Metabolic bone disease histopathology Flashcards
Functions of bone
STRUCTURE structure and shape to body MECHANICAL site for muscle attachment PROTECTIVE vital organs and bone marrow METABOLIC reserve of calcium
State the composition of bone
Outline what is contained in the metaphysis
Composition:
INORGANIC - 65%
- calcium hydroxyapatite (10Ca 6PO4 OH2)
- is storehouse for 99% of Ca in the body
- 85% of the phosphorous, 65% Na & Mg
ORGANIC - 35%
-bone cells and protein matrix
Metaphysis:
The region joining the diaphysis to the epiphysis is known as the Metapyhsis and during growth this will contain the cartilage structure known as the growth plate during and is the region in long bones that contains the bulk of the trabecular or cancellous bone.
What type of proteins in bone
collagen (Type 1 mostly with some type V) 10-20% water and ~5% non-collagenous protein & carbohydrate.
What can cause bone marrow failure
Certain cations rg radium strontium and lead are ‘bone seeking’. They can be radioactive or toxic and cause bone marrow failure.
What are condyles and trochlea
Condyles are knuckle shaped and a trochlea is grooved like a pulley
What type of bone on the outside of the shaft and the medullary region
Outside: cortical
Inside: bone marrow and trabecular bone
When do bones show in X ray
Bone has to be 50% mineralised to be seen on X-ray
Image on slide 7
The image shows a lytic poorly circumscribed lesion in the diaphysis which has eroded cortex and caused a periosteal reaction.
Classify cortical vs. cancellous
- Where
- % of skeleton
- Appendicular/axial
- % calciied
- function
finish
..1. Cortical=long bones
Cancellous= vertebrae and pelvis
- Cortical= 80% of skeleton, cancellous=20%
- Cort.=appendicular cancell=axial
- cort=80-90% calcifified, cancell=15-25% calcified
- Cort=mainly structural, mechanical, and protective
cancell=mainly metabolic and large SA
Classify types of anatomical bone
Flat (cranial/rib… protect organs), long (femur/tib… support weight and facilitate ovement), short/cupoid (carpals and tarsals, stabalise and facilitate movement), irregular (complex shape like the vertebrae or the pelvis. That allows them to protect a specific organ or set of organs), sesamoid (patella… protective function)
Mascroscopic classification of bone
Trabcular/cancellous/spongy
cortical/compact
Microscopic classification of bone
when do you get non-lamellar bone
Woven (immature)
Lamellar (mature)
Collagen fibres are laid down in a disorganized fashion: such as states of high bone turnover(Pagets disease of bone, certain stages of fluoride treatment, tumours) not so tightly packed, random bundles
Microanatomy of bone
How big are osteons
Outline the mechanosensory network in bone
Osteons=structured, circular layers of lamellar bone, centreed around harvesian canal containing blood vessels … 0.2mm diameter
Circumferential lamaellea near periosteum
Interstital lamellae in between the osteons
Trabecular lamellae not in circular layers, but still lamellar layers
Dendritic structures found in lacunae in the lamellae are bone cells called osteocytes and the processes from them are the osteocyte canalicular network that spans throughout the bone and is thought to form a mechanosensory network allowing the repair of damaged bone or remodeling of structure to respond to new stresses being place on a bone.
Differentiate lamallar vs woven bone.
When might one find woven bone
Not in layers, much weaker, collgen disorganised
Woven bone is most often found in the developing skeleton as the cartilage scaffold is first converted to bone, but can also be found in states of rapid grow, or high bone turnover.
Types of bone cell ….and what percentage of them are osteocytes
Which differentiate into what
Osteocytes= mechanosensory netweok embedded in mature bone… 90% of bone cells (t1/2=25 years!)
Osteoclasts=multinuclear cells that resorb bone.!! Haematopoietic lineage
Osteoblasts- produce osteoid to form new bone
OSTEOBLAST (produce osteoid around then, which becomes mineralised and then they form)–> OSTEOCYTE
OSTEOCLAST is of haematopoietic lineage
Outline the bone remodelling cycle
PHYSIOLOGICALLY, THEN when some bone is a bit damaged THEN during bone disease
PHYSIOLOGICA:
BALANCED osteoclastic bone resorption and osteoblastic bone formation…. these processes are also COUPLED through interactions: osteoblasts mediate osteoclast formation and activity by producing RANKL, M-CSF (MACROPHAGE colony stimulating factor, as osteoclast is a macrophage) and RANKL decoy receptor OPG.
Remodelling occurs when osteocytes sense damage, and also produce RANKL as they apoptose, actvating osteoclasts. These then resorb the old bone, and then die away once they have resorbed to the required depth. Then the reversal phase: osteoblasts are recruited to the site and form new bone with some being trapped to become new osteocytes.
Bone disease then occurs if the balance between osteoclastic resorbtion and osteoblastic bone formation is lost.
What do osteoclasts and osteoblasts look like on sldie 18
Osteolast is multinucleated , big
Osteoblasts cuboidal, more flat and on surface
Osteocyte sort of on their own, separate
Indications for bone biopsy
Evaluate bone pain or tenderness
Investigate an abnormality seen on X-ray
For bone tumour diagnosis (benign vs malignant)
To determine the cause of an unexplained infection
To evaluate therapy
Types of bone bopsy
Where is typical location for bone biopsy
CLOSED - needle, core bopsy (jamshidi needle)
OPEN- for sclerotic/inaccessible lesion (surgery)
Bone biopsy may be performed at any site of interest, but if the reason is general and not bone specific then the typical location would be a transilliac biopsy allowing a core sample with plenty of cortical and trabecular bone to study as shown here.
Types of histological stains
H&E (decalcified samples)
Masson-Goldner Trichrome (labels mineralised and unmineralised one)
Tetracycline/calcein leblling (for rate of bone turnover)
