Essays on Calcium :- 1. Physiological Functions of Calcium 2. Absorption of Calcium 3. Blood Calcium 4. Excretion 5. Disease State.

Contents:

  1. Essay on the Physiological Functions of Calcium
  2. Essay on the Absorption of Calcium
  3. Essay on the Blood Calcium
  4. Essay on the Excretion of Calcium
  5. Essay on the Disease State of Calcium

Essay # 1. Physiological Functions of Calcium:

a. Calcium along with phosphorus is essen­tial for the formation and development of bones and teeth.

b. Ionized calcium is required in blood co­agulation process.

c. It regulates the excitability of nerve fibres and nerve centres.

d. It is essential for nerve impulses and mus­cular contraction.

e. It regulates the permeability of mem­branes.

f. It is essential for maintaining the integ­rity of intracellular material.

g. Calcium in the normal ratio with potas­sium maintains the normal activity of mus­cles.

h. It is required for the activation of several enzymes such as succinate dehydrogenase, ATPase and certain proteolytic enzymes.

Essay # 2. Absorption of Calcium:

Calcium is taken in diet as calcium phosphate, car­bonate, tartarate and oxalate. Calcium is actively absorbed in the upper small intestine. The active transport process is regulated by 1, 25-dihydroxy-cholecalciferol, a metabolite of vitamin D which is produced in the kidney in response to low plasma Ca++ concentrations.

The absorption of it is influ­enced by the following factors:

a. Vitamin D promotes absorption of cal­cium.

b. Acidic pH favours calcium absorption; be­cause calcium salts, particularly phos­phates and carbonates, are quite soluble in acid solutions and are relatively insolu­ble in alkaline solutions. Hence, alkali decreases its absorption.

c. Organic acids, lactose and basic amino acids in the diet favour calcium absorp­tion.

d. Higher levels of proteins in the diet help to increase the absorption of calcium.

e. Calcium: Phosphorus ratio of 1 : 1 (2:1 or 1:2) is the most convenient for the absorp­tion of both.

f. High concentration of magnesium in the diet decreases absorption.

g. Phytic acid (inositol hexaphosphate), which occurs in cereal grains, forms in­soluble salts (phytin) with calcium and magnesium resulting in the impaired ab­sorption of calcium.

h. Fatty acids interfere with calcium absorp­tion because of the formation of insoluble calcium salts of fatty acids which are ex­creted in the feces.

i. Presence of excess fibres in the diet inter­feres with the absorption of calcium.

j. Oxalic acid in the diet forms insoluble cal­cium oxalate which is excreted in the feces decreasing calcium absorption.

k. The percentage of calcium absorption de­creases as its intake increases.

l. Parathyroid hormone increases the intes­tinal absorption of calcium.

l. After the age of 55 to 60 years, there is gradual diminution of intestinal transport of calcium.

n. Adrenal glucocorticosteroids diminish in­testinal transport of calcium.

Essay # 3. Blood Calcium:

There is virtually no calcium in erythrocytes. The calcium content of plasma (usually determined in serum) is 8.4 to 10.2 mg/100 ml. During infancy and early childhood, the average values approach the upper limit of this range and fall with advanc­ing age.

Calcium exists in the plasma in three frac­tions—ionized or diffusible calcium, protein bound (non-diffusible) and complexed (citrate and phos­phate). In the usual determination of calcium, all these fractions are measured together. About 2 mg of the total calcium occurs in ion­ized form, about 5 mg occurs in non-ionized form and about 2 mg in the complex form.

Factors Influencing Blood Calcium Level:

a. Parathyroid Hormone:

In the fasting state (i.e. no absorption from the intestine), the normal plasma calcium concentration is maintained primarily by its rate of excre­tion and its mobilization from the bones through the action of the parathyroid hor­mone.

b. Vitamin D:

It enhances absorption of cal­cium from the intestine and thus maintain the normal plasma calcium concentration.

c. Plasma Proteins:

Half of the blood cal­cium (non-diffusible fraction) is bound to plasma protein (chiefly albumin) and thus any decrease in these proteins will be ac­companied by a decrease in the total cal­cium level.

d. Plasma Phosphate:

A reciprocal relation­ship exists between the concentration of calcium and phosphate ions in plasma. The marked increase in serum phosphate causes a fall in serum calcium concentra­tion.

e. Calcitonin:

An increase in the ionized cal­cium levels in the plasma is the stimulus for the production of calcitonin which then causes a deposition of calcium in bone.

