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More Ch. 6 6.5 – 6.10. Bone Growth, Composition and Conditions . Ossification . Skeleton begins to form in embryo at 6 week During all future development bone undergoes increases in size and ossification Ossification = bone formation Calcification = deposition of calcium

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More ch 6 6 5 6 10

More Ch. 66.5 – 6.10

Bone Growth, Composition

and Conditions


Ossification

Ossification

  • Skeleton begins to form in embryo at 6 week

  • During all future development bone undergoes increases in size and ossification

    • Ossification = bone formation

    • Calcification = deposition of calcium

    • Endochondral ossification = bone replaces cartilage that was already presesnt

    • Intramembranous ossification = bone develops directly from connective tissue

  • Bone growth continues through adolescence, and on average until about age 25

  • Toes “done” by age 11; pelvis and wrists may still be growing at 25. Lots of growth happens in relation to puberty hormones


Endochondryal ossification

Endochondryal Ossification

  • Chondros = cartilage

  • Endo = inside

  • Most bones start as hyaline cartilage and are “models of adult bone” size and shape

  • Cartilage gradually replaced by bone

  • Time line:

    • 6 weeks proximal end of limb bone present but as hyaline cartilage

    • New cartilage on outer surface

    • Cells at center enlarge, blood vessels grow

    • Primary ossification starts and spread toward ends

    • Increases in length and in diameter

    • Centers of epiphyses calcify and become spongy bone

    • Cap of cartilage remains at articulation

    • Region of cartilage between epiphysis and diaphysis = lengthening bone


Figure 6 10 endochondral ossification step 1 7

Figure 6-10 Endochondral Ossification (Step 1-7)

As the cartilage

enlarges,

chondrocytes near

the center of the

shaft increase

greatly in size. The

matrix is reduced to

a series of small

struts that soon

begin to calcify. The

enlarged

chondrocytes then

die and disintegrate,

leaving cavities

within the cartilage.

Blood vessels grow

around the edges of

the cartilage, and

the cells of the

perichondrium

convert to

osteoblasts. The

shaft of the

cartilage then

becomes

ensheathed in a

superficial layer of

bone.

Blood vessels

penetrate the cartilage

and invade the central

region. Fibroblasts

migrating with the

blood vessels

differentiate into

osteoblasts and begin

producing spongy

bone at a primary

ossification center.

Bone formation then

spreads along the

shaft toward both

ends.

Remodeling occurs

as growth continues,

creating a medullary

cavity. The osseous

tissue of the shaft

becomes thicker,

and the cartilage

near each epiphysis

is replaced by shafts

of bone. Further

growth involves

increases in length

and diameter.

Enlarging

chondrocytes within

calcifying matrix

Epiphysis

Medullary

cavity

Medullary

cavity

Blood

vessel

Primary

ossification

center

Superficial

bone

Diaphysis

Spongy

bone

Metaphysis

Bone

formation

Hyaline cartilage

Capillaries and

osteoblasts migrate

into the epiphyses,

creating secondary

ossification centers.

Soon the epiphyses are

filled with spongy bone.

An articular cartilage

remains exposed to the

joint cavity; over time it

will be reduced to a thin

superficial layer. At each

metaphysis, an epiphyseal

cartilage separates the

epiphysis from the

diaphysis.

This light micrograph shows the ossifying

surface of an epiphyseal cartilage. The pink

material is osteoid, deposited by osteoblasts in

the medullary cavity. On the shaft side of the

epiphyseal cartilage, osteoblasts are

continuously invading the cartilage and replacing

it with bone. On the epiphyseal side, new cartilage

is continuously being added. The osteoblasts are

therefore moving toward the epiphysis, which is

being pushed away by the expansion of the

epiphyseal cartilage. The osteoblasts won’t catch

up to the epiphysis, as long as both the

osteoblasts and the epiphysis “run away” from

the primary ossification center at the same rate.

Meanwhile, the bone grows longer and longer.

