Bone

Question 1

What are the main functions of bone tissue?

Answer 1

Support body weight and protects internal organs

Provides leverage for body movements

Mineral storage site

Helps regulate blood calcium levels

Question 2

What are general characteristics of bone tissue?

Answer 2

ECM (bone matrix) > cells

Fibers > Ground substance
Fibers are collagen I fibers
Ground substance is GAGs, proteoglycans, and multi-adhesive glycoproteins

Question 3

What are the 5 main bone cells?

Answer 3

Osteoblasts - bone builders

Osteocytes - bone maintainers

Osteoclasts - bone dissolvers

Osteoprogenitor cells - bone stem cells

Bone lining cells - inactive osteoblasts that protect the endosteal surface

Question 4

What covers the external and internal surface of bone tissue?

Answer 4

External - periosteum

Internal - endosteum, lines marrow cavity and neurovascular canal. Covers surfaces of spongy bone

Question 5

What are 2 things that are associated with bone but are not bone?

Answer 5

Bone marrow - red marrow and yellow marrow are 2 types of specialized CT inside bones

Growth plates - bands of hyaline cartilage that are replaced with bone

Question 6

What are the components of long bones?

Answer 6

Diaphysis (Shaft) - long cylindrical portion with marrow cavity

Epiphysis - end of long bone and has articular cartilage to cover articulating surfaces

Metaphysis - regions where diaphyses flares out and approaches epiphysis, location of growth plate in many bone

Question 7

What is the function of the periosteum? What are its characteristics? Active vs. Inactive?

Answer 7

External CT surrounding bone

Covers and protects the outer surfaces of bones except articular surface and places where tendons insert into bone.

Active periosteum - if new bone forming directly underneath it

Inactive (mature) periosteum - if new bone is not actively being formed

Question 8

What are the 2 layers of active periosteum in developing fetal bone?

Answer 8

Outer fibrous layer protects and supports underlying bone. Contains fibroblasts that make collagen I fibers. Vascularized and innervated.

Inner cellular (osteogenic) layer directly contact bone tissue and contains stems cells and osteoblasts. Osteoprogenitor cells differentiate into osteoblasts. Osteoblasts deposited onto bone surface and begin to make and secrete osteoid

Question 9

What are the layers of inactive (mature) periosteum and bone?

Answer 9

Outer fibrous layer protects and supports underlying bone

Inner cellular layer - periosteal cells are inactive osteoprogenitor cells and can reactivate and differentiate into osteoblasts when needed

Question 10

How is periosteum anchored into bone tissue? What is the function?

Answer 10

Sharpey’s fibers

Prevent periosteum from detaching or peeling off the bone

Question 11

What does endosteum do and what are the cells?

Answer 11

Lines marrow cavities of long bones, lines neurovascular canals in compact bone, and covers of bony spicules and trabeculae of spongy bone.

Single row of osteoprogenitor cells and osteoblasts.

Bone lining cells = inactive osteoblasts

Endosteal cells = inactive osteoprogenitor cells

Question 12

What is the difference between bone matrix and osteoid?

Answer 12

Bone matrix - ECM of mineralized bone tissue

Osteoid - unmineralized matrix (organic components only)

Question 13

What fibers are present in bone matrix?

Answer 13

Main is collagen I fibers - impart some flexibility so tissue is not too brittle. Matrix is strongly acidophilic

Collagen V fibrils

Question 14

What are the properties of the ground substance of the bone matrix?

Answer 14

GAGs and proteoglycans: hyaluronan, chondroitin sulfate, and keratan sulfate

Multi-adhesive glycoproteins - most help hold matrix and cells together, Some bind mineral crystals to collagen I fibers.

Growth factors and cytokines - bone morphogenic proteins induce mesenchymal cells and osteoprogenitor cells to differentiate into osteoblasts

Question 15

What are the functions of the minerals in the bone matrix?

Answer 15

Make bone rigid - allows it to resist deformation from compression and other mechanical forces, support body weight, and enable movement (anchors/levers that muscles use to move)

Storage site for minerals

Question 16

What is the main mineral in bone?

Answer 16

Hydroxyapatite crystals

Question 17

What are osteoprogenitor cells? What are they called when inactive?

Answer 17

Stem cells that divide and differentiate into osteoblasts.

When inactive - periosteal cells (periosteum) or endosteal cells (endosteum)

Question 18

What are the functions of osteoblasts?

Answer 18

Synthesize and secrete osteoid and initiate its mineralization - euchromatic nucleus and basophilic cytoplasm

Synthesize and secrete substance that facilitate bone mineralization.

Question 19

What aids osteoblasts to synthesize and secrete substances that facilitate bone mineralization?

Answer 19

Alkaline phosphatase (ALP) - facilitates osteoid mineralization by cleaving phosphate groups from larger minerals

Osteocalcin - facilitates the alignment of hydroxyapatite crystals along surfaces of collagen I fibers to improve bone quality

Question 20

Where are osteoblasts located?

