Chapter 6 skeletorrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
Skeletal system and bone tissue
Terms in this set (186)
Bone tissue is continuously growing, remodeling and repairing itself. Why
It contributes to homeostasis of the body by providing
1) support and protection
2) producing blood cells
3) storing minerals and triglycerides
Bone is composed of several different tissues working together:
Bone or osseous tissue
Dense connective tissue
Each bone in your body is considered?
The construction of new bone tissue and and breaking down of old bone tissue
The entire framework of bones and their cartilages, along with ligaments and tendons, constitute the
The study of bone structure and the treatment of bone disorders
6 functions of the bone and skeleton system
Assistance in movement
Mineral homeostasis (storage and release)
Blood cell production
Skeleton serves as the structure framework for the body by supporting soft tissue and providing attachment points for tendons of most skeletal muscles
Skeleton protects the most vital organs from injury.
Cranial bones protect the brain
Vertebrae protect the spinal cord
Rib cage protects the heart and lungs
Assistance in movement
Most skeletal muscles attach to bones;
When they contract, they pull on on bones to produce movement
Mineral homeostasis (storage and release)
Bone tissue stores several minerals especially calcium and phosphorus, which contribute to the strength of the bone
Bone tissue stores about 99% of the body's calcium
On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.
Blood cell production
Within certain bones, a connective tissue called "red bone marrow" produces red blood cells, white blood cells and platelets which the process is called "hemopoiesis".
Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve
Bone tissue makes up about
18% of the weight of the human body
Red bone marrow (1)
Consists of developing
Macrophages within a network of reticular fibers
Red bone marrow (2)
It is present in developing bones of the fetus and in some adult bones such as
Hip (pelvic) bones
Ends of the humerus (arm bone)
Femur (thigh bone)
Bone marrow in infants
In a newborn, all bone marrow is red and is involved in hemopoiesis.
With increasing age, much of the bone marrow changes from red to yellow
Long bone consists of
Bones shaft or body
The long, cylindrical, main portion of the bone
Growing over; singular is (epiphysis)
Are the proximal and distal ends of the bone
Are the regions between the diaphysis and the Epiphyses
In a growing bone, each Metaphysis contains an (epiphyseal) growth plate, a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length
Bone ceases to grow
At about age 18-21, the cartilage in the epiphyseal plate is replaced by bone, the resulting bony structure is known as epiphyseal line
A thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone.
Articular cartilage reduces friction and absorbs shock at freely moveable joints.
Because articular cartilage lacks a perichondrium and lacks blood vessels, repair of damage is limited
Is a tough connective tissue sheath and it's associated blood supply that surrounds the bone surface wherever it is not covered by Articular cartilage.
Some of the cells enable bone to grow in thickness but not in length
The periosteum also protects the bone, assists in fx repair, helps nourish bone tissue and serves as an attachment point for ligaments and tendons
Medullary cavity (marrow)
Is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults. This cavity minimizes the weight of the bone by reducing the dense bony material where it is least needed.
The long bones tubular design provides maximum strength with minimum weight
Perforating (Sharpey's) fibers
The periosteum is attached to the underlying bone by perforating (Sharpey's) fibers
Which r thick bundles of collagen that extend from the periosteum into the bone extra cellular matrix
Red or yellow bone marrow?
The 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)
Long bone is covered
By articular cartilage at the articular surfaces of its proximal and distal epiphyses and by periosteum around all other parts of the bone
A thin membrane that lines the medullary cavity. It contains a single layer of bone-forming cells and a small amt of connective tissue.
