PHYS: Bone physiology & calcium metabolism Flashcards
Name the antagonist of PTH.
Calcitonin.
The two components of bone are:
- Cellular material.
- Extracellular matrix.
- How much of bone material is inorganic?
- What is the inorganic compound called?
- 70%.
- Hydroxyapatite: Ca10(PO4)6(OH)2
What is the Ca:P ratio in bone (as a range)?
1.3-2.0.
What percentage of calcium in the body is stored in bones?
99%
- Almost all of the protein holding bone together, which can be found in the extracellular matrix is….
- What is the proportion?
- Collagen type I.
- 90-95%.
There is two different lineages of bone cells. How can these lineages be categorised?
- Bone forming cells.
- Bone destroying cells.
- An osteoprogenitor cell is a precursor stem cell. What does it differentiate into?
- What do these differentiate into?
- Osteoblasts.
- Osteocytes.
What is the function of the osteoblasts?
Rebuilding bone.
- Define osteocytes.
- Inside of what structure do they reside?
- How do they get nutrients?
- Held in place mature bone cells.
- They reside in lacunae.
- by extending their cytoplasmic processes into the canalliculi
What cells do monocytes differentiate into?
Osteoclasts.
When plasma calcium levels are low, describe the homeostatic mechanism to increase it.
- CaSR (calcium sensing receptor) is present on the parathyroid glands (and other places) and senses when calcium levels are low.
- Parathyroid hormone is secreted.
- PTH activates osteoclasts.
- Increased osteoclast activity = increased bone degradation –> increased release of Ca2+ from bone.
Is the PTH-mediated mechanism of calcium release fast or slow?
Slow.
What are the five phases of bone remodelling?
- Activation of osteoclasts.
- Resorption of bone.
- Reversal phase.
- Formation of bone (osteoblast activation & mineralisation).
- Resting.
Where does the parathyroid gland sit?
There are two on each side of the thyroid gland in the neck.
Where are osteoclasts found?
Shallow pits on the surface of bone, formed by the osteoclasts themselves. (Howship’s lacunae)
What happens if too much parathyroid hormone is secreted?
What may cause excess PTH secretion?
- Excess bone resorption
- hypercalcaemia
- Calcium blocks sodium channels at NMJ
- CNS/PNS depression
- muscle weakness
- kidney stones
- coma
- Parathyroid tumour
What happens if too little parathyroid hormone is secreted?
What may cause insufficient PTH secretion?
- Not enough calcium mobilised from bone
- hypocalcaemia
- muscle tetany
- fatigue & headaches
- tingling
- seizures
- cardiac arrhythmias
- thyroidectomy
- autoimmune disease
What is the action of Vitamin D in regulating serum calcium?
How is active Vit D made?
- increases dietary absorption, Ca^
- increases kidney resorption (decreases secretion), Ca^
- increases calcification in bone (small effect, Ca down)
Endogenous synthesis of inactive VitD in people with adequate sun exposure. Requires PTH to activate.
What is the action of Calcitonin? What is it’s significance?
It acts to depress the action of osteoclasts, slowing bone resorption and decreasing serum calcium. Also small effect in decreasing resorption from the kidneys (increasing excretion).
In normal people Calcitonin only has a mild/insignificant role.
What is the action of PTH in regulating serum calcium?
Increases serum calcium by
- Increasing kidney resorption (decreases secretion)
- Increasing osteoclast activity & bone resorption
What is caused by a lack of Vitamin D? What are the 2 forms of this disease?
What is it called in adults?
Ricketts - causes soft/weak bones
Type 1: not enough sunlight/dietary deficiency
Type 2: congenital lack of vitamin D receptor
Osteomalacia
What is the osteoid?
The organic bone matrix formed of type 1 collagen and various proteoglycans (ie hyaluronic acid) which form the ground substance.
