Parathyroid Flashcards
How many parathyroid glands are there?
4
Where are they located in relation to the thyroid gland?
Posterior aspect of the thyroid gland
Which cells secrete parathyroid hormone?
Chief cells
What kind of hormone is parathyroid hormone?
A polypeptide
What is the primary stimulus for parathyroid hormone?
Hypocalcaemia
What is the primary inhibitor of parathyroid hormone?
Hypercalcaemia
What is another name for a parafollicular cell?
C-cells
What are parafollicular cells stimulated by?
Hypercalcaemia
What are parafollicular cells inhibited by?
Hypocalcaemia
Where is calcitonin produced from?
Parafollicular cells (or C -cells)
What do parafollicular cells produce?
Calcitonin
What stimulates calcitonin release?
Hypercalcaemia
What stimulates parathyroid release?
Hypocalcaemia
What is a humoral stimulus?
Endocrine function which is controlled by change in electrolytes i.e. hypocalcaemia leading to increased parathyroid release
What kind of stimulus causes calcitonin or parathyroid release?
Humoral stimuli (calcium)
How does PTH effect the bone?
Increase osteoclastic activity by activating osteoblasts to release Rank-ligand, which stimulates Rank receptors on osteoclasts
What doe osteoclasts do?
Resorb bone - releases calcium into the blood
What do osteoblasts do?
Bone deposition - takes calcium from the blood to build bone
What is the significance of Rank Ligand to PTH?
Released by osteoblasts in response to PTH causing activation of the osteoclasts
What is released by increased osteoclastic activity?
Phosphate and calcium
How does PTH affect the blood biochemistry?
Increases phosphate and calcium release via increased osteoclastic activity, increased calcium uptake by kidney (phosphate is excreted) and increased synthesis of active vitamin D causing increased uptake in the GI tract of calcium
How does PTH affect the kidney?
DCT to reabsorb calcium by secondary active transport + increases phosphate excretion + increases the expression of 1-alpha-hydroxalase
What is the overall effect of PTH?
To increase calcium in the blood
How is cholecalciferol formed?
UV light activates 7-dehydrocholestrol to cholecalciferol
What happens to cholecalciferol in the liver
Converted to 25-hydroxycholecalciferol via 25-hydroxalase
What is the role of 1-alpha-hydroxalase in the kidney?
It hydroxalases 25-hydroxycholecalciferol to
1,25-cholecalciferol (calcitriol)
What is another name for calcitriol?
Vitamin D
How is Vitamin D produced?
UV light activates 7-dehydrocholesterol which goes to the liver and is converted to 25-hydroxycholecalciferol, which is converted by the kidney to 1,25-cholecalciferol, otherwise known as calcitriol or vitamin D)
What is the role of Vitamin D?
Increase calcium uptake from the gi tract via calcium channel proteins
What kind of hormone is vitamin D?
A steroid hormone
Which mechanisms cause calcium increase by PTH?
Increased GI uptake via vitamin D, Increased osteoclast activity, Increase resorption of calcium in the kidney
What is the overall effect of calcitonin?
Reduces blood calcium
What does calcitonin do in the bone?
Directly inhibits osteoclastic activity and thereby increases osteoblastic activity
Where do the parathyroid glands develop from in embryological development?
Superior glands - pharyngeal pouch 4
Inferior glands - pharyngeal pouch 3
What is the blood supply to the parathyroid gland?
Inferior and superior thyroid arteries
Where is the gene for PTH located?
Chromosome 11
What is the main cause of primary hyperparathyroidism?
A solitary adenoma of the parathyroid gland
What is the main cause of secondary hyperparathyroidism?
Caused by hypocalcaemia secondary to chronic kidney disease or vitamin D deficiency
What is the main cause of tertiary hyperparathyroidism?
Prolonged stimulation leads to hyperplasia of the parathyroid gland and insensitivity to calcium levels. This is seen in end stage renal failiure
