaces btwn osteons (haversian systems); forms external portion of all bones & the bulk of diaphysis (shaft) of long bones; is found immediately deep to the periosteum and external to spongy bone. -protection/support; resists stresses produced by weight & movement.
during bony callus formation of bone rapir
fibrocartilage converts to spongy bone, & callus is then referred to as a bony (hard) callus. -last 3-4 months
zone of hypertrophic cartilage of epiphyseal plate
ayer consists of large, maturing chondrocytes arranged in columns.
osteons
basic unit of structure in adult compact bone, consisting of a central (haversian) canal w/ its concentrically arranged lamellae, lacunae, osteocytes, and canaliculi.
At puberty, the secretion of sex hormones
causes a dramatic effect on bone growth.
blood cell production
certain bones do hemopoiesis(produce new blood cells. platelets, & wb cells) in RB marrow(connect. tissue) present in fetus & some adult bones like hips, ribs, sternum. -in new born all bone marrow is red & doe meopoiesis -with age RB marrow turns to yellow -funct. of skeletal systm
external circumferential lamellae
circumferential lamellae directly deep to the periosteum , connected to the periosteum by perforating (Sharpey's) fibers.
nutrient artery
near diaphysis center;passes through a hole in compact bone called the nutrient foramen
-Vitamins K & B12
needed for synthesis of bone proteins.
phagocytes
neutrophils/macrophages & osteoclasts remove dead/damaged tissue around hematoma fracture
bone in certain areas of the shaft of the femur will
not be replaced completely during an individual's life
many small periosteal veins accompany their respective arteries & exit thru
periosteum.
Excessive or deficient secretion of hormones that normally control bone growth can cause
person to be abnormally tall or short
bone-building drugs
promote increasing bone mass
long bones tubular design
provides max strength w/ minumum weight
Estrogens also promote changes in the skeleton that are typical of females like
widening of the pelvis
role of bone in calcium homeostasis is to
"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.
Veins that carry blood away from long bones are evident in three places
(1) 1 or 2 nutrient veins accompany nutrient artery & exit thru diaphysis (2) numerous epiphyseal & metaphyseal veins accompany their respective arteries & exit thru epiphyses & metaphyses (3) many small periosteal veins accompany their respective arteries & exit thru periosteum.
Osteoporosis primarily affects middle-aged and elderly people, 80% of them women. Older women suffer from osteoporosis more often than men for two reasons
(1) Women's bones= less massive than men's (2) production of estrogens in women declines dramatically at menopause, but production of main androgen, testosterone, in older men wanes gradually and only slightly.
Medications used to treat osteoporosis
(1) antireabsorptive drugs-slow down the progression of bone loss (2) bone-building drugs promote increasing bone mass.
Among the antireabsorptive drugs are
(1) bisphosphonates, which inhibit osteoclasts (Fosamax®, Actonel®, Boniva®, and calcitonin); (2) selective estrogen receptor modulators, which mimic the effects of estrogens without unwanted side effects (Raloxifene®, Evista®) (3) estrogen replacement therapy (ERT), which replaces estrogens lost during & after menopause (Premarin®), & hormone replacement therapy (HRT), which replaces estrogens & progesterone lost during & after menopause (Prempro®). ERT helps maintain and increase bone mass after menopause.
osteocyte
- maintians bone tissue -from bone cell lineage
Spongy bone tissue is different from compact bone tissue in two respects.
-1=spongy bone tissue is light, which reduces weight of bone allowing it to move more easily when pulled by skeletal muscle -2= trabeculae of spongy bone tissue support & protect red bone marrow. Spongy bone in hip bones, ribs, sternum (breastbone), vertebrae, & proximal ends of humerus/femur is the only site where red bone marrow is stored and, thus, the site where hemopoiesis (blood cell production) occurs in adults.
vitamins
-Vitamin A stimulates activity of osteoblasts. -Vitamin C = synthesis of collagen, the main bone protein. -vitamin D= build bone by increasing absorption of calcium from foods in gastrointestinal tract into the blood. -Vitamins K & B12 are also needed for synthesis of bone proteins.
treatments for fractures
-according to age, type of fracture, & bone -goal:realignment of the bone fragments, immobilization to maintain realignment, and restoration of function. -fracture ends must be alinged= reduction : closed & open reduction
bone resoprtion
-development , maintance & repair of bone done by osteoclast rufled border facing bone surface- releases lysosomal enzymes/ acids that digest protein/mineral components of underlying ext.cell bone matrix -removal of minerals and collagen fibers from bone by osteoclasts
space travel affect on bones
-lost 20% of bone density, bc of 0 grabitym & limited movement caused strain
support
-strucutral frame work of body supporting soft tissues ^ providing attachement points for tendons/most skeletal muscle -basic funct. of skeletal systm
Impacted
1 end of fractured bone is forcefully driven into the interior of the other.
bone repair
1. Reactive Phase: formation of fracture hematoma, fibrocartilaginous callus formation 2.Reperative Phase: bony callus formation 3. Bone remodeling phase
bone formation 4 principal situation
1. initial formation of bones in embryo/fetus 2. growth of bones during infancy, childhood, & adolescence until their adult sizes are reached 3. remodeling of bone (replacement of old bone by new bone tissue throughout life), 4. repair of fractures (breaks in bones) throughout life.
growth in length of long bones involves the following two major events:
1. interstitial growth of cartilage on epiphyseal side of epiphyseal plate 2. eplacement of cartilage on the diaphyseal side of the epiphyseal plate w/ bone by endochondral ossification.
n the United States, osteoporosis causes more than
1.5 million fractures a year, mainly in the hips, wrists, and vertebrae. Osteoporosis afflicts the entire skeletal system.
functions of bone tissues
1.Supports soft tissue & provides attachment for skeletal muscles. 2.Protects internal organs. 3.Assists in movement, along w/ skeletal muscles. 4.Stores & releases minerals. 5.Contains red bone marrow, which produces blood cells. 6.Contains yellow bone marrow, which stores triglycerides (fats).
Rickets and osteomalacia
2 forms of the same disease that result from inadequate calcification of the extracellular bone matrix, usually caused by a vitamin D deficiency.
stress fractures involve the tibia
25%
bone stores _____ of total body calcium
99%
osteoclasts increase bone resorption & kidneys retain Ca2+ in blood, excrete phosphate in urine & produce calcitriol, & response
= increase Ca2+ blood lvl
If you wanted to develop a drug to lessen the effects of osteoporosis, would you look for a chemical that inhibits the activity of osteoblasts or that of osteoclasts?
