4. Introduction
A few minerals are required for the normal growth and maintenance of
the body.
If the daily requirement is more than 100 mg, they are called major
elements or macro minerals.
Calcium, magnesium, sodium, phosphorus, potassium chloride and
Sulphur belong to this category.
If the requirement of certain minerals is less than 100 mg/day, they are
known as minor elements or microminerals or trace element.
These are the iron, iodine, manganese, copper, zinc, cobalt, molybdenum,
selenium, and fluoride.
Total calcium in the human body is about 1 to 1.5 kg, 99% of which is
seen in the bone and 1% in extracellular fluid.
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5. Source Of Calcium
It is widely distributed in food substances such as milk, cheese, egg-yolk,
beans, lentils, nuts, figs, cabbage.
Milk and its products are the best sources.
Leafy vegetables and hard drinking water.
Calcium is available in several foodstuffs. Percentage of calcium in different
food substance is:
Whole milk = 10%
Low fat milk = 18%
Cheese = 27%
Other dairy products = 17
Vegetables = 7%
Other substances such as meat, egg, grains, sugar, coffee, tea, chocolate, etc.
= 21%
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6. Daily Requirements Of Calcium
It is required 500 mg/day average.
1 to 3 years = 500 mg
4 to 8 years = 800 mg
9 to 18 years = 1,300 mg
19 to 50 years = 1,000 mg
51 years and above = 1,200 mg
Pregnant ladies and lactating mothers = 1,300 mg
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7. Calcium in Bones
Calcium is constantly removed from bone and deposited in bone.
Bone calcium is present in two forms:
1. Rapidly exchangeable calcium/exchangeable calcium which is available
in small quantity in bone and helps to maintain the plasma calcium level
2. Slowly exchangeable calcium /stable calcium which is available in large
quantity in bones and helps in bone remodeling
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8. Body Distribution
The total calcium of the body is 25-35 moles (100-170g).about 99% of the
calcium is found in bones. It exist as carbonate and phosphate of calcium.
About 0.5 percent in soft tissue and 0.1% in ECF. The normal level of
plasma calcium is 9-11mg/dl. The calcium in plasma is of three types
mainly.
1. Ionized calcium(diffusible):- It is about 41% of total. It is physiologically
active form of calcium.
2. Protein bound calcium:-Albumin is the major protein with which calcium is
bound.it is 50%.
3. Complex calcium:- It is probably complex with organic acid. It is 9%
All the three form of calcium remain in equilibrium with each other in
plasma.
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9. Regulation Of Blood Calcium Level
Blood calcium level is regulated mainly by three hormones by altering their
secretion rate in response to change in ionized calcium.
1. Parathormone
2. Vitamin D or 1,25-dihydroxycholecalciferol (calcitriol)
3. Calcitonin.
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10. 1. Parathormone
Parathormone is a protein hormone secreted by parathyroid gland.
Its main function is to increase the blood calcium level by mobilizing calcium
from bone.
PTH secretion in blood is stimulated by a decrease in ionized calcium and
conversely, PTH secretion is stopped by an increase in ionized calcium.
PTH exerts three major effects on both bone and kidney.in the bone PTH
activates a process known as bone resorption, in which activated osteoclast
break down bone and frequently release calcium into ECF.
In the kidney PTH conserve calcium by increasing tubular reabsorption of
calcium ions.
PTH also stimulates renal absorption of vitamin D.
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12. Activation of Vitamin D
•Vitamin D is a group of closely related sterols produced by the action of
ultraviolet light.
•Vitamin D3 (Cholecalciferol) is produced by the action of sunlight and is
converted to 25-hydroxycholecalciferol in the liver.
•The 25-hydroxy-cholaecalciferol is converted in the proximal tubules of
the kidneys to the more active metabolite 1,25-dihydroxy-cholaecalciferol.
•1,25-dihydroxychlecalceriferol synthesis is regulated in a feedback fashion
by serum calcium and phosphate.
•Its formation is facilitated by parathyroid hormone.
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13. 2.Vitamin D or
1,25-dihydroxycholecalciferol (Calcitriol)
Calcitriol release the carrier protein in the intestinal mucosa, which
increase calcium absorption, hence blood calcium level tend to be
increases.
Act independently on bones.
Increase the number and activity of osteoblast the bone forming cells.
Secretion of alkaline phosphate by osteoblast is increase by vitamin D.
Facilitates calcium absorption in the kidney.
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14. 3. Calcitonin
Calcitonin secreted by parafollicular cells of thyroid gland.
It is a calcium-lowering hormone.
Calcitonin is a 32 amino acid polypeptide secreted by the parafollicular cells
in the thyroid gland. It tends to decrease serum calcium concentration and, in
general, has effects opposite to those of PTH.
The actions of calcitonin are as follows:
1. Inhibits bone resorption
2. Increases renal calcium excretion The exact physiological role of calcitonin
in calcium homeostasis is uncertain. The effects of calcitonin on bone
metabolism are much weaker than those of either PTH or vitamin D.
The effect of calcitonin on blood calcium level mainly by decreasing bone
resorption.
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15. Absorption
calcium is taken in the diet principally in the form of calcium phosphate.
Carbonate and tartarate.
Unlike Na and K which are readily absorbed, the absorption of Ca is rather
incomplete.
About 40% of average daily dietary intake of Ca is obtained from gut.
Calcium is absorbed mainly from duodenum and first half of the jejunum,
against the electrical and concentration gradient.
