Bone physiology notes PDF

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02.BONE PHYSIOLOGY1. GROSS ANATOMY OF A LONG BONEi. Epiphysis : Ends of bones: Growth Plate ii. Diaphysis : Bone Shaft iii. Medullary Cavity : yellow marrow (triglyceride store) iv. Spongy (Cancellous) Bone : red marrow (blood cell production) v. Periosteum : membrane with osteoblasts and osteoclast...

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02.11.18

BONE PHYSIOLOGY 1. GROSS ANATOMY OF A LONG BONE i.

Epiphysis: Ends of bones: Growth Plate

ii.

Diaphysis: Bone Shaft

iii.

Medullary Cavity: yellow marrow (triglyceride store)

iv.

Spongy (Cancellous) Bone: red marrow (blood cell production)

v.

Periosteum: membrane with osteoblasts and osteoclasts on inner layer

2. STRUCTURE OF COMPACT BONE

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i.

Lamellae – rings of hard, calcified bone matrix

ii.

Lacunae – spaces which hold osteocyte

iii.

Osteon - Circular column of concentric lamellae

iv.

Haversian Canal – central space containing blood vessels and nerves

v.

Canaliculi – small channel with osteocyte processes

3. SPONGY BONE: i.

similar but different.

ii.

Less dense, spicules of bone – trabeculae

iii.

Spaces for marrow

4. HISTORY OF BONE: KEY CELL TYPES

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5. OSTEOPROGENITOR CELLS Mesenchyme: from mesodermal tissue (middle layer). Forms connective tissue i.

Mesenchymal bone stem cells i.e. capable of proliferation

ii.

Produce osteoblasts

iii.

Found on the inside of the periosteum

iv.

Proliferative, so are involved in growth and repair

6. OSTEOBLASTS A. Bone creators i.

Secrete collagen to create a matrix (scaffold), which will become calcified (osteogenesis)

ii.

Mature into osteocytes once they are surrounded by the calcified matrix

7. OSTEOCYTES A. Bone repair i.

Osteocytes are found in lacunae, surrounded by calcified matrix

ii.

Cell processes connect through the canaliculi in lamellae. The cells form gap junctions where they meet.

iii.

Do not divide (mature cell type)

iv.

Help to maintain protein and mineral content of matrix

v.

Help repair damaged bone

8. OSTEOCLASTS A. Bone destroys: resorb/break down bone

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i.

Giant, multinucleated cells

ii.

Secrete acids (hydrogen ions) and proteases to dissolve bone (osteolysis) -

Hydrogen dissolves crystals

-

Proteases dissolve bone matrix

iii.

Line the medullary cavity

iv.

Different cell lineage: come from the same lineage as white blood cells (macrophages)

BONE PHYSIOLOGY - FUCTION 9. BONE FUNCTION: PROTECTION

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i.

Protects the vulnerable organs: brain, heart, liver, lungs etc

ii.

Support against gravity

iii.

Postural framework for movement

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BONE FUNCTION: SUPPORT AND MOVEMENT/LEVERAGE Support and attachment sites for muscle groups

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11.

BONE IS A CONNECTIVE TISSUE: IMPORTANT FOR MINERAL STORGAE What is bone composed of? A. Low cellular component i.

ii.

Collagen matrix (osteoid) -

Gives elasticity and resistance

-

Framework for mineral deposition

Mineral deposited on matrix (calcification) -

Calcium, sodium, magnesium, carbonate

-

Contributes strength

-

Main component are crystals of calcium and phosphate: of hydroxyapatite: Ca10(PO4)6(OH)2

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iii.

Mineral salts give bone its rigidity and resistance to compression; without collagen, bones would be very brittle and easily broken

iv.

The main purpose of collagen fibres is to provide a degree of elasticity to resist breakage; they also add extra strength to the bone

12.

BONE AND CALCIUM HOMEOSTASIS A. 99% of Ca++ is found in bone i.

This means that tis primary function is to maintain normal plasma concentration.

B.

Plasma calcium levels need to be maintained at a steady level. (9-11mg/100mL)

C.

Consequences of disruption

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i.

Neuromuscular excitability (twitching) via binding to plasma proteins acting as ion channels

ii.

Ca2+ also needed for blood clotting and production of enzyme cofactors

13.

CALCIUM HOMEOSTASIS Bone resorption (breakdown) results in the release of calcium into the bloodstream A. Parathyroid hormone (PTH) increases bone resorption

B. Calcitonin inhibits bone resorption C. The release of both hormones is controlled by negative feedback cycles

14.

CALCIUM HOMEOSTASIS: AN EXAMPLE OF NEGATIVE FEEDBACK

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15.

BONE MARROW i.

In infants, red marrow is found in the medullary cavity and all areas of spongy bone

ii.

In adults, it is found in the diploe of flat bones, and the head of the femur and humerus

16.

