2.6 Anatomy Chapter 6

• Function:
• 1. provide support and shape to the body
• 2. provide attachment sites for muscle (impt for movement)
• 3. protection
• 4. acts as a storage depot for essential minerals ( Calcium and phosphate)
• 5. blood-cell formation, fat storage (red/yellow marrow)
• [6. Energy metabolism: osteoblasts secrete hormones related to blood sugar)

• Characteristics:
• 1. composed of bones, cartilages, and joints

• Characteristics:
• 1. Most abundant
• 2. Chondrocytes appear spherical
• 3. Made of collagen fibers
• 4. Resists compression well (bc of large amts of water)
• 5. Provides support through flexibility and resilience

• Location:
• 1. articular cartilage
• 2. cartilage attaching ribs to sternum
• 3. most cartilage in respiratory structures
• 4. forms embryonic skeleton

• Characteristics:
• 1. similar to hyaline, but matrix has elastic fibers as well as collagen
• 2. more elastic, more tolerant to repeated bending

• Location:
• 1. Epiglottis
• 2. External Ear

• Characteristics:
• 1. resists both strong compression and strong tension
• 2. consists of thick collagen fibers surrounding chondrocytes in lacunae

• Location:
• 1. anulus fibrosis portion of vertebral discs
• 2. articular discs of joints, ex. Knees
• 3. pubic symphysis

Appositional growth: "from outside"; chondroblasts in perichondrium actively secrete matrix

Interstitial growth: "from within"; chondrocytes within the cartilage divide and secrete new matrix

cartilage stops growing in late teens, and cells do not divide again

• 35% organic components (collagen)
• - contribute flexibility and tensile strength
• - baking at high temperature destroys organic portion

• 65% inorganic hydroxyapatites (mineral salts: calcium phosphate)
• - provide exceptional hardness to resist compression, endurance
• - soaking in acid dissolves mineral salts

• 1. Osteogenic cells: stem cells that differentiate into bone-forming osteoblasts
• 2. OsteoBlasts: cells that actively produce and secrete organic components of bone matrix
• 3. Osteoid: bone matrix secreted by osteoblasts (crystallized calcium salts within)
• 4. Osteocytes: function to keep bone matrix healthy; no longer producing new osteoid
• 5. OsteoClasts: cells responsible for bone resorption (derived from white blood cells; secrete HCl and lysosomal enzymes)

• 1. Long bones: longer than they are wide; consists of a shaft and two ends
• most bones in limbs: humerus, femur, tibia, fibula, ulna, radius, phalanges, metacarpals
• 2. Short bones: typically cube-shaped; sesamoid bone: "sesame seed-shaped"
• occur in wrist and ankle: tarsals, carpals; coccyx, patella
• 3. Flat bones: thin, flattened, usually curved
• most cranial bones, ribs, sternum, scapula, clavicle
• 4. Irregular bones: anything that doesn't fit into the previous categories
• vertebrae, coxal, mandible, sacrum

• Diaphysis/ epiphyses
• Articular cartilage
• Periosteum: two sublayers: superficial layer of dense irregular connective tissue (resists tension), deep layer consisting of osteoblasts and osteoclasts (bone remodeling)
• Endosteum: covers internal bone surfaces (also osteogenic)
• Perforating (Sharpey's) fibers: bundles of collagen that connect periosteum to bone matrix

• Sites of Muscle and Ligament Attachment
• 1. Tuberosity - Large rounded projection; roughened
• 2. Crest - Narrow ridge of bone; usually prominent
• 3. Trochanter - Large, blunt, irregularly shaped process (only on femur)
• 4. Line - Narrow ridge of bone; less prominent than crest
• 5. Tubercle - Small, rounded projection or process
• 6. Epicondyle - Raised area on or above a condyle
• 7. Spine - Sharp, slender, often pointed projection
• 8. Process - Any bony prominence

• Surfaces that form Joints
• 1. Head - bony expansion carried on a narrow neck
• 2. Facet - smooth, nearly flat articular surface
• 3. Condyle - rounded articular projection, often articulating with a fossa

