Parathyroid Flashcards
How many parathyroid glands are there?
Usually 4
What percentage of patients have 5 parathyroid glands?
5%
What percentage of patients have 3 parathyroid glands?
10%
What is the usual position of the inferior parathyroid glands?
Posterior and lateral behind the thyroid and below the inferior thyroid artery
What is the most common site of an extra parathyroid gland?
Thymus gland
What percentage of patients have a parathyroid gland in the mediastinum?
1%
If only 3 parathyroid glands are found at surgery, where can the 4th one be hiding?
Thyroid gland, thymus, mediastinum, carotid sheath, tracheoesophageal groove, behind the esophagus
What is the embryologic origin of the superior parathyroid glands?
4th pharyngeal pouch
What is the embryologic origin of the inferior parathyroid glands?
3rd pharyngeal pouch
What supplies blood to the parathyroid glands?
Inferior thyroid artery
What percentage of patients have all 4 parathyroid glands supplied by the inferior thyroid arteries exclusively?
80%
What is DiGeorge’s syndrome?
Congenital absence of the parathyroid glands and the thymus
What is the most common cause of hypercalcemia in hospitalized patients?
Cancer
What is the most common cause of hypercalcemia in outpatients?
Hyperparathyroidism
What cell type produces PTH?
Chief cells
What are the major actions of PTH?
Increases blood calcium levels (takes from bone breakdown, GI absorption, increased resorption from kidney, excretion of phosphate by kidney)
Decreases serum phosphate
How does vitamin D work?
Increases intestinal absorption of calcium and phosphate
Where is calcium absorbed?
Duodenum and proximal jejunum
What is primary HPTH?
Increased secretion of PTH by parathyroid glands.
Marked by elevated calcium, low phosphate.
What is secondary HPTH?
Increased serum PTH resulting from calcium wasting cause by renal failure or decreased GI calcium absorption, rickets or osteomalacia.
Calcium levels are usually low.
What is tertiary HPTH?
Persistent HPTH after correction of secondary HPTH.
Results from autonomous PTH secretion not responsive to the normal negative feedback due to elevated Ca levels.