Flashcards in Metabolic Bone Disease – Histopathology Deck (40)
What are the three main functions of bones?
Mechanical – support and site for muscle attachment
Metabolic – reserve of calcium
What are the two main components of bone and what are their relative proportions?
Inorganic (65%) – calcium hydroxyapatite (store of 99% of the body’s calcium, 85% of the phosphorous and 65% of Na and Mg)
Organic (35%) – bone cells and protein matrix
Describe the classification of bone as cortical and cancellous.
80% of skeleton
Mainly mechanical and protective role
Vertebrae and pelvis
20% of skeleton
What are the indications for bone biopsy?
Evaluate bone pain or tenderness
Investigate abnormality seen on X-ray
For bone tumour diagnosis
To determine the cause of unexplained infection
To evaluate therapy
What are the two types of bone biopsy?
Closed – needle – core biopsy with Jamshidi needle
Open – for sclerotic or inaccessible lesions
What are the three types of bone cell?
Osteoblast – build bone by laying down osteoid
Osteoclast – multinucleate cells of the macrophage family that resorb bone
Osteocyte – osteoblast like cells
Where are osteocytes found?
What cytokine is important for stimulating the differentiation of osteoclast precursors into pre-osteoclasts?
M-CSF (this is produced by osteoblasts)
Which cells produce RANKL and what is its effect?
It stimulates the maturation of osteoclasts
What do mature osteoblasts produce that blocks the RANK/RANKL binding?
How are bones classified anatomically?
What type of ossification leads to the formation of:
a. Long Bones
b. Flat Bones
a. Long bones
b. Flat bones
How else can bone be classified?
Trabecular (cancellous) or compact (cortical)
Woven (immature) or lamellar (mature)
What is metabolic bone disease?
Disordered bone turnover due to imbalance of various chemicals in the body (vitamins, hormones, minerals etc.)
Overall effect is reduced bone mass (osteopaenia) often resulting in fractures from little or no trauma
What are the three main categories of metabolic bone disease?
Related to endocrine abnormality (e.g. Vit D and PTH)
Non-endocrine (e.g. age-related osteoporosis)
Describe the staining of calcified and uncalcified bone.
Calcified – green
Uncalcified – orange
What are the primary causes of osteoporosis?
What are the secondary causes of osteoporosis?
Describe the histology of osteoporotic bone.
Weak trabecular bridging
Holes and cysts
What is osteomalacia and what can it be caused by?
Condition of defective bone mineralisation that can be caused by:
Vitamin D deficiency
Phosphate deficiency (usually related to chronic renal disease)
What are the metabolic and endocrine consequences of vitamin D deficiency?
Secondary hyperparathyroidism --> increased bone resorption
Hypocalcaemia – neuronal excitability causing muscle twitching, spasms, tingling and numbness
Describe the histology of osteomalacia.
No calcification of bone
More uncalcified osteoid
Bones are very bendy and cannot carry musculature very easily
What are the clinical consequences of osteomalacia?
Fracture (horizontal fractures at Looser’s zone at the neck of the femur are commonly seen)
What is used to investigate mineralisation?
Fluorescent tetracycline labelling
What are the consequences of hyperparathyroidism?
Hypercalcaemia (increased Ca2+ reabsorption)
Hypophosphataemia (increased phosphate excretion in the urine)
Osteitis fibrosa cystica (due to increased osteoclast activity)
List the four organs that are directly or indirectly affected by parathyroid hormone to control calcium metabolism.
Proximal small intestine
State some causes of primary hyperparathyroidism.
Chief cell hyperplasia
State some causes of secondary hyperparathyroidism.
Chronic renal insufficiency
Vitamin D deficiency
What are the symptoms of hyperparathyroidism?
Stones, Bones, Abdominal Groans and Psychic Moans
Stones – calcium oxalate renal stones
Bones – osteitis fibrosa cystica
Abdominal Groans – acute pancreatitis
Psychic Moans – psychosis and depression