Lecture 14 - Calcium metabolism

Question 1

What is the parathyroid gland formed from embryologically?

Answer 1

Third and fourth brachial artery

Question 2

Where and how many PTH glands?

Answer 2

• Behind thyroid glands

- x4

Question 3

What are some importance of calcium?

Answer 3

• Hormone secretion (insulin)
• Muscle contraction
• Nerve conduction
• Exocytosis

Question 4

How is calcium vital for bone formation?

Answer 4

Ca+K: Hydroxyapatite crystals, a major component of bone

Question 5

What regulates Ca conc. in blood?

Answer 5

• PTH + calcitriol

Question 6

How does PTH affect calcium and K homeostasis?

Answer 6

• PTH ⬆️, K ⬇️
• ⬆️Ca reabsorption from kidney
• ⬆️osteoclast resoption –> increase bone turnover
• ⬆️absorption of Ca from food (small intestine)

Question 7

What types of Vit. D are present in the diet?

Answer 7

• Ergocalciferol (D2): obtain from mushrooms (less potent version of vit D
• Cholecalciferol (D3): Liver of fatty fish

Question 8

How does Vit D act in Ca & K homeostasis?

Answer 8

• Decrease PTH production
• ⬆️Ca reabsorption from kidney
• ⬆️mineralisation of Ca to bone
• ⬆️absorption of Ca and K from food (small intestine)

Question 9

What parameters define hypercalcaemia?

Answer 9

• Serum calcium >2.51mmol/L

>3 is severe

Question 10

What are some symptoms of hypercalcaemia?

Answer 10

• Moans –> Constipation
• Bones –> bone aches
• Stones –> Kidney stones
• Groans –> Confusion
• Thirst and polyuria

Question 11

What indication does high calcium and low PTH show?

N.B PTH can drive hypercalcaemia

Answer 11

• High Ca due to diff factor (not PTH from parathyroid gland)
• Most likely= cancer –> produce PTH like peptide

Question 12

What are some examples of cancers with high calcium?

Answer 12

• Myeloma (blood cancer)

- Bone metastases (Bronchus, Thyroid, Breast, Kidney)

Question 13

Other than cancers what can be a cause of high Ca and low PTH?

Answer 13

• TB
• Sarcoidosis: growth of tiny cancers in lung
• Granulomas that secrete calcitriol

Question 14

What does high Ca and high PTH suggest?

Answer 14

• Not cancer

- Primary hyperparathyroidism: benign parathyroid adenoma

Question 15

What are the effects of primary hyperparathyroidism?

Answer 15

• High Ca, Low K

- ⬆️bone turnover

Question 16

What is the treatment for acute severe hypercalcaemia (medical emergency–> SEVERE DEHYDRATION)?

Answer 16

• Fluid into veins (normal saline 0.9%)

- Treat underlying cause

Question 17

What are the parameters of hypocalcaemia?

Answer 17

• Serum Ca <1.9mmol/L

- Symptoms severe if sudden drop

Question 18

What does hypocalcaemia result in?

Answer 18

• Hyperexcitability of NS (neuromuscular junction)

- Leads to paraesthesia (pins & needles), tetany (involuntary muscle contraction), paralysis, convulsions

Question 19

What are some causes of hypocalcaemia?

Answer 19

• Vit D deficiency

- Hypoparathyroidism

Question 20

How does low vit D result in secondary hyper-PTH?

Answer 20

• Low Vit D –> low Ca/K –> High PTH

- Stimulation of Ca sensing receptors reduces PTH

Question 21

What are some causes of Vit D deficiency? And what does it result in adults or children if severe?

Answer 21

• Lack of sunlight
• Dietary deficiency
• GI disease
• Kidney disease
• Pigmented or covered skin
• Result in rickets in children, osteomalacia in adults

Question 22

What is the diff. btw osteoporosis and osteomalacia?

Answer 22

• Osteomalacia = normal structure of bone but under mineralised
• Osteoporosis= structurally degraded but fully mineralised

Question 23

What does osteomalacia result in?

Low Ca

Answer 23

• Gluteal muscle weakness leads to waddling gait (bend legs)

- Multiple fractures

Question 24

What is the levels of substances in hypo-PTH?

Answer 24

• Low Ca & PTH

- High K

Question 25

What are some causes of hypo-PTH? | look out for scar in neck

Answer 25

- Surgical removal/damage of PTH gland - Pathology of PTH gland - Failure of 3rd or 4th brachial artery

Question 26

How to treat acute severe hypo-PTH? | a med emergency

Answer 26

- Assess airway and conscious level - ECG monitor for heart - Intravenous Ca and monitoring

Question 27

List some risk factors for osteoporosis.

Answer 27

- Menopausal women - Smoking and immobile - Endocrine disease (hypo-PTH) - Family history

Question 28

What are some sources of Ca?

Answer 28

- Diet (Dairy products major source)= 800-1200mg per day - Intestine net uptake is 175mg/day (same as Ca excreted in urine) - Bone calcium deposition (controlled by K) is 280mg/day - Kidney reabsorb Ca

Question 29

How is free Ca (biologically active) measured?

Answer 29

- Total Ca measured: Free ionised/ Bound to albumin/ Bound to low-molecular weight organic anions (citrate) - Levels adjusted depending on albumin

Question 30

What are effects of PTHrP? | related peptide

Answer 30

- Increase Ca release from bone - Reduce renal Ca excretion - Reduce renal absorption - X increase renal C-1 hydroxylase --> calcitriol X increase

Question 31

How much Ca in body?

Answer 31

- 1kg - Vast majority of this present in the skeleton and teeth. Soft tissues contain about 10g of calcium and approx 1g is present in the extracellular fluid.

Question 32

How many PTH glands are there in a human body?

Answer 32

4

Question 33

What type of hormone is PTH?

Answer 33

Peptide hormone

Question 34

How does PTH exert its effects on the GI tract?

Answer 34

- Indirectly through promoting the formation of calcitriol

Question 35

How do principal cells in these glands sense plasma calcium concentration?

Answer 35

GPCR activated by calcium