Calcium is the most abundant mineral found in the body. It is the major ingredient in the inorganic component of the bone and takes part in various biochemical reactions. These mechanisms include, the clotting process, neural transmission and muscular contraction which includes the cardiac muscle. It is however essential that the levels of calcium in the body are controlled. Too much calcium will lead to cardiac failure, and too little will lead to tetany, which if severe it can lead to muscular convulsions.
Vitamin D and the parathyroid hormone can keep these levels in check mainly by mobilising calcium from the bone if it is too low and shunting it be back into the bone if there is too much. Both low and high calcium levels are due to factors involving vitamin D or PTH. Benign high levels of calcium due to too much absorption may lead to calcification of the soft tissue.
Lack of calcium in the diet can lead to osteoporosis in which the bone is less dense and therefore brittle and weak. In women, osteoporosis can be due to lack of oestrogens after menopause or oophorectomy. Calcium is usually ubiquitous in diet, but often, a small amount of food provides reasonable amounts, of which dairy products are best.
Physiological Roles of Calcium Ions
- Calcium in many different types of cells activate on the membrane, depolarisation and mediate calcium influx in response to action potentials and subthreshold depolarising signals.
- Calcium entering the cells through the voltage-gated Calcium channels serves as a second messenger of electrical signals which initiates many different cellular events.
- In the cardiac and smooth muscles, cells activation of the calcium channels initiates contraction directly by increasing cytosolic calcium concentration.
- In skeletal muscle cells, the voltage-gated calcium channels in the transverse tubule’s membrane interact directly ryanodine-sensitive calcium release channels in the sarcoplasmic reticulum and activate them to initiate rapid contraction.
- In neurons, Voltage-gated calcium channels initiate synaptic transmission
- In endocrine cells, voltage-gated Calcium channels mediate Calcium ion entry that starts secretion of hormones.
Absorption of Calcium
Several factors affect the absorption of calcium from the intestine, For example, vitamin D and Parathyroid Hormone. Some foods such as cereals contain phytic acids which combine with calcium rendering it unabsorbable. Oxalic acid, which is found in spinach and rhubarb can also be problematic only when too much is consumed.
Osteoporosis after menopause is by far the most common condition in Western countries caused by a disruption in calcium metabolism. Osteoporosis is not due to lack of calcium per say, but due to lack of estrogens, which are essential in bone metabolism. Estrogen replacement therapy in women postmenopausal can help with osteoporosis, but not without side effects. There is evidence that a moderate amount of calcium supplement together with exercise can help prevent osteoporosis.
Calcium usually as the chloride is given via the IV route to treat severe low levels of calcium and it is also used in cardiac resuscitation. Calcium ions are essential for myocardial excitation and contraction, coupling and for increasing contractility of the heart. Calcium may be used as a positive inotropic or vasopressor but has no place in the management of arrhythmias unless the arrhythmias are caused by hyperkalaemia, hypocalcaemia, hypermagnesemia or calcium blocker 1. The Australian Resuscitation Council recommends that calcium not to be given on a routine basis during cardiac arrest. Calcium is however used as an antidote to low blood pressure that is caused by calcium channel blockers. Calcium solutions should not be injected intramuscularly or subcutaneously, because they are extreme irritants and may cause necrosis of the tissue.
Causes of Hypocalcemia
- Kidney Dysfunction
- When too much is excreted in urine
- Inadequate consumption of calcium
- disorders that decrease calcium absorption
- Lack of response to a normal level of parathyroid hormone (pseudohypoparathyroidism)No parathyroid glands at birth (for example, in DiGeorge syndrome).
- A low level of magnesium (hypomagnesemia), which reduces the activity of parathyroid hormoneVitamin D deficiency (due to inadequate consumption or inadequate exposure to sunlight
Symptoms of Hypocalcemia
- muscle stiffness
- muscle spasms
- paresthesias, or feelings of pins and needles, in the extremities
- changes in mood, such as anxiety, depression, or irritability
- memory issues
- difficulty speaking or swallowing
- papilledema, or swelling of the optic disc
The Symptoms of Severe Hypocalcemia are:
- congestive heart failure
- laryngospasms, or seizures of the voice box
- dry skin
- brittle nails
- kidney stones or other calcium deposits in the body
Food Rich in Calcium
- Beans and Lentils
- Whey Protein
Zamponi, G. W., Striessnig, J., Koschak, A., & Dolphin, A. C. (2015). The physiology, pathology, and pharmacology of voltage-gated calcium channels and their future therapeutic potential. Pharmacological reviews, 67(4), 821-870.
Catterall, W. A. (2011). Voltage-Gated Calcium Channels. Cold Spring Harbor Perspectives in Biology, 3(8), a003947. http://doi.org/10.1101/cshperspect.a003947