Skeletal Structures

Question 1

What are the three divisions of the skeleton and which bones are in them?

Answer 1

1. Axial skeleton - head, vertebral column, ribs, sternum.
2. Appendicular skeleton - bones of the limbs and bones connecting the limbs to the axial skeleton.
3. Visceral skeleton - bones that develop in the viscera or soft structures (i.e. os penis in carnivores).

Question 2

What are the four functions of bone?

Answer 2

1. Skeleton gives an identifiable form to the body of an animal and protects organs.
2. Function as levers to perform work.
3. Reservoir for calcium and phosphate.
4. Red marrow within the medullary cavity of bone is a source of red blood cells.

Question 3

What is the composition of bone?

Answer 3

95% solid
⅓ of bone is an organic component
⅔ of bone is inorganic hydroxyapatite

5% water

Question 4

What is the basic microscopic structure of bone?

Answer 4

lacunae - small cavities in bone which contain osteocytes
marrow - found in the medullary cavity of long bones

Question 5

What are osteoprogenitor cells?

Answer 5

stem cells that when stimulated, develop into osteoblast.

Question 6

What are Osteoblasts?

Answer 6

differentiated bone forming cells responsible for the production of bone matrix (builds bones).

Question 7

What are osteocytes?

Answer 7

mature bone cells, derived from osteoblasts.

Enclosed by bone matrix that it had previously laid down as an osteoid when it was an osteoblast.

Maintain the bone matrix and are able to synthesize and resorb matrix to a limited extent.

Question 8

What are osteoclasts?

Answer 8

(opposite of osteoblasts) bone-resorbing cells.

Large, motile, often multi-nucleated. Derived from stem cells in blood-producing tissue of bone marrow and spleen. Found in resorption bays (Howship’s Lacunae).

Question 9

What are flat bones?

Answer 9

two plates of compact bone, separated by cancellous bone. They have broad surfaces for attachment of large muscle groups and to protect underlying soft parts.
Example: scapula, pelvic girdle, skull

Question 10

What are irregular bones?

Answer 10

complex and irregularly shaped bones. Neither flat nor long.
Example: vertebrae

Question 11

What are sesamoid bones?

Answer 11

small bones embedded in a tendon.
Example: patella

Question 12

What are short bones?

Answer 12

cube shaped bones, function to diffuse concussion, diminish friction, change direction of tendons.
Example: tarsus and carpus

Question 13

What are long bones?

Answer 13

bones that are longer than they are wide. Found in the limbs and are the supporting columns and levers for the skeleton.
Example: radius & ulna, tibia

Question 14

What is the diaphysis?

Answer 14

long shaft of a bone

Question 15

What is the epiphysis?

Answer 15

two enlarged ends of a long bone

Question 16

What is the metaphysis?

Answer 16

flared portion joining the diaphysis and the epiphysis in a growing bone; contains the physis

Question 17

What is the physis (growth plate)?

Answer 17

plate of cartilage between the diaphysis and the epiphysis of immature long bones. Represents the point of growth in a longitudinal direction.

Question 18

What is the periosteum? (part 1/4 of long bone)

Answer 18

Fibrous covering around bone that is not covered by articular cartilage.

Necessary for bone growth, repair, nutrition and attachment for ligaments and tendons.

Outer layer of dense regular CT (collagen).

Question 19

What is the Articular cartilage/surface? (part 2/4 of long bone)

Answer 19

Smooth layer of hyaline cartilage covering the epiphysis where one bone forms a joint with another bone.

Question 20

What is the medullary cavity? (part 3/4 of long bone)

Answer 20

Space in the diaphysis containing marrow.

Question 21

What is the endosteum? (part 4/4 of long bone)

Answer 21

The fibrous and cellular tissue lining the medullary cavity

Question 22

What is woven bone?

Answer 22

Immature bone that has been laid down but not organized by secondary remodeling

Can be compact or cancellous

Question 23

What is compact bone?

Answer 23

Bone that looks solid and is hard and dense.

Outer layer of bones.

Consists of osteons.

Question 24

What is haversian bone?

Answer 24

Mature bone that has been remodeled

Can be compact or cancellous

Question 25

What is Cancellous/Spongy/Trabecular bone?

Answer 25

Bone that has visible spaces in it

Empty spaces are filled with bone marrow

Located deep to contact bone

Question 26

What is the structure of Haversian bone?

Answer 26

Volkman canals
- Blood vessels serving the external surfaces and marrow cavity are perpendicular to the long axis of the bone and are contained within them.

Osteon
- Circular unit of structure of compact bone in haversian system
consists of central haversian canal surrounded by concentric layers of bone, and lamellae

Question 27

What are the 4 zones of the epiphyseal plate?

Answer 27

Zone of Reserve Cartilage (youngest)
- Chondrocytes begin to divide and organize into columns, forming zone of proliferation

Zone of Proliferation
- Cells divide and produce cartilaginous matrix
- Push epiphysis away from diaphysis, elongating the bone

Zone of Hypertrophy
- Each division of chondrocytes brings about larger cells

Zone of Calcified Matrix (oldest)
- Hypertrophied cells begin to calcify the cartilage matrix
- Calcification and increasing distance from nutritional source causes chondrocytes to die