Flashcards in Parathyroid Deck (16)
Describe the structure and location of the parathyroid
Composed of 4 glands
Found on the back of the thyroid gland
Endocrine cells of the parathyroid = chied cells
What does PTH do?
Maintains calcium homeostasis
What happens if adenoma develops in parathyroid glands?
Secrete excess PTH leading to hypercalcaemia
Increased concentration of circulating calcium
What is the normal range of calcium concentration in our body?
2.3 - 2.4 mM
How is calcium found in the body?
50% is ionised
50% is bound to albumin
What determines the degreee of ionisation of calcium?
When is PTH released?
In low levels of serum calcium concentration
Organs involved in calcium homeostasis
How is the gut involved in calcium homeostasis?
Absorbs dietary calcium
Increased in the presence of Vitamin D
How are the kidneys involved in calcium homeostasis?
Blood calcium is filtered at the glomerulus
Most is reabsorbed along the tubule to maintain homeostasis
How are the bones involved in calcium homeostasis?
Bones contain 99% of body's calcium
In the form of Hydroxyapatite and calcium phosphate
Resorption -> lysis of bone due to malignancy deposits from secondary cancers
What effects does PTH have in decreased serum calcium concentration?
1. Low calcium concentration activates calcium receptors in the parathyroid gland
2. Increases PTH release
3. PTH increases bone resorption
4. PTH increases calcium reabsorption in the kidneys
5. PTH increases calcium absorption by the gut via activation of vitD
6. Increased mobilization and reabsorption of calcium return plasma calcium concentration to homeostatic baseline
How does PTH increase calcium absorption by the gut?
PTH increases activity of alpha 1-hydroxylase in the kidney
This enzyme adds an OH group to the 25(OH) vit D to make 1,25(OH) vit D
1, 25(OH) is the active form of vitamin D
Active form of vitamin D enhances intestinal absorption of calcium
What are the causes of hypercalcaemia?
Increased PTH secretion - parathyroid adenoma
Lysis of bones - invsasion of bone by cancer
Granulomatous disease - pneumonia causes too much vitamin D secretion
What are the causes of hypocalcaemia?
Hyperventilation - increased rate and depth of breathing
Increased expiration of carbon dioxide
Decreased hydrogen ion concentration in plasma