ACBS 400 Bone Structure

What is bone made of?

Collagenous proteins (30%), Non-collagenous proteins (Proteoglycans and Glycoproteins), Minerals (60% calcium and phosphorus), and Water (10%)

What are Proteoglycans?

Small leucine-rich proteoglycans necessary for cell proliferation, mineral deposition, and remodeling

What are Glycoproteins?

Proteins with covalently bound carbohydrates in various patterns (needed for mineral regulation)

Define Epiphysis

the end part of a long bone, initially growing separately from shaft

Define diaphysis

the shaft or central part of a long bone, contains mostly compact bone

Define Metaphysis

the region where epiphysis joins diaphysis

Define epiphyseal/grown plate

a hyaline cartilage plate in metaphysis at each end of a long bone

Define Medullary Space

the hollow part of the bone that contains bone marrow

Define Trabecular/cancellous/spongy bone

A hierarchical, spongy, and porous material composed of hard and soft tissue components, found at epiphysis and metaphyses of long bones in vertebral bodies

Define Compact/cortical bone

the hard, dense outer layer of all bones throughout the body

Define Periosteum

a dense, outer layer of bone that contains vascular connective tissue enveloping bones except at surfaces of joints

Define Endosteum

a membrane lining inner surface of bony wall and bone marrow

List the 4 cells in bones

Osteoblasts, osteoclasts, osteocytes, and osteoprogenitor

Define osteoblasts

mononuclear cells that form new bone (ossification) and originate from mesenchymal cells in bone marrow

What is primary ossification?

the formation of 1-cell thick layer covering surfaces

undergoing remodeling

Define osteoclasts

large multi nucleated cells at bone surface and actively resorb bone

Define osteocytes

Mature, inactive bone cells that used to be osteoblasts and are trapped inside the bone matrix. Lives in bone and maintains it

Define osteoprogenitor

germ cell that turns into other cells in bone

What is a compact bone?

A dense bone where bony matrix is solidly filled with organic ground substance and inorganic salts

What is ground substance?

a substance rich in a mineralized calcium phosphate compound known as hydroxyapatite

Define osteon

cylindrical structures composed of concentric layers of bone tissue called lamellae that surround a central canal

Define Haversian/central canals

Tiny tubes running lengthwise through an osteon that contain blood vessels and nerves

Define Volkmann/perforating canals

channels that contain smaller blood vessels that run perpendicular to Haversian canal (connects Haversian canals to periosteum and medullary cavity)

Define Lacunae

small areas of holes in bone matrix where osteocytes reside

Define Canaliculi

tunnels that form a labyrinth of connections between neighboring osteocytes → where cytoplasmic projections go

What’s the primary component of long bones?

To provide strong structural support

What is Trabecular Bone?

Light, porous bone enclosing many large spaces in a spongy appearance (bone matrix) most often found in long bones, ribs, skull, and vertebrae

Where can trabecular bone be found?

often in epiphysis, metaphysis, and sometimes in medullary space

Define Trabeculae

thin columns and plates of bone that create spongy structure along stress lines

What’s the purpose of trabeculae?

It provides flexibility and improves resistance to fracturing

Is trabecular bone a high level of metabolic activity?

Yes because it stores bone marrow, location of blood cell genesis, and storage for minerals

How to differentiate Periosteum v.s Endosteum

Peri= around

Endo= within

What factors do BOTH Periosteum and Endosteum share

Both are vascular connective tissue layers and contain osteoblasts and fibroblasts

What are the important facts (4) about Periosteum?

1. Covers all bones except at articular surfaces of long bones (i.e. at cartilage)

2. Has 2 layers (Fibrous outer layer and inner connective tissue layer)

3. Mature osteoblasts primary cells

4. Nourishes compact bone and site of attachment for tendons and ligament

How many layers does Periosteum have and what are they?

Has 2 layers: Fibrous outer layer and inner connective tissue layer

What are the important facts (4) about Endosteum?

1. Present in all bones

2. Singular loose connective tissue layer

3. Fibroblasts and hematopoietic cells primarily found here

4. Used for growth, repair, and remodeling of bone

What are the primary cells of Periosteum?

mature osteoblasts

What are the primary cells of Endosteum?

fibroblasts and hematopoietic cells

Define red bone marrow

contains hematopoietic tissue that creates blood cells (small percentage of bone marrow)

Where is red bone marrow located in young animals?

throughout most flat and long bones in young animals and will recede from long bones with maturity in trabecular space

Where is red bone marrow located in adult animals?

found in flat bones of vertebrae, sternum, ribs, and pelvis, along with top ends of humerus and femur

Define yellow bone marrow

Contains mostly adipose tissue. Majority of marrow, but has potential to convert back to red marrow under severe necessity

Where is yellow bone marrow located?

Located primarily in long bone

What minerals make up bone composition?

calcium (Ca2+), phosphorus (phosphate ion), magnesium (Mg2+), sodium(Na+), potassium (K+), chloride (Cl-), and fluoride (F-)

Which minerals are most abundant in bone composition?

Ca2+ and phosphorus

Which salts make up bone composition?

citrate, hydroxyl, and carbonate anions

What are the two main components of bone composition?

Inorganic salts and minerals. All deposited throughout bone matrix

What is Type 1 Collagen?

The main type of collagen in bone (90%), produced by osteoblasts. Vitamin C is required to help form collagen.

What is tropocollagen?

Braided collagen fibrils that have improved strength and rigidity. 5 join together to form microfibril

What is Collagen matrix?

microfibrils laid end-to-end in staggered formation in same direction in single bone metabolic unit

What are the steps of collagen matrix formation?

Type 1 collagen fibril → Tropocollagen fibril → Microbril → Collagen Matrix

Define hydroxyproline

a neutral heterocyclic protein amino acid commonly found in bone and gelatin

Why is hydroxyproline used as an indicator of bone destruction?

When bone collagen is broken down, hydroxyproline levels increase in the blood, indicating bone destruction

Define hydroxylysine

An amino acid unique to collagen-like peptide

What does hydroxylysine do in collagen?

Helps form covalent cross-links between collagen fibrils, which stabilize them and create the banding pattern seen in collagen

Define osteocalcin

A protein found in the extracellular matrix of bone and blood serum. It is produced only by osteoblasts.

What vitamins are associated with osteocalcin production?

Vitamin K is needed for its carboxylation, and vitamin D regulates this process.

What does osteocalcin do during bone mineralization?

Organizes minerals properly. Prevents random hydroxyapatite formation and helps align apatite crystals parallel to collagen fibrils.

How does osteocalcin help with bone remodeling?

It attracts osteoclasts to areas where bone needs to be broken down and remodeled