Endocrine 8: parathormone Flashcards
other names for Parathyroid hormone
- Parathormone
- PTH
- Parathrin
Nature of Parathromone
polypeptide hormone –> 84aa
Mechanism of action of Parathormone
membranous receptors for Gs & Gq:
* Gs: adenyl cyclase —> increase cAMP
* Gq: Phospolypase C —> intracellular calcium —> Protein Kinase C
Describe effect of PTH on bone tissue
Rapid phase=Osteolysis= within minutes:
* binds to receptors of osteocyte of osteocytic membrane —> increase permiability to Ca2+
* Calcium pumps pump Ca2+ into ECM under the effect of Vit. D3 (1,25 DHCC)
Slow Phase= days/ weeks:
1. stimulates Osteblasts to release RANKL & IL-6
2. RANKL & IL-6 stimulates Osteoclast prolifertion
3. Osteoclast break down bone matrix, releasing Ca2+ & PO4- & hydroxyproline
4. they are then released into ECM
Describe effect of PTH on the Kidney:
Decrease phosphate reabsorption in PCT:
* Phosphaturic action
* Hypophosphatemia
PTH & decreased phosphate activate 1 alpha hydroxylase —> activated vitamin D3 (1,25 DHCC)
PTH + 1,25 DHCC:
* Increase Ca+ reabsorption in DCT
* Hypocalcinuria
* Hypercalcenemia
Increase magnesium reabsorption
Describe effect of PTH on intestines
along with 1,25 DHCC, they increase reabsorption of Phosphate & Calcium
state what happens to urine calcium in chronic excessive PTH
Hypocalciuria turns into Hypercalciuria
Describe regulation of PTH
- Not under control of pituitary gland, instead by feedback mechanism of plasma Ca2+ concentration
- when Phosphate level rises (the body need to increases Ca2+):
1.increase PTH
2.increased Phosphate –> Increase in FGF23 –> bind to FGF receptor of kindet —> decrease phosphate reabsorption in PCT & binds to FGF receptor of Parathyroid gland –> increase PTH secretion - Beta adrenergic stimulation –> increase cAMP in parathyroid gland cells –> increase PTH secretion
- 1,25 DHCC inhibits PTH synthesis & secretion
Cause of primary hyperparathyroidism
Parathyroid tumor
Charactaristics of primary hyperparathyroidism
- Hypercalemia
- decreased Neuromuscular excitability
Causes of secondary hyperparathyroidism
Decreased calcium reabsorption:
* Vit. D diffeciency
* Malabsorption syndromes
* Decreased calcium intake
* Bariatric surgeories (GIT bypass)
Renal infufficiency:
causing phosphate retention (secondary decrase in calcium)
charactars of secondary hyperparathyroidism
Elevated PTH with normal to low serum Calcium
cause of tertiary hyperparathyroidism
long period of secondary hyperparathyroidism –>nodules independent and do not comply with feedback mechanism
lab results show:
* Low/ non changes plasma calcium
* High plasma PTH
* High phosphate
Diagnosis ?
secondary hyperparathyroidism
High Phosphate caused by phosphate retention in renal insufficinecy
lab results show:
* normal/high calcium
* High plasma PTH
* High phosphate
Diagnosis ?
teritary hyperparathyroism; despite high calcium nodules are independent and not complying with feedback
