Chapter 6 (Bones and Skeletal Tissue)

Question 1

Skeletal cartilage

Answer 1

made of highly resilient, molded cartilage tissue that consists primarily of water
– Contains no blood vessels or nerves

Question 2

Perichondrium

Answer 2

layer of dense connective tissue surrounding cartilage like a
girdle
– Helps cartilage resist outward expansion
– Contains blood vessels for nutrient delivery to cartilage

Question 3

Cartilage is made up of

Answer 3

chondrocytes, cells encased in small cavities
(lacunae) within jelly-like extracellular matrix

Question 4

Three types of cartilage:

Answer 4

hyaline, elastic, cartilage

Question 5

Hyaline cartilage

Answer 5

 Provides support, flexibility, and resilience
 Most abundant type; contains collagen fibers only
 Articular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose
tip)

Question 6

Elastic cartilage

Answer 6

 Similar to hyaline cartilage, but contains elastic fibers
 External ear and epiglottis

Question 7

Fibrocartilage

Answer 7

 Thick collagen fibers – has great tensile strength
 Menisci of knee; vertebral discs

Question 8

Cartilage grows in two ways:

Answer 8

appositional and interstitial

Question 9

Appositional growth

Answer 9

 Cartilage-forming cells in perichondrium secrete matrix against
external face of existing cartilage
– New matrix laid down on surface of cartilage

Question 10

Interstitial growth

Answer 10

 Chondrocytes within lacunae divide and secrete new matrix, expanding
cartilage from within
– New matrix made within cartilage

Question 11

There are seven important functions of bones

Answer 11

1. Support
    For body and soft organs
2. Protection
    Protect brain, spinal cord, and vital organs
3. Movement
    Levers for muscle action
4. Mineral and growth factor storage
    Calcium and phosphorus, and growth factors reservoir
5. Blood cell formation
    Hematopoiesis occurs in red marrow cavities of certain bones
6. Triglyceride (fat) storage
    Fat, used for an energy source, is stored in bone cavities
7. Hormone production
    Osteocalcin secreted by bones helps to regulate insulin secretion,
   glucose levels, and metabolism

Question 12

206 named bones in human skeleton

Answer 12

 Divided into two groups based on location

Question 13

Axial skeleton

Answer 13

 Long axis of body
 Skull, vertebral column, rib cage

Question 14

Appendicular skeleton

Answer 14

 Bones of upper and lower limbs
 Girdles attaching limbs to axial skeleton

Question 15

Bones are also classified according to one of four shapes:

Answer 15

1. Long bones
    Longer than they are wide
    Limb bones
2. Short bones
    Cube-shaped bones (in wrist and ankle)
    Sesamoid bones form within tendons (example: patella)
    Vary in size and number in different individuals
3. Flat bones
    Thin, flat, slightly curved
    Sternum, scapulae, ribs, most skull bones
4. Irregular bones
    Complicated shapes
    Vertebrae and hip bones

Question 16

Bones are organs because they contain different types of tissues

Answer 16

Bone (osseous) tissue predominates, but a bone also has nervous
tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial
cells in its blood vessels

Question 17

Three levels of structure

Answer 17

– Gross
– Microscopic
– Chemical

Question 18

Structure of short, irregular, and flat bones

Answer 18

– Consist of thin plates of spongy bone (diploe) covered by compact bone
– Compact bone sandwiched between connective tissue membranes
 Periosteum covers outside of compact bone, and endosteum covers
inside portion of compact bone
– Bone marrow is scattered throughout spongy bone; no defined marrow
cavity
– Hyaline cartilage covers area of bone that is part of a movable joint

Question 19

Structure of typical long bone

Answer 19

All long bones have a shaft (diaphysis), bone ends (epiphyses), and
membranes
 Diaphysis: tubular shaft that forms long axis of bone
– Consists of compact bone surrounding central medullary cavity that
is filled with yellow marrow in adults
 Epiphyses: ends of long bones that consist of compact bone
externally and spongy bone internally
– Articular cartilage covers articular (joint) surfaces
 Between diaphysis and epiphysis is epiphyseal line
– Remnant of childhood epiphyseal plate where bone growth occurs

Question 20

Membranes: two types (periosteum and endosteum)

Answer 20

– Periosteum: white, double-layered membrane that covers external
surfaces except joints
» Fibrous layer: outer layer consisting of dense irregular
connective tissue consisting of Sharpey’s fibers that secure to
bone matrix
» Osteogenic layer: inner layer abutting bone and contains
primitive osteogenic stem cells that gives rise to most all bone
cells
» Contains many nerve fibers and blood vessels that continue on
to the shaft through nutrient foramen openings
» Anchoring points for tendons and ligaments

