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The moving animal - Gateway > Bone form and function > Flashcards

Bone form and function Flashcards

1
Q

What are long bones?

A

Bones of the leg, arm, primarily compact bones e.g. the tibia

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2
Q

What are short bones?

A

Bones of the wrist and ankle, primarily spongy bones

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3
Q

What are flat bones?

A

Most bones of the cranium, ribs, spongy bone between 2 layers of compact bone

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4
Q

What are irregular bones?

A

Vertebrae, primarily spongy bones

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5
Q

What are the two origins of bones?

A

Long bones - Endochondral ossification

Flat bones - intramembranous ossification

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6
Q

What are the two histological classifications given to bones?

A

Woven - primary immature: woven bone, not organised

Lamellar - Secondary mature: lamellar bone

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7
Q

What is woven bone?

A

Immature, fracture, quick

  • randomly orientated collagen fibres
  • variable collagen fibre diameter
  • rapid matrix mineralisation
  • forms rapidly
  • rapid turnover (remodelling)
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8
Q

What is lamellar bone?

A

Mature, adult

  • regular orientation collagen fibres
  • regular collagen fibre diameter
  • delayed matrix mineralisation
  • forms slowly
  • slow turnover
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9
Q

How can bones be classified anatomically?

A

Spongy (trabecular)
Compact (cortical)
- both are made of the same cells and matrix elements

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10
Q

What is compact bone?

A

Very strong

Made of osteons: central canal (haversian) surrounded by rings of bone matrix (concentric lamellae)

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11
Q

What forms when two osteons merge?

A

One osteon with radiating canaliculi (remainder of the other osteon)

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12
Q

What is between osteons?

A

Interstital lamellae

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13
Q

How do osteocytes communicate?

A

Radiating canaliculi

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14
Q

What is trabecular bone?

A

Forms mesh like structures made of plates and rods
- holes formed are the trabecule
Large surface area but less dense
Very metabolically active due to being highly vascularised

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15
Q

What is the periosteum?

A

Fibrous membrane of connective tissue that covers all bones but not articular surfaces

  • has an important role in bone growth in length but mainly in diameter
  • also important in fracture repair
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16
Q

Describe the macroscopic organisation of bone

A 
From cranial to caudal 
- Cartilage
- Growth plate 
-- both in the epiphysis 
- trabecular bone surrounded by the compact bone 
-- in the metaphysis region 
- bone marrow cavity 
- bone marrow 
- blood vessel 
-- all in the diaphysis region 
Periosteum surrounds all the structures on the outside of the compact bone layer
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17
Q

What are the blood vessels within the bone?

A 
Perforating canals (Volkman's canals) - blood vessels from periosteum penetrate bone 
Vessels of the central canal
18
Q

What does a blood supply to the bone provide?

A

Nutrients to cells
Route for migration for stem cells
Regenerative ability

19
Q

How does a bone function determine its form?

A

Bone adapts its shape dependant on the mechanical force applied to it with 2 targets:
- minimum weight with maximum mechanical strength

20
Q

Why is no bone straight?

A

Deformation due to the force applied

- dependant on the material properties of the bone

21
Q

What material is bone?

A

Composite material

- hydroxyapatite crystals, collagen orientation

22
Q

Describe the microscopic organisation of bone

A

Bone matrix organic (proteins)
- collagen fibres type 1 (90% of the total protein)
- proteoglycans
- non - collagenous proteins
Mineral (inorganic): Crystals of hydroxyapatite (Ca10(PO4)6(OH)2)
- Cells: osteoblasts, osteocytes, osteoclasts

23
Q

What happens if mineral is removed from bone?

A

Too bendable

24
Q

What happens if collagen is removed from bone?

A

Too brittle

25
Q

When is the organic matrix mineralised?

A

Immediately after secretion in case of rapidly forming (woven) bone (fetal, fracture callus)
- in adults m
normally a delay of several days before osteoid mineralises

26
Q

What is the role of hydroxyapatite in bone formation?

A

Tiny crystals surround collagen fibres

- provides rigidity, resistance to compression

27
Q

What is the mineralisation of osteoid dependant on?

A

Hormonally active form of vitamin D (1,25 (OH)2 D3)

28
Q

What does a deficiency in hormonally active vitamin D cause?

A

Results in a failure to mineralise

  • rickets in children
  • osteomalacia in adults
29
Q

What are mineralisation promoters?

A
  • tissue non-specific celeceline phosphate (TNAP)

- phosphate orphan 1 (PHOSPHO1)

30
Q

What are mineralisation inhibitors?

A
  • inorganic pyrophosphate (PPi)

- organic non-collagenous proteins

31
Q

What is NPP?

A

NPP = ectonucleotide pyrophosphatase/phosphodiesterase-1

- NPP1 key regulator of skeletal and soft tissue mineralisation

32
Q

How does NPP work?

A

NPP

ATP →→→→→ AMP + PPi

33
Q

What are osteoblasts?

A

Cells responsible for bone formation

34
Q

What are osteoclasts?

A

Cells responsible for bone reabsorption

35
Q

What are osteocytes?

A

Cells that mediate effect of mechanical loading and regulate phosphate homeostasis

36
Q

Where do osteocytes originate from?

A

Hematopoietic cells in bone marrow

37
Q

Which bone cells originate from mesenchymal stem cells?

A

Osteoblasts

Osteocytes

38
Q

How do osteoblasts work?

A
  • Secrete organic matrix of unmineralised bone (osteoid) and mineralise the matrix with Ca10 (PO4)6 (OH)2
  • Express high levels of alkaline phosphatase, secrete and respond to many growth factors, cytokines and hormones
  • Active or inactive lining cells (non-active osteoblast) cover most bone surfaces
39
Q

How do osteocytes work?

A

Most abundant cell found in bone (90-95% of all bone cells)

  • communicate with each other via canaciuli
  • mechanically responsive cells
  • express high levels of sclerostin (inhibitor of bone formation), FGF23 (regulates phosphate metabolism in the kidney) and rank ligand (acts on osteoclasts to stimulate bone reabsorption)
40
Q

How do osteoclasts work?

A

Polarised, multi-nucleated, motile, bone-reabsorbing cells

  • formed by fusion of promonocytic precursors present in marrow and circulation
  • specialised organ of reabsorption (“ruffled border”) adjacent to bone surface
  • express high levels of carbonic anhydrase II, tartrate - resistant acid phosphatase (TRAP) and cathepsin K
41
Q

What does osteoclastic differentiation depend on?

A

Cytokines
M-CSF
RANK 2

42
Q

How is osteoclastic bone reabsorption performed?

A

2 steps:
- initiated by the dissolution of the mineralised matrix followed by enzyme degredation of the organic matrix
Osteoclasts dissolve minerals by a process of acidification due to secretions of of protons by the vacuolar type proton pump V-ATPase
- acidifies enclosed canunae - pH 4.5
- this leads to de-calcification of hypoxyapatate leading to exposure of organic matrix consisting largely of type one collagen

The moving animal - Gateway (19 decks)

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