Calcium is absorbed from duodenum by carrier mediated active
transport and from the rest of the small intestine, by facilitated diffusion.
Vitamin D is essential for the absorption of calcium from GI tract.
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16. Factor Affecting The Absorption
Ph of intestinal milieu:-
Composition of diet
Sugar and organic acid:-
Phytic acid:- (inositol hexaphosphate)
Oxalate:-
Fibers:-
Minerals:-
o Phosphate and magnesium
o Fe in diet
Vitamin D:-
State of health of individual and Aging:-
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17. Function
Calcification of bone and teeth:-
The process of bone formation and teeth formation is known as
calcification which is a continuous process of bones.
Osteoblast secrete a enzyme alkaline phosphatase which can hydrolyse
certain phosphoric esters.
Calcium play role in blood coagulation by producing substance for
thromboplastic activity of blood.
Calcium has a role in neuromuscular transmission.
Calcium ions are needed for excitability if neurons.
calcium play role in muscle contraction.
Normal excitability of heat is Ca ion dependent.
It play role in secondary and tertiary messenger hormone action.
It play role in permeability of gap junctions.
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18. Excretion
While passing through the kidney, large quantity of calcium is filtered in the
glomerulus.
From the filtrate, 98% to 99% of calcium is reabsorbed from renal tubules into
the blood.
Only a small quantity is excreted through urine.
Most of the filtered calcium is reabsorbed in the distal convoluted tubules
and proximal part of collecting duct.
In distal convoluted tubule, parathormone increases the reabsorption.
In collecting duct, vitamin D increases the reabsorption and calcitonin
decreases reabsorption
About 500 mg of calcium is excreted daily.
Out of this, 400 mg is excreted through feces and 100 mg through urine
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19. Clinical Importance
Hypercalcemia
is total serum Ca concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized
serum Ca > 5.2 mg/dL (> 1.30 mmol/L).
Principal Causes of Hypercalcemia- Hypercalcemia usually results from
excessive bone resorption. There are many causes of hypercalcemia
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20. Hypercalcemia
Clinical effects of an increase calcium level include renal damage, polyuria
(excessive urination), hypokalemia (high k level in blood), hypotonia
(floppy baby syndrome, reduced muscle strength) , depression,
constipation and abdominal pain. The causes are :
Malignancy
- Bony metastases such as breast, lung, prostate and kidney.
- Solid tumors with humeral affects.
- Hematological tumors such as myeloma.(cancer of the plasma cell)
Drugs
Thiazides (reduced renal calcium excretion) and vitamin A toxicity
(activates the osteoclasts)
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21. Hypercalcemia
Primary hyperparathyroidism (adenoma, hyperplasia; related to benigh
tumar.)
- Tertiary hyperparathyroidism (autonomous secretion of PTH)
Lithium induced hyperparathyroidism
High pone turnover
Thyrotoxicosis and immobilization such as Paget's disease.(Paget's
disease is a bone remodeling disorder.)
High level of V.D
Vit.D toxicity and granulomatous diseases such as sarcoidosis and
tuberculosis. (is an inflammatory disease that affects multiple organs in
the body, but mostly the lungs and lymph glands.)
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23. Hypocalcemia
Hypocalcemia is total serum Ca concentration < 8.8 mg/dL (< 2.20
mmol/L) in the presence of normal plasma protein concentrations or a
serum ionized Ca concentration < 4.7 mg/dL (< 1.17 mmol/L). Causes
include hypoparathyroidism, vitamin D deficiency, and renal disease.
•Acute hypocalcemia can also occur in the immediate post-operative
period, following removal of the thyroid or parathyroid glands.
•Hypocalcemia can occur following rapid administration of citrated blood
or large volumes of albumin and in alkalosis caused by hyperventilation.
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24. Hypocalcemia
Increases the neuromuscular activity, may leads to tetany paraesthesia. It
also leads to arrhythmias.(abnormal heartbeat) The causes are:
Drugs
Furosemide (increases renal excretion), enzyme induced drugs e.g.
Phenytoin (induces hepatic enzymes that inactivate Vit.D).
Causes of hypocalcaemia with hypophsphataemia
- Vitamin D deficiency which leads to rickets in children and osteomalcia
(softening of bones) in adults.
- Malabsorption.
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25. Causes of hypocalcemia with
hyperphosphatemia
- Hyperparathyroidism: surgical removal of parathyroid.
- Pseudo hypoparathyroidism (impaired response of kidney and bone to PTH).
Miscellaneous causes of hypocalcemia (rare)
- Acute pancreatitis.(inflammation of pancreas)
- Sepsis.(inflammation of whole body due to known infection)
- Sever hypomagnesaemia.
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26. Clinical manifestations of
Hypocalcemia
Clinical manifestations of Hypocalcemia
• Hypocalcemia is frequently asymptomatic.
• Major clinical manifestations of hypocalcemia are due to
disturbances in cellular membrane potential, resulting in neuromuscular
irritability.
• Clinical signs include: tetany, carpopedal spasm and laryngeal stridor.
• Sensory symptoms consisting of paresthesia of the lips, tongue, fingers,
and feet
• Generalized muscle aching and spasm of facial musculature are also
there
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27. Clinical manifestations of
Hypocalcemia
Clinical manifestations of Hypocalcemia
• Hypocalcemia may lead to cardiac Dysrhythmias, decreased cardiac
contractility, causing hypotension, heart failure or both.
• Many other abnormalities may occur with chronic hypocalcemia, such as
dry and scaly skin, brittle nails, and coarse hair.
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