Bone or osseous tissue
Contains an abundant extra cellular matrix that surrounds widely separated cells
The extra cellular matrix is about
30% collagen fibers
55% crystallized salts
Most abundant mineral salt is
It combines with another mineral salt, calcium hydroxide, to form crystals of HYDROXYAPATITE
As these mineral salts are deposited in the framework formed by the collagen fibers of the extra cellular matrix, the crystallize and tissue hardens. The process is CALCIFICATION
Initially thought calcification occurred when enough mineral salts were present to form crystals
We now know that the process requires the presence of collagen fibers
Bones hardness and flexibility
Hardness depends on the crystallized inorganic mineral salts
Flexibility depends on its collagen fibers
Like reinforcing metal rods in concrete, collagen fibers and other organic molecules provide tensile strength, resistance to being stretched or torn apart
4 types of cells present in bone tissue
Osteogenic cells - Osteoprogenitor cells
Osteogenic cells or osteoprogenitor cells
-found in intter layer of periosteum and endosteum
Buds or sprouts
Are bone building cells
-form matrix and collagen fibers
the ending -blast means that cell secretes extra cellular matrix
mature bone cells that no longer secrete matrix
The ending -cyte means that the cell maintains the tissue
degradation of matrix
The breakdown of bone extra cellular matrix is called - resorption is part of the normal development, maintenance, and repair of bone
-clasts means that the cell breaks down extra cellular matrix
They help regulate blood calcium level
% of compact bone vs spongy bone in the body
80% of the skeleton is compact bone
20% is spongy
Compact bone tissue
Contains few spaces and is the strongest form of bone tissue
Found beneath the periosteum of all bones and makes up the bulk of the diaphysis of long bones
Provides protection and support and resists the stresses produced by weight and movement
Osteons or haversian systems
Compact bone tissue is composed of repeating structural units called Osteons or haversian systems
Central (haversian) canal
Each Osteons consists of concentric lamellar arranged around a central canal
Resembles growth rings of a tree
They are circular plates of mineralized extra cellular matrix of increasing diameter, surrounding a small network of blood vessels, lymphatics and nerves located in the central canal.
Lacunae (little lakes- singular lacuna)
Between the concentric lamellae are small spaces called lacunae which contain osteocytes
Radiates in all directions from the lacunae r tiny Canaliculi which r filled with extracellular fluid.
Inside the Canaliculi are slender finger like processes of osteocytes.
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.
Osteons in compact bone tissue
Are aligned in the same direction and are parallel to the length of the diaphysis
Organization of Osteons
Is not static but changes over time in response to the physical demands placed on the skeleton.
Areas between neighboring Osteons contain lamellae called interstitial lamellae which also have lacunae w/ osteocytes and Canaliculi.
They r fragments of older Osteons that have been partially destroyed during bone rebuilding or growth.
Perforating canals or VOLKMANN'S canals
Blood vessels, lymphatic vessels, and nerves from the periosteum penetrate the compact bone thru transverse perforating canals.
The vessels and nerves of the perforating canals connect w/ those of the medullary cavity, periosteum and central canals.
Are lamellae that r arranged around the entire outer and inner circumference of the shaft of the long bone. They develop during initial bone formation
Outer circumferential lamellae
They r directly deep to the periosteum. They r connect to the periosteum by perforating (sharpeys) fibers.
Inner circumferential lamellae
Those that line the medullary cavity
Spongy bone tissue
Trabecular or cancellous bone tissue
Does not contain Osteons
Is always located in the interior of a bone, protected by a covering of compact bone.
Trabecular (little beams)
Spongy bone tissue that consists of lamellae that r arranged in an irregular pattern of thin columns called trabecular
Between the trabecular r spaces that r visible to the unaided eye. They r filled w/ red bone marrow in bones that produce blood cells and yellow bone marrow (adipose tissue) in other bones
Each trabecular consists of
Concentric lamellae, osteocytes that lie in lacunae and Canaliculi that radiate outward from the lacunae
Spongy bone tissue makes up most of the interior bone tissue of
Short, flat, sesamois and irregular shaped bones.
In long bones it forms the core of the epiphysis beneath the paper thin layer of compact bone and forms a variable narrow rim bordering the medullary cavity of the diaphysis.
Spongy bone differs from compact bone in 2 ways.
Spongy bone tissue is light, which reduces the overall weight of a bone
The trabecular of spongy bone tissue support and protect the red bone marrow.
Spongy bone tissue is located
Hip bones, ribs, sternum,vertebrae, and proximal ends of the humerus and femur is the only site where red bone marrow is stored and the site where hemopoiesis (blood cell production) occurs in adults
Dx procedure that takes advantage that bone is living tissue. A small amt of radioactive tracer compound that is readily absorbed is injected. The degree of uptake is related to the amt of blood flow to the bone.