Answer 20

Bone surfaces and then they becomes osteocytes

Question 21

What are osteocytes and their function? Where are they located?

Answer 21

Most common cell and surrounded by matrix

Each osteocyte sits in a fluid filled chamber called a lacuna. Each lacuna connected to each other by small tunnels called canaliculi

Function is to monitor matrix surrounding their lacuna and do some minor maintenance of it. Has role in bone remodeling

Question 22

What is the function of osteoclasts? What are their properties?

Answer 22

Break down bone matrix during bone repair and remodeling by dissolving its mineral and organic components.

Are very large, multinucleated cells and acidophilic cytoplasm.

Located on bone surfaces and sit in depression called Howship lacunae

Question 23

Distinguish osteoblasts, osteocytes, and osteoclasts

Answer 23

Osteoblasts - on bone surface and secrete osteoid

Osteocytes - In lacuna and surrounded by mineralized bone matrix

Osteoclasts - On bone surfaces and dissolving old ECM

Question 24

What do active osteoclasts do and what are their regions?

Answer 24

Osteoclasts break down matrix.

Resorption chamber are area directly below an active osteoclast where acid enzymes are breaking down bone matrix

4 regions - ruffled border, clear zone, vesicular zone, and basal zone

Question 25

What is the ruffled border of the osteoclast? What does it do?

Answer 25

Region of cell closest to resorption chamber

Hydrolytic enzymes and protons are released across this part of the cell membrane into the resorption compartment below

Region where broken down matrix components are endocytosed

Question 26

What is the clear zone of the osteoclast? What does it do?

Answer 26

Region of cell that forms a tight seal on the bone surface and all around edge of resorption chamber.

Forms a tight seal that isolates the corrosive contents of the resorption chamber from the rest of bone surface

Question 27

What is the vesicular zone of an osteoclast?

Answer 27

Middle area of cell containing unreleased secretory vesicles heading to resorption compartment or towards capillaries

Question 28

What is the basal zone of an osteoclast?

Answer 28

Furthest from resorption chamber and contains nuclei and most cytoplasmic organelles

Question 29

How are inorganic components broken down by osteoclasts?

Answer 29

Release inactive acid hydrolases (acid phosphatase) into resorption chamber

Proton pumps send H into resorption chamber and low pH and activate the acid hydrolases

Minerals released pass into the cytoplas of osteoclasts and transported to capillaries

Question 30

How are organic components broken down by osteoclasts?

Answer 30

Osteoclasts release acid hydrolases (MMPs) into the resorption comparment which break down the organic components of the newly-demineralized matrix

Released components are endocytosed by osteoclasts

Osteoclasts finish breaking down these molecules and transport them to capillaries

Question 31

What is the difference between compact bone and spongy bone?

Answer 31

Compact bone - outer layer of solid bone tissue that remodels throughout life, has osteons

Spongy bone - inner layer of bone tissue, 3D network of thin, bony spicules

Spongy is always deep to layer of compact bone. All bones contain some amount of both

Question 32

What are 3 ways to classify bone tissue?

Answer 32

1. Gross Level Appearance
2. Microscopic Organization
3. How it develops

Question 33

What are the differences between primary and secondary bone tissue?

Answer 33

Primary bone tissue is immature and woven, disorganized

Secondary bone tissue is mature and lamellar. In compact bone so very organized with layers of lamellae, osteons. Spongy bone has lamellae but not osteons

Question 34

What are some characteristics of primary bone?

Answer 34

Forms during fetal development or during bone repair

Irregular bundles of collagen

Temporary tissue

Resorbed by osteoclasts

Replaced by secondary bone

Exception is bone lining tooth sockets remains immature through life

Question 35

What are some characteristics of secondary bone?

Answer 35

Consists of parallel or concentric bone lamellae

Collagen fibers are parallel in lamella

Has more mineral content than primary bone

Stronger than primary bone

May exist as spongy or compact bone

Contains osteons (Haversian systems)

Question 36

Describe the organization of osteon

Answer 36

Osteon is organized around central Haversian canal

Several thin, concentric layers (lamellae) of bone tissue around each Haversian canal

Osteocyte lacunae lie between adjacent lamellae

Canaliculi orientated towards other lacunae or to Haversian canal

Question 37

What is in the Haversian canal?

Answer 37

Contains nerves and blood vessels that provide the nerve and blood supply for every osteocyte in that osteon

Question 38

What are the lamellar systems in compact bone?

Answer 38

Osteons have concentric lamellae

Interstitial lamellae - lamellar fragments interspersed among osteons

Outer circumferential lamellae - extend around outer circumference of bone

Inner Circumferential lamellae - extend along inner margins of the bone marrow cavity