Flashcards in Calcium homeostasis Deck (22)
Function of calcium
Exocytosis in cells.
Build and maintenance of bone.
Many biochemical processes.
- How it is transported 
Mostly found as free ions [50%]
- These are biologically active
Bound to proteins [40%]:
- Albumin (90%)
- Globulin (10%)
Bound to cations [10%]
Physiological range of serum calcium
- Physical signs
Serum calcium <2.15 mmol/L
- Low calcium, makes neurones a lot more permeable to Na+ (Ca2+ competes with Na+)
- Trousseau's sign
- Chvostek's sign
Consequences of hypocalcaemia
- Acute 
- Chronic 
- Abdominal pain
- MSK pain/ weakness
- Neurobehavioral changes
- Kidney stones
Made by chief cells of the parathyroid gland.
Secreted in response to low Ca2+ levels.
- Chief cell contains receptors that are Ca2+ sensing
Ca2+ sensing receptors on chief cells recognise low Ca2+ levels
- Changes shape of the receptor
- Chief cells processes modified to release PTH in the presence of Mg2+
PTH action on receptors
PTH acts on PTH-1 receptors on bone and kidneys
- Changes the shape of the receptor.
- Calcium release
- More absorption of Ca2+ in loop of Henle, DT, CD.
- Less Phosphate reabsorption in PT [prevents calcium phosphate precipitation]
PTH action on bone
PTH activates osteoblasts
- Causes release of rank ligand
Rank ligand activates osteoclasts
- Break down of bone using H+ and enzymes (CATK, TRAP).
- Ca2+ release into the blood.
Calculation of serum Ca2+ based on the amount bound the albumin.
Not accurate if album is <20g/L.
Mg2+ and PTH
- Causes of hypomagnesaemia
Mg2+ is a co-factor required for the release of PTH.
- Low Mg2+ = no PTH release= hypocalcaemia.
Causes of hypomagnesaemia
- GI problems
Sources of Vit.D
- UV from the sun causes the skin to make cholecalciferol [Vit D3]
- Cod liver oil
- Wild oily fish
- Fortified foods
- Irradiated mushrooms
Vit D metabolism
- Vit.D3 Converted to 25-OH, Vit.D
- PTH acts to convert 25-OH, Vit D into 1,25-OH-Vit.D
- 1,25-OH, Vit.D stimulates the insertion of Ca2+ transporters and calbindin
- Allows more absorption of Ca2+
Feedback of PTH and vitamin D
1,25-OH, Vit.D negatively feedbacks to PTH release.
1,25-OH, Vit.D also feedbacks to osteocytes---> Increases FGF-23
- FGF-23 inhibits 1,25-OH production
Serum calcium >2.55mmol/L
- Primary hyperparathyroidism
- Malignancy (of PT)
Overactivity of the PT= high PTH levels
- High Ca2+ levels
- Low Phosphate levels
- High PTH levels
- Bone cysts
- Kidney stones
Causes of primary hyperparathyroidism
Primary hyperplasia of parathyroid.
Imagining of PT adenoma
Sestamibi PT scan
- Measure gamma rays from radioactive decay of technetium sestamibi
- Adenoma absorbs radioactive substance very fast so can be spotted in scan.
- Low calcium
- Low/ normal PTH
- High phosphate levels
- Iatrogenic [70%]
- Hypomagnesemia--> Mg required for PTH secretion
High PT levels not directly caused by the PT gland.
- Problem elsewhere leads to PT hyperplasia.
- Low Ca2+, high PTH.
- Chronic kidney failure [inability metabolise vit.D anf excrete phosphate]
- Malabsorption of vit.D
- Lack of sun exposure
- Extensive bowel surgery
Iatrogenic causes of hypoparathyroidism
- Removal of thyroid could include removing PT gland.
Radial neck surgery