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Skeletal System:

Bone Structure and Development

I).  Function of the skeletal system

A).  support

B).  protection

C).  movement

D).  mineral storage

E).  blood cell formation 

II).  Bones & Muscles  as Levers

Levers have 4 components

1).  Rigid bar


2).  Pivot/fulcrum


3).  Object that creates resistance


4). Force that supplies movement


bone and muscle as a lever


When the arm bends the bone represents the rigid bar


The elbow joint is the pivot


The hand is moved against the resistance or weight (weight of hand)


The muscles supply force


III). Skeletal CartilageHyaline Cartilage

Provides support with  flexibility and resilience.

A).  Articular cartilage

B).  Costal cartilage

C).  Nasal cartilage

D). Epiphyseal cartilage

E).  Embryonic  cartilage

IV). Long Bone Anatomy:

A). diaphysis

B). epiphysis

The epiphysis is usually covered in articular cartilage

C). epiphyseal line or plate

long bone anatomy osteon osteons


V). Bone Structure

A). compact bone

structural units called osteons.

Ostean consists of long cylinders that run parallel to the long axis of the bone.

Structure of an osteon

1). lamella  

2). Haverson’s canal: (oseonic canal)

3). canaliculi or perforating canals

4). lacuna: contain osteocytes (mature bone cells)

Types of osteocytes

i). osteoblasts: build bone

ii). osteoclasts: consume or remove bone


 B). spongy (trabecular) bone

A honeycomb or network of flat pieces called trabeculae that are organized along stress lines

C).  Medullary Cavity


D). Bone Marrow

Soft tissue in the medullary cavity and the trabeculae of the spongy bone

1). red bone marrow:

2). yellow bone marrow:

E). periosteum

The periosteum is supplied with nerve fibers, lymphatic vessels and blood vessels, which enter the bone.

It also contains osteoblasts (bone builders) & osteoclasts (bone breakers)

VI). bone development

A). osteogenesis: Bone tissue formation

1. cell types

i. oseteoblasts: build calcium matrix

ii. osteoclasts: reabsorb calcium matrix

2. ossification: formation of bone

Ossification replaces cartilage with bone matrix

3. Ossificantion Processes

i. Endochondral Ossification Long bones ossify---

along hyaline cartilage model

ossify on the outside with compact bone and move inward


ii. Intramembranous Ossification: Flat bones ossify--

from layers of unspecified connective tissue.

ossify inside with spongy bone and work outward to compact bone

B). Intramembranous Ossification of flat bones

1). An ossification center appears in the connective tissue.

2). A bone matrix is secreted in the fibrous membrane.

3). Woven bone and periosteum form.

4). Bone collar of compact bone forms and red bone marrow appears.

Fontanels Unossified fibrous membranes

C). Endochrondral Ossification of long bones

1). Formation of hyaline cartilage model

2). A bone collar forms around the diaphysis of the hyaline cartilage

3). Cartilage in the center of the diaphysis calcifies and then cavitates

4). The periosteal bud invades the internal cavity and spongy bone forms.   

                            The bud contains a nutrient artery and osteoclasts

5). The diaphysis elongates and a medullary cavity forms

6). The epiphysis ossify.

*Hyaline cartilage remains on the growth plate and the articulating surface.


VII). Bone Remodeling

Weekly recycle 5% to 7% of bone mass. With a replacement of spongy bone every 4 years and a replacement of compact bone every 10 years.

Bone deposit:

Bone reabsorption:

Controlled by:

1). Negative feedback

Ca++loop that maintains blood calcium.

It involves the hormones: Parathyroid Hormone and Calcitonin.


if blood Ca++ is low

 Parathyroid Hormone is released


Ca++ is reabsorbed from bone by osteoclasts


if blood Ca++ is high


 Calcitonin is released


Ca++ is absorbed into the bone by osteoblasts

2). Mechanical & gravitational forces.

Wolf’s Law

Bone grows where stressors are placed on it.

VIII). Bone Fractures

A).  Classification of fractures

1). non-displaced fractures

2). displaced fractures

3). complete fracture

4). incomplete fracture

5). open (compound) fracture

6). closed (simple) fracture

7). closed reduction

8). open reduction



(use 3 Cs)



B).  Types of fractures

1). green stick

2). partial or fissure

3). comminuted fractures

4). transverse fractures

5).  oblique fractures

6).  spiral fractures

7).  depressed fractures

8). compressed fractures

healing of fractures

IX). Repair of Fractures

STEP1:  A hematoma forms over the fracture site.

STEP2:  Fibrocartilaginous callus formation.

STEP3:  Bony callus formation

STEP4:  Bone remodeling


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