Ch 6: The Skeletal System: Bone Tissue

Front 1

What constitutes the skeletal system?

Back 1

The entire framework of bones, cartilage, ligaments & tendons

Front 2

What is osteology?

Back 2

The study of bone structure and the treatment of bone disorders

Front 3

Describe the 6 main functions of the skeletal system:

Back 3

1.Support: supports soft tissues, provides attachment points for tendons, structural framework of body
2.Protection: protects internal organs from injury
3.Assistance in movement:skeletal muscles contract & pull on bones to produce movement
4.Mineral homeostasis (storage and release): store minerals (Ca & P), release minerals to maintain mineral balance, distribute to other parts of body
5.Blood cell production: red bone marrow produces RBC, WBC & platelets by hemopoiesis (hemo= blood; poeisis= making)
6.Triglyercide storage: yellow bone marrows consists of adipose cells, which store fat as potential energy reserve

Front 4

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

Back 4

Red composed of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers; produces RBC, WBC & platelets.
Yellow composed of adipose cells, which store fat as a potential energy reserve

Front 5

What is a long bone?

Back 5

=a bone that has greater length than width

Front 6

A long bone consists of what 7 parts?

Back 6

Diaphysis
Epiphyses
Metaphyses
Articular cartilage
Periosteum
Medullary cavity / marrow cavity
Endosteum
“DEMAPME” FIG 6-1

Front 7

What is the diaphyses?

Back 7

=the long, cylindrical, main portion of the bone Fig 6-1

Front 8

What is the epiphyses?

Back 8

=the proximal and distal ends of the bone Fig 6-1

Front 9

What is the metaphyses?

Back 9

=the regions between the diaphyses and the epiphyses
-in a growing bone, each metaphysis contains an epiphyseal (growth) plate.
*epiphyseal growth plate = a layer of hyaline cartilage that allows the diaphysis of the bone to grow in length. Fig 6-1

Front 10

What is a epiphyseal plate?

Back 10

= a layer of hyaline cartilage in the metaphyses that allows the diaphysis of the bone to grow in length. Fig 6-1

Front 11

What is the articular cartilage?

Back 11

= a thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone Fig 6-1

Front 12

What is the periosteum?

Back 12

=surrounds the external bone surface wherever it is not covered by articular cartilage. Fig 6-1

Front 13

What is the medullary cavity/ marrow cavity?

Back 13

=a hollow, cynlindrical space within the diaphysis that contains fatty yellow bone

Front 14

What is the endosteum?

Back 14

=a thin membrane that lines the internal bone surface facing the medullary cavity

Front 15

Which parts of a long bone contain red bone marrow?

Back 15

Epiphyses and metaphysis

Front 16

What color of bone marrow does the diaphysis contain?

Back 16

Yellow

Front 17

Ch. 4 Review: What are the 6 functions of bone tissue?

Back 17

1)Supports soft tissue and provides attachment for skeletal muscles.
2)Protects internal organs.
3) Assists in movement along with skeletal muscles.
4)Stores & releases minerals
5) Contains red bone marrow, which produces blood cells
6) Contains yellow bone marrow, which stores triglycerides (fats)

Front 18

What does “histology of bone tissue” mean?

Back 18

=the study of the microscopic anatomy of bone tissue

Front 19

Bone / osseous tissue contains an abundant extracellular matrix that surrounds widely separated cells. What makes up the extracellular matrix?

Back 19

Water, collagen fibers & crystallized minerals

Front 20

What is the most abundant mineral salt in the extracellular matrix of bone tissue?

Back 20

Calcium Phosphate Ca3(PO4)2

Front 21

What is hydroxyapatite [Ca10(PO4)6 (OH)2]?

Back 21

=crystals formed by the combination of Calcium phosphate and Calcium hydroxide

Front 22

What does hydroxyapatite do?

Back 22

Combines with other mineral salts and ions for the process of calcification.

Front 23

What is calcification?

