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Module 204: Musculoskeletal system > Bone physiology > Flashcards

Bone physiology Flashcards

1
Q

Bone classifications

A

Long bone or flat bone

  • Long= longer than it is wide
  • Flat= thin, often curved

Cortical or cancellous (macroscopic)

  • Cortical= thick bone, organised in osteons. 80% of skeleton
  • Cancellous= spongy bone

Lamellar vs woven bone (microscopic)

  • Lamellar= secondary to woven bone. Stronger and more flexible
  • Woven= Less organised and stress oriented
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2
Q

Cancellous bone

A

Spongy bone
- Open porous network (bony struts) with blood/ marrow in-between

Less dense than cortical bone

Weaker but more flexible than cortical bone

High turnover to remodel when bone is under stress

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3
Q

Cortical bone

A

Thick bone, organised in osteons
- 80% of skeleton

Slow turnover rate

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4
Q

Composition of bone

A

Cells

  • Osteoclasts
  • Osteocytes
  • Osteoblasts

Extracellular matrix= osteoid.

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5
Q

Osteoclasts

A

Multinucelate bone cell

  • In Howship’s lacunae
  • Can proliferate
  • Same precursor as monocytes

Function–> creates ruffled borders during bone reabsorption

  • Phagocytose bone matrix and crystals (bone degradation)
  • Secretes acids [for hydroxyapatite
  • Secretion of proteolytic enzymes from lysosomes [to digest matrix proteins]
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6
Q

Osteocytes

A

Quiescent bone cells in bone matrix
- Derived from osteoblasts

Functions
- Maintain bone and detects environmental stress

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7
Q

Osteoblasts

A

Mononucleate bone cell located on developing bone surfaces
- Most mitotic, gives rise to osteocytes

Function

  • Formation of new bone
  • Release of signalling substances
  • Produces protein components of acellular matrix
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8
Q

Extracellular matrix

A

Hardened material surrounded cells.

Contains few cells:

  • Inorganic material: minerals, hydroxyapatite
  • Connective tissue sometimes
  • Osteoid (unmineralised bone )
  • Ground substance (organic, acellular)
  • Growth factors
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9
Q

Haversian system

A

Communication system between cells in bone matrix

Osteon
- Functional unit containing everything

Haversian canal

  • Runs parallel to bone and on long axis
  • Lined by lamellae
  • Contains one or two capillaries and nerve fibres

Osteocyte
- Contains radiating processes into canaliculi

Canaliculi
- Canals between lacunae of ossified bone

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10
Q

Acellular components of bone

A

Collagen fibres
- Give flexibility and strength

Hydroxyapatitre

  • Provides rigidity
  • Mainly calcium/phosphate crystals
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11
Q

Ground substance in bone

A

Things in ECM that is not inorganic and not collagen

Includes

  • Proteoglycans
  • Glyosaminoglycans
  • Matrix proteins
  • Water
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12
Q

Glycosaminoglycans

A

Component of ECM (Ground substance)
- Abundant in cartilage

Structure

  • Long polysaccharide
  • Highly negative–> attracts water, repels each other
  • Resists compression
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13
Q

Activation-resorption-remineralisation sequence

A

Controlled by osteoblasts

  1. Osteoblast detects mechanical stresses/ hormonal factors/ cytokines on the bone–> releases IL-6 and other cytokines
  2. IL-6 and other cytokines active osteoclast to begin bone reabsorption
    - Forms ruffled border as it absorbs bone
  3. Reabsorbed bone releases growth factors bound to matrix which activates osteoprogenitor cells into active osteoblasts.
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14
Q

Endochondral ossification

A

Bone is formed on a cartilaginous template.

Chondrocytes proliferate and secrete ECM and proteoglycans.

Osteoblasts then lays down osteoid and begin mineralisation

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15
Q

Intramembranous ossification

A

No cartilage template

Osteoblast lays down osteoid and being mineralisation without cartilage
- Forms tiny bony spicules

Forms woven bone when nearby spicules join into trabeculae.