A drug that inhibits the activity of osteoclasts might lessen the effects of osteoporosis, because osteoclasts are responsible for bone resorption.
Magnesium
Activates enzymes involved in synthesis of bone extracellular matrix.
osteoporosis
Age-related disorder characterized by decreased bone mass & increased susceptibility to fractures, often as a result of decreased levels of estrogens. -porous bones -bone resorption (breakdown) outpaces bone deposition (formation)
why bone marrow biopsy is painful
As the needle penetrates the periosteum, pain is felt. Once it passes through, there is little pain. - needle is inserted into middle of bone to extract RB marrow to examine it for conditions like leukemias, metastatic neoplasms, lymphoma, Hodgkin's disease, & aplastic anemia.
transverse interosteonic/ Volkmans/ Perforating Canals
Blood vessels/ nerves from periosteum penetrate the compact bone & connect w/ those of the medullary cavity, periosteum, & central canals.
hemopoieses
Blood cell, WB cell & platelets production, which occurs in red bone marrow after birth.
about 80% of the skeleton is compact bone and 20% is spongy bone.
Bone isnt completely solid but has small spaces btwn its cells & extracell, matrix components. -Some spaces serve as channels for blood vessels that supply bone cells w/ nutrients. Other spaces are storage areas for RB marrow. -Depending on size & distribution of spaces, the regions of a bone may be categorized as compact or spongy
Mineral homeostasis (storage and release)
Bone tissue makes up 18% of human body weight -stores minerals -calcium and phosphorus=strength of bone. -Bone tissue stores 99% of body's calcium. -On demand, bone releases minerals into blood to maintain critical mineral balances (homeostasis) & to distribute minerals to other parts of the body.
Blood clotting requires
CA2+
Both nerve and muscle cells depend on a stable level of
Ca2+ ion in EC flud to function
calcification
Deposition of mineral salts, primarily hydroxyapatite, in a framework formed by collagen fibers in which the tissue hardens. Also called mineralization -done by Osteoblast- bone building cells
Hormones.
During childhood, hormones most important to bone growth are the insulin-like growth factors (IGFs), which are produced by the liver/ bone tissue. -Thyroid hormones (T3 and T4) from the thyroid gland also promote bone growth by stimulating osteoblasts. -hormone insulin from the pancreas promotes bone growth by increasing the synthesis of bone proteins.
Colles
Fracture of distal end of lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.
pott
Fracture of distal end of the lateral leg bone (fibula), w/ serious injury of distal tibial articulation.
What body functions depend on proper levels of Ca2+?
Heartbeat, respiration, nerve cell functioning, enzyme functioning, & blood clotting
Fluoride
Helps strengthen bone extracellular matrix.
minerals
Large amounts of calcium/phosphorus are needed while bones are growing, as are smaller amounts of magnesium, fluoride, & manganese. These minerals are also necessary during bone remodeling.
demineralization
Loss of calcium and phosphorus from bones
Calcium and phosphorus
Make bone extracellular matrix hard.
during zone of calcified cartilage of epiphyseal plate
Osteoclasts dissolve calcified cartilage, & osteoblasts & capillaries from diaphysis invade the area.
cells from bone cell linage
Osteoprogenitor cell- develops into Osteoblast- forms bone ext.cellular matrix & osteocyte- maintians bone tissue
2 main ways that blood calcium level can be increased
Release of calcium from bone matrix and retention of calcium by the kidneys
zone of proliferating cartilage of epiphyseal plate
Slightly larger chondrocytes arranged like stacks of coins -undergo interstitial growth as they divide & secrete EC matrix. -divide to replace dead chondrocytes at diaphyseal side of the epiphyseal plate.
Comminuted
The bone is splintered, crushed, or broke & into pieces at site of impact, smaller bone fragments lie between the two main fragments
During the process of bone resorption, an osteoclast attaches lightly to bone surface at endosteum or periosteum & forms leakproof seal at edges of ruffled border releasing protein-digesting lysosomal enzymes & acids into sealed pocket.
The enzymes digest collagen fibers/organic substances while acids dissolve bone minerals. -osteoclasts carve out small tunnel in old bone. calcium & phosphorus, enter an osteoclast by endocytosis, cross the cell in vesicles, & undergo exocytosis on side opposite the ruffled border. Now in the interstitial fluid, the products of bone resorption diffuse into nearby blood capillaries. Once a small area of bone has been resorbed, osteoclasts depart and osteoblasts move in to rebuild the bone in that area.
ines of stress in a bone are not static
They change as person learns to walk & in response to repeated strenuous physical activity, like weight training. -lines of stress in a bone also change bc of fractures or physical deformity= organization of osteons is not static but changes over time in response to physical demands placed on the skeleton.
bone scan detects
abnormalities 3 to 6 months sooner than standard x-ray procedures and exposes the patient to less radiation.
Once bone loss begins in females,
about 8% of bone mass is lost every 10 years.
like other connective tissues, bone, or osseous tissue contains
abundant extracellular matrix that surrounds widely separated cells. - extracellular matrix= 15% water, 30% collagen fibers, and 55% crystallized mineral salts. -most abundant mineral salt= calcium phosphate & combines w/ calcium hydroxide to form crystals of hydroxyapatite
adrenal glands of both sexes produce
androgens & other tissues, like adipose tissue, can convert androgens to estrogens hormones responsible for increased osteoblast activity, synthesis of bone extracellular matrix, & sudden "growth spurt" that occurs during the teenage years.
interstitial lamellae
areas between neighboring osteons contain lamellae - also have lacunae w/ osteocytes & canaliculi. - fragments of older osteons that have been partially destroyed during bone rebuilding or growth.
diaphysis
bone's shaft or body—the long, cylindrical, main portion of the long bone
Osteoblast
bone-building cells. -synthesize/secrete collagen fibers & other organic components to build ext.cellular matrix of bone tissue; initiate calcification; bc, trapped w/ ext.cellular matrix & become osteocytes. -from bone cell lineage
-Spongy bone tissue tends to be located where
bones arent heavily stressed or where stresses are applied from many directions.
development of periosteum
conjuction w/ formation of trabeculae, mesenchyme condenses at periphery of bone & develps into periosteum -thin layer of compact bone replaces surface layers of spongy bone, but it remains in center -newly formed bone is remodeled(destroyed/reformed) as bone transforms into adult size/shape
formation of RB marrow
connect. tissue associated w/ blood vessels in trabeculae differentiates
thickness of the epiphyseal plate remains
constant, but the bone on the diaphyseal side increases in length
bones hardness depends on
crystallized inorganic mineral salts
calcium and phosphorus needed to strengthen and harden new bone are
deposited only gradually, & bone cells generally grow & reproduce slowly.