Back 23

=a process in which tissue hardens due to hydroxyapatite combining with other mineral salts and ions, they become deposited in the framework formed by the collagen fibers of the extracellular matrix, they crystallize, and the tissue hardens.

Front 24

What occurs in the process of calcification?

Back 24

Mineral salts first begin to crystallize in the microscopic spaces between collagen fibers. After the spaces are filled, mineral crystals accumulate around the collagen fibers.

Front 25

What does a bone’s hardness depend on? What does a bone’s flexibility depend on?

Back 25

Crystallized inorganic mineral salts
Collagen fibers

Front 26

What 4 types of cells are present in bone tissue?

Back 26

Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts (Figure 6-2)

Front 27

What are Osteogenic cells?

Back 27

= unspecialized stem cells that undergo cell division to develop into osteoblasts

Front 28

What are Osteoblasts?

Back 28

=bone-building cells that initiate calcification and become osteocytes; synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue

Front 29

What does the ending “-blast” in the name of bone cell or any other connective tissue cell mean?

Back 29

Means that the cell secretes extracellular matrix

Front 30

What are Osteocytes?

Back 30

=the main, mature bone cells in bone tissue and maintain its daily metabolism, such as the exchange of nutrients and wastes with the blood.
-Like osteoblasts, do not undergo cell division

Front 31

What does the ending “-cyte” in the name of a bone cell or any other tissue cell mean?

Back 31

Means that the cell maintains the tissue.

Front 32

What are Osteoclasts?

Back 32

=large cells derived from the fusion of as many as 50 monocytes (a type of white blood cell)
- ruffled border on plasma membrane; functions in resorption
Resorption = the breakdown of bone extracellular matrix by lysosomal enzymes and acids that digest the protein and mineral components of the underlying bone matrix; part of the normal development, maintenance, and repair of bone.

Front 33

Why is bone resorption important?

Back 33

Bone resorption is necessary for the development, maintenance, and repair of bone

Front 34

What does the ending “-clast” in bone cell mean?

Back 34

Means that the cell breaks down extracellular matrix.

Front 35

What are the functions of the small spaces between cells and extracellular matrix components in bone?

Back 35

Channels for blood vessels that supply bone cells with nutrients.
Storage for red bone marrow

Front 36

What is compact bone tissue? What is its structure?

Back 36

=the strongest form of bone tissue
-contains few spaces (Fig 6-3a)

Front 37

What are central / Haversian canals?

Back 37

= canals that run longitudinally through the boneand allow vessels and nerves to penetrate compact bone.
-surrounded by concentric lamellae

Front 38

What are concentric lamellae?

Back 38

=rings of calcified extracellular matrix that surround the central canals
-like rings of a tree trunk
-contain small spaces between them called lacunae

Front 39

What are lacunae?

Back 39

=small spaces between concentric lamellae that contain osteocytes
(la-KOO-nē = little lakes)

Front 40

What radiates from all directions of lacunae? What is its structure?

Back 40

Canaliculi = small, tiny channels filled with extracellular fluid and osetocytes (which communicate with neighboring osetocytes via gap junctions)

Front 41

What is the importance of lacunae in bone homeostasis?

Back 41

-connect lacunae with one another and with central canals to create a system of interconnected canals throughout the bone to allow many routes for nutrients and oxygen to reach the osteocytes and removal of wastes.

Front 42

As people age, some central (haversian) canals may become blocked. What effect would this have on the surrounding osteocytes?

Back 42

The central (haversian) canals are the main blood supply to the osteocytes of an osteon (haversian system), so their blockage would lead to death of the osteocytes.

Front 43

What is an osteon/ haversian system?

Back 43

=a repeating structural unit, each consisting of a central haversian canal with its concentrically arranged lamellae, lacunae, osteocytes, and canaliculi.

Front 44

Is the organization of osteons static or dynamic over a lifetime?

Back 44

Dynamic: changes over time in response to the physical demands placed on the skeleton (ex. Learning to walk/ weight training/ fractures)

Front 45

How is spongy bone tissue compared to compact bone tissue?

