Calcium and phosphorus metabolism Flashcards
Only difference between Pi and Ca++
Pi is a component of the phopholipid membrane
% of Ca++ that is free
50%
Respiratory alkalosis causes
Hypocalcemia
Respiratory acidosis causes
Hypercalcemia
Why does respiratory acidosis cause hypercalcemia
Because H+ binds to albumin so Ca++ is now free
Ca++ free depends on
[H+]
Calciotrophic hormones
Vitamin D
PTH
Vitamin D effect on Ca++
Increases intestinal Ca++ absorption
Anabolic hormones
GH and sex hormones
PTH function
Parathyroid hormone controls Ca++ in blood
Half life of PTH
2 minutes
Increased PTH pathologies
Hypocalcemia
Hyperphosphatemia
Catecholamines
What causes PTH inhibition
Hypercalcemia
Vitamin D administration
Hypomagnesemia
Enzyme activating Vitamin D
1-a-Hydroxylase
Functions of PTH
Activate 1-a-hydroxylase
Decrease phosphate
Increase Ca++
How many times does Vitamin D get hydroxylased
2 times, in liver and kidney
Active form of Vitamin D
1.25 Vitamin D
Which Vitamin D do we measure
25 Vitamin D
Osteoblast and osteoclast function
Osteoblast –> bone formation
Osteoclast –> bone destruction
What do osteoblasts bind to in osteoclasts
Osteoblasts have RANKL that bind to RANK in osteoclasts
PTH secretion impact on RANK/RANKL process
PTH stimulates an increase in Ca++
Therefore when PTH is increased, there is an increase in RANKL from osteoblasts binding to RANK in osteoclasts for bone resorption
Inhibitor of RANK/RANKL
Osteoprotegerin (OPG)
How is OPG an inhibitor
It inhibits osteoclasts differentiation and function
Osteoclasts differentiation and bone resorption depends on
RANKL of osteoblasts and OPG
Effect of PTH on kidney on distal convoulted tubule
Increase Ca++ reabsorption
Consequence of increased reabsorption of Ca++ in distal convoluted tubule
Hypercalcemia
Effect of PTH on proximal tubule
Decreased Pi reabsorption
Consequence of decreased Pi reabsorption
Phosphaturia –> increased Pi excretion
What does UV light activate in the process of Vit. D synthesis
Activated proVit D to cholecalciferol
Cholecalciferol undergoes
Double hydroxylation
Effects of Vit. D
Increased bone resorption and formation
Increased Ca++ reabsorption in kidney
Increased Ca++ absorption in intestine
Decreased PTH synthesis
In intestine, Ca++ enters enterocytes through
TRPV6
Inside cell, Ca++ captured by
Calbindin
Ca++-Calbindin reaches bloodstream through
PMCA
Regulation of Vit. D synthesis through
FGF23
FGF23 produced by
Mature osteoblasts
FGF23 binds to
Klotho receptor in kdney
Binding of FGF23 to Klotho receptor in kidney causes
Phosphaturia –> decreased Pi reabsorption –> increased Pi excretion
How does FGF23 impact Vit. D synthesis
FGF decreases calcitriol (1.25 Vitamin D) synthesis by supressing 1-a-hydroxylase
Most rapid response to a hypocalcemia
Increase in PTH
What does PTH activate in hypocalcemia
C1a activation
C1a activation in hypocalcemia causes
Vitamin D activation (slower response than PTH)
Result of hypocalcemia, Ca++, PTH, FGF23
Increased Ca++
Decreased PTH
Decreased FGF23
Main role of PTHrp
In hypercalcemia and malginant tumors
Function of PTHrp
Bone resorption and Ca++ reabsorption causing hypercalcemia
If during hypercalcemia we have normal PTH levels, then we measure
PTHrp
Function of calcitonin
Antiresorptive at bone level
What secretes calcitonin
Parafollicular cells
Calcitonin used in treating
Hypercalcemia
Increased levels of ?? during medulary thryoid cancer
Calcitonin
SUMMARY: PTH impact on Ca++
Increased Ca++
SUMMARY: Vit. D impact on Ca++ and Pi
Increased Ca++ and Pi
SUMMARY: Calcitonin impact on Ca++ and Pi
Decreased Ca++ and Pi
SUMMARY: FGF23 impact on Pi, PTH and Vit. D
Promotes Pi excretion –> phosphaturia
Inhibits PTH
Inhibits Vit. D synthesis