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 endosteum. In this way, the medullary cavity enlarges as the bone increases in thickness
bone resorption results in the
destruction of bone extracellular matrix
If some stimulus causes the blood Ca2+ level to decrease, parathyroid gland cells (receptors)
detect this change & increase their production of cyclic adenosine monophosphate (cyclic AMP) molecule
losure of the epiphyseal plate is a gradual process and the degree to which it occurs is useful in
determining bone age, predicting adult height, establishing age at death especially in infants, children, & teens -ex: open epiphyseal plate= young person, while partially/completely closed epiphyseal plate = older person. - closure of the epiphyseal plate is 1-2 yrs earlier in females.
endochondral ossification 6 steps
development of cartilage model, growth of cartilage model, development of primary ossification center , development of medullary cavity, development of secondary ossification center, & formation of articular cartilage/ epiphyseal(growth) plate
intramembranous ossification 4 steps
development of ossification center, calcification, formation of trabeculae, & development of periosteum
periosteal cells on bone surface,differentiate into osteoblasts-secrete collagen fibers/organic molecules that form bone EC matrix. that
develops them into osteocytes forming bone ridges on either side of periosteal blood vessel. that enlarge & create groove for periosteal blood vessel. -growth in thickness pt 1
development of secondary ossification centers during endochondral ossification
develops when branches of epiphyseal artery enter epiphyses, around time of birth. -spongy bone remains in interior of epiphyses (no medullary cavities are formed here). -proceeds outward from center of epiphysis toward outer surface of bone.
bone scan
diagnostic procedure that takes advantage of the fact that bone is living tissue - radioactive tracer compound thats readily absorbed by bone is injected intravenously. -uptake of tracer is related to amount of blood flow -gamma camera measure radiation, & photograph forms -gray=normal -dark/light=abnormal
Normal bone metabolism—growth in the young and bone remodeling in the adult—depends on several factors.
dietary intake of minerals and vitamins, as well as sufficient levels of several hormones.
In some elderly people, collagen fiber synthesis slows, in part due to
diminished production of growth hormone.
Rickets
disease of children which growing bones become "soft" or rubbery & easily deformed. -Bc new bone formed at epiphyseal (growth) plates fails to ossify, bowed legs & deformities of the skull, rib cage, and pelvis are common.
Bone remodeling phase of bone repair
final phase, remodels callus. -Dead portions of original fragments of broken bone are resorbed by osteoclasts. -Compact bone replaces spongy bone around the periphery of fracture. -Sometimes, fracture line is undetectable, even in a radiograph (x-ray). -However, thickened area on bone surface remains after healed fracture.
zone of calcified cartilage of epiphyseal plate
final zone of epiphyseal plate only few cells thick; consists mostly of dead chondrocytes bc of calcified EC matrix - Osteoclasts dissolve calcified cartilage, & osteoblasts & capillaries from diaphysis invade the area. - osteoblasts lay down bone EC matrix, replacing calcified cartilage by endochondral ossification & calcified cartilage bcms the "new diaphysis" thats firmly cemented to rest of diaphysis of bone.
bone deposition results in
formation of bone extracellular matrix
skeletal system
fremeork of bones & their cartiage
appositional growht
growth of cartilage thickness due to deposition of EC matrix material on cartilage surface of model by new chondroblasts that developed from the perichondrium. -exoenous growht; growht from outer surface
Some bones, like the tibia
have only one nutrient artery
thickened area on bone surface remains after
healed fracture.
Although bone has a generous blood supply,
healing takes months
nutrient foramen
hole in compact bone
calcitonin (CT)
hormone produced by hyroid gland parafollicular cells that lower blood calcium & phosphates by inhibiting bone resorption (breakdown of bone extracellular matrix) & by speeding uptake of calcium & phosphates into bone matrix.
parathyroid hormone (PTH)
hormone secreted by chief (principal) cells of the parathyroid glands that increases blood calcium level & decreases blood phosphate level. -negative feedback systm
Following reduction, a fractured bone may be kept
immobilized by a cast, sling, splint, elastic bandage, external fixation device, or a combination of these devices.
Where in the cartilage model do secondary ossification centers develop during endochondral ossification?
in the regions of the cartilage model that will give rise to the epiphyses.
development of primary ossification cente
in this region of diaphysis, bone tissue has replaced most of cartilage -Endochondral ossification
Moderate weight-bearing exercises maintain sufficient strain on bones to
increase and maintain their density.
gene for PTH within the nucleus of a parathyroid gland cell (the control center) detects
intracellular increase in cyclic AMP (the input). results in PTH synthesis speeding up, & more PTH (the output) is released into the blood.
fontanels harden and turn into sutures by
intramembranous ossification
bone formation/development 2 patterns
intramembranous ossification & endochondral ossification
spongy bone tissue
is light weight to be easily moved by skeletal system & is location where RB marrow is rpotected
help elevate blood Ca2+ lvl
kidneys( decrease loss of Ca2 in blood) & calcitriol(increase absorption of calcium from food)
circumferential lamellae
lamallae arranged around the entire outer and inner circumference of the shaft of a long bone -develop during initial bone formation
zone of resting cartilage of epiphyseal plate
layer nearest epiphysis consisting of small, scattered chondrocytes - cells dont function in bone growth. Rather, they anchor epiphyseal plate to the epiphysis of the bone.
In old age, loss of bone through resorption occurs more rapidly than bone gain. Because women's bones generally are smaller and less massive than men's bones to begin with,
loss of bone mass in old age typically has a greater adverse effect in females. -contribute to the higher incidence of osteoporosis in females.
As people age, some osteonic (haversian) canals may become blocked. What effect would this have on the surrounding osteocytes?
osteonic (haversian) canals are the main blood supply to the osteocytes of an osteon (haversian system), so their blockage would lead to death of the osteocytes.
Compact bone tissue is composed of repeating structural units called
osteons consisting of concentric lamellae arranged around an osteonic (haversian or central) canal
4 cell types in bone tissue
osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts
parathyroid hormone, calcitriol (the active form of vitamin D), and calcitonin are
other hormones that can affect bone remodeling.
Stress fractures are
painful & result from disease processes that disrupt normal bone calcification, such as Osteoporosis
PTH
parathyroid hormone.