Back 45

Spongy does not contain osteons

Front 46

Why is spongy bone tissue called spongy?

Back 46

Because of its appearance, not its texture. (Fig 6-3b)

Front 47

What is the structure of spongy bone tissue?

Back 47

-Consists of trabeculae (lamellae arranged in an irregular lattice of thin columns).
-Macroscopic spaces between the trabeculae

Front 48

What are trabeculae?

Back 48

=lamellae arranged in an irregular lattice of thin columns that make up spongy bone tissue.

Front 49

What is the structure within each trabecula?

Back 49

-Within each trabecula are lacunae (with canaliculi radiating outward from them) that contain osteocytes. (Fig 6-3)

Front 50

What is the significance of the macroscopic spaces between the trabeculae?

Back 50

-Help make bones lighter
-Sometimes filled with red bone marrow, which contains numerous small blood vessels to supply osteocytes with nutrients.

Front 51

How do the osteocytes within the lacunae (within each trabecula) receive nourishment?

Back 51

From the blood circulating through the blood vessels in the spaces between trabeculae.

Front 52

Trabeculae of spongy bone tissue look randomly arranged but how are they really oriented? How does it help?

Back 52

Precisely oriented along lines - helps bones resist stresses and transfer force without breaking of stress

Front 53

What is a nutrient artery?

Back 53

= a large artery that supplies bones with nutrients
-enters through medulla cavity
-divides into proximal and distal branches

Front 54

What is a nutrient foramen?

Back 54

= a hole in compact bone that allows the nutrient artery to pass through

Front 55

What is a nutrient vein?

Back 55

= a vein that carries blood away from long bones

Front 56

What is ossification/ osteogenesis?

Back 56

=process of bone formation

Front 57

Ossification/ osteogenesis occurs in 4 principal situations. What are they?

Back 57

1) initial formation of bones in an embryo and fetus
2) growth of bones during infancy, childhood & adolescence until adult sizes reached
3) remodeling of bone (replacement of old bone by new bone tissue throughout life)
4) repair of fractures (breaks in bones) throughout life

Front 58

What are the 2 methods of bone formation? What do they both involve?

Back 58

Intramembranous ossification
Endochondral ossification
-Both involve the replacement of a pre-existing connective tissue with bone

Front 59

What occurs during intramembranous ossification?

Back 59

Bone forms directly within mesenchyme arranged in sheetlike layers that resemble membranes. (in′-tra-MEM-bra-nus; intra- = within; membran- = membrane)

Front 60

What occurs during endochondral ossification?

Back 60

Bone forms within hyaline cartilage that develops from mesenchyme / replacement of cartilage by bone (en′-dō-KON-dral;endo- = within; -chondral = cartilage)

Front 61

Which bones of the body develop through intramembranous ossification?

Back 61

Flat bones of the skull and mandible (lower jawbone)

Front 62

What are the steps of intramembranous ossification?

Back 62

1)Development of ossification center
2)Calcification
3)Formation of trabeculae
4)Development of periosteum
(Fig 6-5)

Front 63

What occurs during the development of ossification center?

Back 63

-chemical messages cause mesenchymal cells to cluster together & differentiate into osteogenic cells then osteoblasts (cluster site called ossification center)
-osetoblasts secrete extracellular matrix of bone until surrounded

Front 64

What occurs during Calcification?

Back 64

-osteoblasts stop secretion of extracellular matrix
-cells now called osteocytes
-Osteocytes lie in lacunae & extend canaliculi

Front 65

What occurs during the formation of trabeculae?

Back 65

-extracellular matrix develops into trabeculae
-trabeculae fuse with one another to form spongy bone tissue
-blood vessels grow into the spaces between the trabeculae
-connective tissue (associated with blood vessels) differentiates into red bone marrow

Front 66

What occurs during the development of the periosteum?

Back 66

-mesenchyme condense at periphery of bone & develop into periosteum
-a thin layer of compact bone replace the surface layers of the spongy bone
-bone is remodelled (destroyed and reformed) as it transforms into its adult size and shape

Front 67

Review: What is mesenchyme?

