21 Calcium Metabolism Flashcards
Name some cellular processes which require calcium?
Hormone secretion, muscle contraction, nerve conduction, exocytosis, intracellular metabolism
Between what range does the body carefully regulate calcium ion concentration?
1.0-1.3 mmol/L
Why is phosphate so important?
- Part of ATP molecule
- Has role in activating/deactivating enzymes
How do phosphate plasma levels differ from calcium plasma levels?
Phosphate levels- not strictly controlled. Levels fluctuate throughout the day.
How is the homeostasis of calcium and the homeostasis of phosphate linked? (2)
- Both=priniciple components of hydroxyapatite crystals (mineral of bone)
- Both regulated by PTH and calcitriol (+calcitonin)
Calcitrol=active Vitamin D
Which 3 organ systems do PTH, calcitrol and calcitonin act on to regulate calcium and phosphate levels?
- Bone
- Kidneys
- GI tract
What is shown in the following diagram?
Calcium distribution and balance values for a 70kg human
Where is most of the calcium found in the body located?
Bone (approx. 1kg)
What’s the total amount of calcium in the extracellular pool (approximately)?
1g
What is the typical dietary intake of calcium?
800-1200mg
The intestines both absorb and secrete calcium for removal from the body.
What is the approximate net intestinal uptake of calcium per day?
175mg/day
How much calcium does the bone deposit and reabsorb per day?
280mg
What is the approximate calcium excretion in urine per day?
175mg
How much calcium do the kidneys filter daily?
About 10,000 mg
What are the 3 forms in which calcium exists in the body?
- Free ionised species (45%) Physiologically active
- Bound to anionic sites on serum proteins (eg albumin)(45%)
- Complexed with low-molecular-weight organic anions (eg citrate/oxalate)(10%)
What is the total concentration (of all 3 forms of calcium found in plasma) of plasma calcium?
2.7mmol/L
What happens if plasma levels alter (outside normal plasma ?
Hypocalcaemia:
- Hyperexitability of nervous system
- Paresthesia- tetany (intermittent muscular spasms)- paralysis-convulsions
Hypercalcaemia:
- Kidney stone formation
- Constipation
- Dehydration
- Kidney damage
- Tiredness
- Depression
If PTH and Calcitrol are released, what wil happen to serum calcium concentrations?
Raise serum calcium concentration
Which hormone (PTH or calcitrol) is involved in the short term regulation of serum calcium and which is involved in the long term regulation of serum calcium?
PTH= short term
Calcitrol= long term
What are the 2 types Vitamin D prohormones?
- vitamin D2: ergocalciferol
- vitamin D3: cholecalciferol
Where can we obtain vitamin D?
- Sun exposure
- Food
- Supplements
Why must Vitamin D which has been obtained undergo 2 hydroxylation reactions?
Because it is biologically inert- must be activated in body
What is the Parathyroid related peptide and what does it do?
PTHrP= produced by tumour- may lead to hypercalcaemia
Causes:
- increased calcium release from bone
- reduced renal calcium excretion
- reduced renal phosphate reabsorption
(HHM= Hypercalcaemia of malignancy)
Tumour often=
- Breast
- Prostate
- Myeloma
How do the actions of PTHrP and PTH differ?
PTH increases calcitrol concentration, PTHrP does not.
Why is calcium important in the blood clotting cascade?
It is factor IV in the clotting cascade
What is EDTA?
Calcium chelator (binds calcium in selective way)
Fill in the missing labels:
What organs does PTH target?
- Bone
- Intestines
- Kidney
What are the symptoms of chronic hypercalcaemia?
- Renal calculi
- Kidney damage
- Constipation
- Dehydration
- Tiredness
- Depression
(Stone, moans, groans, bones)
What are the symptoms of hypocalcaemia?
- Hyperexcitability of neuromuscular junction
- Lower serum calcium
- Increased Na+ entry into neurones
- Depolarisation-increased liklihood of AP
- Pins and needles
- Tetany (muscle spasms)
- Paralysis
- Convulsions