The periosteum is attached to the underlying bone by
perforating fibers or Sharpey's fibers, thick bundles of collagen that extend from periosteum into bone extracellular matrix.
goal of fracture treatment
realignment of the bone fragments, immobilization to maintain realignment, and restoration of function.
12 wk fetus,
red areas= calcified clear= uncalcified
metaphyses
regions btwn diaphysis/epiphyses -each metapysys in growing bone contains Epiphyseal plate- layer of hyaline cartilage that allow diaphysys of bone to grow in length around 14-24 yrs & is replaced by bone resulting in epiphyseal line
If bone fracture damages the epiphyseal plate, the fractured bone may be
shorter when an adult, bc damage to cartilage (avascular), accelerates closure of epiphyseal plate due to cessation of cartilage cell division, thus inhibiting lengthwise growth of bone.
addition to fractures, osteoporosis causes
shrinkage of vertebrae, height loss, hunched backs, and bone pain.
parts of long bones
spongy bone tissue of the epiphyses and metaphyses contains red bone marrow, and the medullary cavity of the diaphysis contains yellow bone marrow (in adults).
A bone scan is the
standard test for bone density screening, particularly important in screening for osteoporosis in females.
IGFs
stimulate osteoblasts, promote cell division at the epiphyseal plate and in the periosteum, and enhance synthesis of the proteins needed to build new bone.
vitamin A
stimulates activity of osteoblasts.
osteology
study of bone structure & its disorder treatments
what supplies the inner part of compact bone tissue of the diaphysis & the spongy bone tissue and red bone marrow as far as the epiphyseal plates (or lines).
the nutriet artery 2 branches after entering medullary cai=vity
why are bone fractures and bone tumors painful?
the periosteum covering the bone except articuar joints is full of sensory & pain nerves
IGFs are produced in response to
the secretion of growth hormone (GH) from the anterior lobe of the pituitary gland (see Section 18.6).
development of secondary ossification centers
these occur in epiphyses of bone -Endochondral ossification
trabeculare of spongy bone seems unorganized compared to compact bone osteons, however
theyre precisely oriented along lines of stress-characteristic that helps bones resist stresses & transfer force w/out breaking. -Spongy bone tissue located where bones arent heavily stressed or where stresses are applied from many directions. -trabeculae dont achieve final arrangement until locomotion is completely learned; arrangement can even be altered as lines of stress change due to a poorly healed fracture or a deformity.
bones of athletes, which are repetitively and highly stressed, become
thicker and stronger than those of astronauts or nonathletes.
endosteum
thin membrane lining medullary cavity. -contains single layer of bone-forming cells & small amount of connective tissue.
Thyroid hormones (T3 and T4) from
thyroid gland also promote bone growth by stimulating osteoblasts.
Eventually, the ridges fold together and fuse, and the groove becomes a
tunnel that encloses the blood vessel. The former periosteum now becomes the endosteum that lines the tunnel. -growth in thickness pt. 2
role of CT in normal calcium homeostasis is
uncertain because it can be completely absent without causing symptoms.
Osteoprogenitor cells
undergo cell division and develop into osteoblasts, which secrete bone extracellular matrix
osteoprogenitor cell
unspecialized bone stem cells derived from mesenchyme- tissue from which all connective tissues are formed. - only bone cells to undergo cell division; develop into osteoblasts. -found along inner portion of periosteum, in endosteum, & canals w/n bone containing blood vessels. -from bone cell lineage
maintain and build bone mass.
walking, jogging, hiking, climbing stairs, playing tennis, and dancing. Resistance exercises, such as weight lifting, also build bone strength and muscle mass.
Oversecretion of growth hormone (GH) during childhood produces
which a person becomes much taller and heavier than normal
articular cartilage
-thin layer of hyaline cartilage covering epiphysis btwn articulations(joints) w/ other boes -reduces friction/absorbs shock at freely moveable joints -lacks perichondrium & blood vessels= damage repair is limitied
Reparative phase: Bony callus formation phase of bone repair
1 of 2 reparative phase events: areas closer to vascularized healthy bone, osteoprogenitor cells develop into osteoblasts, that produce spongy bone trabeculae that joins living & dead portions of original bone fragments. -fibrocartilage converts to spongy bone, & callus is then referred to as a bony (hard) callus. -The bony callus lasts about 3-4 months.
reparative phase: fibrocartilaginus callus formation
1 of 2 reparative phase events: bridge gap btwn broken ends of bones. -Blood vessels grow into fracture hematoma & phagocytes begin clean up dead bone cells. -Fibroblasts from periosteum invade fracture site & produce collagen fibers. -cells from periosteum develop into chondroblasts & produce fibrocartilage -lead to fibrocartilaginous (soft) callus development- mass of repair tissue consisting of collagen fibers/cartilage that bridges broken ends of bone. -Formation takes about 3 weeks.
bone loss can be dramatic
1% per week
blood vessels
abundant in portions of bone containing red bone marrow, pass into bones from the periosteum
PTH stimulates formation of calcitriol
active form of vitamin D, hormone that promotes absorption of calcium from foods in the gastrointestinal tract into the blood. Both of these actions also help elevate blood Ca2+ level.
bone deposition
addition of minerals and collagen fibers to bone by osteoblasts
Triglyceride storage. Yellow bone marrow
adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve. -function of skeletal systm
Prevention and treatment for rickets and osteomalacia consists of
administration of adequate vitamin D and exposure to moderate amounts of sunlight.
when does epiphyshea; plate close
adult (at about age 18 in females and age 21 in males) -epiphyseal cartilage cells stop dividing & bone replaces all remaining cartilage -replaced by epiphyseal line=inidcated stoping of bone growth
Osteomalacia
adult rickets. New bone formed during remodeling fails to calcify, & person experiences varying degrees of pain & tenderness in bones, especially hip/ legs. -Bone fractures result from minor trauma.
Osteons in compact bone tissue are
aligned in the same direction & are parallel to length of diaphysis= shaft of long bone resists bending/ fracturing even when force is applied from either end. -Compact bone tissue tends to be thickest in those parts of a bone where stresses are applied in relatively few directions.
proportionate dwarfism,
all parts of the body are small but they are proportionate to each other.
Lighter areas or "cold spots" in bone scans
areas of decreased metabolism that absorb less of the radioactive tracer due to decreased blood flow. -indicate degenerative bone disease, decalcified bone, fractures, bone infections, Paget's disease, or rheumatoid arthritis.