Back 67

=the tissue from which almost all connective tissues arise

Front 68

Through which process are most bones formed?

Back 68

Through endochondral ossification (Fig 6-6)

Front 69

What are the steps of endochondral ossification?

Back 69

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

Front 70

What occurs during Development of the cartilage model?

Back 70

-chemical messages cause the mesenchymal cells to cluster in the shape of the future bone
-develop into chrondroblasts
-chondroblasts secrete cartilage extracellular matrix to produce a cartilage model (composed of hyaline cartilage)
-perichondrium (a covering) develops around the cartilage model

Front 71

What occurs during growth of the cartilage model?

Back 71

-chondroblasts get buried in the cartilage extracellular matrix & become chondrocytes
-chondrocytes continuously undergo cell division and the cartilage model grows
-secretion of extracellular matrix continues and cartilage model continues to grow
-chondrocytes in mid-region increase in size
-surrounding extracellular matrix begins to calcify
-other chondrocytes within calcifying cartilage die because nutrients can no longer diffuse quickly enough through the extracellular matrix.
-as these chondrocytes die, lacunae form and eventually merge into small cavities

Front 72

What occurs during development of the primary ossification centre?

Back 72

-nutrient artery comes through nutrient foramen, penetrates calcifying cartilage model
-stimulates cells to differentiate into osteoblasts
-periosteal capillaries grow into the disintegrating calcified cartilage, induces growth of primary ossification centre (region where bone tissue replaces most cartilage)
-osteoblasts form spongy bone trabeculae
-Primary ossification spread to both ends of cartilage model

Front 73

What occurs during development of the medullary (marrow) cavity?

Back 73

-osteoclasts break down some of the newly formed spongy bone trabeculae and create the medullary (marrow) cavity in the diaphysis
-Most of wall of diaphysis replaced by compact bone

Front 74

What occurs during development of the secondary ossification centres?

Back 74

- branches of the epiphyseal artery enter the epiphyses, secondary ossification centers develop (around time of birth)
-spongy bone remains in the interior of the epiphyses unlike the formation of the primary ossification center(no medullary cavities are formed here)

Front 75

What occurs during formation of articular cartilage and the epiphyseal plate?

Back 75

-Hyaline cartilage that covers the epiphysis becomes the articular cartilage

Front 76

Where in the cartilage model do secondary ossification centers develop during endochondral ossification?

Back 76

Secondary ossification centers develop in the regions of the cartilage model that will give rise to the epiphyses.

Front 77

What is the difference in how long bones and other bones in the body grow during infancy, childhood, and adolescence?

Back 77

Long bones grow in length.
Bones throughout the body grow in thickness.

Front 78

What is the epiphyseal (growth) plate? What does it do?

Back 78

=a layer of hyaline cartilage in the metaphysis of a growing bone.
-allows the diaphysis of a bone to increase in length
Fig 6-7

Front 79

What is the only way for the diaphysis to increase in length?

Back 79

Activity of the epiphyseal growth plate: As a bone grows, new chondrocytes are formed on the epiphyseal side of the plate, while old chondrocytes on the diaphyseal side of the plate are replaced by bone. In this way the thickness of the epiphyseal (growth) plate remains relatively constant, but the bone on the diaphyseal side increases in length (Figure 6-7c)

Front 80

How do bones grow in thickness?

Back 80

By appositional growth (growth at the outer surface):
- cells in the periosteum differentiate into osteoblasts
-osteoblasts secrete bone extracellular matrix
-osteoblasts develop into osteocytes
-lamellae added to bone surface
-new osteons of compact bone tissue formed
-At the same time, medullary cavity enlarges as the bone increases in thickness.

Front 81

What is bone remodelling?

Back 81

=the ongoing replacement of old bone tissue by new bone tissue

Front 82

What two processes does bone remodelling involve? Define them.

