Topic 7: Bones and Skeletal System/Chapter 6: Bones and Bone Tissue

Callus

A mass of tissue that forms at a fracture site and connects the broken ends of the bone.

Cartilage Model

A model of hyaline cartilage that forms the shape of a bone that is then differentiated into bone in endochondral ossification.

Matrix Vesicles

Vesicles that contain large amounts of Ca^2+ and PO4^3-. Released by osteoblasts.

Calcified Cartilage

What the cartilage in endochondral ossification becomes as a result of chondrocytes releasing hydroxyapatite crystals in the cartilage matrix.

Open Fracture (Compound Fracture)

When an open wound extends to the site of the fracture or when a fragment of bone protrudes through the skin.

4 Zones of the Epiphyseal Plate

Zone of resting cartilage. Zone of proliferation. Zone of hypertrophy. Zone of calcification.

Hematoma

A localized mass of blood released from blood vessels but confined within an organ or space. Usually forms a clot to stop bleeding.

Osteoporosis (Porous Bone)

A loss of bone matrix.

Osteocyte

A bone cell that is surrounded by matrix. Differentiated from an osteoblast.

Closed Fracture

A broken bone with no open wound.

Comminuted Fracture

A complete fracture in which the bone breaks into more than 2 pieces.

Rickets

A disease resulting from reduced mineralization of the bone matrix caused by insufficient vitamin D. Results in bowed bones and inflamed joints.

Woven Bone

A fairly weak bone that osteoblasts first form in ossification. Collagen fibers are randomly oriented.

Incomplete Fracture

A fracture that does not extend across the bone.

Ruffled Border

A highly folded form of osteoclasts occurs after the clast has attached to the surface of the bone. A specialized area of the membrane for reabsorption of the bone back into the blood stream.

Perichondrium

A protective sheath of connective tissue that surrounds most cartilage. Blood vessels and nerves do not penetrate this.

Receptor Activator of Nuclear Factor KappaB Ligand (RANKL)

A receptor produced by osteoblasts when PTH binds to its receptors. This combines with RANK to convert the osteoblasts into osteoclasts.

Chondrocytes

A rounded cell that is the differentiated form of a chondroblast. Located in a lacuna within the matrix of cartilage.

Lacuna

A space within a matrix that contains a cyte cell.

Basic Multicellular Unit (BMU)

A temporary assembly of osteoclasts and osteoblasts that travels through or across the surface of bone removing old bone matrix and replacing it with new bone matrix. Renews the entire skeleton every 10 years.

Zone of Calcification

A thin layer with hypertrophied chondrocytes and calcified cartilage matrix.

Scurvy

A vitamin C deficiency disease that results in ulceration and hemorrhage almost anywhere in the body.

Osteomalacia

Adult Rickets. A softening of the bones due to calcium depletion from low levels of vitamin D.

Sinuses

Air-filled spaces that are lined by mucous membranes.

Hairline Fracture

An incomplete fracture in which the two sections of bone do not separate.

Greenstick Fracture

An incomplete fracture on the convex side of the curve bone.

Epiphyseal Line

An ossified epiphyseal plate that result when the plate stops growing.

2 Types of Cartilage Growth

Appositional and interstitial.

What type of growth do bones grow by?

Appositional growth.

What type of growth does cartilage grow by?

Appositional or interstitial growth.

Epiphyseal Plate (Growth Plate)

Area of hyaline cartilage between the diaphysis and the epiphysis. Cartilage growth followed by endochondral ossification here results in growth in bone length.

5 Functions of the Skeletal System

Body support Organ protection Body movement Mineral storage Blood cell production

Osteoblasts

Bone forming cells. Produce collagen and proteoglycans. Release matrix vesicles.

