Anatomy- Chp 5

functions of the skeletal system

support, mineral storage, blood cell production, protection, leverage

support

framework for body and soft tissues

mineral storage of skeletal system

stores Ca2+ and phosphate (98& of body calcium in bones0

blood cell production of skeletal system

hematopoiesis; occurs in red bone marrow

protection

_____ of skull (brain), ribs (heart/lungs), vertebrae (spinal cord)

leverage of skeletal system

bones act as levers for muscle movement

bone (osseous) tissue

specialized connective tissue

components of osseous tissue

cells, protein fibers, extracellular matrix hardened by calcium salts

• covered by periosteum (outer surface)

• lined internally by endosteum

bone matrix

2/3 inorganic, 1/3 organic- combo= strong but not brittle

inorganic bone matrix

calcium phosphate, hydroxyapatite crystals- provides compression resistance

organic bone matrix

collagen fibers, proteins- provides tensile strength and flexibility

lamellae

layers of calcified matrix

lacunae

spaces holding osteocytes

canaliculi

tiny channels connecting lacunae

bone cells

osteocytes, osteoblasts, osteoproginator cells, osteoclasts

osteocytes

mature bone cells

• maintain matrix

• regulate calcium exchange

osteoblasts

bone- forming cells

• secrete osteoid

• responsible for osteogenesis

osteoproginator cells

stem cells

• differentiate into osteoblasts

• important for growth and repair

osteoclasts

bone-resorbing cells

• break down bone via osteolysis

• release calcium into blood

strength

bone ____ depends on balance between osteoblasts and osteclasts

compact bone

• dense, strong

• made of osteons (Haversian systems) → central canal (blood vessels), perforating (volkmann’s) canal (connect canals)

• best at resisting force in one direction

spongy bone

• cancellous/trabecular

• lattice of trabeculae

• lighter, more flexible

• resists stress from many directions

• contains red marrow

ossification

bone formationt

types of ossification

intramembranous ossification, endochondral ossification

intramembranous ossification

bone develops from mesenchyme; forms- flat bones of skull, face, clavicle

endochondral ossification

bone replaces hyaline cartilage model; forms- long bones, vertebrae

length bone growth

• occurs at epiphyseal cartilage (growth plate)

• stops at epiphyseal closure

• leaves epiphyseal line

diameter bone growth

• appositional growth

• osteoblasts add bone to outer surface

• osteoclasts remove bone from inner surface

• medullary cavity enlarges as bone thickens

blood and nerve supply

• nutrient artery and vein- diaphysis

• metaphyseal vessels- near growth plate

• epiphyseal vessels- epiphyses

• periosteal vessels- outer bone surface

• bones are highly innervated → fractures are painful

factors regulating bone growth

• minerals

• vitamins

• PTH

• calcitonin

• GH, thyroxine, sex hormones

bone minerals

calcium, phosphate, magnesium

vitamin A

in bone growth; osteoblast activity

vitamin C

in bone growth; collagen synthesis

vitamin D3

in bone growth; calcium absorption

PTH

hormone; in bone growth; increases osteoclast activity

Calcitonin

hormone; in bone growth; inhibits osteoclasts

GH, thyroxine, sex hormones

hormone; in bone growth; stimulates growth

bone maintenance

bone is constantly remodeled; 20% of adult skeleton replaced each year

bone remodling

responds to stress (exercise increases bone mass); lack of stress → bone loss

bone fracture repair

requires intact blood supply, periosteum, endosteum; healed bone is usually stronger at repair site

osteopenia

reduced bone mass (normal aging0

osteoporosis

severe bone loss → fracture risk

faster

women lose bone ___ than men after 30-40 years

bone shape categories

1. long

2. short

3. flat

4. irregular

5. sesamoid

6. sutural (wormian)

