Chapter 6: The Skeletal System I Bone Tissue

tissue and organs of the skeletal system

bone, cartilage, and ligaments

cartilage

embryonic precursor of most bones and covers many joint surfaces

ligaments

hold bone to bone at joint

tendons

attach muscles to bone

functions of the skeleton

support

movement

protection of delicate organs

blood formation in marrow

electrolyte balance - calcium & phosphate

acid-base balance

detoxification

osteology

study of bone

bone

connective tissue with a hard matrix

mineralization (calcification)

process of hardening

other tissue present in bone

blood

bone marrow

cartilage

adipose tissue

nervous tissue

fibrous connective tissue

flat bone

thin, often curved

examples: ribs, skull

long bone

rigid levers for movement

examples: humerus, femur

short bone

glide within joints

example: carpals of wrists

irregular bones

complex shape

examples: vertebrae

sesamoid bone

oval, generally within tendon

example: patella

general features of long bones

compact and spongy bone tissues

two epiphyses (heads) at ends of diaphysis (shaft)

marrow (medullary) cavity

epiphysial line - remnant of growth plate

periosteum - covering

nutrient foramina - tubes/holes in bone for vessel

endosteum - lining

articular cartilage - covering joints

long bone anatomy

general features of short bones

composed of spongy bone sandwiched between plates of compact bone

flat bone anatomy

bone cells

osteogenic (osteoprogenitor) cells, osteoblasts, osteocytes, osteoclasts

osteo- prefix

relating to bone

osteogenic (osteoprogenitor) cells

stem cells

osteoblasts

bone-forming cells

osteocytes

mature bone cells, contribute to bone maintenance/homeostasis

lacunae - cavities that house osteocytes

canaliculi - small canals that connect lacunae

lacunae

cavities that house osteocytes

cancliculi

small canals that connect lacunae

osteoclasts

bone-dissolving macrophages

"blasts build, clasts clean up"

bone cells and their development

bone matrix

one third organic and two thirds inorganic

organic bone matrix

one third of bone matrix

collagen and large protein-carbohydrate complexes

inorganic bone matrix

two thirds of bone matrix

85% hydroxyapatite (crystalized calcium phosphate salt), 10% calcium carbonate, and 5% other inorganic material

compact bone

osteon - basic unit - concentric lamellae, central (haversian) canal

perforating canals

circumferential lamellae

spongy bone

spicules - rods and spines of bone

trabeculae - thin plates of bones

porous appearance - spaces filled with bone marrow

lightweight but strong

bone marrow

soft tissue located in medullary cavities of long bones, spaces within spongy bone, and large central canals with osteons

two types: red marrow (myeloid tissue) and yellow marrow

red marrow (myeloid tissue)

hematopoietic tissue (blood-forming tissue) - both red and white blood cells are made here

yellow marrow

mainly fat

location of red marrow in adults

skull, vertebrae, sternum, ribs, parts of pelvic girdle, and proximal heads of humerus and femur

location of yellow marrow in adults

long bones of limbs

bone development

ossification (osteogenesis)

ossification (osteogenesis)

bone formation

begins within mesenchyme (an embryonic connective tissue)

two methods of ossification - intramembranous and endochondral

intramembranous ossification

produces flat bones of skull and most clavicle

bone develops in fibrous sheet resembling the dermis

endochondral ossification

*most bones develop this way

bone develops from hyaline cartilage model

stages of intramembranous ossification

1. deposition of osteoid tissue into embryonic mesenchyme

2. calcification of osteoid tissue and entrapment of osteocytes

3. honeycomb of spongy bone with developing periosteum

4. filing of space to form compact bone at surface, leaving spongy bone in middle

simple stages of intramembranous ossification

mesenchymal cells line up along vessels, become osteoblasts, make bone

stages of endochondral ossification

1. early cartilage model

2. formation of primary ossification center, bony collar, and periosteum

3. vascular invasion, formation of primary marrow cavity, and appearance of secondary ossification center

4. bone at birth, with enlarged primary marrow cavity and appearance of secondary marrow cavity in one epiphysis

5. bone of child, with epiphysial plate at distal end

6. adult bone with a single marrow cavity and close epiphysial plate

bone elongation

bones grow longer at epiphysial plates

metaphyses

plates made of hyaline cartilage

metaphysis

area of transition from cartilage (epiphyseal plate) to bone (diaphysis) at each end of marrow cavity

zones of metaphysis

think of it as cartilage providing a scaffold for bone to be formed

via endochondral ossification

bone widening and thickening

appositional and intramembranous ossification

apositional growth

growth in diameter and thickness

intramembranous growth

at surface

osteoblasts in periosteum deposit matrix

once matrix hardens, cells become osteocytes

circumferential lamellae are formed (not concentric lamellae)

osteoclasts widen medullary cavity

bone remodeling

absorption of old bone and deposition of new bone

bone is a living and dynamic tissue!

