Hormone regulation calcium and phosphate Flashcards
What regulates calcium absorption?
PTH
What senses change in serum calcium?
Chief cells
What cause PTH release?
Low calcium lvls- stimulate PTH release
High calcium lvls- inhibit PTH release
Does parathyroid hormone cause slow or fast response?
Fast response
Mechanism of PTH?
Ca2+ binds to receptor
Intracellular cascade (Gq cascade)
Ca2+ released from ER
State 4 effects of PTH?
1) IncreaseCa2+ reabsorption in kidneys- decreasing urinary Ca2+ excretion
2) Increases Ca2+ reabsorption in small intestine
3) Stimulates osteoclast break bone down- release Ca2+ and phosphorous
4) Stimulate formation of active form of vitamin D (1α,25-dihydroxyvitamin D)
State 3 effects of vitamin D?
1) Amplify PTH
2) Stimulate vit D prod in kidney- cause Ca2+ and phosphate reabsorption
3) Stimulate osteoclasts break bone into Ca2+ and phosphate
Function calcitonin?
Anti PTH
What produces calcitonin?
Thyroid- C cells
When is calcitonin released?
High plasma concentration of Ca2+
What is released when high conc of Ca2+?
C cells of thyroid release calcitonin
Effects of calcitonin?
Where is vitamin D synthesised?
Skin- exposure to sunlight
Metabolised in liver and kidney to form 1α,25-dihydroxyvitamin D
Outline how vitamin d is activated (flow diagram)
How is vitamin D activated?
1) UV light hits skin
2) 7-dehydrocholesterol
3) Cholecalciferol (vit D3)
4) 25-hydroxylase catalyses reaction
5) 25-hydroxyvitamin D3 formed
6) 1-alpha-hydroxylase catalyses reaction
7) Forms 1,25-dihydroxyvitamin D3
(calcitrol)
What is the active form of vitamin D called?
1,25-dihydroxyvitamin D3
(calcitrol)
What enzyme is involved in cholecalciferol to 25 hydroxyvitamin D3?
25-hydroxylase
What enzyme is involved in 25-hydroxyvitamin D3 to 1, 25 dihydroxyvitamin D3 (calcitrol)
1 alpha hydroxylase
What sets off chain for activation of vit D3?
UV light hitting skin
Converts 7-dehydrocholesterol to cholecalciferol
Where does the activation of vit D3 occur?
1) Skin
2) Liver (cholecalciferol to 25-hydroxyvitamin D3 (calcidiol))
3) Kidney (25 hydroxyvitamin D3 to 1,25 dihydroxyvitamin D3 (Calcitriol)
Outline vit D3 formation?
1) Initially skin or diet
2) Vit D hydrolysed by liver by 25-hydroxylase to form 25-hydroxyvitamin D (calcidiol)
3) Kidney hydrolyses it using 1-hydroxylase to form 1,25-dihydroxyvitamin D (calcitriol)
What stimulates hydrolysis of vit D3 in kidneys?
PTH
What inhibits vit D3 activation?
High calcitriol- inhibit Pth
What effects does calcitonin have?
1) Block PTH release
2) SI- inhibit Ca2+ absorption
3) Stop Ca2+ and phosphate release from bone
4) Kidney- inhibit Ca2+ reabsorption
Give one function of bone related to Ca2+?
Storage (buffer) of Ca2+, Phosphate and magnesium
Give 3 functions of kidney?
1) Respond Ca2+, PTH, vit D and calcitonin
2) Activate vit D
3) Regulate calcium and phosphate reabsorption/exc
Function of parathyroid hormones?
1) Respond to changes in serum calcium
2) Synthesis and secretion PTH
What stimulates PTH?
Low lvls serum calcium
Function of GI tract?
1) Absorb Ca2+ and phosphate
Function thyroid glands?
1) Respond changes in serum calcium
2) Synthesis and excretion of calcitonin
What secretes calcitonin?
Thyroid glands
Effect of PTH on:
Intestine
Kidney
Bone
Net effect serum lvl?
Intestine- increased calcium and phosphate absorption
Kidney- decreased calcium excretion
increased phosphate excretion
Bone- calcium and phosphate resorption
Serum- calcium increase, phosphate decrease
Effect of vit D on:
Intestine
Kidney
Bone
Net effect serum lvl?
Intestine- increased Ca2+ and phosphate absorption
Kidney- decreased excretion
Bone- bone formation increased
Serum- both increase
What growth factor is involved in phosphate regulation?
Function?
FGF23
Suppress phosphate reabsorption
