Calcium Homeostasis Flashcards
Where is the main reservoir of calcium
Skeleton
1200g
Apart from the skeleton calcium can be stored in extra-cellular space why is this important
It is important for cells functions such as
Normal blood clotting
Muscle contractility
Nerve function
What is the total serum calcium
Around 2.4 mol/L
What is the total ionised serum calcium
Around 1.1 mol/L
If calcium is ionised what does this mean
Metabolically active
If calcium is protein bound what does this mean
It is not metabolically active
What are examples of complexed calcium
Citrate
Phosphate
When is albumin most likely going to bind to calcium
At higher pH
What is low iconised calcium associated with
It is associated with contraction of the small muscles of the hands and feet
Low ionised calcium can be an effect of what
Alkalosis
How much calcium do we absorb from our diet
30%
What is a major source of dietary calcium
Dairy products
What are minor sources of dietary calcium
Veg such as broccoli
Cereals such as white bread
Oily fish such as sardines
Where is active absorption of calcium happening
Active absorption occurs in the duodenum and jejunum
Where is passive absorption seen
Passive absorption occurs in the ileum and colon
When do we absorb a higher amount of calcium
When we are put on a low calcium diet
What is calcium absorption mediated by
Calcritriol
What is calcitriol
The active form of vitamin D
How is calcium absorbed
Active transport
Where is exchangeable calcium found
On the bone surface
What happens during bone resorption
Calcium is released from bone slowly by osteoclasts
What does the amount of calcium filtered by the glomerulus depend on
The glomerular filtration rate
What is ultrafilterable calcium
Ionised and complexed
How much of the calcium which is filtered is reabsorbed
98%
Higher levels of calcium will be reabsorbed if what is high
Parathyroid hormone
What causes less calcium to be reabsorbed
Sodium is high
How many amino acids is parathyroid hormone
84 amino acids
What can detect the levels of ionised calcium to stimulate PTH been secreted
Calcium sensing receptors on the parathyroid gland
What regulates the synthesis of PTH
Calcitriol
Where does regulation of PTH take place
Parathyroid chief cell
What does calcitriol stimulate
It stimulates intestinal calcium absorption
Where is calcitonin produced
It is produced by c cells or parafollicular cells of the thyroid
When is calcitonin released
It is secreted due to an increase in serum calcium
What affect does it have on resorption
Lowers bone resorption
What does parathyroid hormones act on
Bone and kidney
What does parathyroid hormone have an effect on
In the kidneys- increased calcium reabsorption, decreased phosphate reabsorption and increases alpha-hydroxylation of 25-OH vit D
In the bone- increased bone remodelling
In the intestines- no direct effect but increase in calcium absorption due to increase in 1,25 vit D
What are bodily responses to a low diet of calcium
Low dietary calcium means less calcium is absorbed which results in lower ionised serum calcium cause high amounts of PTH which results in fast action in exchangeable calcium released from the surface of done and decreased excretion of calcium from the kidney
The slow actions = increased bone resorption and increase in fractional absorption by intestine
To return serum ionised calcium back to normal
What is calcium homeostasis
Example of negative feedback