7. pneumatized

bone markings

used for identification and anatomical landmarks

projections

muscle/ligament attatchment

depressions/openings

nerves and vessels

integration with other systems

• muscular- movement

• cardiovascular- blood supply

• endocrine- hormone regulation

• digestive & urinary- mineral balance

• skeleton acts as mineral reservoir

bone marrow transplant

Transferring healthy bone marrow stem cells from one person into another to replace bone marrow that either is dysfunctional or has been destroyed by chemotherapy or radiation.

bone mineral density test (BMD)

A test to predict the risk of bone fractures by measuring how much calcium and other types of minerals are present in the patient's bones.

closed reduction

The correction of a bone fracture by manipulation without incision into the skin

open reduction

The correction of a bone fracture by making an incision into the skin and rejoining the fractured bone parts, often by mechanical means such as a rod, plate, or screw.

orthopedics

The branch of medicine dealing with the correction of deformities of bones or muscles.

osteogenesis imperfecta (OI)

An inherited (genetic) disorder characterized by extreme fragility of the bones; also called brittle bone disease.

osteomyelitis

An acute or chronic bone infection.

osteopertrosis

A rare hereditary bone disorder in which the bones become overly dense; it presents in one of three forms: osteopetrosis tarda, osteopetrosis congenita, or “marble bone” disease.

osteosarcoma

A type of cancer that starts in the bones; also called osteogenic sarcoma.

paget’s disease

A chronic disorder that can result in enlarged and misshapen bones due to abnormal bone destruction and regrowth.

traction

The application of a sustained pull on a limb or muscle in order to maintain the position of a fractured bone until healing occurs or to correct a deformity.

skeletal system

• skeleton

• cartilage

• ligaments

axial skeleton

skull, thoracic cage, spine

appendicular skeleton

limbs, pectoral girdle, pelvic girdle

functions of skeleton

• support: framework for attachment of other organs

• movement/locomotion: muscles use bones as levers

• storage of minerals (calcium ions, phosphate ions)

• blood cell production (hematopoiesis)

• protection

  • skull protects brain

  • ribs protect heart and lungs

  • vertebrae protect spinal cord

  • pelvic bones protect reproductive organs

hematopoiesis

blood cell production; bone marrow produces erythrocytes, leukocytes, and platelets

osseous tissue

matrix of bone consists of

• hydroxyapatite

• collagen fibers

• bone cells

hydroxyapatite crystals

mainly calcium phosphate (and calcium hydroxide) will resist compression, but inflexible; 2/3 of bone mass

collagen fibers

contribute to tensile strength of bones; imparts limited flexibility to matrix; 1/3 of bone mass

bone cells

2% of bone mass

intramembranous ossification

produces the roofing bones of the skull

endochondral ossification

replaces cartilages of embryonic skull

primary ossification

centers of the diaphyses (bones of lower limb)

steps of intramembranous ossification

1. differentiation of osteoblasts within mesenchyme

2. formation of bony spicules

3. entrapment of blood vessels

4. formation of spongy bone

differentiation of osteoblasts within mesenchyme

• Mesenchymal tissue becomes highly vascularized (many blood vessels form).

• Mesenchymal cells cluster, enlarge, and differentiate into osteoblasts.

• Osteoblasts group together and begin secreting the organic bone matrix (osteoid).

• Osteoid mineralizes as calcium salts crystallize within it.

• The site where bone formation begins is called an ossification center.

formation of bony spicules

• As ossification continues, osteoblasts surrounded by osteoid become osteocytes.

• Osteocytes remain trapped in small spaces called lacunae.

• Bone grows outward from the ossification center in small structures called spicules.

• More mesenchymal cells divide and differentiate into osteoblasts, allowing bone formation to continue.

entrapment of blood vessels

• Bone growth is an active process, so osteoblasts need oxygen and nutrients.

• Blood vessels branch and grow between the spicules, increasing the rate of bone growth.

• As spicules connect, they trap blood vessels within the developing bone.

formation of bony spicules

• Osteoblasts continue depositing bone, forming a bony plate.

