A Seminar

on Calcium Metabolism

contentsIntroductionRole of calciumNormal values,Types,Sources,Daily requirementsAbsorption,Distribution,ExcretionRegulation of blood calcium levelsApplied physiologyImportance of calcium in ProsthodonticsConclusionReferences

Introduction

Most abundant mineral in the body

Calcium interacts with phosphorous forming Calcium phosphate

Role of Calcium

1. Neuronal ActivityCalcium is necessary –

-- For transmission of impulses from pre synaptic to post synaptic region

-- For the release of neurotransmitter from synaptic vescicle

2 Muscular ActivityCalcium mediates excitation-contraction coupling of muscle fibers

Skeletal Muscle - Calcium binds with Troponin c and Tropomyosin

Smooth Muscle – in place of Troponin Calcium binds with Calmodulin

3. Hemostasis

Necessary for activation of clotting factors in blood coagulation

4. Formation of bone and teeth

5. Membrane stabilization

6. Secretary activity of glands

7. Activation of enzymes

Normal Values

Total body Calcium – 1100g(1.5 % of total body weight)

Out of this - 99% in bone

- 4-5 g in soft tissues

- approx 1g in extra cellular fluid

Normal Serum Calcium

- 9-11 mg%

Types 1. Diffusible

Ionised calcium- physiologically active form (50%)

Non Ionised Calcium- Calcium complexed with anions (9%)

2. Non Diffusible (41%)Calcium bound to albuminPhysiologically inactive

Sources Milk, Egg, Fish ,Leafy Vegetables, Cereals

Daily Requirement

Adult - 500 -800mg per day

Children - 1200mg per day

Pregnancy and Lactation -1500mg per day

After age of 50 tendency for osteoporosis may be prevented by-

Calcium (1500mg/day)+ Vitamin D (20mg/day)

Absorption of CalciumMainly from 1st and 2nd part of Duodenum

Absorbed against a concentration gradient

Requires a carrier protein- Calbindin helped by calcium dependent ATPase

Factors Increasing•Vitamin D•Calcitriol•Parathyroid Hormone•Amino Acids..lysine,Arginine

Factors Decreasing• Phytates•Oxalates•Malabsorption Syndrome•High Phosphate content

Factors affecting Absorption

Regulation of Blood Calcium Levels

Three hormones that regulates blood calcium levels

1. Parathyroid hormone

2. 1,25-dihydroxycholecalciferol

3. Calcitonin

1. Parathyroid Hormone(PTH)A polypeptide secreted by chief cells of parathyroid gland

Synthesised from a precursor Prepro-PTH

Acts via activation of adenylyl cyclase

Actions

a. Action on Bones

Increases plasma calcium concentration by promoting bone resorption

Occurs in 2 Phases

Rapid Phase (Early Phase)-Osteolysis

Slow Phase- Activation of Osteoclasts

b. Action on Kidneys

Increases renal tubular reabsorption of calcium

Occurs mainly in the distal tubules, collecting tubules, collecting duct and to a lesser extent in ascending loop of Henle

c. Action on GIT

Increases calcium absorption from intestine-by increasing the formation of 1,25 dihydroxycholecalciferol

2. 1,25 – dihydroxycholecalciferol

Activated form of Vitamin D

Increases calcium absorption from intestine

3. Calcitonin

A peptide hormone secreted by C cells of thyroid gland

Reduces Blood calcium level by acting on-

Bone-deposition of calcium

Kidney-Increases calcium Excretion

Intestine-Prevents Calcium Absorption

Applied Physiology1.Hypoparathyroidism

Decreased secretion of PTH- Hypocalcemia(calcium <8.5mg/dl)

Hypocalcemic tetany – neuromuscular hyper excitability- Occurs if the plasma calcium level falls below 6mg%

Signs and symptoms • Carpopedal Spasm -Trousseau’s Sign(Figure)

• Laryngeal Stridor• ECG Changes• Can be detected by 1, Trousseau’s Sign 2, Chvostek’s Sign 3. Erb Sign

2. Hyperparathyroidism

Increased secretion of PTH-Hyper calcemia

Radiology of hyperparathyroidism

OsteoporosisBone disease characterised by loss of bone matrix and minerals

Due to excessive bone resorption and decreased bone deposition.

Risk factors

1.sedentary life

2.genetic factors

3.early menopause/ ovariectomy

4.excessive alcohol intake

5.prolonged medication with corticosteroids.

6.hypothyroidism,cushings syndrome,

acromegaly, hypogonadism.

3. RicketsBone disease occurring in children due to vitamin D deficiency

4.Osteomalacia(Adult Rickets)

5.Renal OsteodystrophyA consequence of chronic renal failure related to calcium metabolism

Importance of calcium in Prosthodontics

Necessary for the normal growth of bone and teeth.

In osteoporosis, - RRR will be more- affect denture retention – frequent relining is needed

Amount and density of available bone in edentulos site is the primary determining factor in predicting the success of an implant.