MBD - Histopathology

Question 1

Describe the functions of bone

Answer 1

1. Structure
2. Mechanical site for muscle attachment
3. Protective for vital organs
4. Metabolic - reserve of minerals

Question 2

Describe the composition of bone

Answer 2

65% inorganic - store of minerals: calcium, phosphate and magnesium and mainly made out of calcium hydroxyapatite

35% organic - bone cells and protein matrix: required for maintenance of bone

Epiphysis: articular surfaces and subchondral bone
Diaphysis: medullary cavity and cortex and periosteum

Question 3

Describe the bone classifications

Answer 3

1. Anatomical: flat and long (femur), short and cuboid (carpels), irregular (veterbrae) and sesamoid (platella)
2. Macroscopic: trabecular (criss crossing of medulla) and corticol/ compact (thick)
3. Microscopic: woven bone (immature) and lamellar bone (mature)

Corticol: long bones and 80% of skeleton, mostly calcified and have protective and mechanical functions

Cancellous: veterbrae/ pelvis, not very calcifies (15%), mainly metabolic, large surface, trabecular bone (avascular).

Question 4

Describe the functions of different types of bone cells and the bone remodelling cycle (and how to take a biopsy )

Answer 4

1. Osteoclast - multinuclear, resort and remove bone
2. Osteoblast - produce osteoid to form new bone
3. Osteocytes - mechanosensory network embedded in mature bone

Remodelling: osteoblast build bone and lay down osteoids, RANKL in response to stimulation via osteoprotegrin - inhibits RANKL via competitive inhibition so inhibits osteoclasts genesis

Take biopsy via closed needle (jamshidi) or open for sclerotic/ inaccessible lesion

Question 5

Define metabolic bone diseases and give and explain 5 examples of MBD

Answer 5

MBD: a group of diseases that cause reduced bone mass and reduced bone strength, due to chemical imbalances causing altered bone cell activity, rate of mineralisation or changes in bone structure.

1. Osteoporosis: reduced bone density T-score of -2.5. Primary due to post menopause and secondary due to drugs and systemic disease.
2. Osteomalacia: defective mineralisation of normally synthesised bone matrix, rickets in children, deficient of Vit D, deficiency of PO4- (look at symptoms)
3. Hyperparathyroidism: excess PTH: increased Ca2+ in blood and increased PO4- excretion in urine, hypercalcaemia, hypophospatism, osteoitis fibrosa cystica (skeletal change). Primary via parathyroid adenoma, secondary via CKD.
4. Renal osteodystrophy: compromises all the skeletal changes resulting from chronic renal disease.
5. Pagers diseas: divides into 3 stages: osteolytic stage (rapid breakdown), osteolytic - osteosclerotic (bone formation), quiescent osteosclerotic (quiescent stage)