Calcium

Question 1

What happens in Hypocalcaemia?

Answer 1

increases neuronal Na+ permeability leading to hyperexcitation of neurons. In extreme cases causes tetany, if spreads to larynx and respiratory muscles – asphyxiation.

Question 2

What happens in Hypercalcemia?

Answer 2

decreases neuronal Na+ permeability which will reduce excitability and depress neuromuscular activity and in extreme cases, trigger cardiac arrhythmias.

Question 3

Which hormones increase plasma Calcium?

Answer 3

Parathyroid hormone (PTH) 
Calcitriol (produced from Vit D in liver and kidneys)

Question 4

What hormone decreases plasma Calcium?

Answer 4

Calcitonin (remember TONe it DOWN)

Release from parafollicluar cells of the thyroid gland.

Question 5

What does PTH stimulate when relased due to low plasma calcium?

Answer 5

1. Stimulating osteoclasts to ↑ resorption (release) of Ca2+ and phosphate in bone (effects seen within 12-24hrs)
2. Inhibiting osteoblasts thus reducing Ca2+ deposition in bone.
3. Increasing reabsorption of Ca2+ from the kidney tubules, therefore decreasing its excretion in the urine.
4. Increasing renal excretion of phosphate. This elevates free [Ca2+ ] by preventing it from being deposited back into bone, a process that requires phosphate. (as hydroxyapetite which is how calcium is stored in bones).
5. Stimulates the kidney to synthesise calcitriol from vitamin D which promotes calcium absorption at the gut and kidney.

Question 6

What is Calciitrol’s action?

Answer 6

Increase Ca2+ absorption from gut

Facilitates renal absoprtion of Ca
Mobilises Ca stored in bone by stimulating osteoclasts

Question 7

What can a Vit D deficiency cause?

Answer 7

Rickets in children

Osteomalacia in adults

This is due to the increased need to release Ca from the stores in bones.

The bones become deformed, soft and easy to fracture

Question 8

What other hormones effect Ca levels?

Answer 8

1. Cortisol inhibits osteoblasts, increases renal excretion of Ca2+ and phosphate and reduces intestinal absorption of Ca2+ →↓ plasma [Ca2+ ] →↑ PTH →↑ bone resorption. This together with the reduced bone formation can, over time, produce osteoporosis.
2. Insulin increases bone formation, and antagonises the action of cortisol. Diabetics may have significant bone loss.
3. Oestrogen promotes bone formation via oestrogen receptors on osteoblasts. Post-menopausal osteoporosis a major problem.
4. Growth Hormone – constant stimulus for bone formation.
5. Prolactin – promotes calcium absorption from the gut by stimulating synthesis of calcitriol.

Question 9

How does hypOcalcemia present?

Answer 9

serum calcium <2.20

Prolonged QT 
Hypotenison
Arrythmia
Muscle twitching
Carpopedal Spasm
Seizures
Laryngospasm

Question 10

What is Trousseau’s sign?

Answer 10

Presents in hypocalcemia

Flextion of hand and fingers when BP cuff inflated

Question 11

What is Chovstek’s sign?

Answer 11

Occurs in hypocalcemia.

Tap just anterior to earlobe (facial nerve runs under here), causes a twitch of the lip or spasm of all the facial muscles.