Chapter 6 - Skeletal: Bone Tissue

Question 0

What process does bone tissue continually engage in?

Answer 0

Remodelling - construction of new bone tissue and breaking down of old bone tissue

Question 1

What tissues is bone composed of? (6 kinds)

Answer 1

1. Bone (osseous) tissue. 2. Cartilage
2. Dense connective tissue. 4. Epithelium
3. Adipose tissue. 6. Nervous tissue

Question 2

What are the six main functions of the skeletal system?

Answer 2

1. Support
2. Protection
3. Assistance in movement
4. Mineral homeostasis (storage and release)
5. Blood cell production (red bone marrow)
6. Triglyceride storage (yellow bone marrow)

Question 3

Describe the role of bones in blood cell production.

Answer 3

In certain bones, a connective tissue called red bone marrow produces red blood cells, white blood cells and platelets.

Question 4

Which bones contain red blood marrow?

Answer 4

The hip (pelvic) bones, ribs, sternum (breastbone), vertebrae (backbone), skull and end of the bones in the humerus (arm) and femur (thigh) bones.

Question 5

How do red bone marrow and yellow bone marrow differ in composition and function?

Answer 5

Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve. Red bone marrow produces red, white and platelet cells.

Question 6

What 7 parts does a long bone consist of? Describe them.

Answer 6

1. Diaphysis - bones shaft or body
2. Epiphyses - proximal and distal ends of the bone
3. Metaphyses - between the diaphysis and epiphyses. Contains a growth plate (epiphyseal plate). When a bones ceases to grow in length, the growth plate is replaced with bone resulting in an epiphyseal line.
4. Articular cartilage - thing layer of hyaline cartilage covering the part of the epiphysis where the bone forms a joint with another bone.
5. Periosteum - tough connective tissue sheath. Some of the cells allow the bone to grow in width but not length. Protects the bone, assist in fracture repair, help nourish bone tissue and serves as an attachment point for ligaments and tendons.
6. Medullary cavity - a hollow cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels
7. Endosteum - thin membrane that lines the medullary cavity. Contains a single layer of bone forming cells and small amount of connective tissue

Question 7

Why is bone tissue classified as a connective tissue?

Answer 7

Contains an abundant extracellular matrix that surrounds widely separated cells. (15% water, 30% collagen fibres, 55% crystallized mineral salts.

Question 8

What is hydroxyapatite?

Answer 8

When calcium phosphate is combined with calcium hydroxide to form crystals of hydroxyapatite

Question 9

What is calcification?

Answer 9

As hydroxyapatite crystals form they combine with other minerals (such as calcium carbonate, magnesium, fluoride, potassium and sulfate). Then these mineral salts are deposited in the framework formed by the collagen fibres of the extracellular matrix, they crystallize and harden.

Question 10

What bone building cells initialize calcification?

Answer 10

Osteoblasts

Question 11

What does the bones hardness depend on? It’s flexibility?

Answer 11

Hardness –> crystallized inorganic mineral salts

Flexibility –> collagen fibres, provide tensile strength

Question 12

What four types of cells are present in bone tissue?

Answer 12

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

Question 13

What are osteogenic cells?

Answer 13

Unspecialized bone stem cells derived from mesenchyme, only bone cells that undergo cell division - resulting cells develop into osteoblasts. Found along inner portion of the periosteum, in the endosteum and in the canals within bone that contain blood vessels

Question 14

What are osteoblasts?

Answer 14

Bone building cells. Do NOT undergo cell division.
Synthesize and secrete collagen fibres and other organic components needed to build the extracellular matrix.
As osteoblasts surround themselves with extracellular matrix, they become trapped and become osteocytes.

Question 15

What are osteocytes?

Answer 15

Mature bone cells. Main cells in bone tissue.
Maintains daily metabolism, such as exchange of nutrients and wastes with the blood.
Do NOT undergo cell division

Question 16

What are osteoclasts?

Answer 16

Are huge cells derived from the fusion of as many as 50 monocytes (at type of white blood cell) and are concentrated in the endosteum. These cells breakdown the extracellular matrix (resorption) as a normal part of development, maintenance and repair

Question 17

What is compact bone tissue?

Answer 17

The strongest form of bone tissue b/c it contains few spaces.
Found beneath the periosteum of all bones and makes up the bulk of the diaphyses of long bones.

Question 18

What structural unit make up compact bone tissue?

Answer 18

Osteons (harvsian systems).

Each osteon consists of concentric lamellae arranged around a central canal. (Resembles growth rings on a tree)

Question 19

What are concentric lamellae?

Answer 19

Circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels, lymphatics and nerves located in the central canal.

Question 20

What are lacunae?

Answer 20

Small spaces between the concentric lamellae, which contain osteocytes.

Question 21

What are canaliculi?

