Calcium Dysregulation Flashcards
How is Vitamin D made
Synthesised in skin or intake via diet
Where is parathyroid hormone secreted
Parathyroid glands
What things increase serum calcium and phosphate
Vitamin D , Parathyroid hormone ( PTH)
–> regulate calcium and phosphate homeostasis via actions on kidney , bone and gut
How does Vit D and PTH increase serum calcium and phosphate
Regulate calcium and phosphate homeostasis via actions on kidney , bone and gut
What molecule decreases serum caclcium and phosphate
Calcitonin ( Regulates calcium acutely but no negative ect if parafollicular cells are removed ie thyroidectomy)
Where is calcitonin made
Secreted by thyroid parafollicular cells
How can you measure vit D
measure serum 25-OH cholecalciferol vit D
What is the active form of vitamin D
Calcitriol ( 1,25(OH)2-Cholecalciferol)
How is Vitamin D made
2 types : D2 from diet and D3 from sunlight
How is calcitriol made
1) UVB hits skin cells
2) Pre-Vitamin D3
3) Vitamin D3
made in skin cells
4) Vitamin D3 then goes to the gut which combines with Vit D2 from the diet
5) They both then go to liver where they are converted into 25(OH)- cholecalciferol using 25 hydroxylase
6) 25 (OH)- cholecalciferol –> 1,25(OH)2Cholecaliferol ( calcitriol using 1 alpha-hydroxylase in the kidney (renal step)
8) 1,25(OH)2cholecalciferol = active form of Vitamin D = calcitriol
9) 1,25(OH)2 vitamin D (calcitriol) regulates its own synthesis by decreasing transcription of 1-alpha hydroxylase
How does Vit D ( calcitriols) regulate it’s self
1,25(OH)2 vitamin D (calcitriol) regulates its own synthesis by decreasing transcription of 1-alpha hydroxylase
What are the effects of calcitriol
1) acts on bone to increase osteoblast activity ( remember blast not clast –> increases bone synthesis
2) Acts on kidney to increase Ca2+ and PO43- reabsorption
3) Acts on gut to increase Ca2+ absorption and PO42- absorption
note ( increased Ca2+ absorption increases osteoblast activity)
what are the actions of PTH
1) Increased Ca2+ reabsorption from bone
( stimulates osteoclast activity –> opposite of calcitriol)
2) Acts on kidney to : increase ca2+ reabsorption, increase PO43- excretion , increase 1-alpha hydroxylase activity
3) Increased 1-a hydroxylase increases calcitriol synthesis
4) Increased calcitriol —> increased Ca2+ absorption and increased Phosphate absorption in the gut
note excretion of PO43- by kidney and reabsorption by gut balance each other out
How does PTH regulate serum cal and phos levels
1) acts on liver to increase Ca2+, PO43- reabsorption ( will increase plasma Ca2+
2) Acts on liver to increase 1,25(Oh)2D3 synthesis
3) increased calcitriol increases Ca2+ absorption + PO43- absorption in gut ( increases plasma Ca2+)
4) Increase ca2+ mobilisation increases plasma Ca2+
How does FGF23 regulate serum phosphate
note FGF 23 made by osteocytes
1) FGF23 and PTH both inhibit phosphate reabsorption in the kidney through blocking the Na/PO4 cotransporter in the PCT epithelium –> more Na+ and PO43- excretion in urine
2) FGF23 also inhibits calcitriol synthesis which decreases absorption of phosphate from the gut
note( Calcitriol can block the phosphate transporter by stimulating FGF23 (FGF23 has a –ve feedback on calcitriol levels though)
Overall : FGF23 works in 2 ways:
Inhibits PO43-/Na+ cotransporter → increases po43- excretion
Inhibits calcitriol action → DECREASES pO43- REABSORPTION IN GUT
What does hypocalcaemia do to muscles
Sensitives excitable tissues , causing muscle cramps , tetany ( involuntary contraction of muscles , tingling)
What are the signs of Hypocalcaemia
1) Paraesthesia ( hands, moth , feet and lips)
2) Convulsions
3) Arrhythmias
4) Tetany
( mneumonic CATS go numb)
5) Chvostek’s’ sign – facial paraesthesia
6) Trousseau’s sign - carpopedal spasm
What is chvostk’s sign
Facial paraesthesia
caused by hypocalcaemia
What is trousseau’s sign
Carpopedal spasm
caused by hypocalcaemia
What are the causes of hypocalcaemia
1) Low PTH ( hypoparathyridsm) due to Surgical – neck surgery Auto-immune Magnesium deficiency Congenital (agenesis, rare)
2) Low Vitamin D levels due to : Deficiency – diet, UV light, malabsorption, impaired production (renal failure)
what is hypoparathyroidism
Low PTH levels
What can cause hypoparathyroidism
Neck surgery
Auto immune
Magnesium deficiency
Congenital ( agenesis , rare)
What can cause low vitamin D levels
Deficiency –> diet , UV light , malabsorption , impaired production ( renal failure)
What does hypercalcaemia do to muscles
Makes them atonal ( due to reduced neuronal excitability)
