1. Support

2. Storage of minerals & Lipids

3. Blood Cell Production

4. Protection (skulls, ribs, pelvis)

5. Leverage (Change the mangitude & direction of forces generated by the skeletal muscle.)

1. Long Bones: humerus, femur, fingers

2. Flat Bones: roof of skull, rubs, scapulae, sternum

3. Sutural Bones: Tiny bones between cranial bones

4. Irregular Bones: vertebrae, pelvis

5. Short Bones: Carpals, Tarsals

6. Sesmoid Bones: Patella

• Mature bone cells
• Most abundant
• Cannot divide
• Occupies a lacunae
• Linked by gap junctions

Functions:

• Maintain the protein/mineral content of the surrounding matrix
• When released from lacunae, osteocytes can change to osteoblasts to aid in repair of damaged bone.

• Produce new bone matrix through osteogenesis (ossification)
• Osteocytes develop from osteoblasts that have become completely surrounded by bone matrix
• Osteoprogenitor (mesenchymal) cells
• Divide to produce osteoblasts
• Important in repair (e.g., fracture)

• Remove and recycle bone matrix
• Giant cells with 50+ nuclei
• Produced from the same stem cells that produce monocytes and macrophages
• Enzymes secreted by the osteoclasts dissolve matrix and release stored minerals – osteolysis (reabsorption)
• Important in the regulation of calcium and phosphorus concentrations in body fluids

(Haversian Canal) – contains blood vessels (i.e., capillaries and venules)

Process of the synthesis of bone from cartilage.

Intramembranous: transformation of mesenchyme to bone.

Endochondral: Gradual replacement of cartilage by bone during development.

• Sturdy protective area
• Haversian system (osteon)
• Osteocytes are arranged in concentric layers around a central canal
• Central canal
• Lamella
• Thickest in areas of stress
• Strength along the axis of alignment (i.e., straw)

• Lamella are not arranged in osteons
• Trabeculae
• No capillaries or venules
• Nutrients reach the osteocytes by diffusion along canaliculi that open to the surface of trabeculae
• Red bone marrow found between the trabeculae
• Located where bones are not heavily stressed or where stress is from many directions
• Lighter than compact bone
• Yellow bone marrow - contains adipose tissue for energy reserve
• Red bone marrow – blood cell formation

• Chondrocytes near the center increase in size
• The lacunae expand
• The matrix is reduced to thin struts that begin to calcify
• The enlarged chondrocytes surrounded by calcified tissue start to die

• Blood vessels grow into the perichondrium surrounding the shaft of the cartilage
• The cells of the inner layer differentiate into osteoblasts
• The new osteoblasts begin to produce a thin layer of bone around the shaft of cartilage

• The blood supply to the periosteum increases
•   Capillaries and fibrocytes migrate into the heart of the cartilage
•   Fibrocytes differentiate into osteoblasts that replace remaining cartilage with bone
•   Primary ossification center because bone development begins at this site
• Bone development spreads toward both ends of the cartilaginous model
• The diameter of the diaphysis is small and filled with spongy bone with no medullary cavity present

Endochondral Ossification Part 4

• The bone enlarges
• Osteoclasts appear and begin to erode the trabeculae in the center of the diaphysis, creating a medullary cavity

• The epiphysis become filled with spongy bone
• A thin cap of the original cartilage model remains in the joint cavity as articular cartilage; prevents bone-on-bone at joint
• At the metaphysis, a narrow cartilaginous region called the epiphyseal cartilage separates the epiphysis from the diaphysis

Long bones have epiphyseal cartilage, a plate of cartilage that seperates the epiphyses from the diaphysis as long as the long bone is growing in length. An x-ray could tell if the epiphyseal cartilage is present. If it is not, they are at full height.

Appositional: Increase thickness and is responsible for remodling of all the long bones

Endochondral: Turns cartilage into bone, most growth is lengthwise.

• Mesenchymal cells cluster together and secrete organic compounds of the matrix
• The resulting osteoid becomes mineralized through crystallization of calcium salts
• As calcification occurs, mesenchymal cells differentiate into osteoblasts
• The developing bone grows outward from the ossification center (i.e., location where ossification begins) in spicules
• Mesenchymal cell divisions continue to produce additional osteoblasts

• Blood vessels begin to grow in the area
• As spicules meet and fuse, some of these blood vessels   
• become trapped within the developing bone

• Initially the bone consists of spongy bone only, but subsequent remodeling around trapped blood vessels can produce osteons typical of compact bone
•  As growth slows, connective   tissue around bone forms   the periosteum

His poor diet consisting of little nutrients and vitamins would result in a slower healing process. His inactivity may also contribute to a slower reate. (bones may be thin/brittle)

Compare and contrast the functions/actions of calcitonin and parathyroid hormone.

Calcitonin: Homeostatic control of calcium (thyroid)

Parathyroid: homeostatic control of phosphorus (parathyroid)

Vitamin A: Stimulates osteoblasts

Vitamins K&B12: Required for sunthesis of proteins in bone

Vitamin D: Calcium and Phosphours levels.

Heavily stressed bones become thicker and stronger

Bones: Store 99% of calcium in body

Digestive Tract: Absorb Calcium

The Kidneys: Excrete Calcium

Inadequate ossification. Gradually lose osteoblasts activity with age.

• External callus forms
• Enlarged collar of cartilage and bone, encircles the bone at the level of fracture
• The cells of the intact endosteum and periosteum undergo rapid cell division to replace missing cells in the fractured area
• Internal callus forms
• Organizes within the medullary cavity and between the broken ends of the shaft
• Callus cells differentiate into chondrocytes that produce a layer of hyaline cartilage that stabilizes the bone

nOsteoblasts replace the cartilage of the callus

nStruts of spongy bone unite the broken ends

nInternal and external callus form an extensive and continuous brace at the fracture site

nCast can be removed

nPituitary failure leading to inadequate production of growth hormone and resulting in reduced epiphyseal cartilage activity

nThe result is abnormally short bones

nBecoming increasingly rare in US

oSynthetic growth hormone supplementation