BMS 250 - Cartilage Growth, Ossification, and Bone Growth (7.3, 7.4ab, 7.5a)

Step 5 Endochondral Ossification

*Bone replaces almost all cartilage, except articular cartilage and epiphyseal cartilage (at epiphyseal plate)* ---By late bone development, nearly all hyaline cartilage is displaced by bone. ---Hyaline cartilage only remains as articular cartilage and epiphyseal cartilage at the epiphyseal plate.

Step 2 of Endochondral Ossification

*Cartilage calcifies, and a periosteal bone collar forms.* ---Chondroblasts in the center of the cartilage model (future diaphysis) start to hypertrophy (enlarge) and resorb (eat away) some of the surrounding matrix, leaving holes. ---As chondrocytes enlarge, the cartilage matrix beings to calcify ---chondrocytes die and disintegrate leaving calcified cartilage shaft with holes ---As cartilage is calcifying, blood vessels grow toward the cartilage penetrating the perichondrium ---Stem cells in the perichondrium divide to from osteoblasts and start building ---Perichondrium becomes periosteum and osteoblasts start secreting osteoid around the calcified cartilage shaft ---Osteoid hardens and forms a periosteal bone collar around shaft

Step 4 of Intramembranous Ossification

*Lamellar bone replaces woven bone, as compact bone and spongy bone form* ---spaces between the trabeculae are filled and the bone becomes compact bone. ---Layer of compact bone replaces surface layer of spongy bone ---Spongy bone remains in center

Endochondral Ossification

Most bones in the body

5

The epiphyseal plate is composed of ___ zones.

increases

when the external circumferential lamellae increase in number, the bone ____________ in diameter.

Step 6 of Endochondral Ossification

*Lengthwise growth continues until the epiphyseal plates ossify and form epiphyseal lines.* ---When the epiphyseal plate becomes an epiphyseal line, the bone has reached its adult length ---Depending on the bone, most epiphyseal plates ossify to become epiphyseal lines between the ages of 10 and 25.

Step 1 of Intramembranous Ossification

*Ossification centers form within thickened regions of the mesenchyme beginning at the eighth week of development* ---mesenchymal cells divide to form both undifferentiated and committed stem cells ---committed stem cells become osteoprogenitors, which become osteoblasts ---osteoblasts secrete extracellular matrix of bone (osteoid)

Step 2 of Intramembranous Ossification

*Osteoid undergoes calcification.* ---Secretion of extracellular matrix stops ---Osteoblasts have surrounded themselves in their own osteoid and the matrix hardens.

Step 4 Endochondral Ossification

*Secondary ossification centers form in the epiphyses.* ---Development of medullary (marrow) cavity ---Around the time of birth, hyaline cartilage in the center of epiphyses calcifies and begins to degenerate. ---Epiphyseal blood vessels and osteoprogenitor cells enter the epiphyses. ---Secondary ossification forms in the epiphyses as bone replaces calcified cartilage ---Osteoclasts break down some newly formed bone matrix within the diaphysis creating a hollow marrow cavity

Step 1 of Endochondral Ossification

*The fetal hyaline cartilage model develops.* ---during the eighth to twelfth week of development, chondroblasts secrete cartilage matrix and a hyaline cartilage model is formed ---chondrocytes are trapped within lacunae and perichondrium surrounds the cartilage

Step 3 of Endochondral Ossification

*The primary ossification center forms in the diaphysis* ---growth of capillaries and osteoblasts extend from periosteum into the core of the cartilage shaft, invading the holes left by the chondrocytes that disintegrated. -Nutrient artery penetrates perichondrium and calcifying cartilage model through nutrient foramen -The remains of calcified cartilage serve as a template on which osteoblasts begin to produce osteoid (i.e. the primary ossification center) ---Osteoblasts deposit bone extracellular matrix over remnants of calcified cartilage spongy bone trabeculae ---Ossification now proceeds from the primary ossification center toward both epiphyses. ---Osteoblasts begin to secrete compact bone under perichondrium (bone collar) ---Perichondrium now known as periosteum

