12) Calcium & phosphate regulation Flashcards
2 things that increase Ca2+ levels:
PTH VIT D (calcitriol)
How does PTH increase Ca2+ levels?
1) Bone-resporption
2) Kidney-increase reabsorption
3) VIT D-increased production
How does Vit D increase Ca2+ levels?
Increases Ca2+ absorption in gut
What is inactive Vit D and active Vit D also known as?
Inactive=25-OHD3
Active=calcitriol
2 places phosphate is re/absorbed:
Kidney
Gut
How is phosphate reabsorption in the kidney done + regulated?
Na+/PO43- cotransporter in PCT
-PTH & FGF23 inhibit this co-transporter
How is phosphate absorption in the gut regulated?
Calcitriol increases phosphate absorption in gut
FGF23 reduces calcitriol production
What does high PTH levels do to Ca2+ and PO43- levels?
High Ca2+
Low phosphate
Where is FGF23 produced?
Osteocytes
How is PTH release from parathyroid cells regulated?
Ca2+ sensing receptors on parathyroid cells
- high=Ca2+ binds to receptors + inhibits PTH secretion
- low=no Ca2+ binds=no inhibition so PTH secreted
2 sources of VIT D:
Diet
Sun
Where is inactive VIT D stored?
Liver
Where is inactive VIT D activated and what stimulates it’s activation?
Kidney
PTH stimulates second hydroxylation step
How is VIT D activation regulated?
Calcitriol negatively feedsback on PTH production
5 possible causes of VIT D deficiency:
1) diet-lacking/malabsorption
2) lack of sun
3) liver failure-store
4) renal failure-activation
5) VIT D receptor defects
Define VIT D deficiency:
lack of bone mineralisation
What does VIT D deficiency cause in adults vs children:
Children=rickets
Adults=osteomalacia
What do we measure to see if someone is VIT D deficienct?
Inactive vit D (25-OHD3) as calcitriol is hard to measure
How is VIT D deficiency treated?
Inactive VIT D given (ergocalciferol/cholecalciferol)
When must VIT D deficiency treatment be different to normal?
Renal failure-cant activate the inactive VIT D given so active VIT D should be give
What does excess VIT D cause?
Hypercalemia
2 possible causes of excess VIT D?
Excess treatment
Granulatomaous disease
Compare the main effect of hypercalcemia to hypocalcemia:
Hypercalcemia=Ca2+ block Na2+ influx=less excitability
Hypocalcemia=Greater Ca2+ influx=more excitability
What are the symptoms of hypercalcemia?
Stones, abdominal moans, psychic groans
What are the symptoms and 2 symptoms of hypocalcemia?
PCAT
- parasthesia
- convulsions
- arrthymias
- tetany
Chvostek’s (face) + trosseau’s (arm)
3 possible reasons for hypercalcemia?
Primary hyperthyroidism-parathyroid glands producing more PTH
Secondary hyperthyroidism-vit D deficiency
Hypercalcemia of Malignancy-PTH secretion
2 possible reasons for hypocalcemia?
Low PTH
VIT D deficiency
What is pseudohypoparathyroidism?
PTH resistance
What steps should be followed when trying to diagnose hypercalcemia?
Observe a high Ca2+
Check PTH levels
What are the 3 possible causes of hypercalcemia and state what the cause is and how the levels of PTH & Ca2+ are:
1) Primary hyperparathyroidism-parathyroid glands are producing lots of PTH
- high Ca2+, high PTH, low PO43-
- loss of -ve feedback
2) Secondary hyperparathyroidism-VIT D deficiency causes low Ca2+ so more PTH released eventually
- high Ca2+high PTH, low VIT D, low PO43-
3) Hypercalcemia of malignancy-bone cancer causing Ca2+ release
- high Ca2+, low PTH
- negative feedback still working