Darker areas or "hot spots" in bone scans
areas of increased metabolism that absorb more of radioactive tracer due to increased blood flow. -indicate bone cancer, abnormal healing of fractures, or abnormal bone growth
Compact bone replaces spongy bone
around the periphery of the fracture
Periosteal arteries
arteries accompanied by nerves, enter diaphysis thru many interosteonic (Volkmann's/perforating) canals & supply periosteum & outer part of the compact bone
in epiphysis of long bone
articular cartilage, epiphyseal artery & vein -on top portion of bone
A long bone is covered by articular cartilage at
articular surfaces of its proximal and distal epiphyses and by periosteum around all other parts of the bone.
why is damage repair limited in articular joints of long bones
bc articular artilage(hyaline) covering the epiphysis lacks Perichondrium & blood vessels
trabeculae dont achieve their final arrangement until locomotion is completely learned. In fact, the arrangement can
be altered as lines of stress change due to a poorly healed fracture or a deformity.
When placed under stress, bone tissue
becomes stronger through increased deposition of mineral salts and production of collagen fibers by osteoblasts.
demineralization in females
begins after 30, accelerates greatly at 45 as levels of estrogens decrease, & continues until as much as 30% of calcium in bones is lost by age 70.
controlled condition
blood Ca2+ lvl
calcium deposition from
blood into bone
Bone heals more rapidly than cartilage because of
blood supply
Bone is richly supplied with
blood vesseles
How does the medullary cavity enlarge during growth in thickness?
by activity of the osteoclasts in the endosteum.
formation of trabeculae during intramembranous ossification
bone EC matrix forms, & develops into trabeculae fusing w/ eachother forming spongy bone around blood vessel network. connect. tissue associated w/ blood vessels in trabeculae differentiates & turns into RB marrow
development of medullary(marrow) cavity
bone breakdown by osteoclats forms it -Endochondral ossification
osteomalacia or rickets
bone flexible
ossification / osteogenesis
bone formation
in osteoporosis, bone resorption outpaces
bone formation, so bone mass decreases.
endochondral ossification
bone forms within hyaline cartilage that develops from mesenchyme.
hormone insulin from the pancreas promotes
bone growth by increasing the synthesis of bone proteins.
calcium resoprtion from
bone into blood
oseiporosis
bone is breaking
. In a newborn, all bone marrow is red and is involved in hemopoiesis. With increasing age
bone marrow changes from red to yellow
steoporosis is diagnosed by taking a family history and undergoing a
bone mineral density (BMD) test- confirm a diagnosis of osteoporosis, determine the rate of bone loss, and monitor the effects of treatment.
cartilage is replaced by
bone on the diaphyseal side of the plate.
During adulthood, sex hormones contribute to
bone remodeling by slowing resorption of old bone & promoting deposition of new bone. One way that estrogens slow resorption is by promoting apoptosis (programmed death) of osteoclasts.
in osteoporosis Bone mass becomes so depleted that
bones fracture spontaneously, under the mechanical stresses of everyday living. -hip fracture from simply sitting down too quickly.
during infancy, childhoos & adolescence,
bones thruout body grow in thickness by appositional growth, & long bones lengthen by addition of bone material on diaphyseal side of the epiphyseal plate by interstitial growth.
formation of articular cartilage & epuphyseal plate
both structures consist of hyaline cartilage -Endochondral ossification
Orthodontics
branch of dentistry concerned w/ prevention & correction of poorly aligned teeth. The movement of teeth by braces places a stress on the bone that forms the sockets that anchor the teeth. In response to this artificial stress, osteoclasts & osteoblasts remodel the sockets so that the teeth align properly.
fracture
break in bone -named for severity, shape/position of line or how 1st described -may fracture without visibly breaking
open fracture
broken ends of the bone protrude thru skin. Conversely, a closed (simple) fracture does not break the skin
bc enzymes require Ca2+ as cofactor, plasma Ca2+ lvl is regulated
btwn 9-11 mg/100mL -slightes change = fatal - heart attack or respiratory arest
lacunae
btwn concentric lammale small, hollow space that conatin osteocytes
Weight-bearing activities, such as walking or moderate weight lifting, help
build and retain bone mass.
-vitamin D
build bone by increasing absorption of calcium from foods in gastrointestinal tract into the blood.
Adolescents and young adults should engage in regular weight-bearing exercise prior to the closure of the epiphyseal plates to help
build total mass prior to its inevitable reduction with aging. However, people of all ages can and should strengthen their bones by engaging in weight-bearing exercise
bone remodeling
building of new bone tissue and breaking down of old bone tissue
New chondrocytes replace older ones, which are destroyed
by calcification; thus cartilage is replaced by bone on the diaphyseal side of the plate.
crystal of hydroxyapatitie formed by 2 mineral salts
calcium phosphate & combines w/ calcium hydroxide
activity of the epiphyseal plate is the only way that the diaphysis
can increase in length
diaphysis forms from
cartilage model produced by EC matrix secretion of chondroblasts
growth of cartilage model in endochondral ossification
chondrolasts deep in cartilage EX matrix are chondrocytes -interstitial growth- growht from within -appositional growth- growth from outer surface -chondrocyte increase size in midregion & surrounding cartilae EC matrix calcifies- some chondrocytes die bc nutrients cant diffus quikly enough trhu EC matrix, & leave spaces that merge & turn into lacunae
concentric lamellae
circular plates of mineralized ext.cell. matrix of increasing diameter, surrounding a small network of blood vessels & nerves located in the central canal -These tubelike units of bone generally form a series of parallel cylinders that, in long bones, tend to run parallel to the long axis of the bone.
internal circumferential lamellae
circumferential lamellae that line the medullary cavity
As an osteon is forming, osteoblasts under the periosteum deposit new
circumferential lamellae, further increasing thickness of bone. As additional periosteal blood vessels bcm enclosed as in growht in thickness pt1, the growth process continues.
bones flexibility depends on
collagen fiber
calcification requires
collagen fibers -Mineral salts begin to crystallize in microscopic spaces btwn collagen fibers, once filled, mineral crystals accumulate around collagen fibers. - combination of crystallized salts & collagen fibers is responsible for the characteristics of bone.
what provides bones tensile strenght
collagen fibers and other organic molecules -resistance to being stretched or torn apart.
whats responsible for characteristics of bone
combination of crystallized salts & collagen fibers
embryonic "skeleton"
composed of mesenchyme in the general shape of bones, is the site where cartilage formation and ossification occur during the sixth week of embryonic development.
Bone tissue is organized in
concentric lamellae around osteonic canal in compact bone & in irregularly arranged lamellae in trabeculae in spongy bone.