Endochondral Ossification

Bone forms from a preexisting cartilage model. First step: Mesenchymal cells aggregate where bones form and differentiate into osteochondral progenitor cells and then chloroblasts which create the cartilage model surrounded by a perichondrium. Second step: Blood vessels enter the cartilage model causing the formation of osteoblasts which convert the model to bone and the perichondrium into periosteum. Third step: Blood vessels grow into the calcified cartilage allowing osteoblasts and osteoclasts to transform the calcified cartilage into spongy bone. Fourth step: the process continues to turn calcified cartilage into bone, perichondrium into periosteum, and the bone collar thickens and grows. Woven bone remodels to lamellar bone. Fifth Step: secondary ossification centers are created in the epiphyses of long bones. Sixth step: Cartilage is replaced by bone until the epiphyseal plate (and then line once bone is mature) and articular surfaces are the only cartilage left. Seventh step: Spongy and compact bone are fully developed. only cartilage is in the articular cartilage, the original perichondrium is entirely periosteum.

Intramembranous Ossification

Bone forms from preexisting connective tissue membranes. Skull bone, lower jaw bone, and the collarbones develop through this. First step: Embryonic mesenchymal cells differentiate first into osteochondral progenitor cells and then into osteoblasts that produce bone matrix around collagen fibers until they become osteocytes. Second Step: Osteoblasts gather on the surface of the trabeculae to produce more bone which forms spongy bone. Third Step: Cells within spaces of spongy bone become red marrow, cells surrounding bone become periosteum, osteoblasts in the periosteum build compact bone.

Osteoclast

Bone-destroying cells. Breakdown bone to release molecules and ions necessary for body functions. Large and multinucleated. Derived from red bone marrow.

4 Components of the Skeletal System

Bones Cartilage Tendons Ligaments.

Long Bones

Bones that are longer than they are wide. Most bones of the upper and lower limbs.

Flat Bones

Bones with a relatively thin, flattened shape that is generally curved. Skull bones, ribs, breastbone, and shoulder blades.

Irregular Bones

Bones with shapes that don't fit into the other categories. Vertebrae and facial bones.

Osteogenesis Imperfecta

Brittle bone disorder caused by mutations that yield reduced or defective collagen in bones.

Perforating Fibers (Sharpey Fibers)

Bundles of collagen fibers in tendons and ligaments that penetrate the periosteum into the outer part of the bone. Strengthens the attachment of tendons or ligaments to the bone.

Perforating Canals

Canals that run perpendicular to the length of the bone that are the passages for blood vessels to enter the bones.

Appositional Growth

Chondroblasts in the perichondrium add new cartilage to the outside edge of the existing cartilage.

Interstitial Growth

Chondrocytes in the center tissue of the cartilage divide and add more matrix in between existing cells.

Zone of Hypertrophy

Chondrocytes produced in the zone of proliferation mature and enlarge.

Bone Collar

Compact bone on the surface of the cartilage model produced by osteoblasts in endochondral ossification.

Red Marrow

Connective tissue in the spaces of spongy bone or the medullary cavity. The site of blood cell production.

Zone of Proliferation

Contains chondrocytes that produce new cartilage through interstitial growth.

Periosteum

Double-layered connective tissue that covers the outer surface of bone except where articular cartilage is present. Ligaments and tendons attach to bone through this. Blood vessels and nerves supply the bone from here. Where the bone grows in diameter.

Reproductive Hormones

Estrogen and testosterone stimulate bone growth during puberty.

Yellow Marrow

Fat stored within the medullary cavity or in the spaces of spongy bone.

External Callus

Forms a collar around the opposing end of the bone fragments.

Internal Callus

Forms between the ends of a broken bone.

Receptor Activator of Nuclear Factor KappaB (Rank)

Found on the surface of osteoclasts and combines with RANKL to convert osteoblasts into osteoclasts.

Transverse Fracture

Fractures at right angles to the length of the bone.

Oblique Fracture

Fractures that run obliquely to the length of the bone.

Linear Fracture

Fractures that run parallel to the length of the bone.

Spiral Fracture

Fractures that take a helical course around the bone.

Growth Hormone

From the anterior pituitary gland. Increases general tissue growth including bone growth.

Compact Bone

Has more matrix and is denser than spongy bone.

Stellate Fracture

Have breakage lines radiating from a central point.

Dentate Fracture

Have rough, toothed, broken ends.

4 Major Steps of Bone Repair

Hematoma formation Callus formation Callus ossification Bone Remodeling

Articular Cartilage

Hyaline cartilage that covers the ends of bones where they come together to form joints. Has no perichondrium, blood vessels, or nerves.

