Cartilage and Bone

Question 1

What is cartilage? describe 4 properties

Answer 1

Cartilage = structure between dense CT and bone (tough but flexible)

1- Avascular; lacks nerve fibers (recieves nutrients by diffusion from blood vessels located in CT layer)

2- Ground substance contains lots of glycosaminoglycans and chondronectin - an adhesive protein (large molecules that can hold onto water)

3- Presence of collagen and some elastic fibers (gives strength and sturdiness) - these cannot be too thick because diffusion of nutrients must occur

4- Up to 80% water

Question 2

What is perichondrium and its purpose?

Answer 2

Outermembranous wrapping - CT

Perichondrium can form scar tissue in damaged areas because porrly vascularized cartilage does not repair well

Question 3

Describe the mature and immature forms or cartilage cells

Answer 3

Immature = chondroblasts = actively forming cartilage (laying down cartilage/reparining from a fracture)

Mature = chondrocytes = maintaining cartilage

Lacunae = localized clusters of chondrocytes in cartilage = surrounded by a matrix

Question 4

Name the 3 types of cartillage, briefly describe them, their location and their function.

Answer 4

a) Hyaline cartilage = most abundant; firm support and pliability, lots of collagen, appears as glossy blue-white, make up 1-10% of volume
- Found in embryonic skeleton and ends of long bones for cushioning (epiphyseal plates), costal cartilage of ribs, nose, trachea, larynx
- Fnc. Supports and reinforces, resilient cushioning and resists compressive stress

b) Elastic cartilage = like hyaline but with more elastic fibers
- Found in external ear, epiglottic (areas where we need more room to bend the cartilage and still have it go back to its original shape
- Fnc. maintains shape while giving lots of flexibility

c) Fibrocartilage - rows of chondrocytes alternating with rows of collagen fibers
- found in intervertebral discs, pubic symphysis discs of knee joints (where hyaline meets ligament/tendon)
- Fnc. Tensile strenth with ability to absorb compressive shock

Question 5

What are two main functions of bone tissue?

Answer 5

1. Bone reacts to amount of force applied by increasing density and amount of roughening on bone or decreasing density when force is reduced/eliminated (paralysis) = deposition vs resorption
2. Bone stores calcium, it can be resorbed and transferred to bloodstream when needed for muscle contraction

Question 6

What is bone deposition vs resorption

Answer 6

Deposition = when new bone is formed

Resorption = bone mineral is dissolved to release Ca+2 and phosphate to extracellular fluid

Question 7

List some characteristics of bone tissue (7)

Answer 7

1) Support - for standing still (posture)

2) Protection - physical protection for the skill/heart/lungs

3) Anchorage and movement - being able to stand still

4) Mineral storage - storage of calcium or phosphate

5) Blood cell formation - RBCs/WBCs/platelets

6) Fat storage - level of adipost storage (fats)

7) Hormone production (osteocalcin) - produced in bone tissue for metabolism with glucose

Question 8

What are the 4 classifications of bones?

Answer 8

1. Long bones; much longer than wide, shaft and 2 rounded ends mostly compact bone with marrow cavity, spongy bone near joint ends (ex. humerus)
2. Short bones; roughly cube shaped (ex. wrist/ankle), primarily spongy bone and thin outer layer of compact bone
3. Flat bones; thin, flattened and sometimes curved (ex. skull bones/ ribs/breastbone)
4. Irregular bones; leftovers, complicated shapes, primarily spongy bone and thin covering layer of compact bone (ex. vertebrae/hip bones)

Question 9

Difference between compact and spongy bone

Answer 9

Compact (cancellous) bone = deep outer layer; very organized structure

Spongy (trabecular) bone = trabeculae; red marrow found in spongy bone

Question 10

Periosteum?
Endosteum?

Answer 10

Periosteum = outer fibrous layer and inner osteogenic layer (cells capable of laying down bony material)

Endosteum = covers trabeculae of spongy bone and lines canals of compact bone (makes the inner linings for the cell)

Question 11

What is the purpose of calcium salts for bones?

Answer 11

Give hardness and strength for support/protection of softer tissues

Cavities for fat storage (yellow marrow) and synthesis of blood cells (red marrow)

Support of more vulnerable organs

Question 12

Differentiate between (a) osteoprogenitor cell, (b) osteobst, (c) osteocyte and (d) osteoclast

Answer 12

a) Stem cell, gives rise to osteoblasts which then form osteocytes

b) Matrix synthesizing cell responsible for bone growth; immature cells

c) mature bone cells; monitors and maintains the mineralized bone matrix, found in tiny canacls to make sure it has enough nutrients

d) bone resorbing cell; multi nucleus cell, dissolves bone when calcium levels are low in order to balance cells to maintain bone density

Question 13

Name the 3 structures of long bones with a brief description

Answer 13

1. Diaphysis; tubular shaft of a long bone (long axis), collar of compact bone surrounding narrow cavity (medullary cavity)
   - In adults, medullary cavity contains fat (yellow bone marrow cavity)
   - In childhood, more red bone marrow, red then gets replaced with yellow and fat storage in adulthood
2. Epiphyses; rounded extremities of a long bone, aritculation with other bones, compact bone forms thing outer layer, interior filled with spongy bone, thin layer of hyaline (articular) cartilage
3. Epiphyseal plate; betwen diaphysis and each epiphysis, the remnant of the epiphyseal plate

Question 14

Bone structure for bones aside from long bones ?