Normal bone is gray. Darker or lighter may indicate bone abnormalities Hot and cold spots. Bone scan is standard test for bone density screening mostly for osteoporosis in females
Small arteries accompanied by nerves, enter the diaphysis thru many perforating (VOLKMANN'S) canals and supply the periosteum and outer part of the compact bone
Nutrient artery and nutrient foramen
Near the center of the diaphysis a large nutrient artery passes thru a hole in compact bone called he nutrient foremen
Enter the Metaphyses of a long bone and together with the nutrient artery supply the red bone marrow and bone tissue of the Metaphyses
Enter the epiphyses of a long bone and supply the red bone marrow and bone tissue of the epiphyses
Veins that carry blood away from long bones are evident in 3 places
1 or 2 nutrient veins
Numerous epiphyseal veins and Metaphyseal veins
Many small periosteal veins
1) nutrient veins accompany the nutrient artery and exit thru the diaphysis
2) epiphyseal veins and Metaphyseal veins accompany their respective arteries and exit thru the epiphyses
3) periosteal veins accompany their respective arteries and exit thru the periosteum
Bone marrow needle biopsy
Needle passes thru the periosteum and is painful.
Used to determine if u have leukemias, me static neoplasms, lymphoma, hodgkins disease and aplastic anemia.
Ossification or osteogenesis
The process by which bone forms
Bone formation occurs in 4 principle situations
1) initial formation of bones in an embryo or fetus.
2) growth of bones during infancy, childhood, & adolescence until their adult sizes r reached.
3) the remodeling of bone (the replacement of old bone by new bone tissue thru out life)
4) The repair of fractures thru out life
bone formation in embryo and fetus
Involve the replacement of preexisting connective tissue w/ bone
2 patterns of bone ossification
1) intramembranous ossification - the formation of bone directly on or within fibrous connective tissue membranes. - the flat bones of the skull and mandible are formed this way. this is the simpler of the 2
2) endochondral ossification - forms within hyaline cartridge that develops from mesenchyme.
4 phases of Intramembranous ossification
development of the ossification center
Formation of trabeculae
development of the periosteum
Osteoblasts secrete organic extra cellular matrix to form site
Calcium and other mineral salts are deposited & extra cellular matrix hardens or calcified.
Formation of trabeculae
Exttracellular matrix develops into trabeculae that fuse with one another to form spongy bone
Development of the periosteum
Mesenchyme at the periphery of the bone developers into the periosteum
The replacement of cartridge by bone
Most bones in the body are formed in this way, but the process is best observed in the long bone.
6 phases of Endochondral ossificion
Development of the cartridge model
Growth of the cartridge model
Development of the primary ossification center
Develop of the medullary (marrow) cavity
Develop of the secondary ossification centers
Formation of Articular cartilage & epiphyseal (growth) plate
Development of the cartilage model
Mesenchymal cells develop into chondroblasts, which form the cartridge model
Growth of the cartilage model
Growth occurs by cell division of chondrocytes
Development of primary ossification center
In this region of the diaphysis, bone tissue replaces most of the cartilage,
Development of the medullary (marrow) cavity
Bone breakdown by osteoclasts forms the medullary cavity
Development of secondary ossification centers
-blood vessels enter the epiphyses around the time of birth.
-spongy bone is formed but no medullary cavity.
Formation of Articular cartilage and epiphyseal plate (growth plate)
-cartilage on ends of bone remains as articular cartilage (hyaline cartilage)
a covering called the perichondrium develops around the cartilage model.
interstitial (endogenous) growth
growth from within, results in an increase in length
appositional (exogenous) growth
growth of the cartilage in thickness - growth at the outer surface
Once the perichondrium starts to form bone, it is known as the periosteum
The growth in length of long bones involves the following two major events
1) interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate
2) replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification.
epiphyseal (growth) plate
is a layer of hyaline cartilage in the metaphysis of a growing bone that consists of four zones.
