Calcium (The Third Macromineral)

Question 1

How much calcium does the body contain?

Answer 1

1-1.5kg

Question 2

How is calcium stored?

Answer 2

99% of calcium is stored in the skeleton and teeth in the hydroxyapatite form
1% of calcium is stored in soft tissue and ECF

Question 3

What are the three forms in which calcium is circulated?

Answer 3

Ionized Ca²: Phsyiologically active form (50% of circulating calcium)
Protein-bound: Mostly bound to -vely charged albumin (40% of circulating calcium)
Complexed to other substances: Bound to substances like citrate and phosphate (10% of circulating calcium)

Question 4

What factors increase dietary absorption of calcium?

Answer 4

Calcitriol (Vitamin D)
Parathormone (PTH)
Amino acids (Lysine, Arginine)

Question 5

What factors decrease calcium absorption?

Answer 5

Phytates
Oxalates
Iron
Fatty acids
Phosphates

Question 6

What are the biochemical functions of calcium?

Answer 6

Bone mineralization
Muscle contraction
Blood coagulation
Transmission of nerve impulse and synaptic transmission
Membrane permeability (Reduction)
Neuromuscular excitability (Reduction)
Direct activation of enzymes
Calmodulin-mediated activation of enzymes
As an intracellular messenger
Release of hormones
Microfilament mediated processes
Cell-to-cell contact

Question 7

Where is calcium absorbed?

Answer 7

Small intestine

Question 8

Where is calcium excreted?

Answer 8

Urine and feces

Question 9

What is calcium balance?

Answer 9

Amount of calcium intake and its deposition in bone compared to its excretion in urine and feces

Question 10

Describe how calcium balance changes during the life cycle?

Answer 10

Normal adult - Calcium balance is maintained
During growth - A child will be in positive calcium balance
Elderly and in several diseases - Individuals may be in negative calcium balance

Question 11

What factors may decrease calcium absorption?

Answer 11

Less dietary calcium intake
Poor absorption
Vitamin D deficiency

Question 12

What three hormones are involved in regulation of blood calcium levels?

Answer 12

Parathyroid Hormone (PTH)
Calcitrol (1,25(OH)2D3)
Calcitonin

Question 13

Characteristics of PTH

Answer 13

Peptide hormone secreted by parathyroid glands
Decrease in extracellular ionized calcium or an increase in serum phosphate
Concentration stimulates its secretion

Question 14

Characteristics of Calcitriol (active vitamin D)

Answer 14

It increases serum concentrations of calcium and phosphate
It increases absorption of calcium and phosphate from the gut by calcium-binding proteins
Deficiency results in low calcium and phosphate availability causing rickets (in infants and children) or osteomalacia (in adults)

Question 15

Characteristics of Calcitonin

Answer 15

Peptide hormone synthesized and secreted primarily by the thyroid gland (C-cells)
An increase in serum calcium results in an increase in calcitonin, and a decrease causes reduction in calcitonin

Question 16

What is the composition of the bone matrix?

Answer 16

Collagen (90% of bone matrix) and hydroxyapatite

Question 17

What is hydroxyapatite?

Answer 17

Calcium-rich crystals found between collagen fibers

Question 18

Chemical formula of hydroxyapatite

Answer 18

Ca₁₀[PO₄]₆[OH]₂

Question 19

What are the requirements for mineralization of bones?

Answer 19

Calcium and phosphate

Question 20

What conditions are caused by hypocalcemia?

Answer 20

Hypoparathyroidism (True and Pseudo)
Aminoacidurias
Rickets
Osteomalacia
Osteoporosis

Question 21

What conditions are caused by hypercalcemia?

Answer 21

Hyperparathyroidism
Malignancies

Question 22

At what point does consumption of calcium become toxic?

Answer 22

Upper limit 2000-3000mg/day

Question 23

How may calcium toxicity occur?

Answer 23

Ingestion of large amounts of calcium salts
Excess Vitamin D intake

Question 24

Sources of calcium

Answer 24

Milk, yoghurt,, cheese, nuts, seeds as snacks, canned fish with bones
Vegan or lactose intolerant: Tofu

Question 25

What are the risk factors for osteoporosis?

Answer 25

Question 26

Calcium as a second messenger

Answer 26