Answer 14

All have similar structure; compact bone outside, spongy bone inside

Compact - covered with periosteum
Spongy - covered with endosteum

All not cylindrical; no shaft, marrow cavity or epiphyses, DO contain bone marrow between trabeculae

*note - there are still some spaces between trabeculae where RBCs, WBCs and platelets form

Question 15

What is the structural unit for compact bone? Give brief description

Answer 15

Osteon (Haversian system)

osteon = elongated cylinder oriented parallel to long axis of bone

single osteon = group of hollow tubes to bony matrix, each matrix = lamellar bone

Found in layers - the orientation of collagen layers is in successive lamellae

Question 16

What are the 2 canals of the osteon?

Answer 16

1) Central (haversion) canal; runs through middle of osteon - communicating canals

2) Perforating (Volkmanns) canal; perpendicular to long axis and Haversian canals - connecting canals between the central canals

Question 17

Canniculi ?

Answer 17

Small canals that connect the lacunae with each other

Connected to central canal of Haversian sys.

Question 18

Interstitial lamellae ?

Answer 18

Fills the gaps between forming osteons / leftovers osteons that were partially destroyed by bone remodelling

Question 19

Circumferential lamellae ?

Answer 19

sheets of bone located just deep to periosteum

extend around entire circumference of shaft - wraps around outside to smoothen the exterior

Question 20

What is the structure of spongy bone?

Answer 20

Contains trabeculae, lamellary arranged osteocytes and canniculi

Irregularly arranged lamellae and osteocytes interconnected by canniculi

Trabeculae arranged along lines of stress to help bones resist stress

CONTAINS NO OSTEONS only long bones have ostens, spongy bones have no pathways for blood vessels

Because no pathways, nutrients diffuse through canniculi from marrow spaces between trabeculae to reach osteons

Question 21

What is the process of bone formation called?

Answer 21

Osteogenesis or ossification

Question 22

What is intramembranous ossification?

Answer 22

When bone develops from a fibrous CT membrane containing mesenchymal cells

Ex. Cranial bones of the skull and clavicles (flat bones)

Begins at about 8 weeks of embryonic development; result is a bone called membranous bone

Question 23

What is endochondral ossification?

Answer 23

Bone development via the replacement of a hyaline cartilage model which is then gradually dissolved

In all bones belo the skull except the clavicles

More complex; first is made of cartilage then dissolved to be replaced with bony tissue

Result is a bone called endochondral bone

Question 24

What is the difference in the formation of short bones and irregular bones?

Answer 24

In short bones only a primary ossification centre is formed

Most irregular bones are formed using several distinct ossification centres

Question 25

What happens after the completion of secondary ossification?

Answer 25

Hyaline cartilage remains on the epiphyseal surfaces as the articular cartilage

Also remains at junctions of diaphysis and epiphysis where the epiphyseal plate is formed (areas where long bones continue to grow)

Question 26

How do long bones grow during infancy and youth? How does this differ during adolescence?

Answer 26

Grows entirely by interstitial growth of epiphyseal plate - laying down cartilage and ossifying it

All bones grow in thickness by appositional growth - inner material by reshaping

Most bones stop growing during adolescence/early adulthood - only some facial bones (nose/lower jaw) continue to grow throughout life

Question 27

What is the process of long bone lengthening at the epiphyseal plate?

Answer 27

• cartilage wll be made and gradually move down towards adding onto the shaft of the tibia
• as long bone lengthens, the ends will be reshaped/remodeled
• through reshaping of the shaft the diaphysis will get longer
• diaphysis will also get thicker and stronger as the bone lengthens
• bones is then destroyed by osteoclasts and laid down by osteoblasts on both inner and outer surfaces of growing bone

Question 28

Does the epiphyseal plate change its size throughout our lifetime?

Answer 28

The epiphyseal plats stays roughly the same size from childhood because through ossification it will briefly get longer, then ossify and repeating this cycle

It will eventually get thinner to become the epiphyseal line
(females tend to have it thin sooner than males), when bone tissue of the epiphysis and diaphysis fuse and longitudinal growth ends

Question 29

What is growth in width of long bones?

Answer 29

Appositional growth - when layers of bone are laid down on top of one another

1) primarily osteoblasts on periosteal side secreting bone matrix
2) primarily osteoclasts on endosteal side removing bone matrix

There is more laying down than resorbtion so this will eventually get slightly longer

Question 30

What are the steps in the process of a fracture repair?

Answer 30

1) Formation of a hematoma - local bone cells are deprived of oxygen and die

2) Formation of a fibrocartiallagenous callus (soft) - invaded by blood vessels that bring macrophages to clean up the area, osteoclasts resorb damaged bone; fibroblasts, chondroblasts and osteoblasts lay down collage fibers and tissue components

3) Conversion to bony callus (hard) - cartilage converted to trabecular bone

4) Bone remodelling - extra bony material is removed, outer bone of shaft walls converted to compact bone and bone regains its original shape