Ch. 6 - Bones and Organization

How many bones in the axial skeleton? Appendicular?

• Axial; 80 bones (thoracic, skull, and vertebral column)

• Appendicular: 126 bones (limbs and girdle)

206 total

What are ligaments versus tendons?

• Ligaments: bone to bone

• Tendons: bone to muscle

What are the functions of the skeletal system?

1. Support

2. Store minerals and lipids

3. Produce blood cells

4. Protection

5. Leverage

What are the minerals?

• Inorganic ions; Ca2+ and PO43-, Na+ and K+

What are osteoclasts?

• Osteoclasts (“crush bone/matrix): erode bone and release calcium

What are osteoblasts?

• Osteoblasts (builds bone): uses calcium to create new matrix

What are the 5 classification of bones?

1. Flat bones

2. Sutural bones (wormian)

3. Long bones

4. Irregular bones

5. Sesamoid bones

6. Short bones

What is an example of a flat bone?

• Ex: Cranial bones (parietal, frontal, occipital, temporal)

  • thin, concave

What is an example of sutural bones?

• Wormian bones

  • between cranial bones and on sutures

What is an example of a long bone?

• Humerus

  • shaft, long

What is an example of an irregular bone?

• Vertebrae, pelvis

What is an example of sesamoid bones?

• Patellar

What is an example of short bones?

• Carpals and tarsals

What are the three main areas of a long bone?

1. Epiphysis

2. Metaphysis

3. Diaphysis

Where is the epiphysis found on the long bone?

• Found; on each end of bone

What is the epiphysis made up of?

• Spongy bone

• Compact bone outer covering

What is the epiphysis covered by? What is this made up of?

• Articular cartilage; made up of hyaline cartilage (smooth collagen)

  • within joints

Where is the metaphysis found on the long bone?

• Below epiphysis on both ends; connects epiphysis to shaft

Where is the diaphysis found on the long bone? What does it contain?

• Found; middle, the shaft

• Contains medullary cavity (marrow)

What types of bone marrow are found within the medullary cavity in the diaphysis?

1. Red bone marrow: RBC and WBC production (no lymphocytes)

2. Yellow bone marrow: adipose tissue as energy reserve

What is the main difference between compact bone and spongy bone?

• Compact bone; outer area cortex

• Spongy bone; inside where water passes through

Where is the nutrient artery and vein found?

• Found; diaphysis

  • includes nutrient foramen

Where is metaphyseal artery and metaphyseal vein found?

• Found; metaphysis

  • connects to epiphyseal arrtery/veins

What is the function of osteogenic/osteoprogenitor cells?

• Mesenchymal/stem cells; produce cells and differentiate into osteoblasts

What is the order of becoming an osteocyte?

• Osteogenic cells (stem) —> osteoclasts

• Osteogenic cells (stem) —> osteoblasts —> osteocytes

Where are the osteogenic cells found?

1. Inner lining of periosteum

2. Lining endosteum

3. Lining blood vessels

What is the function of the osteoblasts?

• Precursors; produce unmineralized matrix: osteoid through ossification

  • adds calcium to osteoid = osteocytes (bone)

What is the function of osteocytes? What can they not do?

• Maintain cells

  • Mature bone cells CANNOT divide (trapped in lacuna)

  • Maintain protein and minerals

What structures are a part of lacuna? What are their functions

• Osteocytes within lacuna

  • Lamellae: arrange matrix

  • Caniculi: provide channels of nutrients and for interconnection

What is the function of osteoclasts? Why do they release this?

• Osteoclasts (crush): to crush and remodel bone matrix and obtain calcium

  • releases acids and proteolytic; releasing stored minerals into blood stream

What is osteolysis?

• Osteolysis: releasing acids and breaking down proteins by crushing

  • process used by osteoclasts

How is compact bone organized? What does the central canal contain?

• Concentric lamellae; (circular) around central canal

  • osteocytes in lacunae between lamellae

• Central canal; contains blood vessels/nerves

How is spongy bone (in epihysis) organized?

• Lamella forms plates: trabeculae

  • caverns create open network

How do nutrients reach osteons?

• Through caniculi to trabeculae in spongy bone

What is found in trabeculae?

