Calcium and Phosphate Regulation Flashcards
3 effects of PTH?
- PTH increases kidney calcium reabsorption
- PTH promotes calcium release from the bone
- PTH regulates conversion of inactive vitD to active vitD (calcitriol) (which promotes calcium reabsorption from the gut
Effect of PTH on a PCT cell?
Inhibits sodium/phosphate cotransporters
PRIMARY HYPERPARATHYROIDISM causes increased X excretion
phosphate
What hormone Inhibits sodium/phosphate cotransporters (2)
PTH and FGF23
What does FGF23 do
inhibits reabsorption of phosphate by the cotransporter
What secretes FGF23
Osteocytes
Effects of FGF23? (2)
inhibits reabsorption of phosphate by the cotransporter
can also inhibit calcitriol
What inhibits PTH secretion
Calcium binding to Ca receptor in the parathyroid
Effect on PTH with increased Ca in serum?
MORE PTH INHIBITION
Vitamin D is only active after ….
it has been hydroxylated to CALCITRIOL
Active form of vit d?
calcitriol
Inactive form of vit D?
Cholecalciferol
Where is vit D converted to calcitriol
in the kidney
What enzyme converts 25OH-D3 to calcitriol
Renal 1 alpha hydroxylase
Source and name of VitD3?
from skin through UV light makes cholecalciferol
Source and name of VitD2?
From diet, ergocalciferol
What hormone stimulates renal 1alpha-hydroxylase conversion of 25OH-D3 to calcitriol
PTH
What are cholecalciferol and ergocalciferol converted to
25OH-D3
Where are cholecalciferol and ergocalciferol converted to 25OH-D3
Liver
Liver converts what to what (re. vit D)
Cholecalciferol and ergocalciferol converted to 25OH-D3
Causes of vit D deficiency?
- MALABSORPTION OR DIETARY INSUFFICIENCY
- LACK OF DIRECT
- LIVER DISEASE
- RENAL DISEASE
- RECEPTOR DEFECTS (vitamin D resistant rickets Rare)
- autosomal recessive
- resistant to vitamin D treatment
HOW DO HIGH EC CALCIUM AFFECT NERVE AND SKELETAL MUSCLE EXCITABILITY?
Ca2+ blocks Na+ influx, so there’s less membrane excitability
HOW DO LOW EC CALCIUM AFFECT NERVE AND SKELETAL MUSCLE EXCITABILITY?
enables greater Na+ influx, so more membrane excitability
SIGNS AND SYMPTOMS OF HYPOCALCAEMIA
Parasthesia (tingling - hands, mouth, feet, lips)
Convulsions
Arrhythmias
Tetany
How to remember symptoms of hypocalcaemia?
(CATs go numb)
What is used as ASSESSMENT FOR HYPOCALCAEMIA:
Chvosteks sign
TROUSSEAU’S SIGN:
What is Chvosteks sign
Tap facial nerve just below zygomatic arch
Positive response= twitching of facial muscles
Indicates neuromuscular irritability due to hypocalcaemia
What is TROUSSEAU’S sign
Inflation of BP cuff for several minutes
Positive response= carpopedal spasm= neuromuscular irritability due to hypocalcaemia
CAUSES OF HYPOCALCAEMIA (4)
- Vitamin D deficiency
- Low PTH levels Hypoparathyroidism
- surgical neck surgery
- Auto-immune
- Magnesium deficiency - PTH resistance e.g. pseudohypoparathryoidism
- Renal failure
- Impaired 1alpha hydroxylation
- Decreased production of 1,25(OH)2D3
(liver failure too probably0)
HYPERCALCAEMIA:
SIGNS AND SYMPTOMS: (3)
STONES- RENAL EFFECTS:
- Polyuria and thirst
- Nephrocalcinosis, renal colic, chronic renal failure]
ABDOMINAL MOANS- GI EFFECTS:
- Anorexia, nausea, dyspepsia, constipation, pancreatitis
PSYCHIC GROANS- CNS EFFECTS:
Fatigue, depression, impaired concentration, altered mentation, coma
Saying to remember hypercalcaemai symptoms?
‘stones, abdominal moans and psychic groans’
Causes of hypercalcaemia
- Primary hyperparathyroidism
- Malignancy Tumours/metastases often secrete a PTH-like peptide
- Conditions with high bone turnover (hyperthyroidism, Paget’s disease of bone- immobilised patient)
- Vitamin D excess (rare)
Hyperparathyroidism levels of:
Calcium
Phosphate
PTH
Calcium - raised
Phosphate - low
PTH - raised
Hypercalcaemia of malignancy levels of:
Calcium
Phosphate
PTH
Calcium - Raised
Phosphate - normal or raised
PTH - Low
VITAMIN D DEFICIENCY STATES results in: (4)
softening of bone, bone deformities, bone pain; severe proximal myopathy
Result of vit D deficiency in children?
Rickets
Result of vit D deficiency in adults?
OSTEOMALACIA
what is primary hyperparathyroidism
No negative feedback of calcium on PTH secretion, autonomous PTH secretion despite hypercalcaemia
What is secondary hyperparathyroidism often
Vit D deficiency usually, so poor calcium absorption so PTH increases
Effects of VitD? (4)
Calcium absorption in gut
Calcium maintenance n bone
Calcium renal increased absorption
-ve feedback on PTH
Why might Ca level be normal in vitamin D deficiency
may be normal if secondary hyperparathyroidism has developed
VIt D deficiency serum levels of: VitD Calcium Phosphate PTH
Vit D- low obvs
Calcium - low or normal if secondary hyperparathyroidism has developed
Phosphate - low
PTH - high
TREATMENT OF VIT D DEFICIENCY:
IN PATIENTS WITH NORMAL RENAL FUNCTION?
Give 25 hydroxy vit D
Patient converts this to 1,25 dihydroxy vit D via 1alpha hydroxylase
(ERGOCALCIFEROL= 25 hydroxy D2 and CHOLECALIFEROL= 25 hydroxy D3)
TREATMENT OF VIT D DEFICIENCY:
IN PATIENTS WITH RENAL FAILURE:
Inadequate 1alpha hydroxylation Can’t activate 25 hydroxyl vit D preparations
Give ALPHACALCIDOL 1alpha hydroxycholecalciferol
Alphacalcidol is used in….
TREATMENT OF VIT D DEFICIENCY:
IN PATIENTS WITH RENAL FAILURE
Vit D excess can lead to … (2)
hypercalcaemia and hypercalciuria due to increased intestinal absorption of calcium
Vit D excess can occur as result of (2)
- Excess treatment with active metabolites of vit D (e.g. alphacalcidol)
- Granulomatous diseases such as sarcoidosis, leprosy and TB (macrophages in the granuloma produce 1alpha hydroxylase to convert 25(OH) D to active metabolite
cholecalciferol is made by…
the skin and UV
ergo is absorbed from …
diet
Why is osteomalacia and rickets reemerging in the UK
Shit diet and not much sunlight bc of lifestyles now
