1. Supports the body
2. Protects vital internal organs
3. Allows for body movement by having bone function as an anchoring point for muscles while using joints to act as levers

1. Storage of minerals in the form of calcium and phosphate ions (up to 1000x more Ca++ than any other tissue, stored in the form of hydroxyapatite crystals)
2. Storage and production of blood cells in the red bone marrow
3. Storage of lipids in the yellow bone marrow
4. Plays a small role as a buffer by helping blood resist pH changes by absorbing and releasing alkaline phosphate and carbonate salts

• Long: length > width (e.g. femur, phalanges)
• Short: length = width, found only in the carpals and tarsals, completely covered in cartilage
• Flat: thin, flat (e.g. ribs, scapula, some skull bones)
• Irregular: variety of shapes (e.g. vertebrae, facial bones)
• Sesamoid: small and nodular, embedded within tendons (e.g. patella)

• The shaft of the bone, found between the metaphyses.
• Comprised of the medullary cavity AKA marrow cavity, which is a hollow tube within the diaphysis containing yellow marrow (in children it can contain red marrow), blood vessels and endosteum (a delicate reticular CT membrane lining the medullary cavity and canals that pass through compact bone and trabeculae containing osteogenic cells and osteoblasts)

• Osteogenic AKA osteoprogenitor cells: stem cell derived from embryonic mesenchymal cell; undergoes mitosis; develops/differentiates into an osteoblast
• Osteoblast: immature bone-forming cell; no mitosis; synthesizes and secretes osteoid (organic, unmineralized ground substance)
• Osteocyte: mature cell derived from an osteoblast trapped in a lacuna; no mitosis; exchanges Ca++ and P into and out of bone to regulate bone shape and densityl exchanges nutrients and wastes with blood
• Osteoclast: modified macrophage that dissolves or 'eats' bone via acidic secretions

• A line produced where adult skull bones join. It makes skull bones immovable, decreasing the chance of Fx or dislocations.
• Coronal, sagittal, lambdoid, squamous

• A pliable membrane of uncalcified cartilage that joins skull bones during fetal life and early childhood; allows for brain growth and birth compaction of the skull
• Anterior, posterior, anterolateral (sphenoidal), posterolateral (mastoidal)

In newborns: C-curve

In adults: Cervical curve, lumbar curve

• Kyphosis: exaggerated curve of thoracic area, hunchback. etiology is poor posture or athletic training
• Lordosis: exaggerated curve of the lumbar area; swayback; etiology is obesity, pregnancy, disk degeneration
• Scoliosis: lateral curvature of the thoracic and/or lumbar areas; sideways curved when viewed posteriorly; etiology is muscle weakness on one side

• Central canals along the sagittal plane for blood vessels and nerves
• Perforating/Volkmann's canals along the transverse plane to connect the central/haversian canals to larger blood vessels within the medullary cavity and periosteum
• Lamellae forming concentric rings of calcified matrix around the central canal
• Lacunae containing the trapped osteocyte
• Canaliculi which are small canals radiating from each lacuna; connecting the lacunae with each other and with the central canal for nutrient and waste exchange
• Entirety of above makes up an Osteon/Haversian system

• Located at the epiphysis and metaphysis
• Withstands compression forces
• Composed of trabeculae which is the matrix of spongy bone. Trabeculae are arranged in numerous branching, interlaced spikes/plates of bone. Within these are osteocytes in lacunae
• Red marrow aka myeloid tissue fills the interconnecting spaces between trabeculae and is the site of hematopoiesis. In adults red marrow is more active in flat and irregular bones than in long bones
• Spongy bone is usually sandwiched between 2 layers of compact bone

1. Mesenchymal CT cells migrate to the site where bone is to be laid down
2. If capillaries are present(MUST be present for I.M. Ossification), MCT becomes loose fibrous CT membrane
3. This gives rise to intramembranous ossification

1. Mesenchymal CT cells migrate to site where bone is to be laid down
2. If no capillaries are present (capillaries must NOT be present in order to begin endochondral ossification), MCT is replaced by hyaline cartilage
3. Hyaline cartilage model is used to begin endochondral ossification

1. Mesenchymal CT cells lay down primitive CT in the form of a fibrous membrane at the site of future bones. Cells within the membrane cluster around blood vessels, enlarge, and differentiate into osteoblasts to form an ossification center
2. Osteoblasts secrete osteoid around themselves. The matrix calcifies and osteoblasts become trapped in lacunae where they mature into osteocytes
3. As bone matrix forms it develops into trabeculae and not lamellae. Later the trabeculae will fuse to each other. The vascularized mesenchymal CT between the trabeculae differentiates into a marrow cavity, becoming red marrow. On the outside, the fibrous membrane gives rise to periosteum
4. Eventually the surface layers of spongy bone close to the periosteum are replaced by compact bone

