Bone Metabolism Flashcards
(46 cards)
1
Q
What are bone lamellae?
A
Bone layers
2
Q
What are the 2 types of bone and that is their proportion?
A
- cortical/compact (80%)
- cancellous/trabecular/spongy (20%)
3
Q
What are the properties of compact/cortical bone?
A
- found on edges of bone
- compressive strength
- from osteons laying on top of each other in circular pattern
4
Q
What are the properties of cancellous bone?
A
- inside diaphysis and heads of bone
- mesh like
- relatively strong but bendable for movement
5
Q
What is the medullary cavity?
A
- sits inside shaft
- bone marrow
- lightens skeleton and houses haematopoietic cells
6
Q
What is bone marrow like at birth?
A
- virtually all bone marrow is red bone marrow
- yellow bone marrow forms peripherally and moves towards central axial skeleton
7
Q
What is bone marrow like in adults?
A
- little red bone marrow as don’t need many haematopoietic stem cells
- found in spongy bones of vertebrae, ribs, sternum, cranium and epiphyses of long bones
8
Q
What is woven bone?
A
- less resistant to stress
- can be put down quickly
- more disorganised vs. lamellar
- random collagen I organisation
- immature/mechanically weak, healing
9
Q
What are the 2 categories of bone composition?
A
- organic (35-40%)
- inorganic (60%)
10
Q
What are the components of organic bone material?
A
- collagen type 1
- proteoglycans
- growth factors/cytokines/osteoid
11
Q
What are the features of collagen type I?
A
- 90% tensile strength
- rope-like collagen forming long fibres
12
Q
What are the features of proteoglycans?
A
- compressive strength as hold water
13
Q
What produces organic bone material?
A
- cells = osteoblasts, osteocytes, osteoclasts
14
Q
What is the main inorganic bone component?
A
- calcium hydroxyapatite
15
Q
What are the features of calcium hydroxyapatite?
A
- precipitates onto surface of collagen fibres
- doesn’t cover it properly otherwise bone would be brittle and unbendable
- forms intermittent crystal precipitate leaving little gaps at regular intervals allowing bendability
16
Q
Why is bone not picked up on an MRI?
A
- quite dry -> 5% water
17
Q
What are the main cells found in bone?
A
- osteoprogenitor cells
- osteoblasts
- osteocytes
- osteoclasts
18
Q
What are the features of osteoprogenitor cells?
A
- CT cells
- from mesenchyme during embryonic development
- sits on either side of periosteum and become osteoblasts if needed
19
Q
What are the features of osteoblasts?
A
- secrete mineralised organic component
- become surrounded by it to become an osteocyte
20
Q
What are the features of osteocytes?
A
- remain in bone structure and secrete collagen locally
- have canaliculi
- death signals remodelling
21
Q
What are canaliculi?
A
- processes from osteocytes
- go into canals through bone matrix
- sense how much bone is bending/compressing/crushed
- to sense if new bone is required
22
Q
What are the features of osteoclasts?
A
- from haematopoietic stem cells within bone marrow
- macrophage like cells
23
Q
What are haversian canals?
A
- contain blood vessels
24
Q
Why does bone remodelling occur?
A
- renews bone deterioration
- redistribution of bone matrix along mechanical stress lines
25
What is sclerostin?
- glycoprotein
- secreted by osteocytes when healthy
- inhibits osteoblasts
- switched off when osteocyte dies stimulating bone growth
26
How do osteoclasts and osteoblasts signal?
- bidirectional communication
| - via ligands and receptors to inhibit osteoclasts increasing bone production
27
What is the function of EphrinB2?
- ligand
| - on surface of osteoclasts
28
What is the function of EphB4?
- receptor
| - expressed by osteoblasts
29
What increases ephrinB2 expression?
PTH
30
What is the difference between trabecular and cortical bone?
- trabecular bone 3-10 times quicker than cortical bone as larger SA and responds to stresses on bone quicker
31
What do osteoclasts do in bone production?
- signalled by osteocytes (amoeboid movement)
- attach to area and form leak proof seal
- inferior ruffled border secretes vesicle with HCl and protein digesting enzymes
- HCl dissolves calcium hydroxyapatite and bone mineral part
- protein digesting enzymes break down collagen
- end up with mixture of digested collagen, calcium and phosphate salt taken up by osteoclast
- packed into a vesicle and transported across cytoplasm
- release calcium salts into interstitial fluid
32
What do osteoblasts do in bone production?
- move in and secrete new osteoid which is at first not mineralised
- osteoid mineralised 1 week later
33
How is bone remodelling done using tetracycline?
- antibiotic taken up by mineralising bone and fluoresces
- check if bone being mineralised
- 2 doses 14 days apart (2 lines indicate mineralisation)
34
Where is calcium in bone?
- 99% in skeleton
| - 1% in cells/blood/body fluids
35
What is the function of calcium in bone metabolism?
- signalling molecule
| - regulates muscle contraction, neuronal signalling, heart beats
36
What does maintenance of calcium depend on?
- intestinal absorption
- renal absorption
- skeletal mobilisation
37
What is the function of phosphate in bone production?
- contain in hydroxyapatite
- uses PTH to modulate absorption and excretion
- not as closely regulated as calcium
38
How is calcium regulated?
- low plasma Ca2+ = PTH secretion from parathyroid gland on back of neck
- high plasma Ca2+ = calcitonin release
39
What does PTH promote?
- immediately Ca2+ reabsorption from kidney and PO4- excretion
- LT Ca2+ reabsorption from bone increases number and activity of osteoclasts
40
What does osteoclast formation require?
- RANKL
- M-CSF
(produced by osteoblasts and stromal cells)
41
What is RANK-L?
- osteoblasts have receptor for PTH
- stimulate osteoblasts to produce RANKL -> RANK (receptor) stimulated on osteoclasts
- causes osteoclast precursor to proliferate and differentiate
42
What inducers RANK-L?
- vitamin D
43
What inhibits RANK-L?
- estrogen
44
What is M-CSF?
Macrophage colony-stimulating factor
45
What is OPG?
- decoy receptor for RANKL
- modulates signalling on RANK by soaking up RANKL to stop signalling to osteoclast precursor
- induces synthesis of active vitamin D increases calcium absorption from gut
46
What is the effect of calcitonin?
- released when high calcium
- inhibits osteoclast differentiation and activity
- increases calcium excretion from kidney
- inhibits calcium absorption from intestines