Each trabecula consists of
concentric lamellae, osteocytes that lie in lacunae, & canaliculi that radiate outward from the lacunae. -spongy bone
Osteoblasts in the endosteum deposit bone extracellular matrix, forming new
concentric lamellae. The formation of additional concentric lamellae proceeds inward toward periosteal blood vessel. In this way, the tunnel fills in, and a new osteon is created. -growth in thickness pt3
red bone marrow
consist of developing blood 7cells, adipocytes, fibroblasts, macrophages w/n network of reticular fibers. -present in developing bones of fetus & some adult bones: hip (pelvic) bones, ribs, sternum (breastbone), vertebrae (backbones), skull, and ends of the bones of the humerus (arm bone) and femur (thigh bone).
Even after bones have reached their adult shapes and sizes, old bone is
continually destroyed & new bone is formed in its place. injured bone, replacing it with new bone tissue. Remodeling may be triggered by factors such as exercise, sedentary lifestyle, and changes in diet.
maintain calcium lvl in blood
control rates of calcium resorption from bone into blood & calcium deposition from blood into bone
spongy bone in long bones forms the
core of the epiphyses beneath the paper-thin layer of compact bone, and forms a variable narrow rim bordering the medullary cavity of the diaphysis.
young adults, the rates of bone deposition and resorption are about the same. As the level of sex hormones diminishes during middle age, especially in women after menopause, a
decrease in bone mass occurs because bone resorption by osteoclasts outpaces bone deposition by osteoblasts.
PTH also acts on the kidneys (effectors) to
decrease loss of Ca2+ in the urine, so more is retained in the blood.
brittleness
decreased rate of protein synthesis. - organic part of bone EC matrix, mainly collagen fibers, gives bone= tensile strength & loos if it causes the bones to bcm brittle & susceptible to fracture.
In addition to increasing the susceptibility to fractures, loss of bone mass also leads to
deformity, pain, loss of height, and loss of teeth.
1 or 2 nutrient veins accompany nutrient artery & exit thru
diaphysis
long bone consists of
diaphysis, epiphyses, metaphysis, articular cartilage, periosteum,, perforating fibers, medullary cavity & endosteum
entering the medullary cavity, the nutrient artery
divides into proximal/distal branches that course toward each end of bone. -branches supply inner part of compact bone tissue of the diaphysis & the spongy bone tissue and red bone marrow as far as the epiphyseal plates (or lines).
demineralization in males
does not begin until after age 60, and about 3% of bone mass is lost every 10 years.
Without mechanical stress, bone
doesnt remodel normally because bone resorption occurs more quickly than bone formation.
in osteoporosis bone resorption (breakdown) outpaces bone deposition (formation)
due to depletion of calcium from the body—more calcium is lost in urine, feces, and sweat than is absorbed from the diet.
reactive phase of bone fracture repair phase
early inflammatory phase. Blood vessels crossing fracture line are broken. & hematoma- mass of blood (usually clotted) forms around fracture site forms 6-8 hours after injury. -nearby bone cells dies bc hematoma stop blood flow - Swelling/inflammation occur bc dead bone cells, produce extra cellular debris. -Phagocytes (neutrophils/macrophages) & osteoclasts begin to remove dead/damaged tissue in & around fracture hematoma. - lasts up to several weeks
interstitial growth
endogenous, growth within; cartilage model grows inlength by chondrocyte divison w/ more EC matrix secretion
metaphyseal arteries
enter metaphyses of long bones &, together w/ nutrient artery, supply RB marrow & bone tissue of the metaphyses
epiphyseal arteries
enter the epiphyses of a long bone and supply the red bone marrow & bone tissue of the epiphyses
enzymes require Ca2+ as a
enzymes require Ca2+ as a cofactor (an additional substance needed for an enzymatic reaction to occur)
Intramembranous ossification is the simplest type of bone formation & forms
flat bones of the skull, most of the facial bones, mandible (lower jawbone), and the medial part of the clavicle (collar bone) -baby's fontanels(soft spots) harden this way
Intramembranous ossification involves
formation of bone within mesenchyme arranged in sheetlike layers that resemble membranes.
closed reduction
fractured ends of bone are brought into alignment by manual manipulation, & skin remains intact.
open reduction
fractured ends of bone are brought into alignment by surgical procedure using internal fixation devices like screws, plates, pins, rods, & wires.
oseoclast
functions in resorption, breakdown of bone ext.cellular matrix -formedfrom 50 monocytes(WB cell) in endosteum. -rufled border on side facing bone surface- releases lysosomal enzymes/ acids that digest protein/mineral components of underlying ext.cell bone matrix= bone resoprtion- normal develop./maintance/repair of bone -regulate blood calcium lvls w/ certain hormones -target cells for drug therapy to treat osteoporosis
During endochondral ossification, bone
gradually replaces a cartilage model.
long bone
greater length than width
Bone tissue is continuously ________ & complex and dynamic living tissue
growing, remodeling, & repairing itself; contributes to homeostasis by providing support/ protection, producing blood cells, & storing minerals and triglycerides.
epiphyseal growht plate
hyaline cartilage btwn diaphysis & epiphysis, region responsible for lengthwise growth of long bones that you will learn about next.
formation of articular cartilage & epiphyseal (growth) plate
hyaline cartilage covering epiphyses becomes articular cartilage. Prior to adulthood, hyaline cartilage remains between diaphysis & epiphysis as the epiphyseal (growth) plate, the region responsible for the lengthwise growth of long bones that you will learn about next.
epiphyseal (growth) plate
hyaline cartilage plate in the metaphysis of a long bone; site of lengthwise growth of long bones.
FRAX
incorporates risk factors besides bone mineral density to accurately estimate fracture risk. Patients fill out online survey of risk factors like age, gender, height, weight, ethnicity, prior fracture history, parental history of hip fracture, use of glucocorticoids (for example, cortisone), smoking, alcohol intake, & rheumatoid arthritis. -Using the data, FRAX® provides an estimate of the probability that a person will suffer a fracture of the hip or other major bone in the spine, shoulder, or forearm due to osteoporosis within 10 years.
exercise & strain on bones causes atheletes
increase bone density & its health
achondroplasia
inherited condition which conversion of hyaline cartilage to bone is abnormal & long bones of the limbs stop growing in childhood. Other bones are unaffected, and thus the person has short stature but a normal size head and trunk. = achondroplastic dwarfism -untreatable, but most opt for limb-lengthening surgery
bisphosphonates,
inhibit osteoclasts (Fosamax®, Actonel®, Boniva®, and calcitonin);
Remodeling also removes
injured bone, replacing it w/ new bone tissue. Remodeling may be triggered by factors like exercise, sedentary lifestyle, and changes in diet.
spongy bone tissue makes up most of the
interior bone tissue of short, flat, sesamoid, and irregularly shaped bones
spongy bone is always covered by
layer of compact bone for protection.
epiphyseal plate
layer of hyaline cartilage that allow diaphysys of bone to grow in length around 14-24 yrs & is replaced by bone resulting in epiphyseal line in adults
epiphyseal (growth) plate allows the diaphysis of a bone to increase in
length
How does the epiphyseal (growth) plate account for the lengthwise growth of the diaphysis?
lengthwise growth of the diaphysis is caused by cell divisions in the zone of proliferating cartilage and replacement of the zone of calcified cartilage with bone (new diaphysis).
