PTH

Question 1

What type of hormone is parathyroid hormone (PTH)?

Answer 1

A polypeptide hormone that binds to cell-surface receptors to regulate calcium homeostasis

Question 2

What is the primary physiological role of parathyroid hormone (PTH)?

Answer 2

To maintain serum calcium within a narrow normal range

Question 3

Which cells secrete parathyroid hormone?

Answer 3

Chief cells of the parathyroid glands

Question 4

Where are the parathyroid glands anatomically located?

Answer 4

On the posterior aspect of the thyroid gland

Question 5

What stimulus triggers secretion of parathyroid hormone?

Answer 5

Low levels of free (ionised) calcium in the blood

Question 6

In what three forms does calcium circulate in the blood?

Answer 6

Free calcium, albumin-bound calcium, and calcium complexed with anions

Question 7

Which form of circulating calcium is physiologically active?

Answer 7

Free (ionised) calcium

Question 8

Why is tight regulation of serum calcium essential?

Answer 8

Both hypercalcaemia and hypocalcaemia can cause serious neuromuscular, cardiac and neurological consequences

Question 9

What is the main reservoir of calcium in the human body?

Answer 9

Bone, which contains approximately 1 kg of calcium complexed with phosphate

Question 10

What is the molecular structure of parathyroid hormone?

Answer 10

A single-chain polypeptide consisting of 84 amino acids

Question 11

Which organs are the main effector targets of parathyroid hormone?

Answer 11

Bone and kidney

Question 12

What is the effect of parathyroid hormone on bone?

Answer 12

Increases osteoclastic activity leading to bone resorption and release of calcium and phosphate into the bloodstream

Question 13

How does parathyroid hormone affect calcium handling in the kidney?

Answer 13

Increases calcium reabsorption in the distal convoluted tubule

Question 14

How does parathyroid hormone affect phosphate handling in the kidney?

Answer 14

Increases phosphate excretion

Question 15

How does parathyroid hormone influence vitamin D metabolism?

Answer 15

Stimulates hydroxylation and activation of vitamin D in the proximal convoluted tubule

Question 16

What is the net effect of parathyroid hormone on serum calcium?

Answer 16

Increases serum calcium concentration

Question 17

What is the net effect of parathyroid hormone on serum phosphate?

Answer 17

Decreases serum phosphate concentration

Question 18

How does active vitamin D complement the actions of parathyroid hormone?

Answer 18

It increases intestinal absorption of dietary calcium

Question 19

What mechanism allows vitamin D to increase intestinal calcium absorption?

Answer 19

Increased expression of calcium-binding proteins in intestinal epithelial cells

Question 20

How is parathyroid hormone secretion regulated?

Answer 20

Through a negative feedback loop based on serum calcium levels

Question 21

Describe the negative feedback loop regulating PTH secretion

Answer 21

Low calcium stimulates PTH release, rising calcium suppresses PTH secretion

Question 22

What condition results from excessive parathyroid hormone secretion?

Answer 22

Primary hyperparathyroidism

Question 23

What are common pathological causes of primary hyperparathyroidism?

Answer 23

Parathyroid adenoma, gland hyperplasia or malignancy

Question 24

What symptoms are classically associated with hypercalcaemia due to excess PTH?

Answer 24

Renal calculi, constipation, polyuria, abdominal pain and low mood

Question 25

What definitive treatment may be required for primary hyperparathyroidism?

Answer 25

Surgical removal of the parathyroid glands

Question 26

What is parathyroid hormone–related peptide (PTHrP)?

Answer 26

A polypeptide secreted by some cancers that mimics the actions of PTH

Question 27

Which malignancy classically secretes PTHrP?

Answer 27

Squamous cell carcinoma of the bronchus

Question 28

How does PTHrP differ from true parathyroid hormone?

Answer 28

It cannot activate vitamin D

Question 29

Why does PTHrP cause hypercalcaemia?

Answer 29

It increases bone resorption and renal calcium reabsorption in a manner similar to PTH