• Red bone marrow; found in trabeculae in spongy bone

What is compact bone? What two types of lamellae are found here?

• Compact bone; outer bone tissue layer

  • Circumferential lamellae; range across

  • Interstitial lamellae; fill spaces between osteons

How is compact bone connected?

• Perforated canals (perpendicular)

What is the periosteum? What are the two layers

1. Fibrous layer

2. Cellular inner layer

What are the functions of the periosteum?

1. Isolates bone

2. Route for blood and nervous supply

3. Bone growth and repair

What are the perforating fibers?

• Perforating fibers: attach periosteum to bone matrix

What is the endosteum? What is its function?

• Endosteum; lines medullary cavity

• Function; bone growth, repair, remodeling

What is the endosteum remodeled by?

• Remodeled by osteoclasts

  • Osteoclastic crypts; osteoclasts in depressions

Where is hyaline cartilage found? What is its function?

• Found; make up articular cartilage covering bones and joints

• Function; reduces friction

Where is fibrocartilage found? Function?

• Found; knee joint (meniscus) and intervertebral discs

• Function: resists compression and bone to bone contact

What are the 3 methods for bones to grow?

1. Apositional growth

2. Endochondrol ossification

3. Intramembraneous ossification (no cartilage)

What is the first step of apositional growth

1. Growth along periosteum; osteogenic cells differentiated in to osteoblasts

   • adds circumferential lamellae

   • along outside

What is the second step of apositional growth?

2. Osteoclasts; increase diameter by REMOVING bone (grows wide)

   • along inside

What bones use apositional growth and endochondrol growth to grow?

• Long bones

What is the first step of endochondral ossification?

1. Cartilage model model enlarges

   • Chondrocytes in medullary cavity; enlarge

   • Enlarged chondrocytes on edge; die off

What is the second step of endochondral ossification?

2. Blood vessels grow around cartilage

   • blood vessels around cartilage

   • osteoblasts build on edges of diaphysis: bone collar

What is the third step of endochondral ossification?

3. a. Blood vessels innervate medullary cavity

   b.Primary ossification center formed; spongy bone

What is the fourth step of endochondral ossification?

4. a. Medullar cavity formed

   b. Cartilage replaced by shaft

   c. Chondrocytes/blasts move to metaphysis

What is the fifth step of endochondral ossification?

5. a. Blood vessels innervate ephysis

   b. 2nd ossification center

What is the sixth step of endochondral ossification?

6. a. Formation of articular cartilage

   b. Epiphyseal cartilage separate epiphysis from medullary cavity

What is the seventh step of endochondral ossification?

7. At end of puberty; epiphyseal cartilage replace by epiphyseal line (bone)

   • Osteoblasts replace cartilage with bone

What is the difference between between endochondrol ossification and intramembraneous ossification?

• Intramembraneous ossification; doesn't use cartilage

What bones are made using intramembraneous ossifcation?

1. Cranial (flat) bones/Dermal bones

What is the first step of intramembraneous ossifcation?

1. Stem cells differentiate into osteoblasts secreting osteoid

   • osteoid + minerals = bone matrix: ossification center

What is the second step of intramembraneous ossifcation?

2. Bones grow out of spicules (struts)

   • osteoblasts trapped and mature in osteocytes

What is the third step of intramembraneous ossifcation?

3. Bone spicules fuse; blood vessels get trapped in bone

What is the fourth step of intramembraneous ossifcation?

4. Bone center becomes spongy; due to envelopment of blood vessels

What is the fifth step of intramembraneous ossifcation?

5. Compact bone is built around blood vessels and spongy bone

What does bone deposition mean?

• Bone growth

  • uses osteoblasts

What is the first step of fracture repair?

1. Fracture hematoma; large blood clot closes and seals injury

What is the second step of fracture repair?

2. Both external/internal callus formation

   • Internal callus: spongy bone rebuilt

   • External callus: uses cartilage + spongy bone to close

What is the third step of fracture repair?

3. Spongy bone formation; cartilage of external callus replaced by spongy bone

What is the fourth step of fracture repair?

4. Spongy bone in external callus replaced by compact bone

What is a transverse fracture?

• Break across transverse plane

What is a spiral fracture?

• Wringing in/twisting of bone

What is a greenstick fracture?

• One side of shaft broken/bent