Astronauts subjected to the microgravity of space also
lose bone mass.
2 principal effects of aging on bone tissue
loss of bone mass and brittleness
probem inpsetoporiss
loss of calcium from bones
stimulus disrupts homeostasis by decreasing blood Ca2+ lvl(controlled condition) & parathyroid gland cells (receptors) detect
low Ca2+ concent. which increase cyclic AMP production (input) , controll cente- parathyroid hormone gene turns one releasing PTH= osteoclasts increase bone resorption & kidneys retain Ca2+ in blood, excrete phosphate in urine & produce calcitriol, & response= increase Ca2+ blood lvl
osteopenia
low bone mass 18m ppl, risk for osteoporosis that affect 10m ppl
Although females have much higher levels of estrogens and males have higher levels of androgens, females also have
low levels of androgens, and males have low levels of estrogens.
HRT also helps
maintain and increase bone mass. Women on it have increased risks of heart disease, breast cancer, stroke, blood clots, and dementia.
medullary cavity
marrow cavity -hollow, cylindrical space w/n diaphysis containing fatty YB marrow & numerous blood vessels in adults. -minimizes weight of bone by reducing dense bony material where its least needed. The long bones' tubular design provides maximum strength with minimum weight.
hematoma
mas of blood clotting stoping blood flow & causin bone cells to die & swelling/inflammtion occurs -reactive phase of bone fracture
osteocytes
mature bone cells; main cells in bone tissue & maintain its daily metabolism, like exchange of nutrients/wastes w/ the blood. - Like osteoblasts, osteocytes dont undergo cell division.
perichondrium
membrane covering cartilage
development of cartilage model
mesenchyma cells develop into chondroblasts, which form cartilage model -Endochondral ossification
chondroblast form from
mesenchyme cells crowding together in shape of future bone during endochondrial ossification
ends of long bones are supplied by the
metaphyseal & epiphyseal arteries, which arise from arteries that supply the associated joint.
metaphysis
metaphyseal artery & vein below epiphysis
intramembranous ossification
method of bone formation in which the bone is formed directly in mesenchyme arranged sheet like layers that resemble membranes.
selective estrogen receptor modulators,
mimic the effects of estrogens without unwanted side effects (Raloxifene®, Evista®)
From birth through adolescence
more bone tissue is produced than is lost during bone remodeling.
presence of higher levels of PTH increases
number/activity of osteoclasts (effectors), which step up the pace of bone resorption. The resulting release of Ca2+ from bone into blood returns the blood Ca2+ level to normal.
Treatment options for osteoporosis are varied. With regard to
nutrition, a diet high in calcium is important to reduce the risk of fractures
growth of cartilage model
occurs by chondrocyte division -Endochondral ossification
bone
organ made up of several different tissues working together: bone (osseous) tissue, cartilage, dense connective tissue, epithelium, adipose tissue, & nervous tissue
Estrogens and testosterone stimulate
osteoblast activity and synthesis of bone matrix.
calcification during intramembranous ossification
osteoblasts EC matrix secretion stops & turn into osteocytes, & lie in lacunae & cytoplasmic processes go in all directions in canaliculi. after days, calcium & other mineral salts are deposited & EC matrix hardens/calcifies
As new bone is deposited on the outer surface of bone by
osteoblasts, bone tissue lining medullary cavity is destroyed by osteoclasts in the endosteum.
target cells for drug therapy to treat osteoporosis
osteoclasts
when bones need new mineral or bone formation/breakdown is needed bone cells called
osteoclasts secrete enzymes and acids that break down both the mineral salts and the collagen fibers of the extracellular matrix of bone.
greenstick
partial fracture which 1 side of bone is broken & other side bends; similar to way a green twig breaks on 1 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.
once perichondrium starts forming bone its called
periosteum
Development of the medullary (marrow) cavity during endochondral ossification
primary ossification center grows toward ends of bone, osteoclasts break down some of newly formed spongy bone trabeculae. -leaving a cavity= medullary (marrow) cavity, in the diaphysis (shaft). -Eventually, most of the diaphysis wall is replaced by compact bone.
development of primary ossification center of endochondrial ossification
proceeds inward from ext. surface of bone. nutrient artery penetrates perichondrium & calcifying cartilage model thru its nutrient foramen , causing osteoprogenitor cells to turn into osetoblasts -once perichondrium forms bone= periosteum -Near middle of model, periosteal capillaries grow into disintegrating calcified cartilage, inducing growth of primary ossification center
pituitary dwarfism
proportionate dwarfism is a hyposecretion of GH during childhood -treated medically with administration of GH until epiphyseal plate closure
periosteum functions
protects bone, assists in fracture repair, helps nourish bone tissue, & serves as an attachment point for ligaments & tendons.
protection
protects the most important internal organs from injury. -Ex: cranial bones protect the brain, & rib cage protects the heart and lungs. -basic funct. of skeletal systm
how bone tissue contributes to homeostasis
providing support & protection, producing blood cells, and storing minerals & triglycerides.
epiphyses
proximal and distal ends of long bone
main mechanical stresses on bone are those that result from
pull of skeletal muscles and the pull of gravity.
For bones to unite properly
ractured ends must be brought into alignment trough open /closed reduction
Repair of bone fracture 3 phases
reactive phase, reparative phase 2 parts: 1. fibrocartilaginous callus formation & 2. bony callus formation, & bone remodeling phase
primary ossification center
region where bone tissue replace most of cartilage. -Osteoblasts begin to deposit bone EC matrix over remnants of calcified cartilage, forming spongy bone trabeculae. -spreads from this central location toward both ends of cartilage model.
