Anatomy Ch. 7

Second Step of Endochondral Ossification

osteocytes not chondrocytes produced; formation of primary ossification center, bony collar, and periosteum

Epiphyseal Plate

plate of hyaline cartilage between the epiphysis and diaphysis of a long bone in immature bone, serving as a growth zone for bone elongation through childhood and adolescence; growth center

Range for Endochondral Ossification

sixth week of fetal development though a person's 20s

long bone

A bone that is formed on a cartilage model that is gradually replaced by bone in a process called endochondral ossification. This is responsible for increases in the length of these bones.

flat bone

A bone that is formed within fibrous membranes, such as in the connective tissue of skin,through a process called intramembranous ossification, that doesn't have a cartilage template.

periosteum

A connective tissue that covers the surface of bones.

osteoclast

A large cell that resorbs, or breaks down, the bone matrix.

osteoblast

A matrix-synthesizing cell that is responsible for bone growth.

osteocyte

A mature bone cell that monitors and maintains the mineralized bone matrix , consisting of cells, fibers, and ground substance of proteoglycans and glycoproteins and hydroxyapatite cyrstals. They lie in a the lucanae of bones and have a tentacle-like process reaching to communicate with their neighboring cells.

epiphyseal plate

A plate of hyaline cartilage at the junction of the diaphysis and epiphysis that provides for growth in the length of a long bone.

osteon

A system of interconnecting canals in the microscopic structure of adult compact bone. These are the basic subunits of bone, consisting of rings of bone material around a central canal.

compact bone

A type of bone formed from osteons which maintain the collagen and mineralized ground substance of the hard extracellular mix. This type of bone comprises the thick wall of the diaphysis of a long bone, and forms a thin covering to the epiphyses of long and flat bones.

spongy bone

A type of bone that has no osteon units. Osteocytes are contained in lucanae, interconnected through canniculi. This bone forms as thin spicules, called trabeculae which are small interconnected spikes of bone. There are spaces between the trabeculae that are filled with fluid that is constantly replenished by blood vessels within the bone. Osteocytes are arranged circumferentially, but nutrients bathe the cells from the marrow fluid, instead of from a central canal.

bone

Connective tissue that has an exceptional ability to protect and support the body due to its rocklike hardness. It stores minerals and lipids and is the site of blood cell production. It has a solid collagen fiber network n added matrix element, inorganic calcium salts. It is composed of basic subunits called osteons and is well supplied with nutrients from invading blood vessels.

hydroxyapatite

Crystals composed of mineral salts, mainly calcium phosphates, that make up 65% of bones.

Second Stage of Intramembranous Ossification

Deposition of osteoid tissue and calcium phosphate by osteoblasts on mesenchymal surface; entrapment of first osteocytes and formation of periosteum

Mesenchyme

Embryonic connective tissue from which all tissues develop

marrow

Fat or blood-forming tissue found within bone cavities. It can be called yellow for fat, or red for blood, respectively.

Third Stage of Intramembranous Ossification

Honeycomb of bony trabeculae formed by continued mineral deposition by osteoblasts; creation of spongy bone; osteoclasts resorb and remodel other trabeculae to form a marrow cavity

articular cartilage

Hyaline cartilage that was never replaced by bone during endochondral ossification. It cushions joint movements but wears with age.

Ossification

Process of bone formation

trabeculae

Small, interconnected spikes of bone found in spongy bone. With one of these, osteocytes are arranged circumferentially, but nutrients bathe the cells from marrow fluid rather than from a central canal.

Osteoid Tissue

Soft collagenous matrix similar to bone but without minerals.

Fourth Stage of Intramembranous Ossification

Surface bone filled in by bone deposition, converting spongy bone to compact bone with spongy bone in the middle

osteoporosis

The decreased density and strength of bone resulting from an imbalance between osteoclast and osteoblast activity, resulting in a gradual decrease in the rate of bone formation.

diaphysis

The elongated shaft of a long bone, which before endochondral ossification is composed of cartilage which eventually calcificies, and develops cavities that allow spongy bone to form.

epiphysis

The end of a long bone that is attached to the shaft. When the bone isn't mature yet, hyaline cartilage grows here, but eventually no hyaline cartilage growth will remain, leaving the bone unable to grow in length.

appositional bone growth

The formation of new bone along an existing bone surface. This occurs even after growth plates close, and is the process responsible for most of adult bone remodeling.

central canal

The inner component of a bone, which contains minute blood vessels and nerve fibers that serve the needs of osteocytes.

intramembranous ossification

The process of growth for flat bones through the formation of new bone within fibrous membranes, such as in the connective tissue of skin. First, ossification centers appear in the fibrous connective tissue membrane. Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming the ossification center that produces the first trabeculae of spongy bone. Then, osteoblasts secrete osteoid within the fibrous membrane, which calcifies. Osteoid accumulates and is laid down between embryonic blood vessels, creating a woven bone network. Vascularized mesenchyme condenses on the external face of this woven bone and becomes the periosteum. Finally, lamellar bone replaces the woven bone, forming compact bone plates. Spongy bone persists internally and its vascular tissue becomes red marrow.

endochondral ossification

The process of growth for long bones through the formation of bone on a cartilage model. First, the bone collar forms around the diaphysis of the hyaline cartilage model. Then, cartilage in the center of the diaphysis calcifies and develops cavities. The periosteal bud invades the internal cavities and spongy bone forms. Then, the diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses, which then ossifies. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

Intramembranous and Endochondral

The two methods of ossification in the fetus and young children

Sixth Stage of Endochondral Ossificaton

all remaining cartilage in the epiphyseal plate is generally consumed and the gap between the epiphysis and diaphysis closes by the late teens and early twenties; primary and secondary marrow cavities unite into one; bone can no longer grow in length

Perichondrium

an outer covering of fibrous connective tissue that develops around the cartilage model during ossification

First Stage of Intramembranous Ossification

condensation of mesenchyme into soft sheet permeated with blood capillaries; differentiation of cells into osteogenic cells, beginning of trabeculae

Primary Ossification Center

during endochondral ossificaiton, a region near the middle of the cartilage model where bone tissue replaces most of the disintegrating calcified cartilage

First Step of Endochondral Ossification

early cartilage model: mesenchyme develops into a body of hyaline cartilage, covered with a fibrous perichondrium, in the location of future bone; perichondrium produces chondrocytes for a time

Fifth Stage of Endochondral Ossificaton

epiphyses fill with spongy bone during infancy and childhood; cartilage limited to the articular cartilage covering each joint surface, and to epiphyseal plate separating the primary and secondary marrow cavities on one or both ends of the bone

Fourth Stage of Endochodral Ossification

formation of secondary marrow cavity in the epiphysis which expands out in all directions and is present at birth

Endochondral Ossification

the most common bone formation process, which involves the replacement of hyaline cartilage (developed by mesenchyme) with bone

Chondrocyte

the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans

Intramembranous Ossification

the process of bone formation in the flat bones of the skull and most of the clavicle, where bone forms directly within mesenchyme arranged in sheetlike layers that resemble membranes

Metaphysis

the region of transition from cartilage to bone at the end of the primary bone marrow cavity; synonymous with epiphyseal plate

Secondary Ossification Center

this develops in the epiphyses of bone during endochondral ossification; in longer bones is occurs at both ends, in shorter bones it occurs in only one epiphysis

Third Step of Endochondral Ossification

vascular invasion; formation of primary marrow cavity, and appearance of secondary ossification center