Lec 10 endocrine

Lec:10 Dr.Mohammed Alhamdany
THE PARATHYROID GLANDS
Parathyroid hormone (PTH) plays a key role in the regulation of calcium and phosphate homeostasis and vitamin D metabolism.
Functional anatomy, and physiology
The four parathyroid glands lie behind the lobes of the thyroid, the parathyroid chief cells respond directly to changes in calcium concentrations via a G-protein-coupled cell surface receptor (the calcium-sensing receptor).
PTH acts on the renal tubules to promote reabsorption of calcium and reduce reabsorption of phosphate, and on the skeleton to increase osteoclastic bone resorption and bone formation. PTH also promotes conversion of 25-hydroxycholecalciferol to the active metabolite 1,25-dihydroxycholecalciferol; the 1,25- dihydroxycholecalciferol, in turn, enhances calcium absorption from the gut. More than 99% of total body calcium is in bone. Prolonged exposure of bone to high levels of PTH is associated with increased osteoclastic activity and new bone formation, but the net effect is to cause bone loss with mobilisation of calcium into the extracellular fluid. In contrast, pulsatile release of PTH causes net bone gain, an effect that is exploited therapeutically in the treatment of osteoporosis.
if the serum albumin level is reduced, total calcium concentrations should be ‘corrected’ by adjusting the value for calcium upwards by 0.02 mmol/L (0.1 mg/dL) for each 1 g/L reduction in albumin below 40 g/L.
Presenting problems in parathyroid disease
Hypercalcaemia:
Causes:
With normal or elevated PTH levels
1- Primary or tertiary hyperparathyroidism
2- Lithium-induced hyperparathyroidism
3- Familial hypocalciuric hypercalcaemia
With low PTH levels
1- Malignancy (lung, breast, myeloma).
2- Elevated 1,25(OH)2 vitamin D (vitamin D intoxication, sarcoidosis, other granulomatous disease).
3- Thyrotoxicosis.
4- Paget’s disease with immobilization.
5- Milk-alkali syndrome.
6- Thiazide diuretics.
7- Glucocorticoid deficiency.
Clinical feature:
‘bones, stones,abdominal groans, and psychic moans’
Bone: osteoporosis.
Stone: in the renal
Abdominal Groan: dyspepsia, constipation, and peptic ulcer.
Psychic moans: depression.
In addition to that cause polyuria, and polydipsia, why?
Investigations
The most discriminant investigation is measurement of PTH. If PTH levels are detectable or elevated in the presence of hypercalcaemia, then primary hyperparathyroidism is the most likely diagnosis. High plasma phosphate and alkaline phosphatase accompanied by renal impairment suggest tertiary hyperparathyroidism.
Patients with FHH can present with a similar biochemical picture to primary hyperparathyroidism but typically have low urinary calcium excretion (a ratio of urinary calcium clearance to creatinine clearance of < 0.01).
If PTH is low and no other cause is apparent, then malignancy with or without bony metastases is likely, so we investigate accordingly.