4 zones of epiphyseal (growth) plate
1) zone of resting cartilage
2) zone of proliferating cartilage
3) zone of hypertrophic cartilage
4) zone of calcified cartilage
zone of resting cartilage
The layer is nearest the ipiphysis and consists of small, scattered chondrocytes.
The term resting is used because the cells do not function in bone growth. Rather they anchor the epiphyseal plate to the epiphysis of the bone
zone of proliferating cartilage
Slightly larger chondrocytes in this zone are arranged like stacks of coins. These chondrocytes undergo interstitial growth as they divide and secrete extracellular matrix.
The chondrocytes in this zone divide to replace those that die at the diaphyseal side of the epiphyseal plate.
zone of hypertrophic cartilage
This layer consists of lart, maturing chondrocytes arranged in columns.
zone of calcified cartilage
The final zone of the epiphyseal plate is only a few cells thick and consists mostly of chondrocytes that are dead because the extracelllular matrix around them has calcified.
This zone becomes the "new diaphysis" that is firmly cemented to the rest of the diaphysis of the bone.
epiphyseal (growth) plate
allows the diaphysis of a bone to increase in length.
Epiphyseal plate closes
When adolescence comes to an end (female/18 and males/21). The epiphyseal cartilage cells stop dividing and bone replaces all remaining cartilage.
The epiphyseal plate fades, leaving a bony structure called epiphyseal line.
With the appearance of the epiphyseal line, bone growth in length stops completely.
Open epiphyseal plates vs closed
open plate indicates a younger person
partially closed or completely closed indicates older person
closure of the epiphyseal plate on avg takes place 1-2 yrs earlier in females.
is the ongoing replacement of old bone tissue by new bone tissue
can be triggered by factors such as exercise, sedentary lifestyle and changes in diet
the removal of minerals and collagen fibers from bone by by osteoclasts. acid dissolve the bone minerals
the addition of minerals and collagen fibers to bone by osteoblasts
strength of a bone
is related to the degree to which it is stressed
the branch of dentistry concerned w/ the prevention and 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 and osteoblasts remodel the sockets so that the teeth align properly.
there is an excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition. In response, osteoblasts attempt to compensate, but the new bone is weaker because it has a higher proportion of spongy to compact bone, mineralization is decreased and the newly synthesized extracellular matrix contains abnormal protiens. --the newly formed bone, especially that of the pelvis, limbs, lower bert and skull becomes enlarged, hard and brittle and fractures easily.
factors affecting bone growth and bone remodeling
adequate dietary intake of minerals and vitamins as well as sufficient levels of several hormones
causes a dramatic effect on bone growth. Females have a higher level of estrogens and males have higher levels of androgens. They are responsible for increased osteoblast activity.
Estrogen in both sexes shut growth at epiphyseal (growth) plates, causing elongation of the bones to cease. Lengthwise growth of bones typically ends earlier in females than in males due to their higher levels of estrogens.
Hormonal Abnormalities that affect height
Over secretion of hGH during childhood causes giantism, in which a person becomes much taller and heavier than normal.
Undersecretion of hGH produces pituitary dwarfism in which a person has short stature (usually under 4'10")
The condition can be treated medically with hGH until epiphyseal plate closure
Oversecretion of hGH during adulthood is called acromegaly. Although hGH cannot produce further lengthening of the long bones because the growth plates are already closed, the bones of the hands, feet and jaws thicken and other tissues enlarge.
The eyelids, lips, tongue and nose enlarge and the skin thickens and develops furrows, especially on the forehead and soles.
is an inherited condition in which the conversion of cartilage to bone is abnormal. It results in the most common type of dwarfism, called achondroplastic dwarfism
these individuals are typically about 4' tall as adults. They have an avg size trunk, short limbs, and a slightly enlarged head w/ a prominent forehead adn flattened nose at the bridge. The condition is essentially untreatable, although some individuals opt for limb lengthening surgery
any break in a bone - healing is faster in bone than in cartilage due to lack of blood vessels in cartilage.
