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1

BONES

Provide structure, protect vital organs and play crucial role in mineral homeostasis

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Major cells: Osteoblast

(Bone forming)

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Major cells: Oseoclasts

{Resorptive (removal) cells}

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Major cells: Osteocyte

(Mature osteoblast) → mature bone cell

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Bones classed by shape

Long, flat, short (cuboidal) or irregular

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Bones classed by; other

Compact bone (cortical) and spongy bone (cancellous)

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BONE TURNOVER

- 5-7% recycled weekly and 0.5g enter/leave the adult skeleton every day
- Bones are constantly remodelled
- Mineralisation→ mineral deposition→ organic matrix
- Mineral resorption→ release of minerals→ blood
- Osteoblasts→ build bone {Hydroxyapatite crystals (calcium and phosphate)}
- Osteoclasts→ degrade (corrode) bone

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BONE FORMATION

- Ossification/Osteogenesis→ Bone formation, new bone material forms
- Bone formation begins in fetal life → cartilage or membranes grow into shape of bones
- Intramembranous ossification→ occurs in a limited number of bones→ bones are formed around a membrane that has been formed by mesenchymal cells
- Endochondral ossification→ more common process→ bones formed based on cartilage shape already established in fetus
- Bones grow, repair themselves and change shape in response to stress
- Mature bone repair or remodelling→ begins with production of organic matrix by bone cells

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Bone matrix

Consists of ground substances, collagen and other proteins that help bone formation and maintenance

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BONE REMODELLING: PHASE 1: ACTIVATION

A stimulus (drugs, hormone or physical stress) activates osteoclast production

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BONE REMODELLING: PHASE 2: RESORPTION

Osteoclasts gradually resorb bone; leaves elongated cavity (resorption cavity)

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BONE REMODELLING: PHASE 3: FORMATION

- New bone (secondary bone) is formed by osteoblasts lining the walls of resorption cavity
- Entire process of remodelling takes approx 3-4 months

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BONE REPAIR

- Bone remodelling→ useful for combatting physical stress or microscopic bone injuries
- Larger injuries→ need bone repair
- Bones heal in same stages as soft tissue injuries (but instead of scar tissue; a new bone is formed)

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STAGES OF BONE REPAIR (4)

- INFLAMMATION/ HAEMATOMA FORMATION
- PROCALLUS FORMATION
- CALLUS FORMATION
- REPLACEMENT OF CALLUS

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STAGES OF BONE REPAIR: INFLAMMATION/ HAEMATOMA FORMATION

- Initial phase; inflammatory cells move to site of injury
- A haematoma forms (blood collection outside of blood vessel due to injury)

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STAGES OF BONE REPAIR: PROCALLUS FORMATION

- Soft callus occurs where connective tissue stem cells and blood vessels move to the fracture

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STAGES OF BONE REPAIR: CALLUS FORMATION

- Toughened area→ arises due to woven components being deposited

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STAGES OF BONE REPAIR: REPLACEMENT OF CALLUS

Replacement of callus with true, new bone

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CALCIUM HOMEOSTASIS

- Regulated by 3 hormones: PTH, calcitonin, calcitriol
- Balance between dietary intake, urinary and fecal losses and exchanges between osseous bone tissue

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CALCIUM HOMEOSTASIS: PARATHYROID HORMONE (PTH)

- Secreted by chief cells
- Senses low Ca2+ in plasma→ secretes hormone to increase Ca2+ (decrease in phosphate)
- Will be sensed by the kidneys, bones, GIT

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CALCIUM HOMEOSTASIS: CALCITONIN (THYROCALCITONIN)

- Secreted by parafollicular cells of the thyroid gland
- Decrease Ca2+ in plasma (decrease phosphate, phosphate absorption is increased in GIT)
- Can be in response to eating too much calcium
- Will be sensed by the kidneys, bones (Not GI) Strongest effect on bone

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CALCIUM HOMEOSTASIS: CALCITRIOL (Vit D3, 1,25-dihydroxyvitamin D)

- Active hormone that is modified from absorbed vit D
- Kidney→ Increased reabsorption of calcium and phosphate
- GIT→ Increased absorption of calcium and phosphate
- Bone: Stimulates PTH increased reabsorption of calcium and decreased of phosphate

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FRACTURES: AETIOLOGY AND PATHOPHYSIOLOGY

- Fracture→ a break in bone (Any bone may break)
- Trauma and disease may cause a bone to break

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SIGNS AND SYMPTOMS OF FRACTURES

- Impaired or loss of function
- Unnatural alignment (deformity)
- Swelling
- Possible muscle spasm
- Tenderness and pain
- Bruising or discoloration around the break
- Impaired sensation

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CLASSIFICATION OF FRACTURES: CLOSED

Bone is broken
Skin isn’t broken

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CLASSIFICATION OF FRACTURES: OPEN

- Bone broken and protruding through skin→ bone marrow exposed to external environment
- Risk of infection and osteomyelitis

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CLASSIFICATION OF FRACTURES: GREENSTICK

- Bone is bent on one side with incomplete fracture on the other side

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CLASSIFICATION OF FRACTURES: HAIRLINE

- Crack in bone, but bones remain aligned

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CLASSIFICATION OF FRACTURES: COMMINUTED

Bone in 3 or more pieces

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CLASSIFICATION OF FRACTURES: DISPLACED

Bones are out of anatomical alignment