Chapter 6

what does the skeleton consist of before it is replaced by bone

what does the skeleton consist of before it is replaced by bone

cartilage

what does the skeleton need to flex

they require cartilage

does skeletal cartilage contain blood vessels or nerves

no

does perichondrium contain blood vessels

yes

describe skeletal cartilage

made of highly resilient, molded cartilage tissue that consists primarily of water

describe perichondrium

layer of dense connective tissue surrounding cartilage like a girdle

Helps cartilage resist outward expansion

chondrocytes

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

cartilage is made up of

chondrocytes

describe hyaline cartilage

Provides support, flexibility, and resilience

Most abundant type; contains collagen fibers only

Articular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose tip)

describe elastic cartilage

Similar to hyaline cartilage, but contains elastic fibers

External ear and epiglottis

describe fibrocartilage

• Thick collagen fibers: has great tensile strength

  • Menisci of knee; vertebral discs

hardened cartilage

not the same as bone

cartilage grows in what two ways

appositional growth and interstitial growth

appositional growth

• Cartilage-forming cells in perichondrium secrete matrix against external face of existing cartilage

  • New matrix laid down on surface of cartilage

interstitial growth

• Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within

  • New matrix made within cartilage

what are the 7 important function of bones

support, protection, anchorage, mineral and growth factor storage, blood cell formation, triglyceride fat storage, and hormone production

axial skeleton

• Long axis of body

  • Skull, vertebral column, rib cage

appendicular skeleton

• Bones of upper and lower limbs

  • Girdles attaching limbs to axial skeleton

long bones

• Longer than they are wide

  • Limb bones

short bones

• Cube-shaped bones (in wrist and ankle)

• Sesamoid bones form within tendons (example: patella)

  • Vary in size and number in different individuals

patella is a type of what bone

sesamoid

flat bones

• Thin, flat, slightly curved

  • Sternum, scapulae, ribs, most skull bones

irregular bones

• Complicated shapes

  • Vertebrae and hip bones

bone is called

osseous tissue

what are the 3 levels of bone structure

gross, microscopic, and chemical

describe spongy bone

made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae

describe compact bone

dense outer layer on every bone that appears smooth and solid

open spaces between the trabeculae are filled with

red or yellow bone marrow

what does periosteum do

covers outside of compact bone

endosteum

covers inside portion of compact bone

what is the structure of short, irregular, and flat bones

Consist of thin plates of spongy bone (diploe) covered by compact bone

Compact bone sandwiched between connective tissue membranes

what are the two membranes

periosteum and endosteum

describe periosteum

glistening white, double-layered membrane that covers external surfaces except joints

fibrous layer

• outer layer consisting of dense irregular connective tissue

osteogenic layer

inner layer abutting bone and contains primitive osteoprogenitor stem cells that gives rise to most all bone cells

perforating fibers

bundles of collagen extending into bone matrix

Secure periosteum to underlying bone

Anchoring points for tendons and ligaments

endosteum

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

what are the 7 function of bones

support, protection, anchorage, mineral and growth factor storage, hormone production, triglyceride storage, and blood cell formation

hematopoiesis

occurs in red marrow cavities of certain bones

osteocalcin

secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism

in adults where is red marrow found

within trabeculsr csvities of spongy bone and diploe of flat bones

in newborns where is red marrow found

medullary cavities and spongy bone

bone markings

• Sites of muscle, ligament, and tendon attachment on external surfaces

  • Areas involved in joint formation or conduits for blood vessels and nerves

projections

• sites of muscle and ligament attachment

surfaces

helpt to form joints

depressions

• serve as passageways for vessels and nerves

what are the cells of bone tissue

Osteoprogenitor cells

Osteoblasts

Osteocytes

Bone-lining cells

Osteoclasts

osteoprogenitor cells

• Also called osteogenic cells

• Mitotically active stem cells in periosteum and endosteum

• When stimulated, they differentiate into osteoblasts or bone-lining cells

  • Some remain as osteoprogenitor stem cells

osteoblasts

• 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

bone lining cells

Flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes)

osteoclasts

• 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

all long bones have

diaphysis, epiphysis, and membranes

diaphysis

tubular shaft that forms long axis of bone

epiphysis

• ends of long bones that consist of compact bone externally and spongy bone internally

