Flashcards in Diseases of Bone ( Endocrine Pathology) Deck (39)
What is the purpose of bone?
-protection of organs
-blood cell production (bone marrow)
-Storage of minerals e.g.calcium
Describe the composition of bone.
Made of :
-Cortical Bone (80%)
-Osteoblasts and Osteoclasts.
-Extracellular Matrix and Minerals
-Compact, hard outer layer covered by periosteum.
-forms columns called Osteons which have a central canal containing blood/lymph vessels and nerves.
-Spongy, porous inner layer.
-filled with bone marrow.
-light weight due to porous nature.
Describe the formation of bone.
-Osteoblasts are involved in the formation of bone.
-They help to form Osteoids from collagen.
Which then get mineralized .
-The Osteoblasts get trapped in the bone and become osteocytes.
*Osteoclasts are involved in the reabsorption of bone.
What provides the tensile strength of bone?
Describe the role of Osteoclasts?
Osteoclasts are involved in bone reabsorption.
-They are found in bony pits / reabsorption bays,
- They release enzymes which break down bone and help to increase blood calcium levels.
-they are regulated by Parathyroid hormone.
What is the role of Osteocytes?
Osteocytes are trapped osteoblasts.
They have mechosensory properties that help to relay bone movement.
They help to regulate bone matrix turnover
Describe the effect of Ageing on bone ?
Ageing causes bone mass to increase.
Peak bone density is in the mid 20's .
It the plateus and decreases.
Bone densities in later life is determined by peak bone mass.
Menopause causes a steeper decline in bone mass due to the loss of oestrogen.
*Osteoblasts decrease with age (so no new formation)
*Osteoclasts increase with age (so more reabsorption)
what methods are used to investigate bone disease?
Xray - (structure)
DEXA - (bone mass)
Biochemistry ( turnover )
Biopsy (cellular function)
What are the biochemical markers of bone formation?
Osteoblasts are involved in bone formation and produce
-ProCollagen Type 1 propeptides (P1NP)
*P1NP is most commonly used in clinical practice. It is a precursor of collagen
What are the biochemical markers of bone reabsorption?
Degradation products of bone collagen:
- Crosslinked telopeptides of type 1 collagen. (NTX and CTX)
What is the use of alkaline phosphatase in bone function?
Alkaline Phosphatase is required for the formation of bone.
It indicates osteoblastic activity as it is released by OBs.
It is involved in mineralisation.
It is also used as a liver function test.
What do high levels of alkaline phosphatase indicate?
Release of Alkaline Phosphatase is stimulated by increased bone remodelling so can indicate :
What is P1NP? (Procollagen type 1N propeptide)
P1NP is a bionmarker for bone synthesis.
It is released by osteoblasts.
High levels indicate icnreased osteoblastic activity and bone formation.
What is the significance of collagen cross links (NTX and CTX)
NTX and CTX are produced when collagen is broken down. ie. bone reabsorption/turnover which is done by osteoclasts.
What are the uses of bone markers?
- evaluate bone turnover and loss
- Evaluate treatment effect
-Evaluate complance with medication
What is the T score that indicates osteoporosis?
-2.5 and below
The more negative the T score the lower the bone mass.
Name 3 common bone disorders?
-Ostemalacia / Rickets
What are the risk factors of Osteoporosis?
-menopause (loss of oestrogen causes bone loss)
-long term steroids
-Vitamin D Deficiency
What is Osteoporosis?
1)Decreased Bone Mass
2)Decreased bone qualityy
3)leads to lack of structural function
What is a fragility fracture?
A fracture caused by minimal trauma, e.g. tripping.
What are some secondary causes of Osteoporosis?
Name one from the following categories:
-hypogonadism (decrease in testosterone)
-cushing's (caused by excessive steroid)
-Chronic liver disease
What are bisphosponates used for?
Bisphosphonates are used as an antiresorptive treatment. They affect osteoclasts.
The bisphosphonates are absorbed into the bone. When the osteoclasts ingest the bone the bisphosphonates kill them. This decreases bone breakdown and re-absorption.
What is lytic bone metastases?
Lytic is the destruction of bone driven by osteoclasts. It can be caused by lung and breast cancer.
What is sclerotic bone metastes?
It is the depostion of new bone. Often stimualted by prostate cancer.
If in the spine can compress the spinal cord.
What are the symptoms of bone metastases?
-Pain (worse at night)
numbness/paralysis/trouble urinating (pressing on spinal cord)
-Loss of appetite, nausea, thirst (symptoms of Hypercalcaemia)
-Anaemia (disruption of bone marrow)
What blood test would you do for high calcium levels?
Check the ParaThyroid Hormone levels which indicate reabsorption.
(*When calcium is low, the para thyroid gland released PTH. PTH causes osteoclasts to break down bone. Increasing Ca2+ in blood. negative feedback causes PTH secretion to stop)
What are the symptoms of Hypercalcaemia?
What are the causes of Hypercalcemia?
1) PTH mediated:
-sporadic primary hyperparathyroidism
2)Non PTH mediated:
- Excess Vit D
-Sarcoidosis (increases activated Vit D levels)
What cells secrete parathyroid hormone from the parathyroid gland?