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Flashcards in Parathyroid Deck (16)
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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

Secrete PTH


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?

Blood pH


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


Consequences of hypocalcaemia

Abnormal excitability of muscles and nerves

Muscle spasms - tetany (constant contraction), convulsions