Support (for soft tissues and organs)

Storage of minerals (eg. calcium) and lipids (eg yellow bone marrow)

Blood cell production (eg. red and white in red bone marrow)

Protection (eg. skull protects brain)

Leverage (change forces generated by skeletal muscle)

Sutural bones (between flat bones of skull)

Irregular bones (eg spinal vertebrae, pelvis)

Short bones (eg carpals & tarsal)

Flat bones (eg roof of skull, sternum)

Long bones (eg humerus)

Sesamoid bones (eg. patella, up to 26 although varies)

Osteocyte (Most common, mature bone cell that contains the bone matrix)

Osteoblast (Immature bone cell that secretes the organic components of matrix)

Osteoprogenitor (Stem cell whose divisions produce osteoblasts)

Osteoclast (Multinucleate cell that secretes acids and enzymes to dissolve bone matrix)

Compact bone contains:

Spongy bone contains:

Compact bones contain parallel osteons

Spongy bone contains trabeculae

An adult skeleton has 206 bones

The axial skeleton has 80 bones

The appendicular skeleton has 126 bones

Describe the structure of a long bone

Epiphysis (Expanded ends) - spongy bone

Diaphysis (Tubular shaft) - compact bone, surrounds medullary cavity

Metaphysis (join between diaphysis and epiphysis)

Cells - osteocytes in lacunae

Matrix is dense:

• calcium phosphate, carbonate and hydroxide
• hydroxyapatite
• collagen fibres

Remarkable properties:

• Calcium hard but brittle
• Collagen fibres strong but flexible

• Maintain matrix and repair bone

• In lacunae (compartments)

• Between layers of matrix (lamellae)

• Canaliculi are passages through lamella, join lacunae to each other and blood vessels

• Lamellae arranged in trabeculae (not osteons)

• Bone marrow around the trabeculae

• Blood vessels run through bone marrow

• Nutrients to osteocytes via canaliculi

Compact bone

• Thickest where stresses arrive from a few directions
• Osteons align along these stress lines - strong

Spongy bone

• Where bones are not heavily stressed
• Stresses come from many different directions
• Lighter

Periosteum (outside layer)

• Superficial layer that covers all bones (not in joints)
• Circulatory and nervous supply
• Bone growth

Endosteum (inside layer)

• Growth, repair and remodelling
• Incomplete cellular layer lines medullary cavity, trabeculae and central canals

Osteogenesis: Process of bone formation

Ossification: Process of replacing other tissue (eg. cartilage) with bone

Calcification: The deposition of calcium salts (anywhere)

Endochondrial ossification - bone replaces existing cartilage

- most bones begin as hyaline cartilage

- these cartilage models of bone are then ossified

Intramembranous ossification - bone develops from mesenchymal cells (stem cells)

Endochondrial ossification

STEP 1

• chondrocytes increase in size

• matrix is reduced and calcifies

• Chondrocytes die

Endochondrial ossification

STEP 2

• Blood vessels grow into perichondrium

• Mesenchymal cells differentiate into osteoblasts

• Layer of bone surrounds shaft

Endochondrial ossification

STEP 3

• Blood supply to centre

• Fibroblasts differentiate into osteoblasts and spongy bone

• Primary ossification centre

• Bone spreads to ends

Endochondrial Ossification

STEP 4

• Osteoclasts create medullary cavity

• Increase in length and diametre

Endochondrial ossification

STEP 5

• Blood supply to epiphyses

• Secondary ossification centres

Endochondrial ossification

STEP 6

• Epiphysis becomes filled with spongy bone

• Some cartilage remains (articular)

• Epiphyseal plate forms

• Bone grows as long as the epiphyseal cartilage continues to grow
• On the epiphyseal side new cartilage is added continuously
• On the shaft side osteoblasts invade the cartilage and turn it into bone
• As the osteoblasts make bone and are moving towards the epiphysis, the bone continues to grow as long as the epiphyseal cartilage continues to expand

• Appositional growth
• Osteoblasts in the inner layer of the periosteum deposit bone matrix
• Osteoblasts become surrounded in matrix and differentiate into osteocytes
• Layers of circumferential lamellae
• Deepest layers become replaced with osteons
• Osteoclasts remove matrix at the inner surface
• Medullary cavity enlarges with increased diametre