Question 21

Endosteum

Answer 21

» Delicate connective tissue membrane covering internal bone
surface
» Covers trabeculae of spongy bone
» Lines canals that pass through compact bone
» Like periosteum, contains osteogenic cells that can differentiate
into other bone cells

Question 22

Bone markings

Answer 22

– Three types of markings:
 Projection: outward bulge of bone
– May be due to increased stress from muscle pull or is a
modification for joints
 Depression: bowl- or groove-like cut-out that can serve as
passageways for vessels and nerves, or plays a role in joints
 Opening: hole or canal in bone that serves as passageways for blood
vessels and nerves

Question 23

Cells of bone tissue

Answer 23

– Five major cell types, each of which is a specialized form of the same
basic cell type
1. Osteogenic cells
2. Osteoblasts
3. Osteocytes
4. Bone-lining cells
5. Osteoclasts

Question 24

Osteogenic cells

Answer 24

– Also called osteoprogenitor cells
– Mitotically active stem cells in periosteum and endosteum
– When stimulated, they differentiate into osteoblasts or bone-lining cells
– Some remain as osteogenic stem cells
- Stem cell

Question 25

Osteoblasts

Answer 25

– Bone-forming cells that secrete unmineralized bone matrix called osteoid  Osteoid is made up of collagen and calcium-binding proteins  Collagen makes up 90% of bone protein – Osteoblasts are actively mitotic - Matrix-synthesizing cell responsible for bone growth

Question 26

Osteocytes

Answer 26

– Mature bone cells in lacunae that no longer divide – Maintain bone matrix and act as stress or strain sensors  Respond to mechanical stimuli such as increased force on bone or weightlessness  Communicate information to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur - Mature bone cell that monitors and maintains the mineralized bone matrix

Question 27

Bone-lining cells

Answer 27

– Flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes) – On external bone surface, lining cells are called periosteal cells – On internal surfaces, they are called endosteal cells

Question 28

Osteoclasts

Answer 28

– Derived from same hematopoietic stem cells that become macrophages – Giant, multinucleate cells function in bone resorption (breakdown of bone) – When active, cells are located in depressions called resorption bays – Cells have ruffled borders that serve to increase surface area for enzyme degradation of bone  Also helps seal off area from surrounding matrix - Bone-reabsorbing cell

Question 29

Compact bone

Answer 29

– Also called lamellar bone – Consists of:  Osteon (Haversian system)  Canals and canaliculi  Interstitial and circumferential lamellae

Question 30

Osteon (Haversian system)

Answer 30

– An osteon is the structural unit of compact bone – Consists of an elongated cylinder that runs parallel to long axis of bone  Acts as tiny weight-bearing pillars – An osteon cylinder consists of several rings of bone matrix called lamellae  Lamellae contain collagen fibers that run in different directions in adjacent rings  Withstands stress and resist twisting  Bone salts are found between collagen fibers

Question 31

Canals and canaliculi

Answer 31

– Central (Haversian) canal runs through core of osteon  Contains blood vessels and nerve fibers – Perforating (Volkmann’s) canals: canals lined with endosteum that occur at right angles to central canal  Connect blood vessels and nerves of periosteum, medullary cavity, and central cana

Question 32

Canals

Answer 32

Lacunae: small cavities that contain osteocytes – Canaliculi: hairlike canals that connect lacunae to each other and to central canal – Osteoblasts that secrete bone matrix maintain contact with each other and osteocytes via cell projections with gap junctions – When matrix hardens and cells are trapped the canaliculi form  Allow communication between all osteocytes of osteon and permit nutrients and wastes to be relayed from one cell to anothe

Question 33

Interstitial and circumferential lamellae

Answer 33

– Interstitial lamellae  Lamellae that are not part of osteon  Some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling – Circumferential lamellae  Just deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis  Help long bone to resist twisting

Question 34

Spongy bone

Answer 34

– Appears poorly organized but is actually organized along lines of stress to help bone resist any stress – Trabeculae, like cables on a suspension bridge, confer strength to bone  No osteons are present, but trabeculae do contain irregularly arranged lamellae and osteocytes interconnected by canaliculi  Capillaries in endosteum supply nutrients