Answer 21

Small channels radiating from the lacune, which are filled with extracellular fluid. Inside the canaliculi are slender finger like projections of osteocytes

Question 22

What are interstitial lamellae?

Answer 22

Areas between neighbouring osteons.
Also have lacunae with osteocytes and canaliculi
Fragments of older osteons that have been partially destroyed during bone rebuilding or growth.

Question 23

What are perforating canals?

Answer 23

Canals that allow blood vessels, lymphatic vessels and nerves from the periosteum to penetrate the compact bone

Question 24

What are circumferential lamellae?

Answer 24

Arranged around the entire outer and inner circumference of the shaft of a long bone. Developed during initial bone formation. Connected to the periosteum by perforating fibres.

Question 25

What is spongy bone tissue?

Answer 25

Always located in the interior of a bone, protected by compact bone. Does not contain osteons. Consists of lamellae arranged in an irregular pattern of thin columns of trabeculae. Between the trabeculae are tiny spaces filled with red bone marrow or yellow bone marrow.

Question 26

What does each trabeculae consist of?

Answer 26

Concentric lamellae, osteocytes that lie in the lacunae and canaliculi that radiate outward from the lacunae

Question 27

How is spongy bone different from compact bone?

Answer 27

1. Spongy bone tissue is light | 2. Trabeculae support and protect red bone marrow (where hemopoiesis occurs)

Question 28

What are periosteal arteries?

Answer 28

Small arteries accompanied by nerves, enter the diaphysis through many perforating canals and supply the periosteum and outer part of the compact bone

Question 29

What is the nutrient foramen?

Answer 29

A hole in compact bone through which the nutrient artery passes.

Question 30

What happens to the nutrient artery once it enters the medullary cavity?

Answer 30

Divides into proximal and distal branches that course toward each end of the bone. These branches supply both the inner part of compact bone tissue of the diaphysis and the spongy bone tissue and red bone marrow as far as the epiphyseal plates (or lines). Some bones only have one nutrient artery (tibia) and some have many (femur).

Question 31

Which arteries supply the ends of the long bones?

Answer 31

Metaphyseal and epiphyseal arteries.

Question 32

How does the metaphyseal arteries enter the bone?

Answer 32

Enter the metaphyses of a long bone and together with the nutrient artery, supply the red bone marrow and bone tissue of the metaphyses.

Question 33

How does the epiphyseal arteries enter the bone?

Answer 33

Enter the epiphyses of a long bone and supply the red bone marrow and bone tissue of the epiphyses.

Question 34

Where are veins that carry blood away from the long bones evident?

Answer 34

1. One or two nutrient veins that accompany the nutrient artery (diaphysis) 2. Numerous epiphyseal veins and metaphyseal veins accompany their respective arteries 3. Many small periosteal veins accompany their respective arteries and exit through the periosteum

Question 35

Why does it hurt to have a bone marrow needle biopsy?

Answer 35

There are many nerves and pain receptors in the periosteum that are especially sensitive to rips and/or tears

Question 36

What is ossification? (Also called osteogenesis)

Answer 36

The process by which bone forms

Question 37

In what 4 principal situations does bone grow?

Answer 37

1. Initial formation of bones in an embryo and fetus 2. Growth of bones during infancy, childhood and adolescence 3. Remodelling of bone (replacement of old bone throughout lifetime) 4. Repair of fractures

Question 38

What are the two kinds of bone formation in an embryo and fetus?

Answer 38

1. Intramembranous ossification - bone forms directly within mesenchyme, which is arranged in sheet like layers that resemble membranes 2. Endochondral ossification - bone forms within hyaline cartilage that develops from mesenchyme * both involve replacement of preexisting connective tissue with bone, do not lead to differences in the structure of mature bone

Question 39

What are the steps involved with intramembranous ossification?

Answer 39

1. Development of the ossification center 2. Calcification 3. Formation of trabeculae 4. Development of the periosteum

Question 40

Which bones are formed by intramembranous ossification?

Answer 40

Flat bones of the skull Most facial bones Mandible (lower jawbone) Medial part of the cavicle (collar bone)

Question 41

What are the steps involved with endochondral ossification?

Answer 41

1. Development of cartilage model 2. Growth of cartilage model 3. Development of primary ossification center 4. Development of the medullary cavity 5. Development of secondary ossification center 6. Formation of articular cartilage and the epiphyseal (growth) plate

Question 42

What is appositional (exogenous) growth?

Answer 42

Growth at the outer surface. | Increase in thickness of bones during ossification

Question 43

What is interstitial (endogenous) growth?

Answer 43

Growth from within. | Increase in length of bones during ossification

Question 44

What is the main difference between the primary and secondary ossification centres?

Answer 44

Primary proceeds inward. Secondary proceeds outward. | Primary develops medullary cavity, secondary does not.

Question 45

The growth of long bones involves what two major events?

