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Bones Structure and Function

Skeletal System Organization �  System = Skeletal �  Organs = Bones

�  Each bone is an individual organ

�  Work together as joints (considered later)

�  Tissues = Connective �  Compact Bone �  Spongy (cancellous)

Bone �  Hyaline Cartilage

Skeletal System – Macroscopic Anatomy

� Axial Skeleton �  Head �  Vertebrae �  Ribs �  Pelvic Girdle

� Appendicular Skeleton �  Arms �  Legs

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Bone Types

We will use long bones as our example.

Long Bone – Macroscopic Anatomy Epiphysis (end)

•  covered with hyaline cartilage

•  compact bone forms exterior

•  spongy bone forms interior

•  contains epiphyseal line/plate

Diaphysis (middle) •  compact bone forms

exterior

•  center composed of the medullary cavity containing yellow or red marrow

Fig 7.1

Long Bone – Macroscopic Anatomy

Fig 7.2

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Long Bone – Microscopic Anatomy

�  Osteon = circular structure organized around blood vessels

�  Osteocyte = bone cells

�  Bone matrix = hard calcium-based material between cells

Fig 7.3

Bones – Tissue Types �  Bones and joints are composed primarily of

connective tissue �  Connective tissue is organized by type of

extracellular matrix

Connective Tissue

Non- Fibrous

Bone

Compact Spongy

Adipose Cartilage

Hyaline Elastic Fibro

Fluid

Blood

Fibrous

Dense

Regular Irregular

Loose

Tissue Types – Compact Bone Functions

ü  Hard and provides stability, framework, protection

Structure ü  Matrix has hard mineral structure, based on calcium

ü  Cells and matrix are arranged in regular, concentric pattern

Compact Bone

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Tissue Types – Spongy Bone Functions

ü  Lightens total bone weight and provides space for bone marrow

Structure ü  Matrix is softer mineral, less organized and less of it

ü  Empty spaces between matrix structure are filled with bone marrow

Spongy (cancellous) Bone

Tissue Types – Hyaline Cartilage Functions

ü  Provides soft and smooth covering to end of bone (articular surface)

ü  Helps provide smooth and easy movement between bones (at joints)

ü  Provides the starting material for new bone growth

Structure ü  Matrix is spongy (like jello)

and evenly distributed between the cells

ü  Cells (chrondocytes) are found in pairs within capsules called lacunae

Hyaline Cartilage

Bone Physiology Living bones perform the following processes: � Formation

�  Starts as an embryo, continues through fetal development and after birth

� Growth �  Occurs from before birth through maturity

� Remodel �  Old matrix is removed and replaced with new

matrix � Repair

�  Broken/damaged bones will heal and return to normal structure

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Bone Physiology – Formation �  Fetal bones are made of hyaline cartilage �  As cartilage cells die, they are replaced with spongy bone in diaphysis �  After birth, spongy bone invades diaphysis �  Compact bone replaces spongy bone in diaphysis �  Hyaline cartilage remains on epiphyseal surface and in growth plate

Fig 7.5

Bone Physiology – Growth

Epiphyseal (Growth) Plate

Bone Physiology – Growth

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Bone Physiology – Growth �  Bones grow in length at

the epiphyseal plate – hyaline cartilage in the epiphysis

�  Cartilage cells divide causing the epiphyseal plate (and bone) to grow

�  Cartilage cells die and are replaced by spongy bone

�  As adolescence ends, the growth plate decreases in size and eventually is replaced by bone

Bone Physiology - Remodeling ü  Bone  matrix  is  inorganic  and  

breaks  down  over  <me  ü  Specific  bone  cells  

(osteoclasts)  remove  old,  broken  matrix  

ü  Other  bone  cells  (osteoblasts)  re-­‐make/deposit  new  matrix  

ü  The  en<re  skeleton  is  re-­‐modeled  every  7-­‐10  years  

ü  Remodeling  slows  with  age,  elderly  people  have  thinner  bones  and  are  more  suscep<ble  to  broken  bones  as  a  result  

Bone Physiology - Repair �  Hemotoma, a mass of

clotted blood, forms at the fracture site.

�  A fibrous callus forms, and cartilage matrix is secreted.

�  Spongy bone forms to replace cartilage.

�  Bone remodeling occurs to remove excess material and replace compact bone.

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Bone Physiology Videos �  Intro to Bones -

http://youtu.be/inqWoakkiTc � Osteoblasts + Osteoclasts -

http://youtu.be/78RBpWSOl08 � Remodeling -

http://youtu.be/0dV1Bwe2v6c � Repair –

http://youtu.be/P5HwYWShBhw