1. Mesenchymal CT cells clump together at the site of future bones and differentiate into chondroblasts, which lay down the primitive hyaline cartilage model
2. Perichondrium membrane, which develops around the cartilage model, becomes infiltrated with blood vessels and differentiates into periosteum. The osteoblasts from this perioesteum secrete osteoid around the diaphysis of the model which surrounds it with a bone collar.
3. While the bone collar forms, cartilage grows via chondrocyte mitosis. Hypertrophied chondrocytes calcify, die, and rupture which results in a change in pH. Cartilage deteriorates at the diaphysis, which is stabilized by the bone collar. This region is termed the Primary Ossification Center
4. A periosteal bud (blood vessels, lymphatic vessels, nerve fibers, osteoblasts, osteoclasts, red marrow elements) invades the diaphyseal cavity to form the primary marrow cavity. Osteoblasts secrete osteoid in the diaphysis which develops spongy bone trabeculae.
5. The primary ossification center enlarges and ossification continues from mid-diaphysis towards the ends of the cartilage. Osteoclasts break down trabeculae within the diaphysis.
6. Cartilaginous epiphyses at both ends continue to grow, elongating the cartilage model. Hypertrophied chondrocytes within the epiphysis calcify, die, and rupture, resulting in a change in pH to deteriorate the model, creating a secondary ossification center. (This step is similar to step 3)
7. Osteoclasts hollow out the secondary ossification center, forming a secondary marrow cavity in the epiphysis. This eventually fills with spongy bone. The epiphyseal plate separates the primary and secondary marrow cavities. The plates (one at each end of a long bone) serve as a growth zone for bone elongation.
8. Around the late teens to early twenties the plate is converted to bone and becomes the epiphyseal line. Bones no longer grow in length.

1. Zone of Reserve Cartilage (AKA Resting Zone): inactive cartilage
2. Zone of Cell Proliferation (AKA Growth Zone): Stacks/columns of chondrocytes rapidly undergoing mitosis. This pushes the epiphysis away from the diaphysis, lengthening the long bone
3. Zone of Cell Hypertrophy: Stacks of older chondrocytes enlarge
4. Zone of Calcification: Cartilage matrix calcifies around the hypertrophic chondrocytes
5. Zone of Bone Deposition (AKA ossification zone): Hypertrophic chondrocytes deteriorate and die, then are digested by osteoclasts, and then quickly get covered by bone matrix from marro cavity's osteoblasts. This forms spongy bone trabeculae, which lengthens the bone at the epiphyseal-metaphyseal junction

• Appositional: bone widening/thickening
• Interstitial: bone elongation

• Growth Hormone: Pituitary gland
• Parathyroid Hormone: Parathyroid glands
• Calcitonin hormone: Thyroid gland
• Estrogen/Testosterone: gonads

• Pituitary Dwarfism - decreased hGH in child, long bones don't develop
• Gigantism - increased hGH in child
• Acromegaly - increased hGH in adult

• When blood Ca++ levels are too high
• Stimulates osteoblast activity, inhibits osteoclast activity, lowering blood Ca++ levels

• Vitamin A: needed for osteoclast activity during normal dev
• Vitamin C: needed for collagen synthesis for the bone matrix (C for Collagen)
• Vitamin D: needed for absorption of Ca++ from the large intestines.

• Greenstick: incomplete/partial break across the bone whereby one side of the bone is broken but the other side is merely bent
• Simple: complete break, bone does not penetrate through the skin
• Compound: complete break, bone protrudes through the skin (Note: this is a medical emergency)
  Comminuted: bone is splintered/fragmented at the site
• Oblique: complete break at an angle other than transverse or parallel to the longitudinal axis of the bone
• Spiral: complete break, secondary to excessive twisting of the bone 

1. Fx of Bone results in rupture of internal and external blood vessels, forming a hematoma in the first 6-8 hours. Surrounding tissue becomes inflamed, swollen, and painful.
1. 48 hours post-Fx the hematoma is invaded by blood vessels that form a soft fibrous mass termed Granulation tissue (containing osteoclasts, macrophages, osteogenic cells, fibroblasts)
2. 2-3 weeks Post-Fx a soft callus forms
1. Fibroblasts deposit collage into the granulation tissue
2. Some fibgroblasts and osteogenic cells differentiate into chondroblasts, which form fibrocartilage to replace the granulation tissue
3. Cocoon-like mass of all the above forms a 'soft' splint between the fractured ends of the bone, hence the name soft callus
3. 6-9 weeks post-Fx the soft callus is replaced by a hard callus via
1. fibroblasts and osteogenic cells differentiate into osteoblasts to form a bone splint around and within the fractured ends of the bone, termed a hard callus
2. NOTE: the broken bone must be immobilized during this period
4. Remodeling of bone: hard callus remains for the next 3-4 months
1. Osteoclasts begin to dissolve the hard callus
2. Osteoblasts deposit spongy bone which fills in the gap between the fractured ends of the bone

• Reduction: bringing the ends together in normal alignment (closed via traction or manual manipulation, open reduction with internal fixation (ORIF), or external fixation via a Hoffman device)
• Immobilization: splint or cast