Answer 45

1. Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate 2. Replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification

Question 46

The epiphyseal plate is a layer of hyaline cartilage in the metaphysis of a growing bone that consists of what 4 zones?

Answer 46

1. Zone of resting cartilage (anchor plate to epiphysis) 2. Zone of proliferating cartilage (interstitial growth) 3. Zone of hypertrophic cartilage (maturing chondrocytes) 4. Zone of calcified cartilage (dead chondrocytes, b/c the extracellular matrix has calcified. Osteoclasts dissolve the calcified cartilage and osteoblasts and capillaries from the diaphysis invade the area)

Question 47

What happens if a bone fracture damages the epiphyseal plate?

Answer 47

The fractured bone may be shorter than normal once adult stature is reached. This is b/c damage to cartilage, which is avascular, accelerates closure of the epiphyseal plate due to cessation of cartilage cell division

Question 48

Describe the four steps involved with bone growth (in thickness)?

Answer 48

1. Ridges in periosteum create groove for periosteal blood vessel 2. Periosteal ridges fuse, forming and endosteum-lined funnel 3. Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming a new osteon 4. Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels

Question 49

What is the difference between bone remodelling, bone resorption and bone deposition?

Answer 49

Bone remodelling - ongoing replacement of old bone tissue with new Bone resorption - removal of minerals and collagen fibres from bone by osteoclasts Bone deposition - addition of minerals and collagen fibres to bone by osteoblasts

Question 50

What are the renewal rates of compact and spongy bone tissue per year?

Answer 50

Compact - 4% per year | Spongy - 20% per year

Question 51

What are the other benefits of remodelling?

Answer 51

If newly formed bone is subjected to heavy loads, it will grow thicker and stronger. The shape if a bone can be altered for proper support based on the stress patterns experienced during the remodelling process. New bone is more resistant to fracture than old bone

Question 52

How does bone resorption occur?

Answer 52

An osteoclast attaches tightly to the bone surface at the endosteum or periosteum and firms a leakproof seal at the edge of the ruffled border. It releases protein-digesting lysosomal enzymes and several acids into the sealed pocket. The enzymes digest collagen fibres and other organic substances while acids dissolve bone minerals. Carve out a small tunnel in the bone Degraded bone proteins and extracellular matrix minerals enter an osteoclast by endocytosis, cross the cell in vesicles and undergo exocytosis on the side opposite the ruffled border. Now in the interstitial fluid, the products of bone reabsorption diffuse into nearby blood capillaries. Once a small area of bone has been resorbed, osteoblasts move in to rebuild the bone in that area.

Question 53

What is othodontics?

Answer 53

Branch of dentistry concerned with the prevention and correction of poorly aligned teeth. Braces place artificial stress on teeth that osteoclasts and osteoblasts remodel the tooth to alleviate the stress.

Question 54

What is Paget's disease?

Answer 54

An excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition. Osteoblasts attempt to compensate. But new bone is weaker, b/c it has a higher proportion of spongy bone, mineralized is decreased and newly synthesized extracellular matrix contains abnormal proteins. New bones are hard, brittle and fracture easily.

Question 55

What factors affect bone growth and remodelling?

Answer 55

1. Minerals (calcium, phosphorus, magnesium, fluoride, and manganese) 2. Vitamins (A stimulates osteoblasts, C needed for synthesis of collagen, D increases the absorption of calcium from food) 3. Hormones (IGF's [insulinlike growth factors], hGH [human growth hormone], thyroid hormones)

Question 56

What causes growth to shut down (in length)?

Answer 56

During puberty, estrogen and androgen are responsible for the "growth spurt". Ultimately, sex hormones, especially estrogen in both sexes shut down growth at epiphyseal (growth) plates, causing elongation of the bones to cease.

Question 57

How does estrogen slow resorption?

Answer 57

By promoting apoptosis (programmed death) of osteoclasts

Question 58

What is giantism?

Answer 58

A person is much taller and heavier than normal. Caused by over secretion of hGH during childhood

Question 59

What is pituitary dwarfism?

Answer 59

A person with a short stature. Caused by an under-secretion of hGH during childhood. Can be treated with hGH until the epiphyseal plate closure. Proportionate sized limbs.

Question 60

What is acromegaly?

Answer 60

Over secretion of hGH during adulthood, cannot produce lengthening of bones b/c growth plates are sealed. It does cause the hands, feet and jaws to thicken and other tissues enlarge.

Question 61

What is achondroplasia?

Answer 61

Inherited condition in which the conversion of cartilage to bone is abnormal. Results in achondroplasic dwarfism. Results in short limbs, slightly enlarged head with a prominent forehead and flattened nose. Condition is untreatable.

Question 62

What is a fracture?

Answer 62

Any break in a bone

Question 63

What is a stress fracture?

