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Role of Calcium in Cardiovascular Function

By Connie Lawrence,2014-11-26 12:28
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Role of Calcium in Cardiovascular Function

    Role of Calcium in Cardiovascular Function

    Learning Objectives

    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

     Hypercalcemia

    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

    Calcium Homeostasis

    THREE HORMONE AND THREE ORGAN

     PTH

     ACTIVATED VITAMIN D

     CALCITONIN

     BONE

     KIDNEY

     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

    excretion

    ; 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.

    Vitamin D

     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

    phosphorous

    ; Mineralization of osteoid occurs spontaneously when adequate amounts of

    calcium and phosphorous are available

    Calcitonin

     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.

    Calcium Regulation