• Depressions/ Openings
• (for vessels and nerves)
• 1. Foramen - round/oval opening through a bone
• 2. Groove - Furrow
• 3. Fissure - Narrow, slit-like opening
• 4. Notch - Indentation at the edge of a structure
• (others)
• 5. Fossa - Shallow, basin-like depression, often an articular surface
• 6. Meatus - Canal-like passageway
• 7. Sinus - Cavity within a bone, filled with air and lined with mucous membrane

• Central (Haversian) Canal: carries blood vessels, nerves, lymphatic vessels
• Osteocyte: mature bone cells in Lacunae: chambers
• Concentric Lamellae: circular tubes surrounding a central canal like rings in a tree trunk
• Interstitial Lamellae: incomplete remnants of Circumferential Lamellae: at internal and external layer of compact bone
• Osteon: central canal and all concentric lamellae surrounding it
• Canaliculi: tiny canals going outward from central canal to lacunae; provides connecting network for nutrient supply
• Perforating (Volkmann's) Canals: run perpendicular to central canal, from periosteum to bone interior

• Membrane bones form directly from mesenchyme without cartilaginous model
• - All bones in skull except base, and clavicles
• Week 8 of embryonic development: mesenchymal cells cluster and become osteoblasts that secrete organic bone matrix that become mineralized --> become osteocytes
• New bone tissue forms btwn blood vessels that result in woven bone tissue, mesenchyme condenses externally and becomes periosteum.
• Trabeculae at periphery thicken and form compact bone, sandwiching an internal spongy bone.

• All bones from the base of the skull down, except clavicles
• - first modeled in hyaline cartilage, gradually replaced by bone
• - begins late in second month of development, not complete until early adulthood
• - increases in length and width

• 1. Bone collar forms around diaphysis
• 2. Cartilage calcifies in center of diaphysis
• 3. Periosteal bud (blood vessel) invades internal cavity, forming spongy bone (primary ossification center)
• 4. Diphysis elongates, medullary cavity forms; secondary ossification centers appear in epiphyses
• 5. Epiphyses ossify; cartilaginous epiphyseal plates form (hylaine cartilage only in epiphyseal plate and articular cartilages)

• Resting Zone: cartilage cells nearest epiphysis; small and inactive
• Proliferation Zone: cartilage cells forming tall stacks, top cells divide quickly, pushing epiphyseal plate further away, lengthening bone
• Hypertrophic Zone: older chondrocytes enlarge and signal matrix to calcify
• Calcification Zone: matrix becomes calcified, chondrocytes die, leaving trabeculae
• Ossification Zone: trabeculae covered with bone tissue by osteoblasts

• Simple fracture: bone breaks cleanly, does not penetrate the skin
• Compound fracture: bone breaks in multiple pieces; penetrates skin
• Closed reduction: bone ends realigned by physician (no surgery required)
• Open reduction: bones realigned by pins/wires (through surgery)
• Healing requires 6-8wks for a simple fracture in healthy young adults

• 1. Hematoma formation (inflammation occurs)
• 2. Fibrocartilaginous callus formation: new blood vessels form, proliferation of osteoblasts, filling of cavity with soft callus which becomes dense CT containing fibro- and hyaline cartilage.
• 3. Bony callus formation: Within a week, bone trabeculae form via endochondral ossification and unite the two fragments
• 4. Bone remodeling occurs: months after repair, bone remodels due to mechanical stresses

• Osteoporosis: "bone porous condition"
• low bone mass and deterioration of microscoopic architecture
• - bone resorption outpaces bone deposition (osteoclast activity > osteoblast activity)
• - treated by supplemental calcium and vitamin D

• Osteomalacia and Rickets: "soft bones"
• bones are inadequately mineralized (lack of vitamin D and calcium phosphate)
• - calcification does not occur, bone softens and weakens
• - epiphyses in children become thickened
• - cured by drinking vitamin D-fortified milk, or sunlight exposure