Answer 63

A series of microscopic fissures in bone that forms without any evidence of injury to other tissues. Result from repeated, strenuous activity such as running, jumping, or aerobic dancing. Standard x-Rays often fail to reveal them, but bone scans show them.

Question 64

What are the different types of fractures? (6)

Answer 64

1. Open (compound) - broken ends protrude through the skin, a closed (simple) does not break the skin 2. Comminuted - bone is splintered, crushed 3. Green stick - partial fracture, only occurs in children, one side is broken, the other side is bent. 4. Impacted - one end of the fractured bone is forcefully driven into the interior of the other 5. Pott - fracture of distal end of the lateral leg bone (fibula), with serious injury of the distal tibial articulation 6. Colles' - fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly

Question 65

How does treatment of fractures vary?

Answer 65

Vary according to age, type and bone involved. | Realignment, immobilization and restoration of function

Question 66

What is reduction?

Answer 66

Fractured ends are brought into alignment | "Setting the fracture"

Question 67

What is a closed reduction? An open reduction?

Answer 67

Closed - bones are brought into alignment by manual manipulation Open - brought into alignment by a surgical procedure using internal fixation devices such as screws, plates, pins, rods and wires

Question 68

What are the steps involved in repairing a bone fracture?

Answer 68

1. Formation of fracture hematoma 2. Fibrocartilaginous callus formation 3. Bony callus formation 4. Bone remodelling

Question 69

Why does it take months for a bone to heal?

Answer 69

Calcium and phosphorus needed to strengthen and harden new bone are deposited only gradually and bone cells generally grow and reproduce slowly. The temporary disruption in their blood supply also helps explain the slowness of healing of severely fractured bones.

Question 70

How much calcium does bone store for the body?

Answer 70

99%

Question 71

How is calcium regulated in the body?

Answer 71

By controlling the rate of calcium resorption from bone into blood and of calcium deposition from blood to bone, to keep it in homeostasis

Question 72

What body functions rely on calcium to function properly?

Answer 72

Both nerve and muscle cells depend on a stable level of CA+2 in extracellular fluid, blood clotting also requires it.

Question 73

What can happen if the calcium levels go above or below 9-11 mg/100 mL?

Answer 73

Concentration too high - heart can stop | Concentration too low - breathing may cease

Question 74

What is the parathyroid hormone (PTH)?

Answer 74

Hormone increases calcium levels, secreted by the parathyroid glands, operates via a negative feedback system.

Question 75

Explain the negative feedback system for PTH. (When calcium levels are too low)

Answer 75

1. Stimulus disrupts homeostasis by decreasing calcium level 2. Parathyroid glands detect lowered calcium concentration 3. Increased production of cyclic AMP 4. PTH gene "turned on" by presence of cyclic AMP 5. Increased release of PTH 5. PTH increases activity of osteoclasts (bone resorption) and kidneys retain calcium in blood 6. Increases calcium level in blood

Question 76

What happens if calcium levels are too high?

Answer 76

Parafollicular cells in the thyroid gland secrete CT, which inhibit the activity of the osteoclasts, speeds blood calcium uptake by bone and accelerates deposition to bone. CT promotes bone formation and decreases blood level calcium

Question 77

How does exercise and mechanical stress affect bone tissue?

Answer 77

When placed under stress, bone has the ability to become stronger through increased deposition of mineral salts and production of collagen fibres by osteoblasts. Without mechanical stress, bone does not remodel normally b/c bone resorption occurs faster than than bone formation.

Question 78

What impacts bone growth more, walking or running?

Answer 78

Running, b/c high-impact intermittent strains more strongly influence bone deposition as compared with lower-impact strains

Question 79

What are the two main mechanical stresses on bones?

Answer 79

1. Pull of skeletal muscles | 2. Gravity

Question 80

Why do bones decrease in mass?

Answer 80

Bone resorption by osteoclasts outpaces bone deposition by osteoblasts.

Question 81

What are the two principal effects of aging on bone tissue?

Answer 81

1. Loss of bone mass - results from demineralization | 2. Brittleness - results from decreased rate of protein synthesis

Question 82

What is osteoporosis?

Answer 82

A condition of porous bones. Bone resorption outpaces bone deposition. Due to depletion of calcium from the body, more calcium is lost in urine, feces and sweat than is absorbed through diet.

Question 83

What is osteoarthritis?

Answer 83

Degeneration of articular cartilage such that bony end touch

Question 84

What is osteomyelitis?

Answer 84

An infection of bone characterized by high fever, sweating, chills, pain, nausea, pus formation, edema, and warmth over afflicted bone

Question 85

What is osteopenia?

Answer 85

Reduced bone mass due to a decrease in the rate of bone synthesis to a level too low to compensate for normal bone resorption

Question 86

What is osteosarcoma?

Answer 86

Bone cancer that affects osteoblasts, occurs most often in teenagers