Sesh 11- Ca regulation and the Parathyroid Gland

Question 1

What is the normal range for serum Calcium?

Answer 1

2.2-2.6 mMol/L

Question 2

Where is most of the calcium in the body?

Answer 2

Stored in the skeleton as hydroxyapatite crystals

Question 3

What effect does PTH have on bone?

Answer 3

Increases bone turnover/ resorption by activating osteoclasts, causing Ca and phosphate release

Question 4

What 2 effects does PTH have on the kidney?

Answer 4

• Increases Calcium reabsorption, and phosphate excretion

- Increases conversion of calcidiol to calcitriol (active vit D)

Question 5

What effect does active vitamin D have on the GIT?

Answer 5

Increases transcellular Ca and phosphate absorption

Question 6

What enzyme, measurable in the blood, indicates increase bone turnover?

Answer 6

Alkaline phosphatase

Question 7

What stimulus increases PTH secretion?

Answer 7

Hypocalcaemia

Question 8

How does calcitriol increase Ca absorption from GIT?

Answer 8

Increases availability of Ca-binding proteins

Question 9

From what cells is PTH secreted?

Answer 9

Chief/principal cells of the parathyroid gland

Question 10

What from cells is calcitonin secreted?

Answer 10

C/ parafollicular cells of the thyroid gland

Question 11

What is the effect of calcitonin on bone?

Answer 11

Increases Ca reabsorption into bone.

Minor clinical role

Question 12

What symptoms would be indicative of hypocalcaemia, and why?

Answer 12

-Tetany e.g. carpopedal spasm
  NB: tetany of laryngeal muscles can kill, so needs treating quickly
-Chvostek's sign
-Convulsions
-Paraesthesia around mouth and fingers

-As hypocalcaemia reduce t/h for nerve firing, so get hyper excitability at the NMJ

Question 13

What are the 4 cardinal signs/symptomsof chronic hypercalcaemia?

Answer 13

1. Bones (pain, osteomalacia/porosis)
2. Stones (renal calculi)
3. Moans (pyschiatric- lethargy, depression)
4. Groans (abdo pain, constipation)

Question 14

Describe 2 ways in which malignancies can cause hypercalcaemia.

Answer 14

1. Metastasise to bone, and activate osteoclasts

2. Can produce PTHrp (e.g squamous cell carcinomas of lung, head and neck)- binds to PTH R’s

Question 15

Why do bags of blood contain citrate?

Answer 15

To chelate Ca2+, so that blood doesn’t clot…(Ca2+= important co-factor in the clotting cascade)

Question 16

Name 4 cancers that commonly metastasise to bone

Answer 16

1. Breast
2. Lung
3. Renal
4. Thyroid
   - NB: prostate does too, but is osteoblastic

Question 17

Name 2 causes of secondary hyperparathyroidism

Answer 17

1. Vitamin D deficiency

2. Chronic Kidney Disease

Question 18

What is the difference between osteoporosis and osteomalacia?

Answer 18

• Osteoporosis- loss of bone density& structure but normal mineral:matrix. Means prone to fracture.
• Osteomalacia- reduced mineral:matrix, but normal structure. Means prone to bending.

Question 19

How would you treat severe hypercalcaemia?

Answer 19

Rehydration

Question 20

What is the most common cause of hypocalcaemia?

Answer 20

Accidental damage/ removal of parathyroid glands during thyroidectomy