healing of bone is still slow process due to vessel damage
Type of fractures
Open (compound) fx and closed (simple) fx
The broken ends of the bone protrude thru the skin. Conversely, a closed (simple) fx does not break the skin
broken ends of the bones are fragmented
Partial fx in which one side of the bone is broken and the other side bends
Occurs only in children whose bones are not fully ossified
One end of the fractured bone is forcefully driven into the interior of the other
Fx of the distal end of the lateral leg bone (fibula)
distal fibular fx
Fracture of the distal end of the lateral forearm bone (radius)
distal radial fx
bone may fx without visibly breaking
a series of microscopic fissures that result from repeated strenuous activities such as running, jumping or aerobic dancing. - quite painful - shin splints
What % of stress fractures involve the tibia
Treatment for fractures
vary according to age, type of fracture and the bone involved
Reduction - setting a fx
closed reduction - fractured ends of a bone are brought into alighment by manual manipulation and the skin remains intact (restore pieces to nrmal position by manipulation)
open reduction - fracture eds of a bone are brought into alighment by a surgical procedure using internal fixation devices such as screws, plates, pins, rods and wires. (surgery)
The repair of a bone fracture involves the following steps
1) formation of fracture hematoma
2) fibrocartilaginous callus formation
3) bony callus formation
4) bone remodeling
Formation of fracture hematoma
-damaged blood vessels produce clot in 6-8 hours, bone cells die
-inflammation brings in phagocytic cells for clean-up duty
-new capillaries grow into damaged area
-this stage may last up to several weeks
fibrocartilaginous callus formation
-Fibroblasts invade the procallus & lay down collagen fibers
-chondroblasts produce fibrocartilage (strongest cartilage) to span the broken ends of the bone.
-Takes about 3 wks
Bony callus formation
-osteoblasts secrete spongy bone that joins 2 broken ends of bone
-the bony callus lasts about 3-4 months
-compact bone replaces the spongy in the bony callus
-surface is remodeled back to normal shape
Bone heals more rapidly than cartilage
because its blood supply is more plentiful
bone is the body's major calcium reservior
storing 99% of total body calcium
the active form of Vitamin D, a hormone that promotes absorption of calcium from foods in the gastrointestinal tract into the blood. helps elevate blood Ca+2 level
CT inhibits activity of osteoclasts, speeds blood Ca+2 uptate by bone, and accelerates Ca+2 depositions into bones
parathyroid hormone (PTH)
Ca+2 exchange is regulated by hormones, the most impt is PTH which is secreted by the parathyroid glands. This hormone increases blood Ca+2 level.
2 main ways that blood calcium level can be increased
1) release of calcium from bone matrix
2) retention of calcium by the kidneys
2 principal effects of aging on bone tissue
1) loss of bone mass
Loss of bone mass results in demineralization, the loss of calcium and other minerals from bone extracellular matrix.
This loss usually begins after age 30 in females, accelerates greatly around age 45 as levels of estrogens decrease and continues until as much as 30% of the calcium in bones is lost by age 70. Once bone loss begins in females, about 8% of bone mass is lost every 10 yrs.
Males - 60 rs and about 3% of bone mass lost every 10 yrs
results from a decreased rate of protein synthesis.
collagen fibers slow which give bone tinsel strength.
literally a condition of porous bones, affects 10 million people a years in the US.
The bone resorption (breakdown) outpaces bone deposition (formation). In large part, this is due to depletion of calcium from the body
Woman suffer from Osteoporosis more than men for 2 reasons
1) Womans bones are less massive than men's bones
2) production of estrogens in women decilines dramatically at menopause, while production of the main androgen, testosterone, in older men wanes gradually and only slightly.
medications used to treat osteoporosis are generally of 2 types
1) antireabsorptive drugs - slow down the progression of bone loss
2) bone-building drugs - promote increasing bone mass
2 forms of disease that result from inadequate calcification of the extracellular bone matrix, usually caused by a vit D deficiency
-calcium salts are not deposited properly
-bones of growing children are soft
-bowed legs, skull, rib cage, and pelvic deformities result
-rickets more kids WWII - Dec 9, 1941 stimulus that led us to k now we had mal-nutrician people running around as people were enlisting and getting physicals
-rickets today - due to obesity (bow legs)
is the adult counterpart of reckets, sometimes called "adult rickets".