Question 35

Chemical Composition of Bone

Answer 35

 Bone is made up of both organic and inorganic components – Organic components  Includes osteogenic cells, osteoblasts, osteocytes, bone-lining cells, osteoclasts, and osteoid – Osteoid, which makes up one-third of organic bone matrix, is secreted by osteoblasts » Consists of ground substance and collagen fibers, which contribute to high tensile strength and flexibility of bone

Question 36

Organic components

Answer 36

– Resilience of bone is due to sacrificial bonds in or between collagen molecules that stretch and break to dissipate energy and prevent fractures – If no additional trauma, bonds re-form

Question 37

Inorganic components

Answer 37

– Hydroxyapatites (mineral salts)  Makeup 65% of bone by mass  Consist mainly of tiny calcium phosphate crystals in and around collagen fibers  Responsible for hardness and resistance to compression – Bone is half as strong as steel in resisting compression and as strong as steel in resisting tension – Lasts long after death because of mineral composition – Can reveal information about ancient people

Question 38

Ossification (osteogenesis)

Answer 38

is the process of bone tissue formation – Formation of bony skeleton begins in month 2 of development – Postnatal bone growth occurs until early adulthood – Bone remodeling and repair are lifelong

Question 39

Endochondral ossification

Answer 39

– Bone forms by replacing hyaline cartilage – Bones are called cartilage (endochondral) bones – Form most of skeleton – Forms essentially all bones inferior to base of skull, except clavicles – Begins late in month 2 of development – Uses previously formed hyaline cartilage models – Requires breakdown of hyaline cartilage prior to ossification – Begins at primary ossification center in center of shaft  Blood vessels infiltrate perichondrium, converting it to periosteum  Mesenchymal cells specialize into osteoblasts

Question 40

Intramembranous ossification

Answer 40

– Bone develops from fibrous membrane – Bones are called membrane bones begins within fibrous connective tissue membranes formed by mesenchymal cells – Forms frontal, parietal, occipital, temporal, and clavicle bone

Question 41

Formation of the Bony Skeleton

Answer 41

Five main steps in the process of ossification: 1. Bone collar forms around diaphysis of cartilage model 2. Central cartilage in diaphysis calcifies, then develops cavities 3. Periosteal bud invades cavities, leading to formation of spongy bone  Bud is made up of blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts 4. Diaphysis elongates, and medullary cavity forms  Secondary ossification centers appear in epiphyses 5. Epiphyses ossify  Hyaline cartilage remains only in epiphyseal plates and articular cartilages

Question 42

Four major steps are involved:

Answer 42

1. Ossification centers are formed when mesenchymal cells cluster and become osteoblasts 2. Osteoid is secreted, then calcified 3. Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae  Outer layer of woven bone forms periosteum 4. Lamellar bone replaces woven bone, and red marrow appear

Question 43

Postnatal Bone Growth

Answer 43

 Long bones grow lengthwise by interstitial (longitudinal) growth of epiphyseal plate  Bones increase thickness through appositional growth  Bones stop growing during adolescence – Some facial bones continue to grow slowly through life

Question 44

Growth in Length of Long Bones

Answer 44

 Interstitial growth requires presence of epiphyseal cartilage in the epiphyseal plate  Epiphyseal plate maintains constant thickness – Rate of cartilage growth on one side balanced by bone replacement on other  Epiphyseal plate consists of five zones: 1. Resting (quiescent) zone 2. Proliferation (growth) zone 3. Hypertrophic zone 4. Calcification zone 5. Ossification (osteogenic) zone

Question 45

Epiphyseal plate consists of five zones:

Answer 45

1. Resting (quiescent) zone – Area of cartilage on epiphyseal side of epiphyseal plate that is relatively inactive 2. Proliferation (growth) zone – Area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing – New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening 3. Hypertrophic zone – Area with older chondrocytes closer to diaphysis – Cartilage lacunae enlarge and erode, forming interconnecting spaces 4. Calcification zone – Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate 5. Ossification zone – Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction – Spicules are then eroded by osteoclasts and are covered with new bone by osteoblasts – Ultimately replaced with spongy bone – Medullary cavity enlarges as spicules are eroded

Question 46

Three “either/or” fracture classifications

Answer 46

Three “either/or” fracture classifications – Position of bone ends after fracture  Nondisplaced: ends retain normal position  Displaced: ends are out of normal alignment – Completeness of break  Complete: broken all the way through  Incomplete: not broken all the way through – Whether skin is penetrated  Open (compound): skin is penetrated  Closed (simple): skin is not penetrated

