Parathyroid disorders and calcium imbalance Flashcards
what parathyroid surface receptors are responsible for detecting calcium and phosphate level changes in the blood ?
Chief cells of the parathyroid glands. If the calcium is decreased or phosphate is increased the chief cells signal the parathyroid glands to secrete more PTH.
What is the action of PTH on bone cells ?
*PTH stimulates osteoblasts to release RANKL and Moncyte colony stimulating factor leading to the maturation of osteoclast precurssor cells to osteoclasts which breaks down bones and release clacium and phosphate into the blood.
*PTH also increase renal excretion of phosphate and reduce calcium excretion.
* It activates vitamin D or calcitriole which enhances GI absorption of vitamin D.
What is the most common cause of hypoparathyroidism ?
Thyroidectomy
What is DiGeorge syndrome ?
It is a congenital condition in which there is agenesis of third and fourth pharyngial arches causing the agenesis of parathyroid glands and thymus resulting in hypoparathyroidism.
What is Psuedo-hypoparathyroidism ?
It is characterised by high or normal PTH with renal PTH resistance.
What is Albright hereditary osteodystrophy or Psuedo-hypoparathyroidism type 01A ?
It is an autosomal dominant condition in which there is mutation in the Gs protein alpha subunit and it is always inherited from the mother. The defect in Gs protein result in PTH receptor dysfunction in kidneys and bones.
What are the classical symptoms of Albright hereditary osteodystrophy or Psuedo-hypoparathyroidism type 01A ?
- Shortened 4th and 5th digits.
- Short stature
*Obesity - Developmental delay.
What is Pseudo-pseudo-hypoparathyroidism ?
It is a subtype of Albright’s hereditary dystrophy with similar physical features. However, the gene is passed on from the father and no PTH resistance.
What is the cause of tetany in hypoparathyroidism ?
Low calcium and high phosphate makes the neurons highly sensitive to excitation this leads to Tetany.
What is the cause of primary hyperparathyroidism ?
It is caused by increased PTH release regardless of calcium levels due to parathyroid adenoma or carcinoma or hyperplasia.
What are the symptoms of hyperparathyroidism ?
Stones - renal stones and galstones with dehydration.
Thrones- Polyuria due to impaired Na and H2O reabsorption.
Bones- bone pain due to chronic hormone driven demineralisation.
Grones- Constipation and muscle wekness due to decreased muscle contraction due to excess calcium mediated neuronal inhibition.
Psychiatric overtones- Depression and confusion due to excess clacium mediated inhibition.
What is osteitis fibrosa cystica ?
These are also called brown tumours they develop due to increased osteoclast driven bone resorption and osteoclast and hemosederine deposit. It commonly associated with primary hyper parathyroidism.
What are the signs of osteitis fibrosa cystica ?
Salt and pepper sign of the skull due to subperiostal erosions. Similar process can affect the phalanxes.
What are the lab findings in primary hyperparathyroidism ?
- Hypercalcemia and hypophsphatenemia
- Significantly elevated PTH and ALP.
- SIgnificantly elevated cAMP in urine.
What is the cause of secondary hyper parathyroidism?
The main cause is CKD causing hyperphosphatemia, impaired conversion of inactive vitamin D to Calcitriol resulting in reduced GI uptake of calcium and presents with symptoms of CKD, renal osteodystrophy, and calcification of blood vessels and soft tissue.
