The Role of Calcium in Calcium Balancing

Calcium is an important ion which regulates many important functions in our body. Any alteration in normal levels of Calcium ( 9-11 mg/dl) causes non-tolerable symtpoms in the patients. It plays a great role in maintenance of proper functioning of neuromuscular excitation and growth of body organs.

Calcium Balance

It is maintained by an interplay of Absorption, Exchange, Secretion and Excretion.

• Absorption of ingested calcium. It occurs mainly in the duodenum by an energy-dependent active transport which involves activity of calcium-dependent ATPase at the brush border of epithelial cells. It is regulated by 1.25 dihydroxycholecalciferol.
• Exchange of calcium between bone and ECF. Bone resorption in the remodeling process is stimulated by PTH and inhibited by sex hormones, calcitonin and phosphate. Bone deposition is promoted by physical stress to the bone provided by walking, sex hormones and growth hormones. In old age when sex hormones are reduced, there occurs an increased tendency to bone resorption( Postmenopausal osteoporosis). Osteoporosis also occurs in Cushing’s syndrome and growth hormone deficiency.
• Secretion of calcium from extracellular fluid (ECF). 
• Excretion of calcium in the faecal matter and urine.

Also Read: Thyroid Hormones: Synthesis, Functions and Clinical Scenario

Hormonal Regulation of Plasma Calcium Level

Plasma calcium level within a narrow range (9-11mg/dl). The hormones regulating plasma calcium levels include:

Calcitropic Hormones

The 3 primarily involved in the calcium homeostasis are:

• Parathyroid hormone (PTH)
• Active form of Vitamin D ( 1,25 dihydroxycholecalciferol)
• Calcitonin

Parathyroid hormone related protien ( PTHrP)

It is a local hormone that acts on the PTH receptors and in important for skeletal development in utero.

Other hormones

The other hormones include:

• Growth hormone has a stimulatory effect on bone deposition.
• Sex hormone have inhibitory effects on bone resorption.
• Glucocorticoids have a stimulatory effect on Bone resorption.
• Growth factors have a stimulatory effect on bone deposition.

Also Read: Adrenal Gland Hormones : Functions, Symptoms and Disorders

Role of Hormones in Calcium regulation

Parathyroid Hormones

Hypocalcemia is regulated by :

• Reduced calcium intake causes reduced serum calcium which causes release of Parathyroid hormone from Parathyroid gland.
• Parathyroid hormone normalizes serum calcium levels by following mechanisms:
  • Reduced renal loss of Calcium by increasing resorption of calcium and excretion of phosphorus.
  • In Bone- It causes resorption of bone which causes elevation in calcium and phosphorus levels.
  • In GIT- It causes resorption of calcium and phosphorus.
  • It increases conversion of 25-hydroxyvitamin D to 1,25 dihydroxyvitamin D which further increases intestinal absorption of calcium and phosphate.
  • These mechanisms lead to normalization of serum calcium levels.

Role of Vitamin D

• Increases intestinal absorption of calcium and phosphate
• Increases renal reabsorption of calcium and phosphate
• Decreases parathyroid hormone secretion
• Increases mineralization of bone

Role of Calcitonin

• Decreased bone resorption
• Decreased renal calcium resorption
• These ultimately lead to decrease in serum calcium levels. Calcitonin plays an important role in normalization of serum calcium levels during hypercalcemia.

Also Read: Hemostasis: Stages, Steps and Clinical Applications

Functions of Calcium

• Development of bone and teeth.
• Neuromuscular excitation
• Blood coagulation
• Membrane integrity and plasma membrane transport
• Mediates intracellular action of hormones by acting as a second messenger ( epinephrine in liver glycogenolysis) and third messenger (ADH)
• Activation of enzymes like pancreatic lipase
• Release of hormones and neurotransmitters like insulin, PTH , Calcitonin
• Calmodulin mediated action of calcium
• Regulation of secretory processes
• Cell to cell contact and adhesion of cells in tissues required for cell to cell communication
• Prolongs systole by acting on myocardium.

Also Read: Synapse: Components, Types and Function

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