Lecture 7 - calcium balance Flashcards
What are the main functions of calcium in the body?
- cell signalling (vessel exocytosis, muscle fibre contraction, altered enzyme function)
- blood clotting
- apoptosis
- skeletal strength
- membrane excitability (controls sodium permeability).
What does an hypercalcaemia do to cell excitability?
- Decreases Na permeability.
- takes cell further away from threshold
- less likely to contract
- can lead to cardiac arrthymias if heart stops beating
What does a hypocalcaemia do to cell excitability?
- Increases Na permeability.
- brings cell closer to threshold
- more likely to excite cell
- leads to tetany (contraction) of muscles
- can lead to asphyxia if larynx and respiratory muscles tetany.
How much of the bodies calcium is stored in the bones?
99%
its stored with phosphate (hydroxyapatite)
How much of the bodies calcium is stored in the intracellular fluid?
0.9%
mostly stored in the mitochondria and sarcoplasmic reticulum
only a tiny amount is free in the cytosol
How much of the bodies calcium is stored in the extracellular fluid/plasma?
- 1%
- 05% is free/unbound
- 04% is bound to plasma proteins
- 01% is bound to anions (bicarbonate or phosphate)
How much percentage of the bodies calcium is physiologically active?
0.05%
How many millimolars of calcium is physiologically active in the body?
1.2mM
How much does the calcium in skeletal muscle weigh?
1kg.
What happens to calciums binding to plasma proteins when the pH rises?
- more calcium binds to the plasma proteins, decreasing the calcium concentration in the plasma.
- there’s less h+ ions competing to bind to the plasma protein.
What happens to the calciums binding to plasma proteins when the pH falls?
- the plasma concentration of calcium will increase.
- less calcium will bind to the plasma proteins
- because there is more acidic H+ ions to bind to the plasma proteins
What will hypocalcaemia cause?
Muscle tetany.
asphyxiation.
Where do we get our calcium from?
entirely from the diet.
Where does the calcium leave the body?
by the kidney and faeces
What controls calcium concentration in the ECF/plasma?
Stores of calcium in the bone.
The bone favours maintaining calcium concentration over providing bone strength (it will give up calcium even if bones get weaker).
Where in the body acts as a storage place for calcium?
The bone.
- you can add to the stores or take calcium out of it
Which cells control bone turnover?
- osteoblasts = build new bone
- osteocytes = these are differentiated osteoblasts and controls the osteoblasts and osteoclasts
- osteoclasts = breakdown old bone
what sort of environment aids calcium breakdown, releasing bone calcium to the plasma?
An acidic environment.
How do osteoclasts break down old bone?
- secrete H+ cells
- creates acidic environment
- acid breaks down calcium salts
- also creates proteolytic enzymes to digest the extracellular matrix
- the acidic environment dissolves the calcium salts and releases it into the plasma
Which hormones increase plasma calcium concentrations?
Parathyroid
calcitriol
Which hormone decreases calcium concentrations?
Calcitonin
How many parathyroid glands are there?
4
Where are the parathyroid glands usually located?
on the posterior surface of the thyroid gland
1 in 10 people have them in different places eg - the arm
What happens to the parathyroid glands during thyroid surgery?
You should try to preserve the parathyroid glands when removing the thyroid gland.
Even if 1 or 2 is left this will be enough.
The parathyroid gland is essential for life.