BONE MARROW: LIPID STORAGE AND BLOOD CELL PRODUCTION In between the trabeculae, we find bone marrow, which is highly vascularized. Why? A. Red bone marrow i.

Supplies nutrients to osteocytes

ii.

Forms red and white blood cells

B.

Yellow bone marrow i.

Yellow because it stores fat

ii.

May convert back to Red Bone Marrow if there is severe bleeding

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BONE PHYSIOLOGY – FORMATION AND REMODELLING 17.

FORMATION OF BONE Ossification (osteogenesis) is the process of bone formation. A. Bone forms: i.

During development

ii.

During childhood growth

iii.

To remodel bone, e.g. in response to stress

iv.

Repair

18.

FORMATION AND GROWTH A. During development and growth, chondrocytes and cartilage deposition create a model, which will be replaced by bone B.

Growth and deposition of bone requires a healthy diet and exercise

C.

Diet: i.

Minerals: Calcium, phosphorus, magnesium, fluoride

ii.

Vitamins: D (collagen), A (osteoblast activity), K

iii.

Protein

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19.

20.

BONE REMODELLING: DEPOSITION VS RESORPTION i.

Deposition of bone is by osteoblasts from the outside (periosteal layer)

ii.

Resorption by osteoclasts on the inside (endosteal layer)

CONSEQUENCES OF CHANGES TO THE BALANCE OF RESORPTION AND DEPOSITION i.

Remodeling is constant but is more prevalent during periods of stress on the bone or repair. -

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Physical stress increases deposition

ii.

During growth, deposition is greater than resorption, so bones grow and get stronger.

iii.

Aging- the balance shifts and bones can get weaker.

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21.

BREAKDOWN OF BONE: BONE RESORPTION i.

Osteoclasts form grooves called resorption bays as they break down bone matrix

ii.

Hydrogen ions and hydrolytic enzymes are released to dissolve bone (osteolysis)

iii.

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-

Hydrogen dissolves crystals so that they are soluble

-

Enzymes dissolve bone matrix

The products of bone breakdown end up in the blood plasma, thus increasing plasma Calcium levels

22.

EFFECT OF AGING AND EXERCISE ON BONE To get started right away, just tap any placeholder text (such as this) and start typing. A. Exercise affects bone density: i.

High impact has the greatest effect

ii.

Swimming and low impact sports have less impact

B. Lack of exercise and aging both result in lowering of bone density: i.

Approximately 1%/week of 3-8% every 10 years.

A. Bone mass decreases with age as resorption increases above deposition rate. Demineralisation of bone B. Bone mass also decreases with inactivity – 1% per week C. Sex differences: i.

8% loss every 10 years vs 3% loss

ii.

♀ lose 30% by 70

iii.

Increases at 30, increases again at 45 and menopause

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23.

REMODELING: INCREASING BONE DENSITY i.

New bone will be thicker and stronger if it is stressed (eg heavy loads applied) when growing. (Wolff’s Law)

ii.

Athletes (eg archers) will have higher bone density in bones subject to the most stress.

iii.

As the bone is forming, the trabeculae orient along stress lines to increase the strength, making new bone stronger than the original

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BONE PHYSIOLOGY: REMODELING – PUTTING IT INTO PRACTICE 24.

FRACTURE TYPES A. Open fracture: skin broken

i. B.

Comminute fracture: splintering/crushing

i.

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C.

Greenstick fracture: more common in children

i. D.

Impacted fracture: force pushes into interior

i.

25.

SOME COMMON FRACTURES: A. Pott

i. 18

B.

Colles

i.

26.

PHASES OF BONE HEALING 1: REACTIVE PHASE i.

Blood vessels crossing the line of the fracture are broken

ii.

A blood clot (fracture haematoma) rapidly forms around the fracture site

iii.

Surrounding bone cells die due to lack of vascularisation (blood supply)

iv.

Cell death and inflammation

v.

Clean-up operation: immune system

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27.

PHASES OF BONE HEALING 2: REPARATIVE PHASE i.

Vasculogenesis of the haematoma- removal of dead cells by phagocytes

ii.

Fibroblasts move into the fracture site and start to build a new framework of collagen fibres

iii.

Cells from the periosteum develop into chondroblasts and produce fibrocartilaginous callus

iv.

The ends of the bone are beginning to be stabilised

v.

This takes about 3 weeks

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28.

PHASES OF BONE HEALING 3: REPARATIVE PHASE AND CALLUS FORMATION i.

Osteoprogenitor cells from the periosteum develop into osteoblasts and produce spongy bone trabeculae

ii.

Trabeculae join up living and dead bone fragments

iii.

Fibrocartilage is converted to spongy bone, and the callus is now called a bony callus

iv.

The bony callus lasts about 3-4 month

29.

PHASES OF BONE HEALING 4: BONE REMODELLING PHASE A. Remodelling of the repaired bone: i.

Osteoclasts resorb dead bone

ii.

Spongy bone is replaced by compact bone

iii.

A thickened area may remain on the surface of the bone

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