Back 82

Bone resorption = removal of minerals & collagen fibers from bone by osteoclasts; destruction of bone extracellular matrix
Bone deposition = addition of minerals and collagen fibers by osteoblasts; formation of bone extracellular matrix

Front 83

What is a fracture?

Back 83

=any break in a bone

Front 84

What are the steps in repair of a bone fracture?

Back 84

Formation of fracture hematoma
Fibrocartiliginous callus formation
Bony callus formation
Bone remodelling (Fig 6-9)

Front 85

What occurs during Formation of fracture hematoma?

Back 85

-a mass of blood (fracture hematoma) forms around the site of the fracture
-phagocytes & osteoclasts remove dead or damaged tissue around the fracture hematoma
-takes ~6-8 hours to form

Front 86

What occurs during Fibrocartiliginous callus formation?

Back 86

-fibroblasts from the periosteum invade the fracture site & produce collagen fibers
-cells from the periosteum develop into chondroblasts & produce fibrocartilage
-these events develop a fibrocartilaginous callus (a mass of repair tissue consisting of collagen fibers & cartilage that bridge the broken ends of the bone)
-takes ~3 weeks

Front 87

What occurs during Bony callus formation?

Back 87

-osteogenic cells develop into osteoblasts
-osteoblasts start to produce spongy bone trabeculae
-trabeculae join living and dead portions of the original bone fragments
-fibrocartilage converted to spongy bone
-bony callus formed & lasts 3-4 months

Front 88

What occurs during Bone remodelling of the callus?

Back 88

-osteoclasts resorb dead portions of broken bone
-compact bone replaces spongy bone around fracture

Front 89

How do our bones maintain the level of calcium in the blood?

Back 89

to control the rates of calcium resorption from bone into blood and of calcium deposition from blood into bone.

Front 90

What is the role of bone in calcium homeostasis?

Back 90

Help “buffer” the blood Ca2+ level, releasing Ca2+ into blood plasma (using osteoclasts) when the level decreases, and absorbing Ca2+ (using osteoblasts) when the level rises.

Front 91

Ca2+ exchange is regulated by hormones. What is the most important hormone? Where does it comes from? What does it do?

Back 91

Parathyroid hormone (PTH)
-secreted by parathyroid glands
-increases blood Ca2+ level

Front 92

How is PTH activity regulated?

Back 92

via a negative feedback system (Figure 6-10). If some stimulus causes the blood Ca2+ level to decrease, parathyroid gland cells (receptors) detect this change and PTH synthesis speeds up.
-presence of higher levels of PTH increases number & activity of osteoclasts (effectors), which step up the pace of bone resorption
-The resulting release of Ca2+ from bone into blood returns the blood Ca2+ level to normal.

Front 93

What body functions depend on proper levels of Ca2+?

Back 93

Heartbeat, respiration, nerve cell functioning, enzyme functioning, and blood clotting all depend on proper levels of calcium.

Front 94

PTH stimulates formation of cacitriol. What is it? What does it do?

Back 94

= a hormone secreted by the parathyroid glands
-promotes bone resorption by osteoclasts
-enhances recovery of calcium ions from urine
-promotes formation of the active form of vitamin D (calcitriol).

Front 95

What is calcitonin (CT)? What does it do?

Back 95

=a hormone secreted by the thyroid gland and works to decrease blood Ca2+ level
-inhibits bone resorption by osteoclasts. Fig 18.14

Front 96

What is osteoporosis?

Back 96

=a condition of porous bones; when bone resorption outpaces bone deposition
-depletion of calcium from body through urine, feces, and sweat than is absorbed from diet
-bone mass depletes; bones fracture spontaneously

Front 97

What is osteoarthritis?

Back 97

= degeneration of articular cartilage such that the bony ends touch; the resulting friction of bone against bone worsens the condition.
- associated with elderly

Front 98

What is Osteomyelitis?

Back 98

= infection of bone characterized by high fever, sweating, chills, pain, nausea, pus formation, edema, and warmth over the affected bone and rigid overlying muscles.
-caused by bacteria which may reach the bone from outside the body, by blood, or sites of infection in other part of the body