Negative feedback system
regulation of blood calcium (Ca2+) concentration
what does the bone do on demand?
releases minerals into blood to maintain critical mineral balances (homeostasis) & to distribute minerals to other parts of the body. -funct. of skeletal systm
newly formed bone is remodeled(destroyed/reformed) as bone transforms into adult size/shape
remodeled(destroyed/reformed) as bone transforms into adult size/shape
5% of the total bone mass in the body is being
remodeled; remodeling also takes place at diff. rate in diff. region of body
healthy adults, stress fractures result from
repeated, strenuous activities such as running, jumping, or aerobic dancing.
distal portion of the femur is
replaced about every four months.
endochondral ossification
replacement of cartilage by bone -most bones formed this way; best observed in long bones
bone remodeling
replacement of old bone by new bone tissue, involing bone resorption, & bonde deposition
Bone formation follows one of two patterns both involve
replacement of preexisting connect. tissue w/ bone, dont lead to differences in structure of mature bones, but are simply different methods of bone development.
estrogen replacement therapy (ERT)
replaces estrogens lost during & after menopause (Premarin®), & hormone replacement therapy (HRT), which replaces estrogens & progesterone lost during & after menopause (Prempro®). ERT helps maintain and increase bone mass after menopause.
Dead portions of original fragments of broken bone are
resorbed by osteoclasts.
epiphyseal line
results after epiphyseal plate is done with. -results after all growing has occured; no lenght growing takes after line is formed
resulting release of Ca2+ from bone into blood
returns the blood Ca2+ level to normal.
bone growht in thickness
ridges in periosteum create groove for periosteal blood vessels, & periosteal ridges fuse forming endosteum-lined tunnel, osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming new osteon, bone grows outward as osteoblasts in periosteum build new circumfernetial lamellae. osteon formation repeats ar new eriostel ridges fold over blood vessels
miacalcin
salmon calcitonin drug that treats osteoporosis by slowing bone resorption.
during development of ossification center, osteoblasts
secerete EC matrix of bone till theyre surrounded by it
periosteum is rich in
sensory nerves, some of which carry pain sensations. -especially sensitive to tearing & tension= severe pain from a fracture or bone tumor.
stress fracture
series of microscopic fissure in bone that forms w/out any evidence of injury to other tissues
reduction
setting fracture
the femur has
several nutrient arteries
Ultimately sex hormones, especially estrogens in both sexes
shut down growth at epiphyseal (growth) plates, causing elongation of bones to cease. -Lengthwise growth of bones typically ends earlier in females than in males due to their higher levels of estrogens.
ossification center
site of cluster of mesenchyme cells
development of ossification center
site where bone will develop; chemical messages cases mesenchyme cells to cluster together & defferentiate= 1st into osteoprogenito then osteoblasts cells -sites of clusters= ssification center -osteoblasts secrete EC matrix of bone until theyre surrounded by it
development of cartilage model for endochandral ossification
site where born is going to form, chondroblast form from mesenchyme cells crowding toegether in shape of future bone -chondroblasts secrete cartilae EC matrix producing cartilage model (future diaphysis) consisting of hyaline cartilage -perichondrium develops around cartilage model
Assistance in movement.
skeletal muscles attach to bones; when they contract, they pull on bones to produce movement. -basic funct. of skeletal systm
Women on ERT have a
slightly increased risk of stroke and blood clots.
antireabsorptive drugs
slow down the progression of bone loss
temporary disruption in bones blood supply also helps explain
slowness of healing of severely fractured bones
canaliculi
small channel/canal radiating from lacunae filled w/ ext.cell. fluid where they connect lacunae -inside canals are the finger like processes of osteocytes -connects w/ other lacunae & central canals forming interconnected cannals where osteocytes can communicate via gap junction, & is route for nutrients & oxygen & waste removal
how can you make bone rubbery & flexible?
soaking bone in acidic solution like vinegar, as it dissolves its mineral salts
lacunae formation during endochondrial ossification during development of cartilae model
some chondrocytes die bc nutrients cant diffuse quikly enough thru EC matrix, & leave spaces that merge
disproportionate dwarfism
some parts of body are normal size or larger than normal while others are smaller than normal. =EX: trunk can be average size while the limbs are short & head may be large in relation to the rest of the body, w/ prominent forehead & flattened nose at the bridge. -most common cause is a condition called achondroplasia
Among the bone-building drugs is parathyroid hormone (PTH),
stimulates osteoblasts to produce new bone (Forteo®)
Research has shown that high-impact intermittent
strains more strongly influence bone deposition as compared with lower-impact constant strains. -running & jumping stimulate bone remodeling more dramatically than walking.
bone tissue has the ability to alter its
strength in response to changes in mechanical stress.
If a person is bedridden or has a fractured bone in a cast,
strength of the unstressed bones diminishes because of the loss of bone minerals and decreased numbers of collagen fibers.
shape of a bone can be altered for proper support based on the
stress patterns experienced during the remodeling process. Finally, new bone is more resistant to fracture than old bone.
Remodeling has several other benefits Since the strength of bone is related to the degree to which it is
stressed, if newly formed bone is subjected to heavy loads, it will grow thicker & be stronger than the old bone.
Nerves accompany the blood vessels that
supply bones
6 functions of skeletal system
support, protection, assistance in movement, mineral homeostasis(storage & release), blood cell production, & triglyceride storage
Vitamin C
synthesis of collagen, the main bone protein.
Fibrocartilaginous (soft) callus formation
takes 3 wks, mass repair tissue consists collagen fibers/cartilage that bridges broken ends of bone.
elicate balance exists between the actions of osteoclasts and osteoblasts.
too much tissue= bone bcms thick/heavy -too much mineral deposited= spurs= thick bumps that interfere w/ joint movement -loss of calcium/tissue= weak bones/breaking(oseoporosis)/flexible, as in rickets or osteomalacia
periosteum
tough connect. tissue sheath & blood supply surround bone surface where no articular cartilage is. -composed of Outer Fibrous layer- dense irreg. connect. tissue & inner osteogenic layer- cells -some cells allow bone growth in thicknes but not length -protects bone, assists in fracture repair, helps nourish bone tissue, & serves as an attachment point for ligaments & tendons.
spongy bone
trabecular or cancellous bone tissue; no osteons -located in interior of bone, protected by compact bone. - lamellae arranged in irregular pattern of thin columns called trabeculae btwn them are visible spaces filled w/ red bone marrow in bones that produce blood cells, & YB marrow (adipose tissue) in other bones. Both bone marrow have small blood vessels that provide nourishment to osteocytes. Each trabecula consists of concentric lamellae, osteocytes that lie in lacunae, & canaliculi that radiate outward from the lacunae.