Role of Calcium in Cardiovascular Function
By the end of this lecture the students should be able to understand: • Calcium metabolism
• Calcium regulation
• The role of calcium in cardiac muscle contraction
• Calcium, excitation contraction coupling and T-tubules in cardiac muscle • The role of Calcium in vascular smooth muscle
• Calcium channel blockers
• Normal ranges of extracellular calcium • Hypocalcemia
Role of Calcium
• An essential intracellular and extracellular cation
• Extracellular calcium is required to maintain normal biological function of nervous system, the
musculoskeletal system, and blood coagulation
• Intracellular calcium is needed for normal activity of many enzymes;
– Preservation of the integrity of cellular membrane
– Regulation of endocrine and exocrine secretary activities
– Activation of compliment system
– Bone metabolism
Calcium Metabolism • Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains
adequate calcium levels.
• Derangements of this mechanism lead to hypercalcemia or hypocalcemia, both of which can
have important consequences for health.
• Total Body Calcium
• 99% of the bodies calcium is in the bone in calcium phosphate compounds
• 1% of total body calcium is intracellular
• 0.1% of total body calcium is in extracellular fluid
• Calcium in Plasma
• In ECF:
• Unionized Calcium=50%
– 41% is bound to plasma proteins
– 9% is bound to anions like citrate and phosphate • Ionized calcium=50%
• It is the ionized form of Calcium which is free and is of functional significance
THREE HORMONE AND THREE ORGAN
• ACTIVATED VITAMIN D
• SMALL INTESTINE
Parathyroid Hormone (PTH)
• If blood levels of ionized calcium drop by as little as 0.1 mg/dl, secretion of PTH is stimulated ; PTH acts directly on distal portion of the nephron to decrease urinary excretion of calcium
mediated by cAMP.
; PTH powerfully inhibits tubular reabsorption of phosphate and thus increases urinary phosphate
; PTH stimulates the renal enzyme that converts vit D to its active form but has no direct effects
on intestinal transport of calcium or phosphate.
• Activated Vit D: 1,25(OH)2 Cholecalceferol
GI - increase Ca absorption.
Bone - increase Ca mobilization.
Kidney - increase reabsorption within the distal tubule
; Deficiency of vitamin D severely impairs intestinal transport of both calcium and
; Mineralization of osteoid occurs spontaneously when adequate amounts of
calcium and phosphorous are available
• Secreted from Parafollicular cells of the Thyroid gland in response of hypercalcemia • Aims to decrease extracellular calcium conc.
• Decrease osteoclast activity
• Stimulates a distal tubular – mediated calciuresis.