Class 8 - Bone Tissue

Question 1

What the skeletal system is comprised of (3)

Answer 1

1. Bones
2. Cartilages
3. Ligaments - Hold bones together at joints

Tendons are NOT part of this system, but attach muscle to bone.

Question 2

Functions of the skeleton (7)

Answer 2

1. Support
2. Protection
3. Movement
4. Electrolyte balance - Calcium and phosphate levels
5. Acid-base balance - buffers blood against pH changes by altering phosphate and carbonate salt levels
6. Blood formation - red bone marrow produces
7. Hormone secretion - affect action of insulin and moderate stress response

Question 3

Mineralization/calcification

Answer 3

Crystallization process in which calcium, phosphate, and other ions are taken from blood and deposited on bone.

Osteoblasts produce collagen fibers which spiral length of osteon and become encrusted with minerals

First few crystals act as seed crystals that attract more ions.

Question 4

What individual bones each consist of (6)

Answer 4

Each is an organ with:
1. Bone tissue
2. Bone marrow
3. Cartilage
4. Adipose tissue
5. Nervous tissue
6. Fibrous connective tissue

Question 5

Flat bones (5)

Answer 5

Thin, curved plates; protect soft organs.

Includes:
1. Parietal bones of skull
2. sternum
3. scapula
4. ribs
5. hip bones

Question 6

Long bones (9)

Answer 6

Longer than wide; rigid levers acted upon by muscles; crucial for movement

Includes:
1. Humerus
2. radius
3. ulna
4. femur
5. tibia
6. fibula
7. metacarpals
8. metatarsals
9. phalanges

Question 7

Short bones (2)

Answer 7

Approximately equal in length and width

Includes: bones of wrist and ankle

Question 8

Irregular bones (2)

Answer 8

Elaborate shapes

Includes: Vertebrae, some skull bones

Question 9

Compact bone

Answer 9

3/4 of skeleton by weight

Dense outer shell of bone, encloses marrow cavity.

Question 10

Spongy bone

Answer 10

1/4 of skeleton (by weight)

Loosely organized bone tissue found in center of ends and shafts of long bones and in middle of others.

Covered by compact bone

Question 11

Diaphysis

Answer 11

Shaft of bone that provides leverage

Question 12

Epiphysis

Answer 12

Enlarged end of a long bone. Strengthens joints and anchors ligaments and tendons.

Question 13

Epiphyseal line

Answer 13

Remnant of childhood growth zone (epiphyseal plate)

Question 14

Articular cartilage

Answer 14

Layer of hyaline cartilage that covers joint surface; allows joints to move more freely

Question 15

Nutrient foramina

Answer 15

Minute holes in bone surface that allow blood vessels to penetrate

Question 16

Periosteum + perforating fibers

Answer 16

External sheath covering most of bone.

Has an outer fibrous layer of collagen and inner osteogenic layer of bone-forming cells

Perforating fibers: penetrate underlying bone matrix

Question 17

Endosteum

Answer 17

Thin layer of reticular connective tissue lining the marrow cavity and all internal bone surfaces

Question 18

Flat bone structure

Answer 18

Sandwich-like; inner and outer tables of compact bone enclosing layer of spongy between (called diploe in cranium)

Question 19

Four types of bone cells

Answer 19

1. Osteogenic cells
2. Osteoblasts
3. Osteocytes
4. Osteoclasts

Question 20

Osteogenic cells + locations

Answer 20

Stem cells found in endosteum and inner layer of periosteum.

Arise from embryonic mesenchyme; multiply continuously and give rise to osteoblasts.

Question 21

Osteoblasts + 2 locations

Answer 21

Bone-forming cells in endosteum and inner layer of periosteum.

Perform osteogenesis— synthesize soft organic matter of matrix and promote its mineralization

Stress stimulates osteogenic cells to multiply rapidly and increase number of osteoblasts which reinforce bone

Question 22

Osteocytes + how they communicate

Answer 22

Former osteoblasts that have become trapped in the matrix they deposited. Some reabsorb bone matrix while others deposit it.

Have cytoplasmic processes which reach into canaliculi and contact neighboring cells’ processes; gap junctions allow for passage of substances

Act as strain sensors— when stressed produce biochemical signals that regulate bone remodeling (hormone osteocalcin)

Question 23

Lacunae and canaliculi

Answer 23

Lacunae - Tiny cavities where osteocytes reside

Canaliculi - Little channels that connect lacunae

Question 24

Osteoclasts + formation

Answer 24

Perform osteolysis, the breakdown of bone as part of bone remodeling.

