Calcium, Phosphorus and Magnesium

Hello :) In this post we'll take a look at the absorption and storage sites of Caclium, Phosphorus and Magnesium as well as the effects of a defecit of these minerals in the diet. 

Calcium

Ninety-nine percent of calcium is stored in the bones while some can be found in cells and the extracellular fluid. Calcium is an important constituent of bones and teeth and is also involved in blood clotting, cellular metabolism, enzyme action, neuromuscular function, and as signal transducers across cellular membranes.

Because of this, deficiencies in calcium in the diet will result in several problems, including:

•  Bone defects, such as: 
• Rickets in young animals, osteomalacia, 
• Soft beaks and thin egg shells in birds 
• Neurological and muscular problems: 
• Paresis 
• Muscular spasms 
• Seizures 
• Cardiorespiratory problems:
• Cardiac arrhythmias 
• Synchronous diaphragmatic flutter (aka “Thumps”).

 The absorption of Calcium occurs mainly in the duodenum of the small intestine but also in the caecum and colon through two ways. The first method is through a saturable, carrier-mediated vitamin D dependent system. This requires the influx of Ca into the epithelial cells via calcium channels and exit of these cells via Ca-ATPase.

The second method is through a non-saturable system that is dependent on the luminal calcium concentration. This method is important in young animals and during pregnancy and lactation. 

Calcitriol stimulates the movement of Ca across membranes by increasing the synthesis of calbindin which is a protein that binds to Ca. Low calcium levels in the blood trigger the release of parathyroid hormone (PTH) which causes the conversion of vitamin D3 in the kidneys to Calcitriol. Calcitriol then increases the uptake of Ca in the gut to increase plasma Ca levels.

Low calcium diets are associated with high Ca absorption while high calcium diets are associated with low uptake in the gut.

Phosphorus

Eighty to Eighty-five percent of the phosphorus in the body is stored in the skeleton, the remainder is found in the soft tissue and fluids. 

Phosphorus has several important functions in the body. It is an important part of the mineral matrix found in bone, it’s also found in phosphoproteins, nuclei acids and phospholipids. It plays a key role in energy transformation (it makes up ATP and ADP), is involved in the regulation of signal transduction and acts as an acid-base buffer in the blood and gut. 

Thus, signs of deficiency include:

• Abnormal bone development: rickets and osteomalacia 
• Subnormal growth, fertility and milk yield 
• Reduced egg production 
• Depraved appetite.

Like calcium, phosphorus is also absorbed from the small intestine and is uptake is also driven by Calcitriol. Excess phosphorus that is absorbed from the gut is excreted through the kidneys and gastrointestinal tract via saliva.

Magnesium

Adult animals only have small reserves of magnesium in their bodies and as such rely on a regular supply from their diets. The absorption of magnesium (Mg) is quite a complex process that is influenced by several factors. In ruminants, high levels of potassium reduce the efficiency of Mg absorption by interfering with its active transport systems. In addition, high levels of calcium, phosphorus, phytate and oxalates reduce the bioavailability of magnesium. 

About seventy percent of the magnesium in the body can be found in the skeleton, about a quarter in the muscles and the remainder in the cells and extracellular space.  

Magnesium is involved in several metabolic reactions, it is essential for the efficient metabolism of carbohydrates and lipids, it’s also involved in cellular respiration, the moderation of neuromuscular activity and the maintenance of cell membrane integrity. 

Deficiencies of magnesium result in nervous irritability, tremors, tetany, seizures, anorexia and reduced weight gain.

That's all for this post, let me know if you have any questions :)