there is a what in between the epiphysis and diaphysis

epiphyseal line

Epiphyseal arteries and veins

vessels that service epiphysis

• Nerves accompany blood vessels and also pass through nutrient foramen

nutrient arteries and veins enter through what

nutrient foramen openings

are bones vascularized or poorly vascularized

well vascularized

osteons can be called what

haversian systems

lamellar (compact bone) consists of

osteons, canals and canaliculi, and Interstitial and circumferential lamellae

osteon

• 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

lamallae

• An osteon cylinder consists of several rings of bone matrix

lamallae contain what

collagen fibers

describe 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 lasts long after death because of mineral composition

Skeletal remains can reveal information about ancient people

bones are made up of what 2 components

Soft organic components such as bone cells and osteoid allow bone to resist tension (stretch)

Hard inorganic components such as mineral salts allow bone to resist compression

describe spongy bone

• 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

lacunae

small cavities that contain osteocytes

canaliculi

hairlike canals that connect lacunae to each other and to central canal

When matrix hardens and cells are trapped, what is formed

canaliculi

osteocytes

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

central haversian canal

runs through core of osteon

Contains blood vessels and nerve fibers

perforating volkmanns canals

canals lined with endosteum that occur at right angles to central canal

Connect blood vessels and nerves of periosteum, medullary cavity, and central canal

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

organic components

osteoprogenitor cells, osteoblasts osteocytes, bone lining cells, osteoclasts, and osteoid

sacrificial bonds

in or between collagen molecules that stretch and break to dissipate energy and prevent fractures

interstitial lamallae

Lamellae that are not part of osteon

Some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling

circumferential lamallae

just deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis

Help long bone to resist twisting

inorganic components of bone

hydroxyapaties that are 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 lasts long after death because of mineral composition

Skeletal remains can reveal information about ancient people

ossification is also called what

osteogensis

ossification

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

pagets disease

• Excessive and haphazard bone deposit and resorption cause bone to grow fast and develop 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 triggered by virus

  • Treatment includes calcitonin and bisphosphonates

preventing and treating osteoporosis

Traditional treatments

Weight-bearing exercise

Adequate Calcium and Vitamin D intake

Bone-sparing drugs that inhibit osteoclasts

what are the risk factors of osteoporosis

insufficient exercise to stress bones

Diet poor in calcium and protein

Smoking

Genetics

• Hormone-related conditions

  • Hyperthyroidism

  • Diabetes mellitus

• Consumption of alcohol or certain medications

• Most often aged, postmenopausal women

  • Affects 30% of women aged 60–70 years and 70% by age 80

  • Estrogen plays a role in bone density, so when levels drop at menopause, women run higher risk

  • Men are less prone due to protection by the effects of testosterone

osteoporosis

group of diseases in which bone resorption exceeds deposit

what happens in osteoprosis

• Matrix remains normal, but bone mass declines

  • Spongy bone of spine and neck of femur most susceptible

    • Vertebral and hip fractures common

Osteomalacia

• Bones are poorly mineralized

  Osteoid is produced, but calcium salts not adequately deposited

  Results in soft, weak bones

  Pain upon bearing weight

rickets

Results in bowed legs and other bone deformities because bones ends are enlarged and abnormally long

how are rickets and osteomalacia caused

vitamin D deficiency or insufficient dietary calcium

what are the 3 major bone diseases

Osteomalacia and rickets

Osteoporosis

Paget’s disease

what are the four main fracture repair

hematoma formation

fibrocartilaginous callus formation

bony callus formation

bone remodeling

bone remolding

• 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

hematoma formation

Torn blood vessels hemorrhage, forming mass of clotted blood called a hematoma

Site is swollen, painful, and inflamed

hematoma

torn blood vessels hemorrhage, forming a mass blood clotted area

fractures

breaks

During youth, most fractures result from trauma

In old age, most result from weakness of bone due to bone thinning

bony callus formation

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

Fibrocartilaginous callus formation

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

closed reduction

physician manipulates to correct position

Open reduction

surgical pins or wires secure ends

Immobilization of bone by cast or traction is needed for healing

Time needed for repair depends on break severity, bone broken, and age of patient

nondisplaced

ends retain normal position