Often reside in reabsorption bays etched into bone surface

Develop from same bone marrow stem cells that give rise to red blood cells, unlike other bone cells

Form from fusion of several stem cells; have multiple nuclei each.
Infoldings imcrease surface area, form ruffled border

Question 25

Composition of osseous tissue matrix (2)

Answer 25

1/3 organic matter - synthesized by osteoblasts. Collagen and carbohydrate-protein complexes. 2/3 inorganic matter - mineral component; 85% hydroxyapatite (calcium salt), 10% calcium carbonate, 5% inorganic ions Combination forms a COMPOSITE material that provides flexibility and strength

Question 26

Why bone matrix is a composite material

Answer 26

Combination of organic (collagen) and inorganic matter (minerals) creates combination of FLEXIBILITY and STRENGTH. —Protein portion gives some flexibility since collagen have sacrificial bonds that dissipate shock under load (osteogenesis imperfecta = defect in collagen) —Mineral portion allows bone to support body weight without sagging. (Rickets = disease of mineral deficiency causing soft bones)

Question 27

Histology of compact bone (5)

Answer 27

1. Concentric lamellae a. Circumferential lamellae - encircle inner-outer region b. Interstitial lamellae - fill irregular regions between osteons. 2. Central canal 3. Perforating canals - connect central canals 4. Collagen corkscrews - Down each lamella to enhance bone strength 5. Cement line - prevents spread of microfractures

Question 28

Bone marrow + 2 types

Answer 28

Soft tissue occupying marrow cavities of long bones and small spaces of spongy bone 1. Red 2. Yellow

Question 29

Red bone marrow (myeloid tissue)

Answer 29

Contains multiple tissues that produce blood cells. In nearly every bone of a child but only in some of adults’.

Question 30

Yellow bone marrow

Answer 30

Fatty marrow that does not produce blood. Found in adults. Can transform back to red marrow in event of chronic anemia (requires making of more blood cells)

Question 31

Ossification/ osteogenesis + 2 methods

Answer 31

Both begin in embryonic mesenchyme. 1. Intramembranous ossification 2. Endochondrial ossification

Question 32

Intramembranous ossification

Answer 32

Produces flat bones of skull, most of clavicle, and part of mandible. Bone develops from osteoid tissue, which calcifies and entraps osteocytes. Also important in lifelong thickening and remodeling of long bones

Question 33

Endochondral ossification

Answer 33

Bone develops from hyaline cartilage model; produces most bones of body

Question 34

Bone elongation

Answer 34

Epiphyseal plate serves as growth zone. Metaphysis: Transitional zone on each side where cartilage is replaced by bone. Structure corresponds to steps of cartilage replacement

Question 35

Describe bone elongation process

Answer 35

Chondrocyte multiplication in zone 2 and hypertrophy in zone 3 push zone of reserve cartilage toward ends of bone, causing elongation Cartilage growth from within = interstitial growth

Question 36

Bones changes which occur by late teens/early twenties (3)

Answer 36

1. Primary and secondary marrow cavities unite into one 2. Junction fills with spongy bone 3. Site of original epiphyseal plate becomes epiphyseal line

Question 37

Achondroplastic vs pituitary dwarfism

Answer 37

Achondroplastic - long bones stop growing in childhood; normal torso, short limbs. Pituitary - lack of growth hormone; normal proportions, short stature

Question 38

Term for bone widening and thickening + 3 steps

Answer 38

Appositional growth - deposition of new tissue at bone surface. Occurs by Intramembranous ossification at bone surface. 1. Osteoblasts of inner layer of periosteum deposit osteoid tissue, become trapped as tissue calcifies. 2. Lay down matrix layers parallel to surface, forming circumferential lamellae. 3. Osteoclasts of endosteum enlarge marrow cavity

Question 39

Bone remodeling - 3 causes, Wolff’s law of bone

Answer 39

Bone continually remodels, replacing 10% of skeleton per year. Collaborative action of osteoblasts and osteoclasts. 1. Repairs microfractures 2. releases minerals into blood 3. reshapes bones in response to disuse Wolff’s law — architecture of bone determined by mechanical stress placed on it. Grow larger in response to stress

Question 40

Ossification vs osteolysis

Answer 40

Ossification - Laying down of new bone material by osteoblasts Osteolysis - Active resorption of bone matrix by osteoclasts. Raises blood calcium levels.