Hyaline cartilage

Epiphysis

Articular cartilage

Cartilage cells undergoing

division and secreting

additional cartilage matrix

Metaphysis

Epiphyseal

cartilage matrix

Spongy

bone

Periosteum

Compact

bone

Epiphyseal

cartilage

Diaphysis

LM  250

Secondary

ossification

center

Medullary cavity

Osteoblasts

Osteoid


Figure 6 10 endochondral ossification step 1 4

Figure 6-10 Endochondral Ossification (Step 1-4)

As the cartilage

enlarges,

chondrocytes near

the center of the

shaft increase

greatly in size. The

matrix is reduced to

a series of small

struts that soon

begin to calcify. The

enlarged

chondrocytes then

die and disintegrate,

leaving cavities

within the cartilage.

Blood vessels grow

around the edges of

the cartilage, and

the cells of the

perichondrium

convert to

osteoblasts. The

shaft of the

cartilage then

becomes

ensheathed in a

superficial layer of

bone.

Blood vessels

penetrate the cartilage

and invade the central

region. Fibroblasts

migrating with the

blood vessels

differentiate into

osteoblasts and begin

producing spongy

bone at a primary

ossification center.

Bone formation then

spreads along the

shaft toward both

ends.

Remodeling occurs

as growth continues,

creating a medullary

cavity. The osseous

tissue of the shaft

becomes thicker,

and the cartilage

near each epiphysis

is replaced by shafts

of bone. Further

growth involves

increases in length

and diameter.

Enlarging

chondrocytes within

calcifying matrix

Epiphysis

Medullary

cavity

Medullary

cavity

Blood

vessel

Primary

ossification

center

Superficial

bone

Diaphysis

Spongy

bone

Metaphysis

Bone

formation

Hyaline cartilage


Figure 6 10 endochondral ossification steps 5 7

Figure 6-10 Endochondral Ossification (Steps 5-7)

This light micrograph shows the ossifying

surface of an epiphyseal cartilage. The pink

material is osteoid, deposited by osteoblasts in

the medullary cavity. On the shaft side of the

epiphyseal cartilage, osteoblasts are

continuously invading the cartilage and replacing

it with bone. On the epiphyseal side, new cartilage

is continuously being added. The osteoblasts are

therefore moving toward the epiphysis, which is

being pushed away by the expansion of the

epiphyseal cartilage. The osteoblasts won’t catch

up to the epiphysis, as long as both the

osteoblasts and the epiphysis “run away” from

the primary ossification center at the same rate.

Meanwhile, the bone grows longer and longer.

Capillaries and

osteoblasts migrate

into the epiphyses,

creating secondary

ossification centers.

Soon the epiphyses are

filled with spongy bone.

An articular cartilage

remains exposed to the

joint cavity; over time it

will be reduced to a thin

superficial layer. At each

metaphysis, an epiphyseal

cartilage separates the

epiphysis from the

diaphysis.

Hyaline cartilage

Epiphysis

Articular cartilage

Metaphysis

Cartilage cells undergoing

division and secreting

additional cartilage matrix

Epiphyseal

cartilage matrix

Spongy

bone

Periosteum

Compact

bone

Epiphyseal

cartilage

Diaphysis

LM  250

Secondary

ossification

center

Osteoid

Osteoblasts

Medullary cavity


More ch 6 6 5 6 10

APPOSITIONAL GROWTH =

Superficial layers of bone forms early in endochondral ossification

New growth in the bones diameter results in layers –

New lamella added in concentric rings around outside while inner layers are recycled

An x-ray of growing epiphyseal

cartilages (arrows)

Epiphyseal lines in an

adult (arrows)


Intramembranous ossification

Intramembranous Ossification

  • Osteoblasts differentiate

    • Fibrous connective tissue ( mesenchymal cells)

    • Matrix is created

    • Crystallization of calcium salts

    • Very active process requiring lots of nutrients

    • Osteoblasts ossification  spicules form

    • Initially only spongy bone

    • Remodeling can lead to compact bone

  • Creates dermal bones

    • Flat bones of skull, mandible (lower jaw), and clavicle (collar bone)


Blood and nerve supply to bones

Blood and nerve supply to bones

  • Bone maintenance and grow require blood supply

  • Osseous tissue is highly vascular

    • Nutrient artery and vein: supply diaphysis, usually only one of each ( femur has more)

    • Enter through foramina – branch into smaller canals

    • Metaphyseal vessels – supply blood to cartilage that is or will be replaced by bone

