Minerals, Calcium, and Magnesium Metabolism

Flashcards for vocabulary review based on lecture notes about minerals, calcium metabolism, and magnesium.

Minerals

Essential for calcification of bone, blood coagulation, neuromuscular irritability, acid-base equilibrium, fluid balance & osmotic regulation.

Major elements/Macro minerals

Minerals with a daily requirement of more than 100 mg.

Micro minerals

Minerals with a daily requirement of less than 100 mg.

Major elements

Includes calcium, magnesium, phosphorous, sodium, potassium, chloride, and sulfur.

Minor elements

Includes iron, iodine, copper, manganese, zinc, molybdenum, selenium, and fluoride.

Calcium

Most abundant mineral in the human body, mainly found in bone.

Dietary Sources of Calcium

Good dietary sources include milk, egg, fish, cheese, beans, lentils, nuts, cabbage, and vegetables.

Daily calcium requirement for adults

500 mg/day

Daily calcium requirement for children

1200 mg/day

Daily calcium requirement during pregnancy & lactation

1500 mg/day

Form of calcium found in bones

Carbonate or phosphate of calcium

Ionized or free calcium

50% of plasma calcium; required for nerve function, membrane permeability, muscle contraction, and hormone secretion.

Bound calcium

40% of plasma calcium; bound to protein, mostly albumin.

Complexed calcium

10% of plasma calcium; complexed with anions including bicarbonate, phosphate, lactate & citrate.

Normal level of plasma calcium

9-11mg/dl

Calcium Absorption Rate

About 40% of dietary calcium is absorbed from the gut

Location of Calcium Absorption

Occurs form the first & second part of duodenum

Calcium Absorption mechanism

Carrier protein helped by calcium-dependent ATPase

Calcium excretion

In stool: 400 mg, in urine: 100 mg

Calcium Absorption Mechanisms

Simple diffusion and active transport

1, 25 DHCC (Calcitriol)

Regulates the synthesis of Ca-binding proteins & transport

Vitamin D role in Calcium Absorption

Induces the synthesis of carrier protein (Calbindin) promoting calcium absorption

Parathyroid hormone role in Calcium Absorption

Increases calcium transport from the intestinal cells by enhancing 1a-hydroxylase activity

Effect of Acidity on Calcium Absorption

Favors calcium absorption because the Ca-salts are soluble in acidic solutions

Effect of Alkaline Medium on Calcium Absorption

Lowers calcium absorption due to the formation of insoluble tricalcium phosphate

Effect of High protein diet on Calcium Absorption

Favors calcium absorption

Amino acids increasing Calcium Absorption

Lysine & arginine

Effect of Amino Acids on Calcium Absorption

Increase the solubility of Ca-salts & thus its absorption

Effect of Sugars and organic acids on Calcium Absorption

Increase the solubility of Ca-salts & increases their absorption

Effect of Phytic acid on Calcium Absorption

Cereals contain phytic acid (Inositol hexaphosphate) forms insoluble Ca-salts & decreases the absorption

Effect of Oxalates on Calcium Absorption

Causes formation of insoluble calcium oxalates, decreasing the absorption

Effect of Fibres on Calcium Absorption

Interferes with the absorption

Effect of Malabsorption syndromes on Calcium Absorption

Causing formation of insoluble calcium salt of fatty acid

Effect of Glucocorticoids on Calcium Absorption

Diminishes intestinal transport of calcium

Effect of Phosphate on Calcium Absorption

High phosphate content will cause precipitation as calcium phosphate decreasing absorption

Effect of Magnesium on Calcium Absorption

High content of Mg decreases the absorption

Ca: P Ratio

2:1

Role of Bone in Calcium Balance

Bone is regarded as a mineralized connective tissue acting as reservoir for calcium

Calcium's role in muscles

Mediate excitation & contraction of muscles

Calcium's role in Nerve conduction

Necessary for transmission of nerve impulses

Calcium role in Blood coagulation

Known as factor IV in blood coagulation process

Activation of enzymes

Calmodulin is a calcium binding regulatory protein, with a molecular weight of 17,000 Daltons

Second messenger

Calcium and cAMP are second messengers for hormones e.g. epinephrine in liver glycogenolysis

Calcium's role in Myocardium

Ca²+ prolongs systole

Organs Dependent on Regulation of plasma calcium level

Bone, Kidney, Intestine

Hormones Dependent on Regulation of plasma calcium level

Calcitriol, Parathyroid hormone, Calcitonin

Role of calcitriol on bone

Stimulates calcium uptake for deposition as calcium phosphate in osteoblasts of bone

Role of calcitriol on kidneys

Minimizing the excretion of Ca 2+ & phosphate by decreasing their excretion & enhancing reabsorption

Role of calcitriol on intestine

Increases the intestinal absorption of Ca2+ & phosphate

Parathyroid hormone (PTH)

Secreted by two pairs of parathyroid glands

Action on the bone: PTH

PTH causes decalcification or demineralization of bone carried out by osteoclasts

Action on the kidney: PTH

PTH increases the Ca2+ reabsorption by kidney tubules elevates blood Ca2+ levels

Action on the intestine: PTH

PTH increases the intestinal absorption of Ca2+ by promoting the synthesis of calcitriol

Calcitonin

Calcitonin is a peptide containing 32 amino acids secreted by parafollicular cells of thyroid gland

Action of Calcitonin on Calcium

Calcitonin promotes calcification by increasing the activity of osteoblasts

Alkalosis and Acidosis's effect on Calcium

Alkalosis favors binding of Ca2+ with proteins; Acidosis favors ionization of Ca2+

Hypercalcemia

The serum Ca2+ level >11 mg/dl

Clinical features of hypercalcemia

Neurological symptoms, Generalized muscle weakness, Gastrointestinal problems, Renal feature, Cardiac arrhythemias

Hypocalcemia

Decreased serum Ca2+ < 8.8 mg/dl

Clinical features of hypocalcemia

Enhanced neuromuscular irritability, Neurologic features, Cardiovascular signs, Cataracts

Rickets

Disorder of defective calcification of bones

Osteoporosis

Characterized by demineralization of bone resulting in the progressive loss of bone mass

Magnesium

Fourth most abundant cation in the body

Magnesium levels in the body

Human body contains 25g of magnesium

Sources of magnesium

Cereals, beans, vegetables, potatoes, meat, milk, fruits & fish

RDA of Magnesium

Adult man: 400 mg/day; Women: 300 mg/day; During pregnancy & lactation: 450 mg/day

Absorption Factors of Magnesium

Calcium, phosphate & alcohol decreases & PTH increases magnesium absorption

Magnesium's biochemical functions

Formation of bones & teeth and to maintain neuromuscular irritability

Co-factor of magnesium

More than 300 enzymes requires magnesium as a cofactor such as Hexokinase and Pyruvate carboxylase

Normal plasma levels of Magnesium

1.7 - 3 mg/dl

Hypomagnesaemia

Decrease in serum magnesium levels <1.7 mg/dl.

Symptoms of Hypomagnesaemia

Impaired neuromuscular function, Hypocalcemia, Tetany, Convulsions & Muscle weakness

Hypermagnesaemia

Increase in serum magnesium > 3.5 mg/dl

Symptoms of Hypermagnesaemia

Depression of the neuromuscular system, lethargy, hypotension, bradycardia