Musculoskeletal - Bone Flashcards by Tom Bell

What are the four types of cells present in bone?

1) Osteoprogenitor cells
2) Osteoblasts
3) Osteoclasts
4) Osteocytes

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What are osteoprogenitor cells?

They are bone stem cells - they form the osteoblasts

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What are osteoblasts? What do they do?

They are bone forming cells.

They line the surface of the bone, secrete collagen which forms the organic matrix of the bone

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What is the name for the organic matrix before it is calcified?

Osteoid

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What are osteocytes?

They are osteoblasts that have got trapped in the organic matrix.
They communicate with each other via fine processes through canaliculi.
They are involved in bone regulation

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What are osteoclasts?

They are large, multinucleated cells with a ruffled border.

Their function is to resorb bone

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Osteoclasts are formed from osteoprogenitor cells. True or false?

False - they are formed from monocytes which fuse together to form the multinucleated cells

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What is the extracellular matrix made up of?

1) Organic matrix (30%)
2) Collagen (type 1 - 90%, some type V)
3) Water
4) Bone mineral - hydroxyapatite

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What properties does calcification give bone?

1) Bending, twisting and stretching resistance

2) Hard

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What is the main property collagen fibres give bone?

Resistance to tensile stress

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What type of junction is present between osteocytes?

Tight Junctions

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What is the the name of the inhibitor of osteoclast activation?

OPG (Osteoprotegerin)

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How does PTH lead to activation of osteoclasts?

1) PTH binds to the osteoblast
2) OPG is inhibited
3) Inhibited OPG means RANKL no longer inhibited
4) RANKL on osteoblast binds to RANK on osteoclast
5) Osteoclast is activated

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What hormones favour bone formation?

Insulin
Growth hormone
Insulin-like groeth factor
Oestrogen
Testosterone
Calcitonin

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What hormones favour bone resorption?

Parathyroid hormone
Cortisol
Thyroid hormone

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Where is parathyroid hormone secreted from?

Parathyroid gland

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What cells secrete parathyroid?

Chief cells

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What affect does PTH have on Vitamin D?

PTH stimulates 1 alpha hydroxylase in the kidney which leads to an increase in 1,25-dihydroxyvitamin D (Active form)

What affect does parathyroid have on the kidneys?

It increases the reabsorption of calcium and increases phosphate clearance by decreasing reabsorption

Where in the nephron does PTH affect the reabsorption of phosphate?

Proximal renal tubules

Where in the nephron does PTH affect calcium reabsorption?

Distal renal tubules

What two ways is vitamin D obtained?

1) Synthesis in the skin

2) Diet

Describe the process of vitamin D synthesis

1) UV from sunlight converts 7-dehydrocholesterol in the skin to vitamin D3
2) Vitamin D3 is converted to 25-hydroxyvitamin D by 25-hydroxylase in the liver
3) 25-hydroxyvitamin D is then converted to 1,25-dihydroxyvitamin D in the kidney by 1-alpha-hydroxylase

1,25-hydroxyvitamin D is the active form of vitamin D

What is the other name for vitamin D3?

Cholecalciferol

What is the other name for 25-hydroxyvitamin D?

Calcifediol or calcidiol

What is the other name for 1,25-dihydroxyvitamin D?

Calcitriol

What affects does vitamin D have?

1) Enhances calcium and phosphate absorption in the intestines 2) It increases reabsorption of calcium in kidenys and decreases reabsorption of phophate 3) Has direct effect on the parathyroid galnds supressing parathyroid hormone secretion

What is osteoporosis?

Where there is a decrease in bone density that makes the bones brittle

What is osteopenia?

Where there is a decrease in bone density but it is not as severe as in osteoporsis

What is the T score for osteopenia?

-1 to -2.5

What is the T score for osteoporosis?

> -2.5

What is the FRAX test?

A tool used to evaluate the 10 year probability of bone fracture risk

Which of these is not used in the FRAX test? ``` Sex Weight and height Previous fracture Parental fracture Smoking Physical activity Smoking Use of steroids Rheumatoid arthritis ```

Physical activity

Why is physical activity not included in the FRAX test?

Because, while it is an important factor, it is often difficult to quantify physical activity especially as an average over long periods of time

What are the four stages of bone fracture healing?

1) Haematoma formation 2) Bone generation 3) Bony callous formation 4) Bone remodelling

How does enchondrial ossification start?

With a hyaline cartilage model

Describe the stanges of enchondrial bone ossification

1) Formation starts with hyaline cartilage model 2) Condrocytes near the centre enlarge rapidly and the matrix begins to calcify - the chondrocytes then die 3) Blood vessels grow around the cartilage and osteoblasts form and lay bone on the surface of the cartilage 4) Blood vessels invade the cartilage and the fibrovblasts differentiate into osteblasts and produce bone - primary ossification centre 5) The cartilage in the shaft is slowly changed for bone 6) Seconadary ossification centres then form in the epipysis 7) plates of cartilage are left between the shaft and the epiphysis - epiphyseal plate

What is the role of the epiphyseal plate?

It is where bone growth occurs

When is the epiphyseal plate present until?

Until a person stops growing in height - therefore only present in children and adolescence

What happens in the haematoma formation in fracture healing?

1) Blood vessels tear which results in haemorrhage 2) Blood clots form sealing vessels 3) Bone cells that are deprived of oxygen die

What happens in the bone generation part of fracture healing?

1) Fibroblasts and osteoblasts enter the area 2) Fibroblasts form the collagen that sticks the two ends of the bone together 3) Osteoblasts form the spongy bone 4) Repair tissue forms fibrocartilagenous callus surrounding breakage - formed of hyaline and fibrocartilage

What happens in the bony callous formation part of fracture healing?

The fibrocartilagenous callus is converted into a bony callus of spongy bone

What happens in the bone remodelling part of fracture healing?

The bony callus is remodelled by osteoclasts and osteoblasts with excess material removed - it can take years to return to original composition and to be smooth