    • Periosteal vessels – blood to periosteum and superficial osteons – branch during ossification

    • All are very interconnected

  • Lymph – connect blood and lymph through osteons

  • Nerves – travel along nutrient artery ( injuries to bones are very painful)


Remodeling

Remodeling

  • Bone matrix constantly being recycled and renewed

  • Used for both maintenance and changes to bone shape and structure

  • Youth – recycle about 1/5 of calcium salts per year; more likely in areas of spongy bone

  • Heavy metals are dangerous because they can be incorporated into bone – stay in circulatory system for many years. (Chernobyl Nuclear reactor leak; 1986 Ukraine, only other level 7 leak is Fukushuma Daiichi in 2011)


Impact of exercise on bones

Impact of Exercise on bones

  • “stresses” on mineral crystals cause bone growth

  • Increases in muscle mass increase both weight and tension on bones = growth

  • Ridges and bumps on bone relate to pull of tendons, diameter of bone relates to mass –

  • non-athletes have more fragile bones (osteoporosis and arthritis)

  • A broken leg with no stress, can lose 1/3 mass while using crutches

  • ? Bedridden and paralyzed


Impact of hormones on bones

Impact of Hormones on bones

  • Calcitrol:

    • made by kidneys

    • increases absorption of Ca and PO4 in digestive tract

  • Growth hormone

    • Made by pituitary

    • Stimulates osteoblast and synthesis of matrix

  • Thyroxine

    • Thyroid

    • Also stimulates osteoblasts and synthesis of matrix

  • Estrogen/ androgens

    • Ovaries and testes

    • Stimulates osteoblasts

    • Estrogen closes epiphysis earlier than androgens

  • Parathyroid hormone

    • Parathyroid glands

    • Stimulates osteoclasts and osteoblasts

    • Increases Ca level in body fluids

  • Calcitonin

    • Thyroid gland

    • Inhibits osteoclasts

    • Reduces Ca in body fluids

    • Triggers kidneys to loose calcium


Impact of nutrition on bones

Impact of Nutrition on bones

  • Dietary sources of calcium and phosphate are required for healthy bone growth and maintenance

  • Also required are: magnesium, fluoride, iron and manganese

  • Vitamin C is needed for enzymatic reaction that makes cartilage

  • Vitamin D is required for calcitrol to cause intestinal absorption of Ca and PO4

  • Vitamins A, K and B12 are also needed for normal bone growth


Nutrition and calcium

Nutrition and Calcium

  • Bones are a mineral reservoir

    • 1-2 Kg of calcium ( 2.2 – 4.4 lbs) in body

    • 99% is in the bones

  • Calcium levels are important for many functions:

    • Permeability of plasma membranes

    • Firing of nerve impulses

    • Contraction of muscle fibers

    • Widely varying ion concentrations can result in seizures or death

    • “electrolytes”


Figure 6 16a factors that alter the concentration of calcium ions in body fluids

Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids

Factors That Increase Blood Calcium Levels

These responses are

triggered when plasma

calcium ion concentrations

fall below 8.5 mg/dL.

Low Calcium Ion Levels in Plasma

(below 8.5 mg/dL)

Parathyroid Gland Response

Low calcium plasma levels cause

the parathyroid glands to secrete

parathyroid hormone (PTH).

PTH

Bone Response

Intestinal Response

Kidney Response

Kidneys retain

calcium ions

Rate of

intestinal

absorption

increases

Osteoclasts stimulated to

release stored calcium ions

from bone

more

Osteoclast

Bone

calcitriol

Calcium absorbed quickly

Calcium conserved

Calcium released

Decreased calcium

loss in urine

↑Ca2+

levels in

bloodstream


Figure 6 16b factors that alter the concentration of calcium ions in body fluids

Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids

Factors That Decrease Blood Calcium Levels

HIgh Calcium Ion Levels in Plasma

(above 11 mg/dL)

These responses are

triggered when plasma

calcium ion concentrations

rise above 11 mg/dL.

Thyroid Gland Response

Parafollicular cells (C cells) in the

thryoid gland secrete calcitonin.