Question 47

Repair involves four major stages

Answer 47

1. Hematoma formation 2. Fibrocartilaginous callus formation 3. Bony callus formation 4. Bone remodeling

Question 48

Hematoma formation

Answer 48

– Torn blood vessels hemorrhage, forming mass of clotted blood called a hematoma – Site is swollen, painful, and inflamed

Question 49

Fibrocartilaginous callus formation

Answer 49

– Capillaries grow into hematoma – Phagocytic cells clear debris – Fibroblasts secrete collagen fibers to span break and connect broken ends – Fibroblasts, cartilage, and osteogenic cells begin reconstruction of bone  Create cartilage matrix of repair tissue  Osteoblasts form spongy bone within matrix – This mass of repair tissue is called fibrocartilaginous callus

Question 50

Bony callus formation

Answer 50

– Within one week, new trabeculae appear in fibrocartilaginous callus – Callus is converted to bony (hard) callus of spongy bone – Bony callus formation continues for about 2 months until firm union forms

Question 51

Bone remodeling

Answer 51

– Begins during bony callus formation and continues for several months – Excess material on diaphysis exterior and within medullary cavity is removed – Compact bone is laid down to reconstruct shaft walls – Final structure resembles original structure  Responds to same mechanical stressors

Question 52

Three major bone diseases:

Answer 52

– Osteomalacia and rickets – Osteoporosis – Paget’s disease

Question 53

Osteomalacia

Answer 53

– Bones are poorly mineralized – Osteoid is produced, but calcium salts not adequately deposited – Results in soft, weak bones – Pain upon bearing weight

Question 54

Rickets (osteomalacia of children)

Answer 54

– Results in bowed legs and other bone deformities because bones ends are enlarged and abnormally long – Cause: vitamin D deficiency or insufficient dietary calcium

Question 55

Osteoporosis

Answer 55

 Osteoporosis is a group of diseases in which bone resorption exceeds deposit  Matrix remains normal, but bone mass declines – Spongy bone of spine and neck of femur most susceptible  Vertebral and hip fractures common

Question 56

Tuberosity

Answer 56

Large rounded projection; may be roughened

Question 57

Crest

Answer 57

Narrow ridge of bone; usually prominent

Question 58

Trochanter

Answer 58

Very large; blunt, irregularly shaped process (the only examples are on the femur)

Question 59

Line

Answer 59

Narrow ridge of bone; less prominent than a crest

Question 60

Tubercle

Answer 60

Small rounded projection or process

Question 61

Epicondyle

Answer 61

Raised area on or above a condyle

Question 62

Spine

Answer 62

Sharp, slender, often pointed projection

Question 63

Process

Answer 63

Any bony prominence

Question 64

Head

Answer 64

Bony expansion carried on a narrow neck

Question 65

Facet

Answer 65

Smooth, nearly flat articular surface

Question 66

Condyle

Answer 66

Rounded articular projection

Question 67

Ramus

Answer 67

Armlike bar of bone

Question 68

Groove

Answer 68

Furrow

Question 69

Fissure

Answer 69

Narrow, slitlike opening

Question 70

Foramen

Answer 70

Round or oval opening through a bone

Question 71

Notch

Answer 71

Indentation at the edge of a structure

Question 72

Meatus

Answer 72

Canal-like passageway

Question 73

Sinus

Answer 73

Cavity within a bone, filled with air and lined with mucous membrane

Question 74

Fossa

Answer 74

Shallow, basinlike depression in a bone, often served as an articular surface

Question 75

Spiral

Answer 75

Ragged break occurs when excessive twisting forces are applied to a bone - common sports fracture

Question 76

Epiphyseal

Answer 76

Epiphysis separates from the diaphysis along the epiphyseal plate Tends to occur where cartilage are dying and calcification of the matrix is occuring

Question 77

Depressed

Answer 77

Broken bone portion is pressed inward - typical of skull fracture

Question 78

Greenstick

Answer 78

Bone breaks incompletely, much in the way a green twig breaks. Only one side of the shaft breaks; the other side bends - common in children, whose bones have relatively more organic matrix and are more flexible than those of adults

Question 79

Paget’s Disease

Answer 79

 Excessive and haphazard bone deposit and resorption cause bone to be made fast and poorly – Called Pagetic bone – Very high ratio of spongy to compact bone and reduced mineralization  Usually occurs in spine, pelvis, femur, and skull  Rarely occurs before age 40  Cause unknown: possibly viral  Treatment includes calcitonin and bisphosphonates