Essay # 4. Excretion of Calcium:

Calcium is excreted in the urine, bile, and diges­tive secretions. Much of that is excreted in the feces which has escaped absorption. Under optimal con­ditions, 75 per cent of dietary calcium is absorbed. The remainder is the fecal calcium which is unabsorbed.

In man, about 10 grams of calcium are filtered in 24 hours by the renal glomeruli. Only about 200 mg appear in the urine which is in the ionic state as well as in the complexes with citrate and other or­ganic anions.

70-90 per cent of the calcium eliminated from the body is excreted in the feces.

A very small amount is excreted into the intes­tine after absorption.

The daily loss of calcium in sweat is about 15 mg. Vigorous physical exercise increases the loss of calcium by the way of sweat.

Essay # 5. Disease State of Calcium:

A. Effects of Parathyroid:

I. In hyperparathyroidism, the following changes occur:

(a) Hypercalcemia (serum calcium 12-22 mg/100 ml).

(b) Decrease in serum phosphate.

(c) Diminished renal tubular reabsorption of phosphate.

(d) Increased phosphatase activity.

(e) Raised urinary calcium and phospho­rus from bone decalcification and de­hydration.

(f) The extra calcium and phosphorus is lost from soft tissues and bones by increased bone destroying activity.

II. In hypoparathyroidism, the following changes occur:

(a) The concentration of serum calcium may drop below 7 mg/100 ml.

(b) Increased serum phosphate and de­creased urinary excretion of calcium and phosphorus.

(c) Normal or occasionally raised serum phosphatase activity.

(d) Normal acid-base equilibrium.

(e) Probably increased bone density.

B. Tetany:

Decreased ionized fraction of serum calcium causes tetany.

This may be due to:

(a) An increase in the pH of blood.

(b) Poor absorption of calcium from the in­testine.

(c) Decreased dietary intake of calcium.

(d) Increased renal excretion of calcium as in nephritis.

(e) Parathyroid deficiency.

(f) Increased retention of phosphorus as in renal tubular disease.

Symptoms:

(a) Muscles lose tone and become flabby.

(b) Affects the face, hands and feet.

C. Rickets:

This disease is characterized by faulty calcifi­cation of bones in children showing serum phos­phate values 1 to 2 mg/100 ml.

This may be due to:

(a) Vitamin D deficiency.

(b) A deficiency of calcium and phosphorus in the diet or a combination of both.

(c) Poor absorption of calcium from the in­testine.

(d) Parathyroid deficiency.

(e) Increased serum alkaline phosphatase ac­tivity.

D. Osteoporosis:

The disease occurs in adults due to the follow­ing causes:

(a) Decalcification of bones as a result of cal­cium deficiency in the diet.

(b) Hypoparathyroidism.

(c) Low vitamin D content of the body.

Symptoms:

(a) Fractures of the brittle bones occur even after minor accident.

(b) Pain due to fractures of vertebrae which may radiate round the trunk, to the but­tocks or down the legs.

E. Renal Rickets:

Renal Rickets are more accurately designated as familial hypophosphatemic rickets which is an inherited disease. Affected males show hypophos­phatemia and severe rickets.

Hypophosphatemic rickets are caused by the following reasons:

(a) Defective transport of phosphate by the intestine and by the renal tubules.

(b) Lowered serum phosphorus and hyperphosphaturia.

(c) Reduced intestinal absorption of calcium and phosphorus.

Vitamin D in ordinary doses does not relieve the disease. Hence, it is sometimes referred to as vitamin D-resistant rickets.

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