Parathyroid

Question 1

Describe the structure and location of the parathyroid

Answer 1

Composed of 4 glands

Found on the back of the thyroid gland

Endocrine cells of the parathyroid = chied cells

Secrete PTH

Question 2

What does PTH do?

Answer 2

Maintains calcium homeostasis

Question 3

What happens if adenoma develops in parathyroid glands?

Answer 3

Secrete excess PTH leading to hypercalcaemia

Increased concentration of circulating calcium

Question 4

What is the normal range of calcium concentration in our body?

Answer 4

2.3 - 2.4 mM

Question 5

How is calcium found in the body?

Answer 5

50% is ionised

50% is bound to albumin

Question 6

What determines the degreee of ionisation of calcium?

Answer 6

Blood pH

Question 7

When is PTH released?

Answer 7

In low levels of serum calcium concentration

Question 8

Organs involved in calcium homeostasis

Answer 8

Gut
Bones
Kidney

Question 9

How is the gut involved in calcium homeostasis?

Answer 9

Absorbs dietary calcium

Increased in the presence of Vitamin D

Question 10

How are the kidneys involved in calcium homeostasis?

Answer 10

Blood calcium is filtered at the glomerulus

Most is reabsorbed along the tubule to maintain homeostasis

Question 11

How are the bones involved in calcium homeostasis?

Answer 11

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

Mineralization

Question 12

What effects does PTH have in decreased serum calcium concentration?

Answer 12

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

Question 13

How does PTH increase calcium absorption by the gut?

Answer 13

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

Question 14

What are the causes of hypercalcaemia?

Answer 14

Increased PTH secretion - parathyroid adenoma

Lysis of bones - invsasion of bone by cancer

Granulomatous disease - pneumonia causes too much vitamin D secretion

Question 15

What are the causes of hypocalcaemia?

Answer 15

Hyperventilation - increased rate and depth of breathing

Increased expiration of carbon dioxide

Decreased hydrogen ion concentration in plasma

Question 16

Consequences of hypocalcaemia

Answer 16

Abnormal excitability of muscles and nerves

Muscle spasms - tetany (constant contraction), convulsions