• Mesenchymal cells aggregate, differentiate into osteoblasts, and begin the ossification process. The bone expands as a series of spicules that spread into surrounding tissues
• As the spicules interconnect they trap blood vessels within the bone
• Over time, the bone assumes the structure of spongy bone. Areas of spongy bone may later be removed, creating medullary cavities. Through remodelling, spongy bone formed in this way can be converted to compact bone

• Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops
• An internal callus forms as a network of spongy bone unites with the inner edges, and an external callus of cartilage and bone stabilizes the outer edges
• The cartilage of the external callus has been replaced by bone, and struts of spongy bone now unite the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced
• A swelling initially marks the location of the fracture. Over time, this region will be remodelled, and little evidence of the fracture will remain
  

• Matrix - firm gel

• Cartilage cells - Chondrocytes

• Avascular (unusual)

Interstitial growth

• Chondrocytes undergo cell division and the daughter cells produce more matrix
• Enlarges cartilage from within (interstitial)
• Important for development from embryo to puberty

Appositional growth

• New layers of cartilage are added to the surface (under the perichondrium)
• Fibroblasts (stem cells) differentiate into immature chondrocytes that add to the matrix

Hyaline (eg. nasal, join ribs to sternum)

 - most common, closely packed collagen fibres make it tough

Elastic (eg. epiglottis, auricle)

- elastic fibres make it resilient and flexible

Fibrous (eg. between pubic bones)

- densely interwoven collagen fibres, extremely durable and tough

Calcium 39%

Potassium 0.2%

Sodium 0.7%

Magnesium 0.5%

Carbonate 9.8%

Phosphate 17%

plus

Organic compounds (mostly collagen) 33%

Which two hormones regulate storage, absorption and excretion of calcium ions?

And what are the three target sites?

Parathyroid hormone

Calcitonin

Bones (storage)

Digestive system (absorption)

Kidneys (secretion)

Parathyroid hormone (PTH) released

• Stimulates osteoclasts which releases stored calcium
• Increases absorption in intestine
• Decrease excretion at kidneys

Calcium concentrations increased and homeostasis restored

Calcitonin released (thyroid gland)

• Inhibits osteoclasts and osteoblasts continue to store calcium in bone
• Decreases absorption in intestine
• Increased excretion at kidneys

Decreased calcium ion concentration and homeostasis is restored

Describe Osteopenia & Osteoporosis

Osteopenia - inadequate ossification causing loss of skeletal mass, normal to a certain extent

Osteoporosis - when the reduction in bone mass is sufficient to compromise normal function

• Osteoblasts (add matrix) reduce activity
• Osteoclasts (remove matrix) continue same level of activity

Synarthrosis - Immovable joint

- Fibrous, cartilaginous, or bony fusion

- Bones of the skull, teeth, epiphyseal cartilages

Amphiarthrosis - slightly movable joint

- Fibrous or cartilaginous

- Between tibia and fibula and between pubic bones

Diarthrosis - freely movable joint

- Synovial joint (further divided into types)

• Gliding
• Hinge
• Pivot
• Ellipsoid (condyloid)
• Saddle
• Ball & socket

Slight nonaxial or multiaxial movement

• Acromioclavicular and claviculosternal joints
• Intercarpal and intertarsal joints
• Vertebrocostal joints
• Sacroiliac joints

Monaxial movement

• Elbow joint
• Knee joint
• Ankle joint
• Interphalangeal joint

Monaxial (rotation)

• Atlas / axis
• Proximal radio-ulnar joint

Biaxial movement

• Radiocarpal joint
• Metacarpophalangeal joints 2-5
• Metatarsophalangeal joints

Describe and give examples of saddle joints

Biaxial movement

• First carpometacarpal joint

Triaxial movement

• Shoulder joint
• Hip joint

Wrist - gliding

Neck - flexion, extension and hyperextension

Vertebral column - angular movements - flexion, extension and hyperextension

Shoulder and knee - angular movements - flexion and extension

Shoulder - abduction, adduction and circumduction

Head, neck and lower limbs - rotation

• Supination and Pronation
• Dorsi flexion and Plantar flexion
• Inversion and Eversion
• Protraction and Retraction
• Elevation and Depression
• Opposition