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16
Q

Factors that govern remodelling of bone

A

Recurrent mechanical stress

Calcium homeostasis

17
Q

Mechanical stress on bone

A

Strengthens bone

Surface osteoblasts and osteocytes detect stresses

  • Stimulates more deposition of bone minerals, inhibits bone resorption
  • Bone trabeculae become more dense

Without weight bearing (i.e bed rest and lack of gravity) = loss in bone density

18
Q

Osteopenia

A

Low bone density

- Considered to be precursor to osteoporosis sometimes

19
Q

Bisphosphonates

  • Mechanism
  • Example
  • Indication
A

Inhibits osteoclast from bone -resorption
- Related to inorganic pyrophosphate= interfere with osteoclast metabolism

Alendronate

For osteoporosis

20
Q

Teriparatide

  • Mechanism
  • Indication
A

Encourage osteoblast formation of bone (PTH portion)

Indication
- Osteoporosis

21
Q

Denosumab

  • Mechanism
  • Indication
A

Prevents osteoclast maturation

- Monoclinary antibody that targets RANK-ligand

22
Q

Osteopetrosis

  • Genetics
  • Mechanism
  • Symptoms
A

Autosomal recessive condition

Mechanism

  • Osteoclast cannot remodel bone= excess bone growth
  • Defective vacuolar proton pump/ chloride channels [cannot secrete acid]

Symptoms–> Excess bone presses on skull foramina

  • Brittle bones
  • Blindness
  • Deafness
  • Severe anaemia

Fatal within 10 year

23
Q

Phases of fracture healing 1

A

Reactive phase- takes a week

  • Haematoma forms
  • Inflammation occurs= granulation tissue

Bone precursor cells from periosteum arrive

24
Q

Phase 2 of fracture healing

A

Soft callus formation [week 2-3]

Woven bone/ hyaline cartilage is formed to join pieces

25
Q

Phase 3 of fracture healing

A

Hard callus formation [week 4-16]

  • Woven bone/ hyaline cartilage is replaced by lamellar bone
  • Lamellar bone turned into tribecular bone
26
Q

Phase 4 of fracture healing

A

Remodelling

  • Osteoclast remodel trabecular bone to original bone shape
  • Trabecular bone is replaced with compact bone where appropriate.
27
Q

PTH and Ca2+

A

Release from chief cells
- Increase plasma calcium

Mechanism
- Stimulates osteoblast to activate osteoclast precursor via RANKL

28
Q

Vit.D and Ca2+

A

1,25-OH Vit D increases plasma Calcium

- Stimulates more absorption in gut and kidney

29
Q

Calcitonin

A

Made by thyroid C cells
- Decreases calcium levels–> stimulates entry into bones

Can be used as treatment for osteoporosis

30
Q

OPG

A

Secreted by osteoblast–> signals reduced bone formation
- Binds to block RANKL

Stimulated by oestrogen in vivo

Stimulated by strontium renovate

31
Q

Calbindin

A

Increase stimulated by calcitriol

- Increases intestinal and kidney absorption of calcium

32
Q

Causes of low plasma calcium

A

Due to loss

  • Pregnancy
  • Lactation
  • Kidney dysfunction

Low intact

  • Insufficient ingestion
  • Rickets due to low vit.D

Parathyroid dysfunction

33
Q

Consequences of chronic hypocalcaemia

A

Skeletal deformities [i.e rickets]

Increased tendency for fractures

Impaired growth

Short stature

Dental deformities

34
Q

Acute hypocalcaemia

A

Causes excitability
- Neurone become much more permeable to Na+

Symptoms = CAT

  • Convulsions
  • Arrhythmias
  • Tetany

Signs
- Chvostek’s sign
- Trousseaus’s sign
-

35
Q

Effects of hypercalcaemia

A

Reduces excitability of neurones

  • Makes neurones more stable
  • High calcium inactivates channels= less ions conducted
36
Q

hypercalcaemia symptoms

A

Constipation

Depression + other psychiatric problems

Abnormal heart rhythm

If severe

  • Coma
  • cardiac arrest

Module 204: Musculoskeletal system (22 decks)

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