wolff's law of bone

wolff's law of bone

bone shape is determined by mechanical stress

bone adapts to withstand stress

form follows function

nutritional factors

calcium and phosphate

vitamin a

vitamin c (ascorbic acid)

vitamin d (calcitriol)

calcium and phosphate

raw materials for calcified ground substance

vitamin a

promotes formation of gylcosaminogylcans (protein-carb) fibers

vitamin c (ascorbic acid)

promotes collagen cross-linking-adding stiffness

vitamin d (calcitriol)

necessary for calcium absorption by small intestine and reduces urinary calcium loss

hormonal factors

calcitonin

growth hormone

estrogen and testosterone (sex steroids)

parathyroid hormone (PTH)

calcitonin

secreted by thyroid gland

stimulates osteoblasts in children and pregnant women

growth hormone

promotes intestinal absorption of calcium

stimulates growth plates and bone elongation

estrogen and testosterone (sex steroids)

stimulate long bone growth during adolescence

parathyroid hormone (PTH)

secreted by parathyroid glands

stimulates bone reabsorption to boost level of calcium in blood

the aging skeletal system

osteopenia

osteopenia

loss of bone (when severe it develops into osteoporosis)

resorption faster than deposition

after age 35 - osteoblasts less active than osteoclasts

after age 40 - females lose 8% of bone mass per decade and males lose 3% of bone mass per decade

fractures more common, heal slowly

fracture types

stress and pathological

stress fracture

caused by abnormal trauma

pathological fracture

occurs in bone weakened by a disease such as osteoporosis

fractures are classified according to

breaking of skin

direction of fracture

separation of bone pieces

treatment of fractures

closed reduction

open reduction

cast (fiberglass)

closed reduction treatment of fractures

nonsurgical manipulation of fragments

open reduction treatment of fractures

surgical setting involving plates, screws, or pins

how long does it take a fracture to heal

8-12 weeks

closed fracture

skin is not broke

(formerly called a simple fracture)

open fracture

skin is broken

bone protrudes through skin or wound extends to fractured bone

(formerly called a compound fracture)

complete fracture

bone is broken into two or more pieces

incomplete fracture

partial fracture that extends only partway across bone

pieces remained joined

nondisplaced fracture

the portions of bone are still in correct anatomical alignment

displaced fracture

the portions of bone are out of anatomical alignment

comminuted fracture

bone is broken into three or more pieces

greenstick fracture

bone is bent toward one side and has incomplete fracture on opposite side

hairline fracture

fine crack in which sections of bone remain aligned

common in skull

impacted fracture

one bone fragment is drive into the marrow cavity or spongy bone of the other

depressed fracture

broken portions of bone forms a concavity

as in skull fractures

linear fractures

fracture parallel to long axis of bone

transverse fracture

fracture perpendicular to long axis of bone

oblique fracture

diagonal fracture

between linear and transverse

spiral fracture

fracture spirals around axis of long bone as the result of a twisting stress such as a skiing accident

x-ray of nondisplaced fracture

x-ray of displaced fracture

x-ray of comminuted fracture

x-ray of greenstick fracture

stages of the healing of a bone fracture

1. hematoma formation - the hematoma is converted to granulation tissue by invasion of cells and blood capillaries

2. soft callus formation - deposition of collagen and fibrocartilage converts granulation tissue into soft callus

3. hard callus formation - osteoblasts deposit a temporary bony collar around the fracture to unite the broken pieces while ossification occurs

4. bone remodeling - small bone fragments are removed by osteoclasts while osteoblasts deposit spongy bone and then convert it to compact bone

osteoporosis

bones lose mass and become subject to pathological fractures

hip, wrist, vertebrae are especially vulnerable

kyphosis ("dowager's hump")

postmenopausal white light built women are at greatest risk

kyphosis ("dowager's hump")

exaggerated thoracic curvature

why are postmenopausal white light build women at greatest risk of osteoporosis

decline of estrogen results in less inhibition of osteoclasts

by age 70 have typically lost 30-50% of bone mass

osteoporosis treatments

bis-phosphonates and parathyroid hormone

osteoporosis prevention

weight bearing exercise

adequate calcium and protein

healthy versus osteoporotic bone

orthopedics

prevention and correction of injuries and disorders of bones, joints, and muscles