Osteology

1. Axial skeleton=skull vertebral column, ribs and sternum

2. Appendicular skeleton=pectoral girdle, upper limbs, pelvic girdle, and lower limbs

3. Functions of the skeletal system

   1. Protection

      1. ribs protect heart and lungs

      2. skull protects brain

      3. vertebrae protect the spinal cord

      4. pelvic bones protect the reproductive organs

   2. Support

      1. provides framework for attachment of organs

   3. Leverage

      1. muscles pull on bones to produce movement

   4. Blood cell production

      1. bone marrow produces erthyocytes, leukocytes, and platelets

   5. Storage of minerals

      • calcium Ions: 98% of bodies

      • phosphate ions

Classification of bones

1. Long bones= Typically longer than they are wide. Consists of a shaft and two ends

2. Flat bones=Thin and flatten, often a bit curved

3. Round/Short bones= Cube shaped bones (wrist and ankle)

   1. Sesamoid bones=special short bones enclosed in tendons

4. Irregular bones= Complicated shape that do not fit into other classifications

Bone Markings

1. Learning bone markings is part of the anatomical language

2. Sites of muscle, ligament, and tendon attachment on external surfacces

3. Areas involved in joint formation or conduits for blood vessels and nerves

   

Histological Organization of Bone

1. Osseous tissue is a supportive connective tissue

   1. bone matrix: calcifed

   2. collagen fibers-contribute to tensile strength of bones

   3. bone cells

2. Composition of bone matrix

   1. osteoid: organic component

      1. ground substance

      2. produced y the osteoblasts

      3. consists mostly of collagen protein fibers-contirbutes to flexibility

   2. Hydroxyapatite: inorganic component

      1. calcium phosphate combines with calcium hydroxide

      2. forms crystals of appetite

   3. crystals then deposit around fiber to harder the matrix

3. BONE CELLS

   1. Osteoprogenitor cells

      1. Derived from mesenchymal cells

      2. produce cells that the mature to become osteoblasts

      3. located in the periosteum and endosteum in adults

      4. initiate ossification in developing bone

      5. 

   2. osteoblasts

      1. Often positioned side by side on bone surfaces

      2. synthesize and secrete osteoid

         1. INITIAL SEMISOLID FORM OF MATRIC

         2. later calcifies

   3. osteocytes

      1. mature bone cells derived from osterovlasts

      2. have lost bone forming ability

      3. maintain protein and mineral content of the matrix

      4. stimulate the release of calcium ions form the bone to the blod

      5. can detect mechanical stress on bone

   4. osteoclasts

      1. Breakdown bone through acidic secretions and lysomal enzymes

      2. EAT BONE. Pac man

         1. plays role in bone remodeling

         2. reabsorb bone minerals such as calcium into blood stream

         3. parathyroid hormone indirectly stimulates osteoclasts to reabsorb calcium from bone when blood calcium drops

   1. LONG BONE

      1. Compact bone: dense outer layer that appears smooth and solid

      2. spongy boen: moade up of a bhonoeycpmb of small needle liek pieces of bone called trabeculae

         1. open spaces r filled with red or ywllo boen marrow

         2. surronds the medullary cavity

      3. Sturcture:

         1. Diaphysis=tubular shaft

            1. consists of compact bone surroning central meduallry caivety thatis fille dwith yellow marrow in adults

         2. epiphyses=ends of long boens

            1. articular cartilage covers articlar joint surfaces

         3. between disphysis and epiphysis is epiphyseal line

            1. remnant of childhood epiphyseal plate where bone grwon occurs

         4. 

   2. Short, irregular, and flat bones= consist of thin plates of spongy bone covered by compact bone

      1. compact bone sanwiched between connective tissue membrnaces

      2. hyaline carilage conver area of bone that is part of a movable joint

4. BONE MEMBRANES

   1. periosteum= white double layered mem brane that covers external surfaces except joints

      1. fibrous layer=dense irregular connective tissue

      2. contians many nerve fibers and blood vessels

      3. perforating fibers= anchoring points for tendons and liagments (collagen projecting into bone)

   2. inner layer (osteogenic) =contains osteoprogeniotr cells, osteoblasts

   3. endosteum

      1. delicate connective tissue membrane covering internal bone surface

      2. covers trabecular of spongy bon

      3. lines canals that pass thorugh compact bone

      4. COMPACT-LAMELLAR BONE

         1. consists of

            1. osteon

            2. canals and canaliculi

            3. intersitial and circymferential lamellae

      5. 

1. Central (Haversian) canal runs through core of osteon

• Contains blood vessels and nerve fibers

  2. Perforating (Volkmann’s) canals:

• Canals connect blood vessels and nerves of periosteum, medullary cavity, and central canal

  3. lacunae=small caivites that c ontian osteocytes

  4. canaliculi=hairlike canals that connect to lacuasne to each other and to central canal

  5. osterobalsts that secrete bone matric maitain contact with each other and osteocytes via cell projection siwth gap juntion

  6. when matric harderns and cells r traped the canaliculi form

     1. allow communication between all osteocytes or osteon and permit nutrients and wastes to be realted from one cell to antoher

BONE DEVELOPMENT

1. ossification (osteognesises) is the process of bone tissue fromation

   1. formation of bony skelton begins in month 2 of developemtn

   2. postanatl bone growth occurs until early adulhoot

   3. always bone remodeling

2. UP to about week 8, fibrous mebrane and hyaline carilage o ffetal skelton are replaced with bone tissue

3. endochondral ossifciatoion

   1. bone forms by replacing hyaline carilage

   2. called cartilage (endochondral bones)

   3. form most of skeleton

   4. intrambranous ossificaiton