Step 3 of Intramembranous Ossification

*Woven bone (young bone) and the periosteum that surrounds it is formed.* ---New bone develops into trabeculae (open lattice of narrow rods and plates of bone) fuse to form spongy bone ---Blood vessels grow into spaces between trabeculae ---CT associated with blood vessels differentiates into red bone marrow in intertrabecular spaces

adulthood

-epiphyseal plate closes and bone replaces all of the cartilage -leaves a bony structure--epiphyseal line

Zone 3: Zone of hypertrophic cartilage

-mitosis ceases -maturing and hypertrophy occurs (enlarging of chondrocytes) -lacunae is thinning

Zone 1: Zone of resting cartilage

-nearest the epiphysis -made up of small chondrocytes in matrix -anchors epiphyseal plate to epiphysis -no direct function in bone growth

Zone 4: Zone of calcified cartilage

-new diaphysis -minerals (salts) deposit between columns of lacunae and hardens -mostly dead chondrocytes due to calcified cartilage around them

Zone 2: Zone of proliferating cartilage

-true interstitial growth happens here -chondrocytes undergo rapid mitosis -chondrocytes are stimulated to split and become chondroblasts who spread matrix then become chondrocytes over and over again -Slightly larger chondrocytes are aligned like a stack of coins into flattened stacks of lacunae that are parallel to the diaphysis

Zone 5: Zone of ossification

-walls of lacunae disintegrate -invasion of blood supply from capillaries and osteoprogenitor cells from medullary cavity -new matrix of bone is deposited by the osteoblasts (lay down osteoid & hyaline cartilage is turned into bone) deposited

Calcified cartilage

A

epiphyseal line

A bony structure that replaces the epiphyseal growth plate between 18 (females) and 21 (males) years of age

periosteum, endosteum

Appositional bone growth occurs in the __________. The cellular layer produces more osteoid which is filled with calcium, making bone. Meanwhile, the osteoclasts in the _________ enlarge the medullary cavity to lower the weight gain.

Hypertrophic cartilage

B

Proliferating Cartilage

C

Step 4 of Interstitial Cartilage Growth

Cartilage continues to grow in the internal regions as chondrocytes continue to produce more matrix.

Step 3 of Interstitial Cartilage Growth

Chondroblasts begin to secrete new cartilage matrix all around them and get pushed apart until they are each in separate lacunae. These cells now reside in their own lacuna and are called chondrocytes.

Step 1 of Interstitial Cartilage Growth

Chondrocytes housed within lacunae are stimulated to undergo mitotic cell division.

Resting cartilage

D

calcium

For bone growth, _______ is required to solidify the matrix.

D, blood

For bone growth, vitamin __ is converted into calcitriol to regulate the levels of calcium in the _____.

Step 2 of Appositional Cartilage Growth

From each stem cell undergoing mitosis, one new undifferentiated stem cells and one committed stem cell that differentiates into chondroblasts are formed. These new chondroblasts are located at the periphery of the older cartilage, where they begin producing and secreting new cartilage matrix.

osteoid, calcification

In the second step of intramembranous ossification, calcium salts are deposited into the ______________. This hardens the matrix. The process is called _______________.

fibroblasts, periosteum, blood vessels

In the third step of intramembranous ossification, mesenchymal cells surrounding the forming bone differentiate into _____________, which then synthesize dense irregular connective tissue. This is the ______________. During this stage, ____________ ___________ also move in through the mesenchyme.

epiphyseal plate

Interstitial growth requires growth in the __________ _____.

Hyaline cartilage

It is found on many joint surfaces. It is pearly bluish in color with firm consistency and has a considerable amount of collagen. It contains no nerves or blood vessels, and its structure is relatively simple.

osteoprogenitor, osteoid, calcium

Mesenchyme cells differentiate into _________________ cells, which are bone stem cells. These then produce and secrete ______________ to make the semi-solid matrix. _________________ is deposited and that makes the matrix solid.

Step 3 of Appositional Cartilage Growth

The chondroblasts, as a result of matrix formation, push apart and become chondrocytes, with each chondrocyte occupying its own lacuna. The cartilage continues to grow at the periphery as chondrocytes continue to produce more matrix.

divide, osteoblasts

The ossification center for intramembranous ossification forms when the mesenchyme cells are stimulated to ___________ and become osteoprogenitor cells. These then differentiate into __________________ and begin to secrete osteoid.