-New adult bone produced during remodeling fails to ossify
-hip fx are common
Prevention and treatment of Rickets and osteomalacia
consists of the administration of adequate vitamine D and exposure to moderate amounts of sunlight
the degeneration of articular cartilage such that the bony ends touch; the resulting friction of bone against bone worsens the condition. Usually associated w/ the elderly
An infectino 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 caued by bacteria, usually Staphylococcus aureaus.
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
Bone cancer that primarily affects osteoblasts and occurs most often in teenagers during their growth spurt; the most common sites are the metaphyses of the thigh bone (femur), shin bone (tibia), and arm bone (humerus).
Metastases occur most ofter in lungs; treatment consists of multidrug chemo and removal of the malignant grown or amputation of the limb.
The skeletal system
typical of other connective tissues in that it consists of cells, fibers and matrix
the matrix is much more abundant than the osteocytes and has a dense population of collagen fibers
has a tensile strength nearly equal to cast iron but is less than one third the weight
contains abumdant inorganic mineral salts, primarily calcium phosphate (hydroxyapatite) and some calcium carbonate
also includes small amts of magnesium hydroxide, fluoride and sulfate
Calcification or mineralization
As these mineral salts are deposited in the framwiork of collagen fibers, they crystallized and the tissue hardens which is called calcification or mineralization and is initiated by osteoblasts.
Types of bone issue; Compact bone
osteon - concentric rings of calcified matrix surrounding a vertically oriented blood vessel
-osteocyets - found in lacunae
Types of osseous tissue; Compact bone
- solid hard layer of bone
-long bones and the external layer of all bones
-resists stresses producted by weight and movement
Type of osseous tissue: Cancelleous
-consists of lamellae that are arranged in an irregular thin plates called trabeculae.
-the spaces between the trabeculae of some bones are filled w/ red bone marrow, which produces blood cells
-makes up most of the bone tissue of short, flat, and irregular shaped bones, most of the epiphysis of long bones and a narrow rim around the medullary cavity of the diaphysis of long bones.
-spongy bone in the coxa, ribs, sternum, vertebrae, & the ephiphyises of long bones is the only site of hemopoiesis in adults.
types of bones
-carpal bones, tarsal bones except calcaneous
-cranial bones, sternum, scapulae, and ribs
-develop in certain tendons where there is considerable friction, tension and physical stress, such as the palms and soles.
-typically measure only a few mm in dia and are not always ossified
-may vary in number from person to person
-exceptions are the patellae
2 types of bones
-small bones locationed within joints (sutures) between cranial bones
-number vaires greatly from person to person
-consist of a shaft (diaphysis) & ends (epiphyses)
-they are usually curved for added strength
-consist primarily of compact bone in their diaphysis & considerable spongy bone in their epiphyses.
anatomy of a long bone
blood and nerve supply of bone
-blood vessels and nerves pass into bones thru the periosteum
-periosteum is rich in sensory nerves
bone growth: Growth in length
-during childhood long bones lengthen by the addition of bone material on the diaphyseal side of the epiphyseal plate
-the epiphyseal plate is a layer of hyaline cartilage in the metaphysis of a growing bone
-the activity of the epiphyseal plate is the only way that the diaphysis can increase in length
-as a bone grows, chondrocytes proliferate on the epiphyseal side of the plate
when stop growing
growth plate seals (epiphyseal)
bone growth (cont); Growth in length
-new chondrocytes cover older ones, which are then destroyed by the process of calcification
-the cartilage is replaced by bone on the diaphyseal side of the plate
-the thickness of the epiphyseal plate remains relatively constant but the bone on the diaphyseal side increases in length
-between the ages of 18-25, the epiphyseal plates closes (female 14-21)
-the epiphyseal cartilage cells stop divising and bone replaces the cartilage
Bone Growth (cont) - Growth in length
-the epiphyseal plate fades, leaving a boney feature called the epiphyseal line
-the appearance of the epiphyseal line signifies that the bone has stopped growing in length
-the clavicle is the last bone to stop growing in length
-if a bone fx damages the epiphyseal plate, the fx bone may be shorter than normal (this is because damage to cartilage accelerates closure of the epiphyseal plate and growth in length is inhibited.
