parathyroid Flashcards
parathyroid pathology revolved around
calcium - hypercalaemia
may be a cause or effect of parathyroid disease
parathyroid disease is not the only cause of hypercalcaemia
normal parathyroid is made up of
thin capsule with islands of parathyroid cells with fat in-between
parathyroid glands are located
four of the at the periphery of the thyroid
cell types in they parathyroid
chief cells with variants (oxyphil and water clear) due to accumulation of other material
parathyroid hormone is produced by
chief cells
parathyroid hormone is released in response to
low serum calcium - free ionised calcium.
actions of parathyroid hormones
- bone resorption
- renal tubular resorption of calcium
- increases conversion of vit D to active (hydroxy) form in the kidney
- with vitamin D, promotes calcium resorption from small intestine
- increases urnary phosphate excretion causing phosphaturia
- net effect is to increase serum calcium
net effect of PTH
increase serum calcium
hypocalcaemia
usually due to accidental damage/removal of parathyroids during thyroid surgery
hypocalcaemia is usually due to
chronic renal failure, vit D deficiency, drugs, or intestinal malabsorption of Ca
hypocalcaemia causes
neuromuscular irritability
calcium. blocks sodium channels, so lower calcium decreases depolarisation threshold
symptoms of hypocalcaemia
CATs go numb
- convulsons, arrythmas, tetany, numbness/paresthesia
acute - syncope, cardiac arrhythmia, laryngospasm
hypercalcaemia is caused by
accelerated bone resorption
excessive GI absorption
Decreased renal excretion of calcium
diseases causing hypercalcaemia
- hyperparathyroidism
- hypercalcaemia of malignancy
- drugs, metabolic/genetic disorders, chronic granulomatous disease
how is hypercalcaemia caused from malignancy
- bone osteolysis due to skeletal metastasis
- metabolic effects of malignant tumours - cytokine mediated
- PTHrP secretion from tumours
excessive parathyroid hormone
increased PTH from parathyroid or PTHrP (parathyroid related protein) causes bone resorption
excessive parathyroid hormone may be caused by
hyperthyroidism due to parathyroid tumours
extolc secretion of pTHrP by some other tumours
disrupted Ca/PO4 homeostasis
retention of phosphate inappropriately activates feedback loop leading to increased PTH secretion
disrupted Ca/PO4 is caused by
renal failure
excess vitamine D
excess vit D causes increases absorption (gut) respiration (kidney) and mobilisation (bone)
excess vit D is caused by
vit D intoxication, sarcoidosis, idiopathic hypercalcaemia of infancy
clinical manifestations of hypercalcaemia
stones, bones, abdominal groans and psychiatric moans
cardiovascular, ocular, dermatological
primary hyperparathyroidism
excesss PTH production from the parathyroid
feedback indepedant production of PTH
one or more involved gland increasing in size while the others atrophy
secondary hyperparathyroidism
other disease process drives increase in PTH production
abnormal homeostatic regulation but normal feedback mehcniasms
glands become hyper plastic
tertiary hyperparathyroidism
autonomous PTH secretion, caused by long standing secondary HP
abnormal feedback mechanisms
usually due to long standing kidney disease
often autonomous nodule within hyper plastic glands
ectopic secretion
parathyroid hormone related protein
paraneoplastic from other malignancies
feedback independent causing atrophy
malignancy of parathyroid
rare
parathyroid adenoma
benign neoplasm of parathyroid epithelium
most hyperparathyroid
usually solitary, occasionally multiple
multiple parathyroid adenoma may indicate
MEN1
parathyroid adenoma histological patterns
sheets, acini, follicles, trabecular uniformity of cell type loss of reticulum;in framework no intraglandular fat rim of normal
parathyroid hyperplasia
increased numbers of cells - polyclonal
typically involves all glands but may be asymmetrical
- usually <1g
mainly chief cells, may have mixed cell type, a nodular pattern
- usually sporadic, may be familial
familial parathyroid hyperplasia
- MEN1 - most patients
- homozygous loss of suppressor gene on chromosome 11
- less commonly MEN 2a