• The plate is perforated by blood vessels.

• As adjacent plates fuse together, the bone structure becomes more complex.

steps of endochondral ossification

1. cartilage calcification and cartilage death

2. formation of bone collar

3. formation of primary ossification center

4. formation of medullary cavity

5. formation of secondary ossification centers

6. formation of epiphyseal plate and bone lengthening

7. epiphyseal closure

Cartilage Calcification and Chondrocyte Death

• Cartilage model enlarges as chondrocytes grow bigger.

• The surrounding cartilage matrix begins to calcify.

• Calcification cuts off nutrient supply.

• Chondrocytes die and break down, leaving empty cavities in the cartilage.

Formation of the Bone Collar

• Blood vessels grow around the outer cartilage.

• Perichondrium cells differentiate into osteoblasts.

• The perichondrium becomes the periosteum.

• Osteoblasts form a bone collar (thin compact bone layer) around the shaft.

Formation of the Primary Ossification Center

• Blood vessels and osteoblasts invade the center of the cartilage.

• They enter the spaces left by dead chondrocytes.

• Calcified cartilage breaks down.

• Osteoblasts replace cartilage with spongy bone.

• Bone formation spreads from the primary ossification center in the shaft toward both ends.

Formation of the Medullary Cavity

• The shaft initially fills with spongy bone.

• Osteoclasts break down bone in the center.

• This creates the medullary (marrow) cavity.

• The shaft becomes thicker while bone continues forming near the metaphysis.

Formation of Secondary Ossification Centers

• Capillaries and osteoblasts enter the epiphyses (ends of the bone).

• Secondary ossification centers form in these regions.

• The timing varies by bone and individual.

• Some bones have these centers present at birth, while others remain cartilage during childhood.

Formation of the Epiphyseal Plate and Bone Lengthening

• The epiphyses fill with spongy bone.

• A layer of cartilage called the epiphyseal plate remains between the epiphysis and diaphysis.

• Cartilage grows on the epiphyseal side, while osteoblasts replace cartilage with bone on the diaphyseal side.

• This process pushes the epiphysis away from the shaft, causing the bone to grow in length.

Epiphyseal Closure

• At maturity, cartilage growth slows while osteoblast activity increases.

• The epiphyseal plate becomes thinner and eventually disappears.

• This is called epiphyseal closure, ending bone length growth.

• The remaining mark is the epiphyseal line, and articular cartilage remains at the joint surface.

achondroplasia

A genetic disorder that causes short-limbed dwarfism because bones don’t grow normally, especially in the arms and legs. It happens when cartilage doesn’t properly turn into bone during growth.

Key idea: normal torso size but short arms and legs due to abnormal bone development.

osteocyte

mature bone cell that maintains the bone matrix

osteoblast

immature bone cell that secretes osteoid, the organic bone matrix

osteoproginator cell

stem cell that divides to produce osteoblasts

osteoclasts

multinucleate cell that secretes acids and enzymes to dissolve bone matrix

osseous tissue types

• compact bone

• spongy bone

compact bone

• dense bone

• dense and solid

• forms walls of bone

• parallel compression

spongy bone

• trabecular bone

• open network of plates

• multidirectional or light train

• surrounds medullary cavity

• bone marrow: connective tissue in medullary cavity

epiphysis

ends of long bones

diaphysis

shaft of long bones

metaphysis

transition between epiphysis and diaphysis

medullary cavity

inner cavity of diaphysis; houses bone marrow

epiphyseal line

growth line

periosteum

membrane on outer surface of bone

• fibrous layers and osteogenic layer (complete, multi cell layer)

• isolates and protects bone from surrounding tissue

• attachment for circulatory and nervous supply

• actively participates in bone growth and repair

• attachment site for tendons and ligaments

perforating fibers

anchors periosteum to bone and other connective tissues

endosteum

membrane on inner surface of bone; single, incomplete layer

• line medullary cavity perforating canals and central canals