Biochemistry:part 1 Flashcards
What is metabolic bone disease?
A group of disease that cause a change in bone density and bone strength by increasing bone resorption, decreasing bone formation or altering bone structure,And may be associated with disturbances in mineral metabolism
What are the five main metabolic bone disorders?
Primary Hyperparathyroidism
Osteomalacia/Rickets
Osteporosis
Renal Osteodystrophy
Paget’s Disease
What are the main components of bone strength?
Mass
Material
Microarchitecture
Macroarchitectue
When is peak bone mass reached?
Around 25 years
When does bone mass begin to decline?
Around 40 years
NOTE: in women, the decline in bone mass accelerates after menopause
How are cortical bone microfractures repaired?
Bone remodelling
Briefly describe the bone remodelling cycle.
A microcrack crosses the canaliculi and severs the osteocyte processes, inducing osteocyte apoptosis
This signals to the surface lining cells, which release factors to recruit cells from the blood and marrow to the remodelling compartment
Osteoclasts are generated locally and resorb the matrix and the mitrocrack
Then osteoblasts deposit new lamellar bone
Osteoblasts that become trapped in the matrix become osteocytes
What is the normal range for serum calcium concentration?
2.15-2.56 mmol/L
Describe the distribution of calcium.
46% plasma protein bound (albumin)
47% free calcium
7% complexes (with phosphate or citrate)
What is the ‘corrected’ calcium level?
This compensates for changes in protein level (if proteins are high, itcompensates down)
Corrected calcium = [Ca2+] + 0.02(45-[albumin])
Describe the effect of metabolic alkalosis on calcium distribution.
It makes more calcium bind to plasma proteins thus reducing the free calcium levels
NOTE: venous stasis may elevate free calcium
What are the two main targets of PTH?
Kidneys
Bone
Describe the effects of PTH in:
a. Bone
b. Kidneys
a. Bone
Acute release of available calcium (not stored in hydroxyapatite crystal form)
More chronically, increased osteoclast activity
b. Kidneys
Increased calcium reabsorption
Increased phosphate excretion
Increased stimulation of 1-alpha hydroxylase (thus increasing calcitriol production therefore INcreasing intestinal CaHPO4 production)
Where does the PTH-mediated increase in calcium reabsorption take place in the nephron?
DISTAL convoluted tubule
Where does the PTH-mediated increase in phosphate excretion take place in the nephron?
PROXIMAL convoluted tubule