Trabeculae

Interconnecting rods or plates of bone found in spongy bone. Each one consists of several lamellae.

2 Types of Fetal Bone Formation

Intramembranous ossification. Endochondral ossification. Both initially produce woven bone which is then remodeled into lamellar bone. After remodeling, the 2 types cannot be distinguished.

Medullary Cavity

Large cavity within the diaphysis.

Canaliculi

Little canals within the matrix that are occupied by the extensions of osteocytes.

Lamellar Bone

Mature bone made of thin sheets of lamellae. Collagen fibers run parallel in each sheet of lamellae but at an angle to the fibers in the neighboring lamellae. Osteocytes are in between the layers of lamellae.

Zone of Resting Cartilage

Nearest the epiphysis. Contains slowly dividing chondrocytes.

Vitamin C

Necessary for collagen synthesis by osteoblasts.

3 Types of Bone Cells

Osteoblasts Osteocytes Osteoclasts

Epiphysis

Part of the bone that develops from the center of ossification distinct from diaphysis.

Spongy Bone

Porous bone with less bone matrix relative to the space than compact bone. Consists of interconnecting rods/plates called trabeculae. The spaces in between the trabeculae are filled with bone marrow and blood vessels.

Chondroblasts

Produce a matrix of cartilage around themselves, and then turn into a chondrocyte.

Interstitial Lamellae

Remnants of concentric or circumferential lamellae that were partially removed during bone remodeling. Found between the osteons.

Thyroid Hormone

Required for growth of all tissues including cartilage. Deficiency can result in a smaller individual.

Short Bones

Round, nearly cube shaped bones. Wrist and ankle bones.

Osteoprotegerin (OPG)

Secreted by osteoblasts and other cells to inhibit osteoclast production by binding to RANKL which prevents the osteoblast from binding to RANK and turning into an osteoclast.

Calcitonin

Secreted from the thyroid gland when Ca2+ levels are too high. Inhibits osteoclast activity by binding to receptors on the osteoclasts.

Diaphysis

Shaft of a long bone. Composed primarily of compact bone. Contains the primary center of ossification.

Osteochondral Progenitor Cells

Stem cells that can become osteoblasts or chondroblasts.

Tendons

Strong bands of connective tissue that attach muscles to bones.

Ligaments

Strong bands of fibrous connective tissue that hold bones together.

Primary Ossification Center

The area of bone formation in endochondral ossification where the calcified cartilage is turned into spongy bone.

Complete Fracture

The bone is broken into at least two fragments.

Hydroxyapatite

The calcium phosphate crystal that makes up most of the inorganic material of bone.

Central Canal

The center channel within an osteon. Contains blood vessels running lengthwise along the bone.

Concentric Lamellae

The circular layers of bone matrix that surround the central canal.

Osteon (Haversian System)

The functional unit of a long bone. Composed of concentric rings of matrix surrounding a central tunnel.

Fontanels (Soft Spots)

The larger, membrane covered spaces between the developing skull bones in newborns that have not yet been ossified.

Centers of Ossification

The locations in the membrane where ossification begins.

Parathyroid Hormone (PTH)

The major regulator of blood Ca2+ levels. Secreted from the parathyroid glands when Ca2+ levels are too low and stimulates osteoclast production to release more Ca2+ into the blood.

Ossification (Osteogenesis)

The process of new bone formation by osteoblasts.

Bone Remodeling

The process of osteoclasts breaking down woven bone and osteoblasts forming a new matrix of lamellar bone. Important for bone growth, changes in bone shape, adjustment of the bone to stress, bone repair, and calcium ion regulation in the body.

Circumferential Lamellae

Thin plates that extend around the bone. Some thin bones are composed of only of this in the compact bone.

Endosteum

Thin connective tissue membrane lining the inner cavities of bone. Contains osteoblasts, osteoclasts, and osteochondral progenitor cells.

Impacted Fracture

When one fragment is driven into the spongy portion of the other fragment.

Complicated Fracture

When the soft tissues around the fracture are damaged.