Calcium Metabolism Flashcards
How much calcium Eters and leaves the body each day
1 g in diet, 500mg/d absorbed
500mg/d excreted
- 175 urine
- 325 faeces
Need a natural balance
What are three physics chemical forms plasma calcium come in
Free ionised species
Bound to anionic sites on protein - albumin
Complexed - citrate and oxalate
What is the normal concentration of plasma calcium
2.2 - 2.7mmol/l
Lab tests total calcium and corrected for level of albumin present
What is calcium buffering
As a huge amount of calcium in bones, it acts as a reserved
Around 280mg move in and out every day
How is intracellular ca controlled
Each cell controls its own cytoplasmic concentration
- pumped out of cell and sequested into organell
- enters apart of signalling
Aspects of hypocalcaemia
Excitability of nerves and muscles - worsens as Ca drops
Uncontrolled excitation is called tetany
- parasthesia
- twitching of muscles, normally face
- Contraction of muscles - claw hands
- convulsions - respiratory arrest
Aspects of hypercalcaemia
Nerves and muscle reduce excitability - lethargy, constipation, depres
Calcium precipitation
- damage to kidney and stones
- damage to joints
What remodels bones
Bones are active and living
Bone is made of calcium hydroxyapatite
Remodelled through
- osteoblasts - cells secrete and facilitate matrix formation
- osteoclasts - cells break down matrix and release calcium and phosphate
What are the two key hormones in regulating calcium levels
Vitamin D
Parathyroid hormone
Calcitonin - more in animals and no know function in humans
What are the actions of parathyroid hormone
Immediate actions - binds oestoblasts
- inhibits bone formation
- stim release of Chen msg to stim oestoclast to increase bone breakdown and release calcium and phosphate
Also acts on kidney
- stimulate reabsorption of filters calcium
- increase loss of phosphate in urine
What is the normal calcium concentration in
Extracellular
Intracellular
Free solution
2.1 mmol/l
10-5 mmol/l
1.1-1.4 mmol/l
About a kg in bone
