PTH Flashcards
Actions of PTH
- Increased calcium reabsorption
- Decreased phosphate reabsorption
- Increased 1-alpha-hydroxylation of 25-OH vit D
- Increased bone remodelling
- Bone resorption > bone formation
PTH has no direct effect on what
- Intestines
But increased calcium absorption because of increased 1,25 (OH)2 vit D
Calcium homeostasis is an example of what?
Negative feedback
Why is calcium important?
Functioning of nerves and muscles
Appropriate changes in PTH
Maintain calcium balance
Inappropriate changes in PTH
Cause calcium imbalance
How is corrected calcium calculated?
Corrected calcium =
total serum calcium + 0.02 * (40-serum albumin).
What are the consequences of hypocalcaemia?
Parasthesia
Muscle spasm (hands and feet, larynx, premature labour)
Seizures
Basal ganglia calcification
Cataracts
ECG abnormalities (long QT)
Chvostek’s sign
Tap over the facial nerve and look for spasm of facial muscles.
Trousseau’s sign
Inflate the blood pressure cuff to 20mm Hg above systolic for 5 mins.
Causes of hypocalcaemia
Vitamin D deficiency (increased calcium absorption in the intestines)
Hypoparathyroidism (due to surgery or radiation).
Hypoparathyroidism due to syndromes
Di George
o HDR
o Kenney-Caffey
o Sanjad –Sakati
o Kearns-Sayre
o Blomstrand chondrodysplasia
Di George syndrome
Developmental abnormality of third and fourth branchial pouches.
Hypoparathyroidism
Thymic aplasia
Immunodeficiency
Cardiac defects
Cleft palate
Abnormal facies
Genetic causes of hypoparathyroidism
Recessive
Dominant
X-linked
Autoimmune causes of hypoparathryoidism
Isolated
Polyglandular type 1
(chronic mucocutaneous candidiasis, hypoparathyroidism, autoimmune adrenal insufficiency).
Hypoparathyroidism due to infiltration
Haemochromatosis
Wilson’s disease
Metal accummulation.
Hypoparathyroidism can also occur due to deficiency in what?
Magnesium (PTH in vesicle which needs to be trafficked to cell surface ← this required magnesium (hypomagnesaemia due to alcohol etc).
Decreased PTH leads to
Decreased renal calcium reabsorption > increased relative calcium excretion.
Increased renal phosphate reabsorption > increased serum phosphate > Decreased formation of 1,25 (OH2) D
Decreased bone resorption.
Decreased intestinal calcium absorption.
DECREASED SERUM CALCIUM!
Pseudohypoparathyroidism
Resistance to PTH (Type 1 Albright hereditary osteodystrophy - mutation with deficient Galpha subunit).
- Short stature
- Obesity
- Round facies
- Mild learning difficulties
- Subcutaneous ossification
- Short fourth metacarpals
- Other hormone resistance
What are non-primary causes of hypercalcaemia?
Tourniquet on for too long.
Blood sample is old and haemolysed.
What are the symptoms of hypercalcaemia?
Thirst, polyuria
Nausea
Constipation
What are the consequences of hypercalcaemia?
Confusion and coma
Renal stones
ECG abnormalities (short QT)
Causes of hypercalcaemia?
90% of cases:
Malignancy
- bone mets, myeloma, PTHrP, lymphoma
- Primary hyperparathyroidism
- Thiazides
- Thyrotoxocosis
- Sarcoidosis
- Familial hypocalciuric / benign hypercalcaemia
- Immobilisation
- Milk-alkali
- Adrenal insufficiency
- Phaeochromocytoma
What are the consequences of primary hyperparathyroidism?
Bones:
- osteitis fibrosa cystica (skull cysts)
- osteoporosis (sub-periosteal erosion of the phalanges)
Stones:
- kidney stones
Groans:
- psychic - confusion
Moans:
- abdominal
- constipation
- acute pancreatitis
