MSK Flashcards
What are the major sources of dietary calcium?
- Dairy products
- Vegetables
- cereals
- Oily fish
What is PTH secreted in response to?
Low calcium levels
What does PTH act on to increase Ca2+ levels?
1) Increased bone resorption
2) Increased calcium resorption from the jejunum and ileum
3) Increased calcium resorption in the kidneys
Where is vitamin d3 or cholecalciferol formed?
In the skin, in response to UV light. Causes activation of 7-dehydrocholesterol which creates vitamin D3.
Where does vitamin d3 travel to, and what happens?
Cholecalciferol travels to the liver to become 25(OH)D3 or calcifediol
Where does calcifediol travel to?
To the kidneys, where PTH stimulates the conversion of calfiediol to calcitriol, the active form of vitamin D
What does 1,25(OH)D3 do?
1) Increases bone turnover to increase Ca2+ resorption
2) Increases Ca2+ from kidneys and the collecting duct
3) Increases Ca2+ resorption in the gut
What happens when there is an excess in phosphate levels?
Excess hydroxyapetite formation. Spreads to the joints and causes calcification in joints
What histological stain would you use to assess bone minerlisation?
Goldner’s trichrome stain
What are the main sources of phosphate?
Animals
dairy
soy
seeds
Where is most phosphate passively reabsorbed in the kidney, and how?
Proximal convoluted tubule, via a Na+/Phosphate cotransporter
How does PTH affect phosphate levels?
Acts on the kidneys to increase phosphate excretion, but acts on the bone and gut to increase serum phosphate
What secretes FGF-23 and to what stimulus?
Osteoclasts. In response to PTH, high phosphate levels, 1,25(OH)D3, Dietary phosphate loading
What affect does FGF-23 have on phosphate levels?
Works to reduce phosphate. Acts by increasing phosphate excretion in the urine, and works to prevent the 1Alpha hydroxylation of vitamin D3, decreasing gut absorption of phosphate
What is the function of Klotho?
Klotho works with FGF-23, and makes non-specific FGF receptors bind with FGF-23