Calcitonin

Intestinal Response

Bone Response

Kidney Response

Kidneys allow

calcium loss

Rate of intestinal

absorption

decreases

Osteoclasts inhibited while

osteoblasts continue to lock

calcium ions in bone matrix

less

Bone

calcitriol

Calcium excreted

Calcium absorbed slowly

Calcium stored

Increased calcium

loss in urine

↓Ca2+

levels in

bloodstream


Fractures

Fractures

  • Crack or break in bone

  • Often from stress in unusual direction

  • Need blood supply and portions of endosteum and periosteum in order to survive

  • Repair:

    • Spongy bone forms

    • External callus of cartilage stabilizes bone

    • Cartilage is replaced by bone

    • Remodeling removes dead bone or extra layers

  • Fracture types:

    • Transverse, displaced, compression, spiral, epiphyseal, communicated (shatter), greenstick


Figure 6 17 types of fractures and steps in repair

Figure 6-17 Types of Fractures and Steps in Repair

Epiphyseal fracture

Compression

fracture

Transverse fracture

Colles fracture

Greenstick fracture

Pott’s fracture

Comminuated

fracture

Spiral fracture

Displaced fracture

Epiphyseal fractures, such as this

fracture of the femur, tend to

occur where the bone matrix is

undergoing calcification and

chondrocytes are dying. A clean

transverse fracture along this line

generally heals well. Unless

carefully treated, fractures

between the epiphysis and the

epiphyseal cartilage can perman-

ently stop growth at this site.

Compression fractures

occur in vertebrae

subjected to extreme

stresses, such as

those produced by the

forces that arise when

you land on your seat

in a fall.

Transverse fractures,

such as this fracture of

the ulna, break a bone

shaft across its long

axis.

Displaced fractures

produce new and

abnormal bone

arrangements;

nondisplaced fractures

retain the normal

alignment of the bones

or fragments.

Spiral fractures,

such as this fracture

of the tibia, are

produced by twisting

stresses that spread

along the length of

the bone.

Comminuted fractures,

such as this fracture of

the femur, shatter the

affected area into a

multitude of bony

fragments.

A Colles fracture, a

break in the distal

portion of the radius,

is typically the result

of reaching out to

cushion a fall.

In a greenstick fracture,

such as this fracture of

the radius, only one side

of the shaft is broken, and

the other is bent. This

type of fracture generally

occurs in children, whose

Long bones have yet to

ossify fully.

A Pott’s fracture

occurs at the ankle

and affects both

bones of the leg.

TYPES OF

FRACTURES

Fractures are named according

to their external appearance,

their location, and the nature of

the crack or break in the bone.

Important types of fractures are

illustrated here by

representative x-rays. The

broadest general categories are

closed fractures and open

fractures. Closed, or simple,

fractures are completely

internal. They can be seen only

on x-rays, because they do not

involve a break in the skin.

Open, or compound, fractures

project through the skin. These

fractures, which are obvious on

inspection, are more dangerous

than closed fractures, due to the

possibility of infection or

uncontrolled bleeding. Many

fractures fall into more than one

category, because the terms

overlap.

REPAIR OF AFRACTURE

Fracture

hematoma

External

callus

Internal

callus

External

callus

Dead

bone

Bone

fragments

Spongy bone of

external callus

Periosteum

A swelling initially

marks the location of

the fracture. Over time, this

region will be remodeled,

and little evidence of the

fracture will remain.

An internal callus forms as a

network of spongy bone

unites the inner edges, and an

external callus of cartilage and bone

stabilizes the outer edges.

The cartilage of the external

callus has been replaced by

bone, and struts of spongy bone now

united the broken ends. Fragments of

dead bone and the areas of bone

closest to the break have been

removed and replaced.

Immediately after the

fracture, extensive

bleeding occurs. Over a

period of several hours, a

large blood clot, or fracture

hematoma, develops.


Diseases and disorders

Diseases and Disorders

  • Osteopenia = inadequate ossification

    • Aging ; begins between 30 and 40

    • Lose 3% per decade

    • Vertebrae and jaw lose mass faster - spinal issues and loss of teeth

  • Osteoporosis – enough bone is lost to compromise normal function

    • Also related to decreasing estrogen and androgens

    • More of an issue in women because of menopause

  • Cancers


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