False, interstitial growth declines

True/False - As cartilage matures, interstitial growth continues

True

True/False - Later growth is primarily appositional growth

Step 1 of Appositional Cartilage Growth

Undifferentiated stem cells at the internal edge of the perichondrium begin to divide. (Note the perichondrium contains mesencyhmal cells as well as these stem cells.)

Step 2 of Interstitial Cartilage Growth

Upon the completion of mitosis (cell division), two cells occupy a single lacuna; they are now called chondroblasts.

osteoblasts and osteoclasts

What two players work together to provide appositional bone growth?

spongy

When the spaces left by the ossification are left open, the bone has become ______________.

compact

When the spaces left by the ossification centers are filled, the bone has become ____________.

resting, inactive

Zone 1 of the epiphyseal plate is the _______ cartilage. This is closest to the epiphysis, and contains mature cells. Its is relatively _________.

proliferating, growth

Zone 2 of the epiphyseal plate is the _____________ cartilage. This is the "______ zone." The chondrocytes here are rapidly dividing.

hypertrophic, enlarge

Zone 3 of the epiphyseal plate is the ____________ cartilage. At this location the chondrocytes cease their division and begin to hypertrophy, or _______. They begin to eat at the cartilage around them and leave holes.

calcified

Zone 4 of the epiphyseal plate is the _________ cartilage. Calcium has moved in to the holes created and the cells are dying.

ossification

Zone 5 of the epiphyseal plate is where ___________ occurs. The remaining spaces in the cartilage are invaded by blood vessels, nerves, and osteoprogenitor cells, which become osteoblasts. These secrete osteoid and take over the cartilage.

six

_________ basic steps take place in endochondral ossification.

four

__________ basic steps take place in interstitial cartilage growth

ossification, 8

__________ is the term for the formation and development of osseous tissue. This process begins around week ___ of development.

three

____________ basic steps take place in appositional cartilage growth

four

____________ basic steps take place in intramembranous ossification.

intramembranous, mesenchyme

______________ ossification occurs within a mesenchyme connective tissue model. In this type of ossification, bone replaces the _______ tissue.

Hyaline cartilage

attaches ribs to the sternum covers the ends of some bones cartilage within growth plates model for formation of most bones

interstitial of cartilage growth

begins in internal region of cartilage with chondrocytes

appositional of cartilage growth

begins in peripheral region of cartilage's edge with mesenchymal stem cells

endochondral ossification

begins with a hyaline cartilage model

intramembranous of ossification

begins with mesenchyme in the area of the future dermis

intramembranous ossification

bone growth or production within a thin membrane of mesencyme

interstitial bone growth

dependent on the growth of the cartilage in the epiphyseal plate

appositional of cartilage growth

early and later in embryonic development

interstitial of cartilage growth

early in embryonic development

Intramembranous Ossification

flat skull bones, mandible, clavicle, fontanel ossification

interstitial bone growth

growth occurs in zone 2 while hypertrophy occurs in zone 3

interstitial bone growth, zone 5, zone 2

growth stops when the rate of ___________ is greater than ___________

epiphyseal (growth) plate

layer of hyaline cartilage in the metaphysis of a growing bone that consists of 5 zones

external circumferential lamellae

layers of bone matrix deposited by the osteoblasts in the inner cellular layer of the periosteum

intramembranous of ossification

occurs in flat bones of the skull, some of the facial bones (zygomatic bone and maxillae), the mandible, and the central part of the clavicle

endochondral ossification

occurs in long bones (upper and lower limbs), the pelvis, the vertebrae, and the ends of the clavicle

appositional bone growth

occurs within the periosteum

appositional bone growth

osteoblasts secrete osteoid/matrix at the internal layer of the periosteum

appositional bone growth

osteoclasts resorb bone internally to make room for medullary (marrow) cavity

ossification

producing bone tissue from existing mesenchymal connective tissue or from a hyaline cartilage model

cartilage growth

producing cartilage from chondrocytes undergoing mitosis or from stem cells undergoing mitosis

bone growth

producing of bone tissue by osteoblasts

interstitial growth

results in growth in length

appositional

results in growth in width

interstitial bone growth

specific events occur in five zones