factors affectiving bone growth
---calcium and phosphorus
---vitamins K and B12
-Sufficient levels of hormones
---insulinlike growth factor
---hGH - human growth factor
---T3 and T4
Lack estrogen causes
both men or women that lack estrogen receptors on cells grower taller than normal
-estrogen responsible for closure of growth plate
-even after bones have reached their adult shapes and sizes they continue to be renewed.
-bone remodeling is an ongoing process whereby osteoclasts carve out small tunnels in old bone tissue and then osteoblasts rebuild it
-a full cycle of bone remodeling may take as little as 2-3 months or much longer, depending on where it is occurring
bone remodeling serves 3 purposes
1) it renews bone tissue before deteriortion
2) it redistributes bone matrix along lines of mechanical stress.
3) is the way that injured bone heals
To achieve homeostasis
the bnoe-resorbing actions of osteoclasts must balance the bone-making action of osteoblasts
-most abundant mineral in the body
-big part of homeostasis
-99% in bones/teeth
-1% in ECF and ICF
Functons of calcium in body fluids
-binds w/ proteins that participate in transmission of nerve impulses and muscle cell contractions
-promotes blood clotting
-aids in mainting bp
-activation of some enzymes
calcium homeostasis and bone tissue
-skeleton is reservoir of calcium and phosphate
-Ca++ are essential for:
-nerve & muscle cell function
-enzyme function in many biochemical reactions
-Small changes in blood levesl of Ca++ can be deadly (plasma level maintained 9-11mg/100ml (glucose 70-110mg/ld) - this is handled by neg feedback system
- cardiac arrest if too high
- respriatory arrest if too low
factors that affect calcium absorption
-lactose in children
Endocrine system control
-Parathyroid hormone (PTH) is secreted if plasma Ca++ levels drop below normal:
-osteoclast activity incrased
-kidneys retain Ca++
-Calcitonin is secreted from parafollicular cells in thyroid if Ca++ plasma levels get too high
-increases osteoblastic activity
-decreases osteoclastic activity (osteoclasts produces acids to break down the salts)
Ca++ imbalances: HYPERCALCEMIA
- increased risk of urinary stone formation and kidney dysfunction
-stunted growth in children
- bone loss (osteoporosis) in adults
-decreased bone mass resulting in porous bones
-those at risk
- white, thin, post menopausal, smoking, drinking, female with family hx
- athletes who are not menstruating due to decreased body fat & decreased estrogen levels
- people allergic to milk or with eating disorders whose intake of calcium is too low
**Prevention or derease in severity
- adequate diet, weight-bearing exercise & estrogen replacement therapy (for menopausal women)
- behavior when young may be most impt factor
Osteoporosis and calcium
age 30 bone mass good - menopause - age 60
Woman who entered adulthood w/ enough calcium in her bones to last a lifetime and if you have less bone mass starting out; may not have enough to last.
consequences of osteoporosis
-approx 300,000 hospitalized/year due to hip fx
-approx 25% of these die w/in the first year post-opt
-approx 25% of these survivors will never walk again unaided
(break unsually occurs prior to fall) break causes fall not fall causes break.
Exercise & Bone Tissue
-pull on bone by skeletal muscle & gravity is mechanical stress
-stress increases deposition of mineral salts & production of collagen (calcitonin prevents bone loss)
-lack of mechanical stress results in bone loss
-reducted activity while in a cast
-astronauts in weightlessness
-weight-bearing exercises build bone mass (walking or weight-lifting)
Aging and Bone Tissue
-Bone is being built thru adolescence, holds its own in young adults, but is gradually olost in aged
-Demineralization = loss of minerals
- very rapid in women 40-45 as estrogens levels decrease
-in males, begins after age 60
-Decrease in protein synthesis
-decrease in growth hormone
-decrease in collagen production which gives bone its tensile strength
-bone becomes brittle & susceptible to fx