Calcium Flashcards
In which 2 ways can calcium be carried around in the body
Ionised or unionised
What ion binds to albumin in the same way as calcium
Hydrogen
Describe the binding of hydrogen/ calcium in acidosis
Increased ionised calcium as less binding to albumin
Describe the binding of hydrogen/ calcium in alkalosis
Decreased in ionised calcium because more bound to albumin
Why do some people experience tinging in their lips and extremities when they hyperventilate
Reduction in ionised calcium- symptoms of hypocalciumia
2 main roles of calcium
Structural role
Intracellular signalling
Is calcium higher inside or outside the cell
Outside
Which channels are responsible for firing of action potential
Fast sodium channels
What happens if you reduce calcium in the blood
Nerves are more likely to fire- tachyarrythmias, fibrillation, cardiac arrest
What does calcium do the fast sodium channels
Stabilises them
What % of body phosphate is mineralised in the bone
85%
What is released by parathyroid gland
Parathyroid hormone
What type of hormone is PTH
Peptide hormone
What are the pharyngeal arches made of
Bone and cartilage
What 2 cell types are present in the parathyroid
Oxyphilic and chief cells
Which cells release PTH
Chief cells in the parathyroid gland
When do oxyphil cells appear
Puberty
Describe the order that different organs process parathyroid hormone in
Rough ER–> golgi–> vesicles
What is the biggest trigger to PTH released
Low levels of serum calcium
What is represented by the maximal secretory rate of PTH
Parathyroid reserve
Capacity to repsond to hypocalcaemia
What receptor senses low levels of calcium
Calcium sensing receptor
What kind of receptor is the calcium sensing receptor
G protein coupled receptor
What happens if calcium sensing receptor is activated
- Reduces PTH secretion
- Increases breakdown of stored PTH
- Suppresses transcription of PTH gene
- Blocks stimulation of cAMP
Other than calcium, what else activates calcium sensing receptor
Magnesium, certain amino acids
Other than calcium, what else may determine PTH secretion
Activated vitamin D (calcitriol) suppresses PTH
Phosphate stimulates
What is the action of PTH in the kidney
Decreases calcium excretion
Increases phosphate excretion
What is the action of PTH on bone
Increases calcium and phosphate resorption
What is the action of PTH in the intestine
Increases absorption of calcium and phosphate
Some evidence for direct effects but mainly indirectly through calcitriol
How much calcium resorption occurs in the proximal tubule
65%
What drives calcium resorption in the proximal tubule
Voltage gradient
How much resorption occurs in the loop of Henle
20%
What inhibits calcium resorption in the loop of Henle
Loop diuretics
What % of calcium is absorbed in the distal tubule
10%
Which area of the kidney is PTH dependent in terms of calcium resorption
Distal tubule
What calcium channels are found in the distal tubule
TRPV calcium channels
What is the action of PTH in the distal tubule
Upregulate:
- TRPV calcium channels
- Calcium ATPase channels
- Na/Ca exchanger
What does PTH downregulate in the kidney, and what is the effect of this
- Downregulation of NaPi transporters= reduced phosphate reabsorption
PTH stimulates gluconeogenesis in which area of the kidney
Proximal tubule
PTH inhibits the reabsorption of what in the kidney
Sodium, water, bicarbonate
What is the effect of PTH and calcitriol on the bone
- Stimulate RANKL production, signalling for bone resorption
- Downregulation of osteoprotegerin
What is the relationship beween bone resorption and formation
They are equal
What is the relationship between bone remodelling and formation in menopausal women
Resorption> formation
What is the effect of PTH on IGFI and IL 1
Increases
What is the effect of glucocorticoids on bone remodelling
- Reduce osteoblast numbers
- Increase RANKL
What is the effect of oestrogen on bone remodelling
Inhibiits bone remodelling
What are some radiological signs of primary hyperparathyroidism
Terminal tuft erosion
Rugger jersey spine
Brown tumour
Subperiosteal erosion
What kind of receptor is the vitamin D receptor
Nuclear and membrane bound
What is the effect of vitamin D in the bone
- Reduces type 1 collagen expression
- Increases osteocalcin and RANKL
- Facilitates osteoclast differentiation
What is the effect of vitamin D on phosphate
- Increases gut absorption
- Increases levels of GFG23 to remove it via renal excretion
What is the effect of vitamin D on cellular proliferation
Reduces it
What is the effect of vitamin D on amino acid uptake
Deficiency–> myopathy
What is FGF 23
A phosphatonin- a hormone that reduces serum phosphate levels
What happens if there is an activating mutation if FGF23
Autosomal dominant hypophosphataemic rickets
What do you call a tumour induced osteomalacia
Paraneoplastic FGF23
What may happen if there are low levels GFG23
Familial tumoral calcinosis
Where is calcitonin released from
Thyroid C cells
What is primary hyperparathyroidism
Absence of hypocalcaemia
May be caused by parathyroid adenoma, carcinoma, hyperplasia
What does primary hyperparathyroidism lead to
Hypercalcaemia
What is secondary hyperparathyroidism
Compensation for hypocalcaemia
When should asymptomatic primary hyperparathyroidism be treated
Low BMD Renal calculi Renal impairment Calcium >3.0 Age <50
What scan should be used to localise an adenoma
MIBI scan
What happens in hypocalcaemia
Convulsion
Arrythmia
Tetany
Paraesthesia
What can lead to hypocalcaemia
Chronic kidney disease
Vit D deficiency
How is hypoparathyroidism treated acutely
IV or oral calcium supplement
How is hypoparathyroidism treated chronically
VIt D orally
What is familial hypocalciuric hypercalcaemia
Inactivating mutations of CaSR
- parathyroid can’t sense high calcium
- PTH not suppressed by high calcium
- CaSR in kidney not activated
- PTH-calcium curve shifts to the right
What serum results would be seen in familial hypocalciuris hypercalcaemia
High serum Ca
Low urine Ca
High serum Mg
